Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

Damage Mechanisms Affecting Damage Mechanisms Affecting Fixed Equipment in the Refining Fixed Equipment in the Refining

IndustryIndustry

Temper EmbrittlementTemper Embrittlement Description of DamageDescription of Damage

– Temper embrittlement is the reduction in toughness due Temper embrittlement is the reduction in toughness due to a metallurgical change that occur in some low alloy to a metallurgical change that occur in some low alloy steels as a result of longsteels as a result of long--term exposure in the term exposure in the temperature range about 650° F to 1100° F (343° C to temperature range about 650° F to 1100° F (343° C to 593° C)593° C)

– This change causes an upward shift in the ductile-to-This change causes an upward shift in the ductile-to-brittle transition temperature as measured by Charpy brittle transition temperature as measured by Charpy impact testingimpact testing

– This phenomenon is related to to the concentration of This phenomenon is related to to the concentration of low-melting point elements (P, Sb, Sn, and S) in the low-melting point elements (P, Sb, Sn, and S) in the grain boundaries, the crack path is intergranular.grain boundaries, the crack path is intergranular.

Affected MaterialsAffected Materials– Primarily 2.25Cr-1Mo low alloy steel, 3Cr-1Mo (to a lesser Primarily 2.25Cr-1Mo low alloy steel, 3Cr-1Mo (to a lesser

extent), and the high-strength low alloy Cr-Mo-V rotor extent), and the high-strength low alloy Cr-Mo-V rotor steelssteels

– Older generation 2.25Cr-1Mo materials manufactured prior Older generation 2.25Cr-1Mo materials manufactured prior to 1972 may be particularly susceptible. Some high to 1972 may be particularly susceptible. Some high strength low alloy steels are also susceptiblestrength low alloy steels are also susceptible

– The C-0.5Mo and 1.25Cr-1Mo alloy steels are not The C-0.5Mo and 1.25Cr-1Mo alloy steels are not significantly affected by temper embrittlement. significantly affected by temper embrittlement.

Temper EmbrittlementTemper Embrittlement

Critical FactorsCritical Factors– Alloy steel composition, thermal history, metal temperature Alloy steel composition, thermal history, metal temperature

and exposure timeand exposure time

– Susceptibility to temper embrittlement is largely determined by Susceptibility to temper embrittlement is largely determined by the presence of the alloying elements manganese and silicon, the presence of the alloying elements manganese and silicon, and tramp elements phosphorus, tin, antimony and arsenicand tramp elements phosphorus, tin, antimony and arsenic

– Temper embrittlement of 2.25Cr-1Mo steels develops more Temper embrittlement of 2.25Cr-1Mo steels develops more quickly at 900° F (482°C) than in the 800°F (440°C)quickly at 900° F (482°C) than in the 800°F (440°C)

– Some embrittlement can occur during fabrication heat Some embrittlement can occur during fabrication heat treatmenttreatment

– This form of damage will significantly reduce the structural This form of damage will significantly reduce the structural integrity of a component containing a crack-like flaw. integrity of a component containing a crack-like flaw.


Affected Units or EquipmentAffected Units or Equipment– Temper emrittlement occurs in a variety of process units Temper emrittlement occurs in a variety of process units

after long therm exposure to temperatures above 650°F after long therm exposure to temperatures above 650°F (343°C)(343°C)

– Equipment susceptible to temper embrittlement is most often Equipment susceptible to temper embrittlement is most often found in hydroprocessing units, particularly reactors, hot found in hydroprocessing units, particularly reactors, hot feet/effluent exchanger components, and hot HP separators. feet/effluent exchanger components, and hot HP separators.

– Welds in these alloys are often more susceptible than the Welds in these alloys are often more susceptible than the base metal and should be evaluated. base metal and should be evaluated.


Appearance of Morphology Appearance of Morphology of Damageof Damage– Temper embrittlement is a Temper embrittlement is a

metallurgical change that is metallurgical change that is not readily apparent and can not readily apparent and can be evaluated through impact be evaluated through impact testingtesting

– Temper embrittlement can be Temper embrittlement can be identified by an upward shift identified by an upward shift in the ductile-to-brittle in the ductile-to-brittle transition temperature transition temperature measured in a Charpy V-notch measured in a Charpy V-notch impact test, as compared to the impact test, as compared to the non-embrittled or de-non-embrittled or de-embrittled material. (Fembrittled material. (Figig. 4-5). 4-5)


Figure 4-5 - Plot of CVN toughness as a function of temperature showing a shift in

the 40-ft-lb transition temperature

Prevention/migrationPrevention/migration– Cannot be prevented if the material contains critical levels of the Cannot be prevented if the material contains critical levels of the

embrittling impurity elements and is exposure in the embrittling embrittling impurity elements and is exposure in the embrittling temperature rangetemperature range

– To minimize the possibility of brittle fracture during start-up and To minimize the possibility of brittle fracture during start-up and shutdown, shutdown, isis use usedd a pressurization sequence to limit system a pressurization sequence to limit system pressure to about 25% of the maximum design pressure for pressure to about 25% of the maximum design pressure for temperatures below a MPTtemperatures below a MPT

– MPT‘s generally range from 350°F(171°C) for the earliest, most MPT‘s generally range from 350°F(171°C) for the earliest, most highly temper embrittled steels, down to 150°F (38°C) or lower for highly temper embrittled steels, down to 150°F (38°C) or lower for newer, temper embrittlement resistant steelnewer, temper embrittlement resistant steel

– If weld repairs are required, the effects of temper embrittlement If weld repairs are required, the effects of temper embrittlement can be temporarily reversed by heating at 1150°F (620°C) for 2 can be temporarily reversed by heating at 1150°F (620°C) for 2 hours per 1 inch of thickness, and rapidly cooling to room hours per 1 inch of thickness, and rapidly cooling to room temperaturetemperature


New MaterialsNew Materials– The best way to minimize the like hood and extend of temper The best way to minimize the like hood and extend of temper

embrittlement is to limit the acceptance levels of manganese, embrittlement is to limit the acceptance levels of manganese, silicon, phosphorus, tin, antimony, and arsenic in the base silicon, phosphorus, tin, antimony, and arsenic in the base metalmetal

– A common way to minimize temper embrittlement is to limit A common way to minimize temper embrittlement is to limit the „Jthe „J**“ factor for base metal and the „X“ factor for weld “ factor for base metal and the „X“ factor for weld metal, based on material composition as follows:metal, based on material composition as follows:

JJ** = (Si + Mn) = (Si + Mn)(P + Sn)(P + Sn)101044

X = (10P + 5Sb + 4Sn + As)/100X = (10P + 5Sb + 4Sn + As)/100

– Typical J* and X factors used for 2.25 Cr steel are 100 and 15, Typical J* and X factors used for 2.25 Cr steel are 100 and 15, respectivelyrespectively


Inspection and MonitoringInspection and Monitoring– A common method of monitoring is to install blocs of A common method of monitoring is to install blocs of

original heats of the alloy steel material inside the reactororiginal heats of the alloy steel material inside the reactor

– Samples are periodically removed for impact testingSamples are periodically removed for impact testing

– Process condition should be monitored to ensure that a proper Process condition should be monitored to ensure that a proper pressurization sequence is followed to help prevent brittle pressurization sequence is followed to help prevent brittle fracture due to temper embrittlementfracture due to temper embrittlement


Description of DamageDescription of Damage– Brittle fracture is the sudden rapid fracture under stress Brittle fracture is the sudden rapid fracture under stress

where the material exhibits little or no evidence of ductility where the material exhibits little or no evidence of ductility or plastic deformationor plastic deformation

Affected materialsAffected materials– Carbon steel and low alloy steel are prime concern, Carbon steel and low alloy steel are prime concern,

particularly older steel particularly older steel

– 400 series SS are also susceptible400 series SS are also susceptible

Brittle FractureBrittle Fracture

Critical FactorsCritical Factors– When the critical combination of 3 factors is reached, brittle fracture can occur:When the critical combination of 3 factors is reached, brittle fracture can occur:

» The materials‘ fracture toughness (resistance to crack like flaws) as measured in a The materials‘ fracture toughness (resistance to crack like flaws) as measured in a Charpy impact testCharpy impact test

» The size, shape and stress concentration effect of a flawThe size, shape and stress concentration effect of a flaw

» The amount of residual and applied stresses on the flawThe amount of residual and applied stresses on the flaw

– Susceptibility to brittle fracture may be increased by the presence of embrittling Susceptibility to brittle fracture may be increased by the presence of embrittling phasesphases

– Steel cleanlines and grain size have a significant influence on thoughness and Steel cleanlines and grain size have a significant influence on thoughness and resistance to brittle fractureresistance to brittle fracture

– Thicker material section also have a lower resistance to brittle fractureThicker material section also have a lower resistance to brittle fracture

– Brittle fracture occurs only at temperature below the Charpy impact transition Brittle fracture occurs only at temperature below the Charpy impact transition temperature, the point at which the toughness of the material drops off sharplytemperature, the point at which the toughness of the material drops off sharply


Affected Units or EquipmentAffected Units or Equipment– Equipment manufactured to the ASME Boiler and Pressure Equipment manufactured to the ASME Boiler and Pressure

Vessel Code, Section VIII, Division 1, prior to the December Vessel Code, Section VIII, Division 1, prior to the December 1987 Addena, were made with limited restriction on notch 1987 Addena, were made with limited restriction on notch toughness for vessels operating on cold temperaturestoughness for vessels operating on cold temperatures

– Equipment made to the same code after this date were subject Equipment made to the same code after this date were subject to the requirements of UCS 66to the requirements of UCS 66

– Most processes run at elevated temperature so the main Most processes run at elevated temperature so the main concern is for brittle fracture during start-up, shutdown or concern is for brittle fracture during start-up, shutdown or hydrogen/thickness testinghydrogen/thickness testing

– Brittle fracture can also occur during an autorefrigeration even Brittle fracture can also occur during an autorefrigeration even in units processing light hydrocarbons such as methane, in units processing light hydrocarbons such as methane, ethane/ethylene, propane/propylene or butaneethane/ethylene, propane/propylene or butane

– Brittle fracture can occur during ambient temperature Brittle fracture can occur during ambient temperature hydrotesting due to high stresses and low hydrotesting due to high stresses and low ttoughness at the oughness at the testing temperaturetesting temperature


Appearance or Morphology of DamageAppearance or Morphology of Damage– Crack will typically be straight, non-branchng, and largely Crack will typically be straight, non-branchng, and largely

devoid of any associated plastic deformation (FIG 4-6 to FIG devoid of any associated plastic deformation (FIG 4-6 to FIG 4-7)4-7)

– Microscopicaly, the fracture surface will be composed largely Microscopicaly, the fracture surface will be composed largely of cleveage, with limited intergranular cracking and vey little of cleveage, with limited intergranular cracking and vey little micro void coalescencemicro void coalescence


Figure 4-6 - 20-inch carbon Figure 4-6 - 20-inch carbon steel pipeline that failed steel pipeline that failed during hydrotest at gouges during hydrotest at gouges on the O.D.on the O.D.

Figure 4-7 - Close-up Figure 4-7 - Close-up photograph showing the photograph showing the gouges and the fracture gouges and the fracture origin (arrow) in one of origin (arrow) in one of thethe gouges.gouges.

Prevention/MitigationPrevention/Mitigation– For new equipment is best prevent by using materials specifically For new equipment is best prevent by using materials specifically

designed for low temperature operation including upset and designed for low temperature operation including upset and autorefrigeration events. autorefrigeration events.

– Brittle fracture is an „event“ driven damage mechanismBrittle fracture is an „event“ driven damage mechanism– Preventative measures to minimize the potential for brittle fracture Preventative measures to minimize the potential for brittle fracture

in existing equipment are limited to controlling the operating in existing equipment are limited to controlling the operating condition, minimizing pressure at ambient temperatures during condition, minimizing pressure at ambient temperatures during startup and shutdown, and periodic inspection at high stress startup and shutdown, and periodic inspection at high stress locationlocation

– Some reduction in the likehood of a brittle fracture may be Some reduction in the likehood of a brittle fracture may be achieved by:achieved by:

» Performing a post weld heat treatment (PWHT) on the vessel if it was not Performing a post weld heat treatment (PWHT) on the vessel if it was not originally done during manufacturing originally done during manufacturing

» Perform a „warm“ pre stress hydroPerform a „warm“ pre stress hydrotesttest followed by a lower temperature followed by a lower temperature hydrotest to extend the Minimum Safe Operating temperature envelopehydrotest to extend the Minimum Safe Operating temperature envelope


Description of DamageDescription of Damage– Thermal fatigue is the result of Thermal fatigue is the result of cycliccyclic stresses caused by variations stresses caused by variations

in temperature. in temperature.

– Damage is in the form of cracking that may occur anywhere in a Damage is in the form of cracking that may occur anywhere in a metallic component where relative movement or metallic component where relative movement or differentialdifferential expansion is constrained, particularly under repeated thermal expansion is constrained, particularly under repeated thermal cyclingcycling

Affected MaterialsAffected Materials– All material of constructionAll material of construction

Thermal FatigueThermal Fatigue

Critical FactorsCritical Factors– Key factors-magnitude of the temperature swing and the Key factors-magnitude of the temperature swing and the

frequency (number of cycles)frequency (number of cycles)

– Time to failure is a function of the magnitude of the stress and Time to failure is a function of the magnitude of the stress and the number of cycles and decreases with increasing stress and the number of cycles and decreases with increasing stress and increasing cyclesincreasing cycles

– Damage is also promoted by rapid changes in surface Damage is also promoted by rapid changes in surface temperature that result in thermal gradienttemperature that result in thermal gradient

– Notches and sharp corners and other stress concentrations may Notches and sharp corners and other stress concentrations may serve as initiation sitesserve as initiation sites


Affected Units or EquipmentAffected Units or Equipment– Mix points of hot and cold streamsMix points of hot and cold streams

– Coke drum shells (coke drum skirts where stresses are promoted Coke drum shells (coke drum skirts where stresses are promoted by a variation in temperature between the drum and skirt)by a variation in temperature between the drum and skirt)

– In steam generating equipment, the most common locations are the In steam generating equipment, the most common locations are the rigid attachments between neighboring tubes in the superheater rigid attachments between neighboring tubes in the superheater and reheater. and reheater.

– Tubes in the high temperature superheater or reheater that Tubes in the high temperature superheater or reheater that penetrate trough the cooler waterwall tubes may crack at the penetrate trough the cooler waterwall tubes may crack at the header connection if the tube is not sufficiently flexibleheader connection if the tube is not sufficiently flexible

– Steam actuated soot blowers may cause thermal fatigue damage if Steam actuated soot blowers may cause thermal fatigue damage if the first steam existing the soot blower nozzle contains condensatethe first steam existing the soot blower nozzle contains condensate


Figure 4-11 - Thermal fatigue Figure 4-11 - Thermal fatigue cracks on the inside of a heavy cracks on the inside of a heavy wall SS pipe downstream of a wall SS pipe downstream of a cooler Hcooler H22 injection into a hot injection into a hot hydrocarbon line hydrocarbon line

Figure 4-12 - Bulging in a skirt Figure 4-12 - Bulging in a skirt of a Coke Drumof a Coke Drum

Figure 4-13 - Thermal fatigue Figure 4-13 - Thermal fatigue cracking associated with bulged cracking associated with bulged skirt shown in Figure 4-12 skirt shown in Figure 4-12

Appearance or Morphology of DamageAppearance or Morphology of Damage– Thermal fatigue cracks usually initiate on the surface of the Thermal fatigue cracks usually initiate on the surface of the

component component

– Thermal fatigue cracks propagate transverse to the stress and Thermal fatigue cracks propagate transverse to the stress and they are usually dager-shaped, transgranular, and oxide filledthey are usually dager-shaped, transgranular, and oxide filled

– In steam generating equipment, cracks usually follow the toe In steam generating equipment, cracks usually follow the toe of the filled weld, as the change in section thickness creates a of the filled weld, as the change in section thickness creates a stress raiserstress raiser

– Water in soot blowers may lead to a crazing pattern. The Water in soot blowers may lead to a crazing pattern. The predominant cracks will be circumferential and the minor predominant cracks will be circumferential and the minor cracks will be axial cracks will be axial


Figure 4-15 - Older cracks fill with Figure 4-15 - Older cracks fill with oxide, may stop and restart (note jog oxide, may stop and restart (note jog part way along the crack), and do not part way along the crack), and do not necessarily require a change in section necessarily require a change in section thickness to initiate the crack. thickness to initiate the crack. mmag. ag. 100x, etched100x, etched

Figure 4-14 - In a carbon steel Figure 4-14 - In a carbon steel sample, metallographic section sample, metallographic section through thermal fatigue crack through thermal fatigue crack indicates origin (here at the toe of indicates origin (here at the toe of an attachment weld) and shape an attachment weld) and shape mmag. 50x, etchedag. 50x, etched

Prevention/mitigationPrevention/mitigation– Best prevent is trough the design and operation to minimize Best prevent is trough the design and operation to minimize

thermal stresses and thermal cyclingthermal stresses and thermal cycling» Design that incorporate reduction of stress concentrators, blend grinding of Design that incorporate reduction of stress concentrators, blend grinding of

weld profiles, and smooth transitions should be usedweld profiles, and smooth transitions should be used» ControlControllled rates of heating and cooling during startup and shutdown of ed rates of heating and cooling during startup and shutdown of

equipment can lower stressesequipment can lower stresses» Differential thermal expansion between adjoining components of dissimilar Differential thermal expansion between adjoining components of dissimilar

materials should be consideredmaterials should be considered» Design should incorporate sufficient flexibility to accommodate differential Design should incorporate sufficient flexibility to accommodate differential

expansionexpansion» In steam generating equipment, slip spacers should slip and rigid attachment In steam generating equipment, slip spacers should slip and rigid attachment

should be avoidedshould be avoided» Drain lines should be provided on soot-blowers to prevent condensate in the Drain lines should be provided on soot-blowers to prevent condensate in the

first portion of the soot blowing cyclefirst portion of the soot blowing cycleIn some cases, a liner or sleeve may be installed to prevent a colder liquid In some cases, a liner or sleeve may be installed to prevent a colder liquid

from contacting the hotter pressure boundary wallfrom contacting the hotter pressure boundary wall


Inspection and MonitoringInspection and Monitoring– MT and PT MT and PT areare effective methods of inspection effective methods of inspection

– External SWUT inspection can be used for non-intrusive External SWUT inspection can be used for non-intrusive inspection for internal crackinginspection for internal cracking

– Heavy wall reactor internal attachment welds can be Heavy wall reactor internal attachment welds can be inspected using specialized ultrasonic techniquesinspected using specialized ultrasonic techniques


Description of DamageDescription of Damage– Erosion is the accelerated mechanical removal of surface Erosion is the accelerated mechanical removal of surface

material as a result of relative movement between, or impact material as a result of relative movement between, or impact of solid, liquids, vapour or any combination thereofof solid, liquids, vapour or any combination thereof

– Erosion-corrosion is a description for the damage that occurs Erosion-corrosion is a description for the damage that occurs when corrosion contributes to erosion by removing protective when corrosion contributes to erosion by removing protective films or scales, or by exposing the metal surface to further films or scales, or by exposing the metal surface to further corrosion under the combined action of erosion and corrosioncorrosion under the combined action of erosion and corrosion

Affected materialsAffected materials– All metals, alloys and refractoriesAll metals, alloys and refractories

Erosion/Erosion - CorrosionErosion/Erosion - Corrosion

Critical FactorsCritical Factors– Metal loss rates depend on the velocity and concentration of impacting medium, Metal loss rates depend on the velocity and concentration of impacting medium,

the size and hardness of impacting particles, the hardness and corrosion the size and hardness of impacting particles, the hardness and corrosion resistance of material subject to erosion, and the angle of impact resistance of material subject to erosion, and the angle of impact

– Softer alloys that are easily worn from mechanical damageSofter alloys that are easily worn from mechanical damage

– Increasing hardness of the metal substrate is not always a good indicator of Increasing hardness of the metal substrate is not always a good indicator of improved resistance to erosion, particularly where corrosion plays a significant improved resistance to erosion, particularly where corrosion plays a significant role. role.

– For each environment-material combination, there is often a threshold velocity For each environment-material combination, there is often a threshold velocity above which impacting objects may produce metal lossabove which impacting objects may produce metal loss

– The size, shape, density and hardness of the impacting medium affects the metal The size, shape, density and hardness of the impacting medium affects the metal loss rate loss rate

– Increasing the corrosivity of the environment may reduce the stability of Increasing the corrosivity of the environment may reduce the stability of protective surface films and increase the susceptibility to metal loss protective surface films and increase the susceptibility to metal loss

– Factors which contribute to an increase in corrosivity of the environment, such Factors which contribute to an increase in corrosivity of the environment, such as temperature, pH, etc., can increase susceptibility to metal loss. as temperature, pH, etc., can increase susceptibility to metal loss.


Affected Units or EquipmentAffected Units or Equipment– All types of equipment exposed to moving fluids and/or All types of equipment exposed to moving fluids and/or

catalyst as piping systems, particularly the bends, elbows, tees catalyst as piping systems, particularly the bends, elbows, tees and reducers; piping systems downstream of letdown valves and reducers; piping systems downstream of letdown valves and block valves etc. (Fig. 4-23, Fig. 4-24, Fig. 4-25) and block valves etc. (Fig. 4-23, Fig. 4-24, Fig. 4-25)

– Erosion can be caused by gas borne catalyst particles or by Erosion can be caused by gas borne catalyst particles or by particles carried by a liquid such as a slurry. In refineries, this particles carried by a liquid such as a slurry. In refineries, this form of damage occurs as a result of catalyst movement in form of damage occurs as a result of catalyst movement in FCC reactor/regenerator systems in catalyst handling FCC reactor/regenerator systems in catalyst handling equipment (valves, cyclones etc) and slurry piping as shown on equipment (valves, cyclones etc) and slurry piping as shown on picturespictures

– Hydroprocessing reactor effluent piping may be subject to Hydroprocessing reactor effluent piping may be subject to erosion-corrosion by ammonium bisulfideerosion-corrosion by ammonium bisulfide


Figure 4-23 - Erosion of Figure 4-23 - Erosion of a 9Cr coker heater a 9Cr coker heater return bendreturn bend

Figure 4-24 - Cast iron Figure 4-24 - Cast iron impeller in untreated impeller in untreated cooling water after four cooling water after four years ofyears of serviceservice

Figure 4-25 – Close-up of figure 4-24 showing Figure 4-25 – Close-up of figure 4-24 showing both erosion-corrosion at the vane tips and both erosion-corrosion at the vane tips and pitting on the pressure side of the vanespitting on the pressure side of the vanes

Appearance or Morphology of DamageAppearance or Morphology of Damage– Erosion and erosion-corrosion are characterized by a localized loss in Erosion and erosion-corrosion are characterized by a localized loss in

thickness in the form of pits, grooves, gullies, waves, rounded holes and thickness in the form of pits, grooves, gullies, waves, rounded holes and valleys.valleys.

– Failures can occur in a relatively short time. Failures can occur in a relatively short time. Prevention/Mitigation Prevention/Mitigation

– Improvements in design involve changes in shape, geometry and Improvements in design involve changes in shape, geometry and materials selection materials selection

– Improved resistance to erosion is usually achieved through increasing Improved resistance to erosion is usually achieved through increasing substrate hardness using harder alloys, hard facing or surface-hardening substrate hardness using harder alloys, hard facing or surface-hardening treatments treatments

– Erosion-corrosion is best mitigated by using more corrosion-resistant Erosion-corrosion is best mitigated by using more corrosion-resistant alloys and/or altering the process environment to reduce corrosivity alloys and/or altering the process environment to reduce corrosivity

– Heat exchangers utilize impingement plates and occasionally tube Heat exchangers utilize impingement plates and occasionally tube ferrules to minimize erosion problems.ferrules to minimize erosion problems.

– Higher molybdenum containing alloys are used for improved resistance Higher molybdenum containing alloys are used for improved resistance to naphthenic acid corrosion to naphthenic acid corrosion


Inspection and Monitoring Inspection and Monitoring – Visual examination of suspected or troublesome areas, as well Visual examination of suspected or troublesome areas, as well

as UT checks or RT as UT checks or RT

– Specialized corrosion coupons and on-line corrosion Specialized corrosion coupons and on-line corrosion monitoring electrical resistance probes (in some applications)monitoring electrical resistance probes (in some applications)

– IR scans are used to detect refractory loss on stream.IR scans are used to detect refractory loss on stream.

Related Mechanisms Related Mechanisms – Specialized terminology has been developed for various forms Specialized terminology has been developed for various forms

of erosion and erosion-corrosion in specific environments of erosion and erosion-corrosion in specific environments and/or services. and/or services.

– This terminology includes: cavitation, liquid impingement This terminology includes: cavitation, liquid impingement erosion, fretting etc. erosion, fretting etc.


Description of DamageDescription of Damage– Fatigue cracking is a mechanical form of degradation that Fatigue cracking is a mechanical form of degradation that

occurs when a component is exposed to cyclical stresses for an occurs when a component is exposed to cyclical stresses for an extended period, often resulting in sudden, unexpected failure.extended period, often resulting in sudden, unexpected failure.

– These stresses can arise from either mechanical loading or These stresses can arise from either mechanical loading or thermal cycling and are typically well below the yield strength thermal cycling and are typically well below the yield strength of the material.of the material.

Affected Materials Affected Materials – All engineering alloys are subject to fatigue cracking although All engineering alloys are subject to fatigue cracking although

the stress levels and number of cycles necessary to cause the stress levels and number of cycles necessary to cause failure vary by material failure vary by material

Mechanical FatigueMechanical Fatigue

Critical FactorsCritical Factors– Geometry, stress level, number of cycles, and material properties Geometry, stress level, number of cycles, and material properties

(strength, hardness, microstructure)(strength, hardness, microstructure)– Design: Fatigue cracks usually initiate on the surface at notches Design: Fatigue cracks usually initiate on the surface at notches

or stress raisers under cyclic loading or stress raisers under cyclic loading – Metallurgical Issues and Microstructure Metallurgical Issues and Microstructure – Carbon Steel and Titanium: These materials exhibit an Carbon Steel and Titanium: These materials exhibit an

endurance limit below which fatigue cracking will not occur, endurance limit below which fatigue cracking will not occur, regardless of the number of cycles regardless of the number of cycles

– 300 Series SS, 400 Series SS, aluminium, and most other non-300 Series SS, 400 Series SS, aluminium, and most other non-ferrous alloys:ferrous alloys:

» These alloys have a fatigue characteristic that does not exhibit an These alloys have a fatigue characteristic that does not exhibit an endurance limitendurance limit

» Maximum cyclical stress amplitude is determined by relating the stress Maximum cyclical stress amplitude is determined by relating the stress necessary to cause fracture to the desired number of cycles necessary in a necessary to cause fracture to the desired number of cycles necessary in a component's lifetime – typically 10component's lifetime – typically 1066 to 10 to 1077 cycles cycles


Affected Units or EquipmentAffected Units or Equipment– Thermal CyclingThermal Cycling

» Equipment that cycles daily in operation such as Equipment that cycles daily in operation such as coke drumscoke drums

» Equipment that may be auxiliary or on continuous standby but sees Equipment that may be auxiliary or on continuous standby but sees intermittent service such as auxiliary intermittent service such as auxiliary boilerboiler

» Quench nozzle connections that see significant temperature deltas Quench nozzle connections that see significant temperature deltas during operations such as during operations such as water washing systemswater washing systems

– Mechanical Loading Mechanical Loading » Rotating shafts on centrifugal pumps and compressors that have stress Rotating shafts on centrifugal pumps and compressors that have stress

concentrations due to changes in radii and key ways.concentrations due to changes in radii and key ways.

» Components such as small diameter piping that may see vibration from Components such as small diameter piping that may see vibration from adjacent equipment and/or wind.adjacent equipment and/or wind.

» High pressure drop control valves or steam reducing stations can cause High pressure drop control valves or steam reducing stations can cause serious vibration problems in connected piping.serious vibration problems in connected piping.


Appearance or Morphology of DamageAppearance or Morphology of Damage – The signature mark of a fatigue failure is a „clam shell“ type The signature mark of a fatigue failure is a „clam shell“ type

fingerprint that has concentric rings called „beach marks“ fingerprint that has concentric rings called „beach marks“ emanating from the crack initiation site (Figure 4-29 and emanating from the crack initiation site (Figure 4-29 and Figure 4-30). This signature pattern results from the Figure 4-30). This signature pattern results from the „„waveswaves““ of crack propagation that occur during every cycle above the of crack propagation that occur during every cycle above the threshold loading threshold loading

– Cracks nucleating from a surface stress concentration or Cracks nucleating from a surface stress concentration or defect will typically result in a single „clam shell“ defect will typically result in a single „clam shell“ fingerprint (Figure 4-31, Figure 4-32 and Figure 4-33.).fingerprint (Figure 4-31, Figure 4-32 and Figure 4-33.).

– Cracks resulting from cyclical overstress of a component Cracks resulting from cyclical overstress of a component without significant stress concentration will typically result without significant stress concentration will typically result in a fatigue failure with multiple points of nucleation and in a fatigue failure with multiple points of nucleation and hence multiple „clam shell“ fingerprintshence multiple „clam shell“ fingerprints


Figure 4-31 - Fatigue crack in Figure 4-31 - Fatigue crack in a 16-inch pipe-to-elbow weld a 16-inch pipe-to-elbow weld in the fill line of crude oil in the fill line of crude oil storage tank after 50 years in storage tank after 50 years in service service

Figure 4-32 - A cross-section Figure 4-32 - A cross-section through the weld showing the through the weld showing the crack locationcrack location

Figure 4-33 - The surface of the Figure 4-33 - The surface of the fracture faces of the crack shown in fracture faces of the crack shown in Figure 4-31 and Figure 4-32 Figure 4-31 and Figure 4-32

Prevention / Mitigation Prevention / Mitigation – Good design that helps minimize stress concentration of Good design that helps minimize stress concentration of

components that are in cyclic service components that are in cyclic service

– Select a metal with a design fatigue life sufficient for its Select a metal with a design fatigue life sufficient for its intended cyclic service intended cyclic service

– Allow for a generous radius along edges and corners Allow for a generous radius along edges and corners

– Minimize grinding marks, nicks and gouges on the surface of Minimize grinding marks, nicks and gouges on the surface of components components

– Insure good fit up and smooth transitions for welds. Minimize Insure good fit up and smooth transitions for welds. Minimize weld defects as these can accelerate fatigue crackingweld defects as these can accelerate fatigue cracking

– Remove any burrs or lips caused by machining Remove any burrs or lips caused by machining

– Use low stress stamps and marking tools Use low stress stamps and marking tools


Inspection and MonitoringInspection and Monitoring – NDE techniques such as PT, MT and SWUT can be used to NDE techniques such as PT, MT and SWUT can be used to

detect fatigue cracks at known areas of stress concentrationdetect fatigue cracks at known areas of stress concentration

– VT of small diameter piping to detect oscillation or other VT of small diameter piping to detect oscillation or other cyclical movement that could lead to crackingcyclical movement that could lead to cracking

– Vibration monitoring of rotating equipment to help detect Vibration monitoring of rotating equipment to help detect shafts that may be out of balanceshafts that may be out of balance

– In high cycle fatigue, crack initiation can be a majority of the In high cycle fatigue, crack initiation can be a majority of the fatigue life making detection difficult fatigue life making detection difficult

Related Mechanisms Related Mechanisms – Vibration induced fatigueVibration induced fatigue


Description of DamageDescription of Damage– A form of corrosion that occurs from moisture associated with A form of corrosion that occurs from moisture associated with

atmospheric conditions. Marine environments and moist atmospheric conditions. Marine environments and moist polluted industrial environments with airborne contaminants are polluted industrial environments with airborne contaminants are most severe most severe

– Dry rural environments cause very little corrosion Dry rural environments cause very little corrosion

Affected MaterialsAffected Materials– Carbon steel, low alloy steels and copper alloyed aluminium Carbon steel, low alloy steels and copper alloyed aluminium

Atmospheric CorrosionAtmospheric Corrosion

Critical Factors: Critical Factors: – Physical location (industrial, marine, rural); moisture Physical location (industrial, marine, rural); moisture

(humidity), particularly designs that trap moisture or when (humidity), particularly designs that trap moisture or when present in a cooling tower mist; temperature; presence of salts, present in a cooling tower mist; temperature; presence of salts, sulfur compounds and dirt sulfur compounds and dirt

– Corrosion rates increase with temperature up to about 250°F Corrosion rates increase with temperature up to about 250°F (121°C). Above 250°F (121°C), surfaces are usually too dry for (121°C). Above 250°F (121°C), surfaces are usually too dry for corrosion to occur except under insulation corrosion to occur except under insulation

– Chlorides, HChlorides, H22S, fly ash and other airborne contaminates from S, fly ash and other airborne contaminates from

cooling tower drift, furnace stacks and other equipment cooling tower drift, furnace stacks and other equipment accelerate corrosion accelerate corrosion

– Bird turds can also cause accelerated corrosion and unsightly Bird turds can also cause accelerated corrosion and unsightly stains stains


Affected Units or EquipmentAffected Units or Equipment– Piping and equipment with operating temperatures sufficiently low to Piping and equipment with operating temperatures sufficiently low to

allow moisture to be present.allow moisture to be present.– A paint or coating system in poor condition.A paint or coating system in poor condition.– Equipment may be susceptible if cycled between ambient and higher or Equipment may be susceptible if cycled between ambient and higher or

lower operating temperatures.lower operating temperatures.– Equipment shut down or idled for prolonged periods unless properly Equipment shut down or idled for prolonged periods unless properly

mothballed.mothballed.– Tanks and piping are particularly susceptible. Piping that rests on pipe Tanks and piping are particularly susceptible. Piping that rests on pipe

supports is very prone to attack due to water entrapment between the pipe supports is very prone to attack due to water entrapment between the pipe and the support.and the support.

– Orientation to the prevailing wind and rain can also be a factor.Orientation to the prevailing wind and rain can also be a factor.– Piers and docks are very prone to attack.Piers and docks are very prone to attack.– Bimetallic connections such as copper to aluminum electrical connections Bimetallic connections such as copper to aluminum electrical connections


Appearance Appearance – The attack will be general or localized, depending upon The attack will be general or localized, depending upon

whether or not the moisture is trappedwhether or not the moisture is trapped

– If there is no coating or if there is a coating failure, corrosion If there is no coating or if there is a coating failure, corrosion or loss in thickness can be generalor loss in thickness can be general

– Localized coating failures will tend to promote corrosionLocalized coating failures will tend to promote corrosion

– Metal loss may not be visually evident, although normally a Metal loss may not be visually evident, although normally a distinctive iron oxide (red rust) scale formsdistinctive iron oxide (red rust) scale forms

Prevention/Mitigation Prevention/Mitigation – Surface preparation and proper coating application are Surface preparation and proper coating application are

critical for long-term protection in corrosive environmentscritical for long-term protection in corrosive environments


Inspection and Monitoring Inspection and Monitoring – VT and UT are techniques that can be used VT and UT are techniques that can be used

Related Mechanisms Related Mechanisms – Corrosion under insulation Corrosion under insulation


Description of Damage Description of Damage – Corrosion of piping, pressure vessels and structural Corrosion of piping, pressure vessels and structural

components resulting from water trapped under insulation or components resulting from water trapped under insulation or fireproofing fireproofing

Affected Materials Affected Materials – Carbon steel, low alloy steels, 300 Series SS and duplex Carbon steel, low alloy steels, 300 Series SS and duplex

stainless steelsstainless steels

Corrosion Under Insulation (CUI)Corrosion Under Insulation (CUI)

Critical Factors Critical Factors – Design of insulation system, insulation type, temperature, environment Design of insulation system, insulation type, temperature, environment – Poor design and/or installations that allow water to become trapped will Poor design and/or installations that allow water to become trapped will

increase CUIincrease CUI– Corrosion rates increase with increasing metal temperature up to the point Corrosion rates increase with increasing metal temperature up to the point

where the water evaporates quickly.where the water evaporates quickly.– Corrosion becomes more severe at metal temperatures between the boiling Corrosion becomes more severe at metal temperatures between the boiling

point 212°F (100°C) and 250°F (121°C)point 212°F (100°C) and 250°F (121°C)– Cyclic thermal operation or intermittent serviceCyclic thermal operation or intermittent service– Equipment that operates below the water dewpoint tends to condense water Equipment that operates below the water dewpoint tends to condense water

on the metal surface thus providing a wet environmenton the metal surface thus providing a wet environment– Plants located in areas with high annual rainfall or warmer, marine locations Plants located in areas with high annual rainfall or warmer, marine locations

are more prone to CUI than plants located in cooler, drier, mid-continent are more prone to CUI than plants located in cooler, drier, mid-continent locations.locations.

– Environments that provide airborne contaminants such as chlorides or SOEnvironments that provide airborne contaminants such as chlorides or SO22


Affected Units or Equipment Affected Units or Equipment – Carbon and low alloy steels are subject to pitting and loss Carbon and low alloy steels are subject to pitting and loss

in thickness.in thickness.

– 300 Series SS, 400 Series SS and duplex SS are subject to 300 Series SS, 400 Series SS and duplex SS are subject to pitting and localized corrosion.pitting and localized corrosion.

– 300 Series SS are also subject to Stress Corrosion 300 Series SS are also subject to Stress Corrosion Cracking (SCC) if chlorides are present, while the duplex Cracking (SCC) if chlorides are present, while the duplex SS are less susceptible SS are less susceptible


Affected Units or Equipment Affected Units or Equipment – Design IssuesDesign Issues

» CUI can be found on equipment with damaged insulation, vapor CUI can be found on equipment with damaged insulation, vapor barriers, weatherproofing or mastic, or protrusions through the barriers, weatherproofing or mastic, or protrusions through the insulation or at insulation termination points such as flanges insulation or at insulation termination points such as flanges

» Equipment designed with insulation support rings welded directly to Equipment designed with insulation support rings welded directly to the vessel wall the vessel wall

» Piping or equipment with damaged/leaking steam tracing Piping or equipment with damaged/leaking steam tracing

» Localized damage at paint and/or coating systems Localized damage at paint and/or coating systems

» Locations where moisture/water will naturally collect before Locations where moisture/water will naturally collect before evaporating and improperly terminated fireproofing evaporating and improperly terminated fireproofing


Appearance or Morphology of Damage Appearance or Morphology of Damage – Damage may be highly localized (Figure 4-38 and Figure Damage may be highly localized (Figure 4-38 and Figure

4-39) 4-39)

– In some localized cases, the corrosion can appear to be In some localized cases, the corrosion can appear to be carbuncle type pitting (usually found under acarbuncle type pitting (usually found under afailed paint/coating system) failed paint/coating system)

– For 300 Series SS, specifically in older calcium silicate For 300 Series SS, specifically in older calcium silicate insulation, localized pitting and chloride stress corrosion insulation, localized pitting and chloride stress corrosion cracking can occur cracking can occur


Figure 4-38 - CUI of Figure 4-38 - CUI of CS level bridleCS level bridle

Figure 4-39 - Profile RT of Figure 4-39 - Profile RT of

level bridle in Figure 4-38level bridle in Figure 4-38

Prevention/MitigationPrevention/Mitigation– Mitigation is best achieved by using appropriate paints/ coatings and Mitigation is best achieved by using appropriate paints/ coatings and

maintaining the insulation/sealing/vapor barriersmaintaining the insulation/sealing/vapor barriers– High quality coatings, properly appliedHigh quality coatings, properly applied– Careful selection of insulating materials Careful selection of insulating materials – Low chloride insulation should be used on 300 Series SS to minimize the Low chloride insulation should be used on 300 Series SS to minimize the

potential for pitting and chloride SCCpotential for pitting and chloride SCC– Utilize multiple inspection techniques to produce the most cost effective Utilize multiple inspection techniques to produce the most cost effective

approach, including:approach, including:» Partial and/or full stripping of insulation for visual examinationPartial and/or full stripping of insulation for visual examination» UT for thickness verificationUT for thickness verification» Real-time profile x-ray (for small bore piping)Real-time profile x-ray (for small bore piping)» Neutron backscatter techniques for identifying wet insulationNeutron backscatter techniques for identifying wet insulation» Deep penetrating eddy-current inspectionDeep penetrating eddy-current inspection» IR thermography looking for wet insulation and/or damaged and missing IR thermography looking for wet insulation and/or damaged and missing

insulation under the jacketinsulation under the jacket» Guided wave UT Guided wave UT


Related MechanismsRelated Mechanisms– Atmospheric corrosion, oxidation and chloride SCC Atmospheric corrosion, oxidation and chloride SCC


Description of DamageDescription of Damage– General or localized corrosion of carbon steels and other General or localized corrosion of carbon steels and other

metals caused by dissolved salts, gases, organic metals caused by dissolved salts, gases, organic compounds or microbiological activity compounds or microbiological activity

Affected Materials Affected Materials – Carbon steel, all grades of stainless steel, copper, Carbon steel, all grades of stainless steel, copper,

aluminium, titanium and nickel base alloys aluminium, titanium and nickel base alloys

Cooling Water CorrosionCooling Water Corrosion

Critical Factors Critical Factors – Fluid temperature, type of water and the type of cooling system, Fluid temperature, type of water and the type of cooling system,

oxygen content, and fluid velocitiesoxygen content, and fluid velocities– Increasing oxygen content tends to increase carbon steel Increasing oxygen content tends to increase carbon steel

corrosion rates corrosion rates – Brackish and salt water outlet temperatures above about 115 °F Brackish and salt water outlet temperatures above about 115 °F

(46°C) may cause serious scaling (46°C) may cause serious scaling – Velocities should be high enough to minimize fouling and drop Velocities should be high enough to minimize fouling and drop

out of deposits but not so high as to cause erosion out of deposits but not so high as to cause erosion – Low velocities can promote increased corrosion (sedimentation) Low velocities can promote increased corrosion (sedimentation) – The copper/zinc alloys can suffer SCC if any ammonia or The copper/zinc alloys can suffer SCC if any ammonia or

ammonium compounds are present in the water or on the ammonium compounds are present in the water or on the process sideprocess side

– titanium may suffer severe hydriding embrittlement titanium may suffer severe hydriding embrittlement


Affected Units or Equipment Affected Units or Equipment – Cooling water corrosion is a concern with water-cooled heat Cooling water corrosion is a concern with water-cooled heat

exchangers and cooling towers in all applications across all exchangers and cooling towers in all applications across all industries industries

Appearance or Morphology of Damage Appearance or Morphology of Damage – Cooling water corrosion can result in many different forms of Cooling water corrosion can result in many different forms of

damage including general corrosion, pitting corrosion (Figure 4-damage including general corrosion, pitting corrosion (Figure 4-40), MIC, stress corrosion cracking and fouling 40), MIC, stress corrosion cracking and fouling

– General or uniform corrosion of carbon steel occurs when General or uniform corrosion of carbon steel occurs when dissolved oxygen is present dissolved oxygen is present

– Localized corrosion may result from under-deposit corrosion, Localized corrosion may result from under-deposit corrosion, crevice corrosion or microbiological corrosion crevice corrosion or microbiological corrosion

– Deposits or crevices can lead to under-deposit or crevice Deposits or crevices can lead to under-deposit or crevice corrosion of any of the affected materials corrosion of any of the affected materials


Figure 4-40 - Cooling water corrosion on the ID. Figure 4-40 - Cooling water corrosion on the ID. of a CS heat exchanger tube operating at 86°F of a CS heat exchanger tube operating at 86°F

Prevention/MitigationPrevention/Mitigation– proper design, operation and chemical treatment of cooling proper design, operation and chemical treatment of cooling

water systemswater systems

– Design for process side inlet temperatures below 135°F (57°C) Design for process side inlet temperatures below 135°F (57°C)

– Minimum and maximum water velocities must be maintained, Minimum and maximum water velocities must be maintained, particularly in salt water systemsparticularly in salt water systems

– The metallurgy of heat exchanger components may need to be The metallurgy of heat exchanger components may need to be upgraded for improved resistance (especially in waters with upgraded for improved resistance (especially in waters with high chloride contenthigh chloride content, , low velocitylow velocity, , high process high process temperaturestemperatures, and/or , and/or poorly maintained water chemistrypoorly maintained water chemistry) )

– Periodic mechanical cleaning of tube ID's and OD's should be Periodic mechanical cleaning of tube ID's and OD's should be performed in order to maintain clean heat transfer surfaces performed in order to maintain clean heat transfer surfaces


Inspection and Monitoring Inspection and Monitoring – Cooling water should be monitored for variables that Cooling water should be monitored for variables that

affect corrosion and fouling including, pH, oxygen affect corrosion and fouling including, pH, oxygen content, cycles of concentration, biocide residual, content, cycles of concentration, biocide residual, biological activity, cooling water outlet biological activity, cooling water outlet temperatures, hydrocarbon contamination and temperatures, hydrocarbon contamination and process leaks.process leaks.

– Periodic calculation of U-factors (heat exchanger Periodic calculation of U-factors (heat exchanger performance measurement)performance measurement)

– Ultrasonic flow meters can be used to check the Ultrasonic flow meters can be used to check the velocity of water in the tubes.velocity of water in the tubes.

– Splitting representative tubes Splitting representative tubes


Related MechanismsRelated Mechanisms– Microbiologically induced corrosion chloride stress Microbiologically induced corrosion chloride stress

corrosion cracking and galvanic corrosion corrosion cracking and galvanic corrosion


Description of Damage Description of Damage – General corrosion and pitting in the boiler system and General corrosion and pitting in the boiler system and

condensate return piping condensate return piping

Affected Materials Affected Materials – Primarily carbon steel, some low alloy steel, some 300 Series Primarily carbon steel, some low alloy steel, some 300 Series

SS and copper based alloys SS and copper based alloys

Boiler Water Condensate Corrosion Boiler Water Condensate Corrosion

Critical Factors Critical Factors – Concentration of dissolved gas (oxygen and carbon dioxide), Concentration of dissolved gas (oxygen and carbon dioxide),

pH, temperature, quality of the feedwater and the specific pH, temperature, quality of the feedwater and the specific feedwater treating system feedwater treating system

– The chemical treatment for scale and deposit control must be The chemical treatment for scale and deposit control must be adjusted to coordinate with the oxygen scavenger for the adjusted to coordinate with the oxygen scavenger for the specific water service and boiler specific water service and boiler

– Ammonia SCC of Cu-Zn alloys can occur due to hydrazine, Ammonia SCC of Cu-Zn alloys can occur due to hydrazine, neutralizing amines or ammoniacal compounds neutralizing amines or ammoniacal compounds


Affected Units or Equipment Affected Units or Equipment – Corrosion can occur in the external treatment system, Corrosion can occur in the external treatment system,

deaerating equipment, feedwater lines, pumps, stage heaters deaerating equipment, feedwater lines, pumps, stage heaters and economizers, the steam generation system on both the and economizers, the steam generation system on both the water and fire sides and the condensate return system water and fire sides and the condensate return system

Appearance or Morphology of DamageAppearance or Morphology of Damage– Pitting type damage - can show up anywhere in the system Pitting type damage - can show up anywhere in the system

– Carbon dioxide corrosion tends to be a smooth grooving of the Carbon dioxide corrosion tends to be a smooth grooving of the pipe wall pipe wall


Prevention/Mitigation Prevention/Mitigation – Oxygen scavenging treatments typically include catalyzed Oxygen scavenging treatments typically include catalyzed

sodium sulfite or hydrazine depending on the system sodium sulfite or hydrazine depending on the system pressure level along with proper mechanical deareator pressure level along with proper mechanical deareator operation. A residual of the oxygen scavenger is carried into operation. A residual of the oxygen scavenger is carried into the steam generation system to handle any oxygen ingress the steam generation system to handle any oxygen ingress past the deaerator.past the deaerator.

– If the scale/deposit control/magnetite maintenance treatment If the scale/deposit control/magnetite maintenance treatment scheme does not minimize carbon dioxide in the condensate scheme does not minimize carbon dioxide in the condensate return system, an amine inhibitor treatment might be return system, an amine inhibitor treatment might be required required


Inspection and Monitoring Inspection and Monitoring – Water analysis is the common monitoring tool used to assure Water analysis is the common monitoring tool used to assure

that the various treatment systems are performing in a that the various treatment systems are performing in a satisfactory manner satisfactory manner

– Monitored parameters: pH, conductivity, chlorine or residual Monitored parameters: pH, conductivity, chlorine or residual biocide, and total dissolved solids to check for leaks in the biocide, and total dissolved solids to check for leaks in the form of organic compounds form of organic compounds

– Deaerator cracking problems can be evaluated off-line at Deaerator cracking problems can be evaluated off-line at shutdowns by utilizing properly applied wet fluorescence shutdowns by utilizing properly applied wet fluorescence magnetic particle inspectionmagnetic particle inspection

Related MechanismsRelated Mechanisms– COCO22 corrosion, corrosion fatigue, and erosion/erosion- corrosion, corrosion fatigue, and erosion/erosion-

corrosion corrosion


Description of Damage Description of Damage – Corrosion of carbon steel and other alloys resulting from their Corrosion of carbon steel and other alloys resulting from their

reaction with sulfur compounds in high temperature reaction with sulfur compounds in high temperature environments. The presence of hydrogen accelerates corrosion environments. The presence of hydrogen accelerates corrosion

Affected Materials Affected Materials – All iron based materials including carbon steel and low alloy All iron based materials including carbon steel and low alloy

steels, 300 Series SS and 400 Series SS.steels, 300 Series SS and 400 Series SS.

– Nickel base alloys are also affected (depending on Nickel base alloys are also affected (depending on composition, especially chromium content)composition, especially chromium content)

– Copper base alloys form sulfide at lower temperatures than Copper base alloys form sulfide at lower temperatures than carbon steel carbon steel

Sulfidation Sulfidation

Critical Factors Critical Factors – Major factorsMajor factors: Alloy composition, temperature and : Alloy composition, temperature and

concentration of corrosive sulfur compoundsconcentration of corrosive sulfur compounds

– Susceptibility of an alloy to sulfidation is determined by its Susceptibility of an alloy to sulfidation is determined by its ability to form protective sulfide scales ability to form protective sulfide scales

– Sulfidation of iron-based alloys usually begins at metal Sulfidation of iron-based alloys usually begins at metal temperatures above 500°F (260°C) temperatures above 500°F (260°C)

» The typical effects of increasing temperature, chromium content and The typical effects of increasing temperature, chromium content and sulfur content on metal loss are shown in Figure 4-65 and Figure 4-66 sulfur content on metal loss are shown in Figure 4-65 and Figure 4-66

– the resistance of iron and nickel base alloys is determined by the the resistance of iron and nickel base alloys is determined by the chromium content of the material chromium content of the material

– Sulfidation is primarily caused by HSulfidation is primarily caused by H22S and other reactive sulfur S and other reactive sulfur

species as a result of the thermal decomposition of sulfur species as a result of the thermal decomposition of sulfur compounds at high temperatures compounds at high temperatures


Affected Units or Equipment Affected Units or Equipment – Piping and equipment in high temperature environments Piping and equipment in high temperature environments

where sulfur-containing streams are processedwhere sulfur-containing streams are processed

– Coker, vacuum, visbreaker and hydroprocessing unitsCoker, vacuum, visbreaker and hydroprocessing units

– Heaters fired with oil, gas, coke and most other sources of Heaters fired with oil, gas, coke and most other sources of fuel - depended on sulfur levels in the fuelfuel - depended on sulfur levels in the fuel

– Boilers and high temperature equipment exposed to sulfur-Boilers and high temperature equipment exposed to sulfur-containing gasescontaining gases

Appearance or Morphology of Damage Appearance or Morphology of Damage – Depending on service conditions, corrosion is most often in Depending on service conditions, corrosion is most often in

the form of uniform thinning but can also occur as the form of uniform thinning but can also occur as localized localized corrosion or high velocity erosion-corrosion damagecorrosion or high velocity erosion-corrosion damage


Figure 4-65 - Modified McConomy curves Figure 4-65 - Modified McConomy curves showing typical effect of temperature on showing typical effect of temperature on high temperature sulfidation of steels and high temperature sulfidation of steels and stainless steelsstainless steels

Figure 4-66 - Multiplier for corrosion Figure 4-66 - Multiplier for corrosion rates in Figure 4-65 based on differing rates in Figure 4-65 based on differing sulfur content of processsulfur content of process fluidfluid

Prevention/MitigationPrevention/Mitigation– Resistance to sulfidation is generally achieved by upgrading to Resistance to sulfidation is generally achieved by upgrading to

a higher chromium alloy a higher chromium alloy

– Aluminum diffusion treatment of low alloy steel components is Aluminum diffusion treatment of low alloy steel components is sometimes used to reduce sulfidation rates and minimize scale sometimes used to reduce sulfidation rates and minimize scale formation (it may not offer complete protection)formation (it may not offer complete protection)

Inspection and Monitoring Inspection and Monitoring – Process conditions should be monitored for increasing Process conditions should be monitored for increasing

temperatures and/or changing sulfur levels temperatures and/or changing sulfur levels

– Temperatures can be monitored through the use of tubeskin Temperatures can be monitored through the use of tubeskin thermocouples and/or infrared thermography thermocouples and/or infrared thermography

– Evidence, of thinning can be detected using external ultrasonic Evidence, of thinning can be detected using external ultrasonic thickness measurements and profile radiography thickness measurements and profile radiography


Related Mechanisms Related Mechanisms – Sulfidation is also known as sulfidic corrosion Sulfidation is also known as sulfidic corrosion


Description of Damage Description of Damage – Surface initiated cracks caused by environmental cracking of Surface initiated cracks caused by environmental cracking of

300 Series SS and some nickel base alloys under the combined 300 Series SS and some nickel base alloys under the combined action of tensile stress, temperature and an aqueous chloride action of tensile stress, temperature and an aqueous chloride environment. environment. The presence of dissolved oxygen increases The presence of dissolved oxygen increases propensity for crackingpropensity for cracking

Environment-Assisted Cracking Environment-Assisted Cracking

Chloride Stress Corrosion Cracking Chloride Stress Corrosion Cracking

Affected Materials Affected Materials – All 300 Series SS are highly susceptibleAll 300 Series SS are highly susceptible– Duplex stainless steels are more resistantDuplex stainless steels are more resistant– Nickel base alloys are highly resistant Nickel base alloys are highly resistant

Critical Factors Critical Factors – Chloride content, pH, temperature, stress, presence of oxygen Chloride content, pH, temperature, stress, presence of oxygen

and alloy composition and alloy composition – Increasing temperatures increase the susceptibility to cracking Increasing temperatures increase the susceptibility to cracking – Increasing levels of chloride increase the likelihood of Increasing levels of chloride increase the likelihood of

cracking cracking – Alternate exposures to wet-dry conditions or steam and water Alternate exposures to wet-dry conditions or steam and water

are also conducive to cracking are also conducive to cracking – SCC usually occurs at pH values above 2 SCC usually occurs at pH values above 2

Chloride Stress Corrosion CrackingChloride Stress Corrosion Cracking

Critical Factors Critical Factors – Cracking usually occurs at metal temperatures above about Cracking usually occurs at metal temperatures above about

140°F (60°C), (but also can be found at lower temperatures) 140°F (60°C), (but also can be found at lower temperatures)

– Highly stressed or cold worked components, such as expansion Highly stressed or cold worked components, such as expansion bellows, are highly susceptible to crackingbellows, are highly susceptible to cracking

– Oxygen dissolved in the water normally accelerates SCC but it Oxygen dissolved in the water normally accelerates SCC but it is not clear whether there is an oxygen concentration threshold is not clear whether there is an oxygen concentration threshold below which chloride SCC is impossiblebelow which chloride SCC is impossible

– Nickel content of the alloy has a major affect on resistance (8 to Nickel content of the alloy has a major affect on resistance (8 to 12 %)12 %)

– Alloys with nickel contents above 35% are highly resistant and Alloys with nickel contents above 35% are highly resistant and alloys above 45% are nearly immune alloys above 45% are nearly immune


Affected Units or Equipment Affected Units or Equipment – All 300 Series SS piping and pressure vessel components in All 300 Series SS piping and pressure vessel components in

any process units are susceptible to Cl SCCany process units are susceptible to Cl SCC

– Water-cooled condensers and in the process side of crude Water-cooled condensers and in the process side of crude tower overhead condenserstower overhead condensers

– Drains in hydro processing units during start-up/shutdown if Drains in hydro processing units during start-up/shutdown if not properly purgednot properly purged

– Bellows and instrument tubing, particularly those associated Bellows and instrument tubing, particularly those associated with hydrogen recycle streams contaminated with chlorideswith hydrogen recycle streams contaminated with chlorides

– External CExternal Cll SCC has also been a problem on insulated SCC has also been a problem on insulated surfaces when insulation gets wetsurfaces when insulation gets wet

– Boiler drain linesBoiler drain lines


Appearance or Morphology of Damage Appearance or Morphology of Damage – Surface breaking cracks can occur from the process side or Surface breaking cracks can occur from the process side or

externally under insulation (Figure 4-77)externally under insulation (Figure 4-77)

– The material usually shows no visible signs of corrosionThe material usually shows no visible signs of corrosion

– Characteristic stress corrosion cracks have many branches Characteristic stress corrosion cracks have many branches and may be visually detectable by a craze-cracked and may be visually detectable by a craze-cracked appearance of the surface (Figure 4-78, Figure 4-79 and appearance of the surface (Figure 4-78, Figure 4-79 and Figure 4-80)Figure 4-80)

– Metallography of cracked samples typically shows branched Metallography of cracked samples typically shows branched transgranular cracks (Figure 4-81 and Figure 4-82) transgranular cracks (Figure 4-81 and Figure 4-82)

– Sometimes intergranular cracking of sensitised 300 Series SS Sometimes intergranular cracking of sensitised 300 Series SS may also be seenmay also be seen

– Fracture surfaces often have a brittle appearance Fracture surfaces often have a brittle appearance


Figure 4-77 - External cracking Figure 4-77 - External cracking of Type 304SS instrument of Type 304SS instrument tubing under insulation tubing under insulation

Figure 4-78 - Cracking on the shell side of Figure 4-78 - Cracking on the shell side of Type 316L SS tubes in steam service at Type 316L SS tubes in steam service at 450°F (232°C), showing tubes after PT 450°F (232°C), showing tubes after PT inspection. The cracks can be seen in the inspection. The cracks can be seen in the

center tube (arrow)center tube (arrow)

Figure 4-79 - Close-up of Figure 4-79 - Close-up of the tube in Figure 4-78 the tube in Figure 4-78 showing tight cracks with a showing tight cracks with a spider web appearance spider web appearance

Figure 4-80 - Other fine Figure 4-80 - Other fine branching cracks on the surface branching cracks on the surface of SS that appear more clearly of SS that appear more clearly after PTafter PT inspectioninspection

Figure 4-81 - Photomicrograph Figure 4-81 - Photomicrograph of a cross-section of sample in of a cross-section of sample in Figure 4-79 showing fine Figure 4-79 showing fine branching cracks. (Unetched, branching cracks. (Unetched, Mag. 50x) Mag. 50x)

Figure 4-82 - Another Figure 4-82 - Another photomicrograph of a photomicrograph of a cross-section of a cracked cross-section of a cracked tube illustrating the tube illustrating the transgranular mode of transgranular mode of cracking initiating on the cracking initiating on the surface. (Etched)surface. (Etched)

Fracture surface of Fracture surface of TG SCC (austenitic TG SCC (austenitic stainless steel)stainless steel)

Surface of Surface of mechanical fracture mechanical fracture of the same steelof the same steel

Prevention/MitigationPrevention/Mitigation– Use resistant materials of constructionUse resistant materials of construction

– Use low chloride content water and dry out thoroughly and Use low chloride content water and dry out thoroughly and quicklyquickly

– Properly applied coatings under insulationProperly applied coatings under insulation

– Avoid designs that allow stagnant regions where chlorides Avoid designs that allow stagnant regions where chlorides can concentrate or depositcan concentrate or deposit

– A high temperature stress relief of 300 Series SS after A high temperature stress relief of 300 Series SS after fabrication may reduce residual stressesfabrication may reduce residual stresses


Inspection and Monitoring Inspection and Monitoring – Cracking is surface connected and may be detected Cracking is surface connected and may be detected visuallyvisually

in some cases.in some cases.

– PTPT (no extremely fine) or phase analysis EC techniques are (no extremely fine) or phase analysis EC techniques are the preferred methods.the preferred methods.

– Eddy current inspection methods (condenser tubes as well as Eddy current inspection methods (condenser tubes as well as piping and pressure vessels)piping and pressure vessels)

– Special surface preparation methods, including polishing or Special surface preparation methods, including polishing or high-pressure water blast (high pressure services)high-pressure water blast (high pressure services)

– UTUT

– RT - not sufficiently sensitive to detect cracks except in RT - not sufficiently sensitive to detect cracks except in advanced stagesadvanced stages where a significant network of cracks has where a significant network of cracks has developeddeveloped


Related Mechanisms Related Mechanisms – Caustic SCC and polythionic acid SCC Caustic SCC and polythionic acid SCC


Description of Damage Description of Damage – A form of fatigue cracking in which cracks develop under A form of fatigue cracking in which cracks develop under

the combined affects of cyclic loading and corrosion. the combined affects of cyclic loading and corrosion. Cracking often initiates at a stress concentration such as a Cracking often initiates at a stress concentration such as a pit in the surface pit in the surface

– Cracking can initiate at multiple sitesCracking can initiate at multiple sites Affected Materials Affected Materials

– All metals and alloys All metals and alloys

Corrosion FatigueCorrosion Fatigue

Critical FactorsCritical Factors– Material, corrosive environment, cyclic stresses and stress Material, corrosive environment, cyclic stresses and stress

raisersraisers

– Cracking is more likely to occur in environments that Cracking is more likely to occur in environments that promote pitting or localized corrosion under cyclic stress promote pitting or localized corrosion under cyclic stress due to thermal stress, vibration or differential expansiondue to thermal stress, vibration or differential expansion

– Corrosion promotes failure at a lower stress and number of Corrosion promotes failure at a lower stress and number of cycles than the materials' normal endurance limit in the cycles than the materials' normal endurance limit in the absence of corrosion and often results in propagation of absence of corrosion and often results in propagation of multiple parallel cracksmultiple parallel cracks

– Crack initiation sites include concentrators such as pits, Crack initiation sites include concentrators such as pits, notches, surface defects, changes in section or fillet welds notches, surface defects, changes in section or fillet welds


Affected Units or Equipment Affected Units or Equipment – Rotating equipment, deaerators and cycling boilers, as well as Rotating equipment, deaerators and cycling boilers, as well as

any equipment subjected to cyclic stresses in a corrosive any equipment subjected to cyclic stresses in a corrosive environment environment

» Rotating Equipment - Galvanic couples between the impeller and the Rotating Equipment - Galvanic couples between the impeller and the pump shaft or other corrosion mechanisms may result in a pitting pump shaft or other corrosion mechanisms may result in a pitting problem on the shaft problem on the shaft

» DeaeratorsDeaerators

» Cycling Boilers - A cycling boiler may see several hundred cold starts Cycling Boilers - A cycling boiler may see several hundred cold starts over its useful life which, because of differential expansion, continually over its useful life which, because of differential expansion, continually cracks the protective magnetite scale, allowing corrosion to continue cracks the protective magnetite scale, allowing corrosion to continue


Appearance or Morphology of Damage Appearance or Morphology of Damage – The fatigue fracture is brittle and the cracks are most often The fatigue fracture is brittle and the cracks are most often

transgranular, as in stress-corrosion cracking, but not branched, transgranular, as in stress-corrosion cracking, but not branched, and often results in propagation of multiple parallel cracksand often results in propagation of multiple parallel cracks

– Fatigue cracking will be evidenced by very little plastic Fatigue cracking will be evidenced by very little plastic deformation except that final fracture may occur by mechanical deformation except that final fracture may occur by mechanical overload accompanied by plastic deformationoverload accompanied by plastic deformation

– In cycling boilers, the damage usually appears first on the water In cycling boilers, the damage usually appears first on the water side of buckstay attachments (Figure 4-83). The cracking pattern side of buckstay attachments (Figure 4-83). The cracking pattern may be circular cracks surrounding the weld between the may be circular cracks surrounding the weld between the buckstay attachment and the waterwall tube. In cross-section, the buckstay attachment and the waterwall tube. In cross-section, the cracks tend to be bulbous with numerous lobes (Figure 4-84). cracks tend to be bulbous with numerous lobes (Figure 4-84). The crack tips themselves may be somewhat blunted but are The crack tips themselves may be somewhat blunted but are oxide filled and transgranularoxide filled and transgranular

– In sulfidizing environments, cracks will have a similar In sulfidizing environments, cracks will have a similar appearance but will be filled with a sulfide scaleappearance but will be filled with a sulfide scale

– In rotating equipment, most cracking is transgranular with In rotating equipment, most cracking is transgranular with minimal branchingminimal branching


Figure 4-83 - Photograph of a carbon Figure 4-83 - Photograph of a carbon steel boiler tube cut in half lengthwise. steel boiler tube cut in half lengthwise. Corrosion fatigue cracks initiate at the Corrosion fatigue cracks initiate at the I.D. of a tube, opposite a buckstay I.D. of a tube, opposite a buckstay attachment on the O.D. (Mag. 1x) attachment on the O.D. (Mag. 1x)

Figure 4-84- Photomicrograph Figure 4-84- Photomicrograph showing the crack morphology showing the crack morphology that is rounded with multiple that is rounded with multiple lobes, and may branch to form lobes, and may branch to form "rabbit ears." (Mag. 25x, etched.)"rabbit ears." (Mag. 25x, etched.)

Prevention/MitigationPrevention/Mitigation– Rotating EquipmentRotating Equipment

» Modify the corrosive environment by using coatings and/or inhibitorsModify the corrosive environment by using coatings and/or inhibitors

» Minimize galvanic couple effectsMinimize galvanic couple effects

» Use more corrosion resistant materialsUse more corrosion resistant materials

– DeaeratorsDeaerators» Proper feedwater and condensate chemical controlProper feedwater and condensate chemical control

» Minimize residual welding and fabrication stresses through PWHTMinimize residual welding and fabrication stresses through PWHT

» Minimize weld reinforcement by grinding weld contours smoothMinimize weld reinforcement by grinding weld contours smooth

– Cycling BoilersCycling Boilers» Start up slowly to minimize the differential expansion strainsStart up slowly to minimize the differential expansion strains

» Always start up with the chemistry of the boiler water under proper Always start up with the chemistry of the boiler water under proper controlcontrol


Inspection and MonitoringInspection and Monitoring– Rotating EquipmentRotating Equipment

» UT and MT techniquesUT and MT techniques

– DeaeratorsDeaerators» Cracking is generally detected with WFMT inspection, Cracking is generally detected with WFMT inspection, » Many of the cracks are very tight and difficult to detectMany of the cracks are very tight and difficult to detect

– Cycling BoilersCycling Boilers» The first sign of damage is usually a pinhole leak on the cold side of a The first sign of damage is usually a pinhole leak on the cold side of a

waterwall tube at a buckstay attachmentwaterwall tube at a buckstay attachment» Inspect highly stressed regions in the boiler by UT or EMATS Inspect highly stressed regions in the boiler by UT or EMATS

techniquestechniques» Cracking may occur at the membranes in the highly stressed regions, Cracking may occur at the membranes in the highly stressed regions,

particularly corners at buckstaysparticularly corners at buckstays

Related MechanismsRelated Mechanisms– Mechanical fatigue and vibration induced fatigue Mechanical fatigue and vibration induced fatigue


Description of Damage Description of Damage – form of stress corrosion cracking characterized by surface-form of stress corrosion cracking characterized by surface-

initiated cracks that occur in piping and equipment exposed initiated cracks that occur in piping and equipment exposed to caustic, primarily adjacent to non-PWHT'd welds to caustic, primarily adjacent to non-PWHT'd welds

Affected Materials Affected Materials – Carbon steel, low alloy steels and 300 Series SS are Carbon steel, low alloy steels and 300 Series SS are

susceptible. Nickel base alloys are more resistant susceptible. Nickel base alloys are more resistant

Caustic Stress Corrosion Cracking Caustic Stress Corrosion Cracking

Critical Factors Critical Factors – Susceptibility to caustic embrittlement in caustic soda (NaOH) and Susceptibility to caustic embrittlement in caustic soda (NaOH) and

caustic potash (KOH) solutions is a function of caustic strength, metal caustic potash (KOH) solutions is a function of caustic strength, metal temperature and stress levels.temperature and stress levels.

– Conditions likely to result in cracking have been established through Conditions likely to result in cracking have been established through plant experience and are presented in Figure 4-85.plant experience and are presented in Figure 4-85.

– Cracking can occur at low caustic levels if a concentrating mechanism is Cracking can occur at low caustic levels if a concentrating mechanism is present present

– Stresses that promote cracking can be residual that result from welding or Stresses that promote cracking can be residual that result from welding or from cold working as well as applied stresses (Figure 4-86; Figure 4-87)from cold working as well as applied stresses (Figure 4-86; Figure 4-87)

– It is generally accepted that stresses approaching yield are required for It is generally accepted that stresses approaching yield are required for SCC so that thermal stress relief (PWHT) is effective in preventing SCC so that thermal stress relief (PWHT) is effective in preventing caustic SCC. Although failures have occurred at stresses that are low caustic SCC. Although failures have occurred at stresses that are low relative to yield, they are considered more rare (Figure 4-88; Figure 4-relative to yield, they are considered more rare (Figure 4-88; Figure 4-91).91).

– Crack propagation rates increase dramatically with temperature and can Crack propagation rates increase dramatically with temperature and can sometimes grow through wall in a matter of hours or days during sometimes grow through wall in a matter of hours or days during temperature excursions, especially if conditions promote caustic temperature excursions, especially if conditions promote caustic concentrationconcentration


Figure 4-85 - Recommended Figure 4-85 - Recommended operating limits for carbon steel operating limits for carbon steel in caustic service in caustic service

Figure 4-86 - Cracking Figure 4-86 - Cracking initiating on the inside surface initiating on the inside surface of a non-stress relieved CS of a non-stress relieved CS heat exchanger bend after 8 heat exchanger bend after 8 years in 15% to 20% caustic years in 15% to 20% caustic service at 140°F to 240°F service at 140°F to 240°F (60°C to 115°C)(60°C to 115°C)

Figure 4-88 - Cracking at Figure 4-88 - Cracking at a boiler tubesheet due to a boiler tubesheet due to caustic concentrating caustic concentrating between the tube and the between the tube and the tubesheet tubesheet

Figure 4-87 - Figure 4-87 - Photomicrograph of a Photomicrograph of a crack in the tube crack in the tube shown in Figure 4-86shown in Figure 4-86

Figure 4-91 - Figure 4-90, etched Figure 4-91 - Figure 4-90, etched

Affected Units or Equipment Affected Units or Equipment – Caustic embrittlement is often found in piping and equipment Caustic embrittlement is often found in piping and equipment

that handles caustic, including Hthat handles caustic, including H22S and mercaptan removal S and mercaptan removal

units, as well as equipment that uses caustic for neutralization units, as well as equipment that uses caustic for neutralization in sulfuric acid alkylation units and HF alkylation units. in sulfuric acid alkylation units and HF alkylation units.

– Failures have occurred in improperly heat-traced piping or Failures have occurred in improperly heat-traced piping or equipment as well as heating coils and other heat transfer equipment as well as heating coils and other heat transfer equipment.equipment.

– Caustic embrittlement may occur in equipment as a result of Caustic embrittlement may occur in equipment as a result of steam cleaning after being in caustic service.steam cleaning after being in caustic service.

– Traces of caustic can become concentrated in BFW and can Traces of caustic can become concentrated in BFW and can result in caustic embrittlement of boiler tubes that alternate result in caustic embrittlement of boiler tubes that alternate between wet and dry conditions due to overfiring between wet and dry conditions due to overfiring


Appearance or Morphology of DamageAppearance or Morphology of Damage– Caustic stress corrosion cracking typically propagates Caustic stress corrosion cracking typically propagates

parallel to the weld in adjacent base metal but can also occur parallel to the weld in adjacent base metal but can also occur in the weld deposit or heat-affected zonesin the weld deposit or heat-affected zones

– The pattern of cracking observed on the steel surface is The pattern of cracking observed on the steel surface is sometimes described as a spider web of small cracks which sometimes described as a spider web of small cracks which often initiate at or interconnect with weld-related flaws → often initiate at or interconnect with weld-related flaws → local stress raiserslocal stress raisers

– Cracks can be confirmed through metallographic Cracks can be confirmed through metallographic examination. Cracks are predominantly intergranularexamination. Cracks are predominantly intergranular

– Cracking in 300 Series SS is typically transgranular, it is Cracking in 300 Series SS is typically transgranular, it is very difficult to distinguish from chloride stress corrosion very difficult to distinguish from chloride stress corrosion cracking (Figure 4-92)cracking (Figure 4-92)


Figure 4-92 - Stainless steel expansion bellows Figure 4-92 - Stainless steel expansion bellows from a steam-driven turbine previously from a steam-driven turbine previously subjected to a caustic carryover upset condition subjected to a caustic carryover upset condition

Prevention/MitigationPrevention/Mitigation– It can be effectively prevented by means of a stress-relieving It can be effectively prevented by means of a stress-relieving

heat treatment - 1150°F (621 °C) is considered an effective heat treatment - 1150°F (621 °C) is considered an effective stress relieving heat treatment for carbon steelstress relieving heat treatment for carbon steel

– 300 Series SS offer little advantage in resistance to cracking 300 Series SS offer little advantage in resistance to cracking over CS.over CS.

– Nickel base alloys are more resistant to cracking and may be Nickel base alloys are more resistant to cracking and may be required at higher temperatures and/or caustic concentrationsrequired at higher temperatures and/or caustic concentrations

– Steamout of non-PWHT'd carbon steel piping and Steamout of non-PWHT'd carbon steel piping and equipment should be avoided. Equipment should be water equipment should be avoided. Equipment should be water washed before steamout. If steamout is required - only low-washed before steamout. If steamout is required - only low-pressure steam should be used for short periods of time to pressure steam should be used for short periods of time to minimize exposureminimize exposure

– Proper design and operation of the injection system is Proper design and operation of the injection system is required - caustic is properly dispersed before entering the required - caustic is properly dispersed before entering the high-temperature crude preheat systemhigh-temperature crude preheat system


Inspection and MonitoringInspection and Monitoring– Crack detection is best performed with WFMT, EC, RT or Crack detection is best performed with WFMT, EC, RT or

ACFM techniques. Surface preparation by grit blasting, high ACFM techniques. Surface preparation by grit blasting, high pressure water blasting or other methods is usually requiredpressure water blasting or other methods is usually required

– PT is not effective for finding tight, scale-filled cracks and PT is not effective for finding tight, scale-filled cracks and should not be used for detectionshould not be used for detection

– Crack depths can be measured with a suitable UT technique Crack depths can be measured with a suitable UT technique including external SWUTincluding external SWUT

– AET can be used for monitoring crack growth and locating AET can be used for monitoring crack growth and locating growing cracksgrowing cracks

Related MechanismsRelated Mechanisms– Amine cracking and carbonate cracking are two other similar Amine cracking and carbonate cracking are two other similar

forms of alkaline SCC forms of alkaline SCC


Description of DamageDescription of Damage– Hydrogen BlisteringHydrogen Blistering

» surface bulges on the ID, the OD or within the wall surface bulges on the ID, the OD or within the wall thickness of a pipe or pressure vessel. thickness of a pipe or pressure vessel.

Hydrogen atoms that diffuse into the steel, and collect at a Hydrogen atoms that diffuse into the steel, and collect at a discontinuity in the steel such as an inclusion or lamination discontinuity in the steel such as an inclusion or lamination combine to form hydrogen molecules that are too large to diffuse combine to form hydrogen molecules that are too large to diffuse out and the pressure builds to the point where local deformation out and the pressure builds to the point where local deformation occurs, forming a blisteroccurs, forming a blister

Blistering results from hydrogen generated by corrosion, not Blistering results from hydrogen generated by corrosion, not hydrogen gas from the process stream. (Figure 5-21 and Figure 5-hydrogen gas from the process stream. (Figure 5-21 and Figure 5-22.) 22.)

Wet HWet H22S DamageS Damage (Blistering/HIC/SOHIC/SSC)(Blistering/HIC/SOHIC/SSC)

Figure 5-21 - Schematic Figure 5-21 - Schematic of hydrogen blistering and of hydrogen blistering and HIC damageHIC damage

Figure 5-22 - Extensive Figure 5-22 - Extensive hydrogen blistering on the hydrogen blistering on the surface of steel pressure surface of steel pressure vesselvessel

Wet HWet H22S Damage S Damage (Blistering/HIC/SOHIC/SSC)(Blistering/HIC/SOHIC/SSC) Description of DamageDescription of Damage

– Hydrogen Induced Cracking (HIC)Hydrogen Induced Cracking (HIC)» Hydrogen blisters can form at many different depths from Hydrogen blisters can form at many different depths from

the surface of the steel, in the middle of the plate or near a the surface of the steel, in the middle of the plate or near a weld. In some cases, neighboring or adjacent blisters that weld. In some cases, neighboring or adjacent blisters that are at slightly different depths (planes) may develop cracks are at slightly different depths (planes) may develop cracks that link them together. Interconnecting cracks between the that link them together. Interconnecting cracks between the blisters often have a stair step appearance, and so HIC is blisters often have a stair step appearance, and so HIC is sometimes referred to as „stepwise cracking“ (Figure 5-23, sometimes referred to as „stepwise cracking“ (Figure 5-23, Figure 5-24 and Figure 5-25) Figure 5-24 and Figure 5-25)

Figure 5-23 - Cross-section of Figure 5-23 - Cross-section of plate showing HIC damage in plate showing HIC damage in the shell of a trim cooler the shell of a trim cooler which had been cooling which had been cooling vapors off a HHPS vessel in a vapors off a HHPS vessel in a hydroprocessing unit hydroprocessing unit

Figure 5-24 - High Figure 5-24 - High magnification magnification photomicrograph of HIC photomicrograph of HIC damagedamage

Figure 5-25 - High magnification photomicrograph Figure 5-25 - High magnification photomicrograph showing stepwise cracking nature of HICshowing stepwise cracking nature of HIC damage damage


– Stress Oriented Hydrogen Induced Cracking Stress Oriented Hydrogen Induced Cracking (SOHIC)(SOHIC)

» SOHIC is similar to HIC but is a potentially more SOHIC is similar to HIC but is a potentially more damaging form of cracking which appears as arrays of damaging form of cracking which appears as arrays of cracks stacked on top of each other. The result is a cracks stacked on top of each other. The result is a through-thickness crack that is perpendicular to the through-thickness crack that is perpendicular to the surface and is driven by high levels of stress (residual or surface and is driven by high levels of stress (residual or applied) applied)

» Usually appear in the base metal adjacent to the weld heat Usually appear in the base metal adjacent to the weld heat affected zones where they initiate from HIC damage or affected zones where they initiate from HIC damage or other cracks or defects including sulfide stress cracks other cracks or defects including sulfide stress cracks (Figure 5-26 and Figure 5-27) (Figure 5-26 and Figure 5-27)

Figure 5-26 - Schematic Figure 5-26 - Schematic showing hydrogen showing hydrogen blistering that is blistering that is accompanied by SOHIC accompanied by SOHIC damage at the weld damage at the weld

Figure 5-27 - Schematic of Figure 5-27 - Schematic of SOHIC damage at a fillet SOHIC damage at a fillet weld that is usually a weld that is usually a combination of SSC andcombination of SSC and

SOHICSOHIC


– Sulfide Stress Corrosion Cracking (SSC) Sulfide Stress Corrosion Cracking (SSC) » Sulfide Stress Cracking (SSC) is defined as cracking of metal under the Sulfide Stress Cracking (SSC) is defined as cracking of metal under the

combined action of tensile stress and corrosion in the presence of water combined action of tensile stress and corrosion in the presence of water and Hand H22SS

» SSC resulting from absorption of atomic hydrogen that is produced by SSC resulting from absorption of atomic hydrogen that is produced by the sulfide corrosion process on the metal surfacethe sulfide corrosion process on the metal surface

» SSC can initiate on the surface in highly localized zones of high SSC can initiate on the surface in highly localized zones of high hardness in the weld metal and heat affected zoneshardness in the weld metal and heat affected zones

» PWHT is beneficial in reducing the hardness and residual stresses that PWHT is beneficial in reducing the hardness and residual stresses that render a steel susceptible to SSC. High strength steels are also render a steel susceptible to SSC. High strength steels are also susceptible to SSC but these are only used in limited applications in the susceptible to SSC but these are only used in limited applications in the refining industry (Figure 5-28 and Figure 5-29)refining industry (Figure 5-28 and Figure 5-29)

Figure 5-28 - Photograph Figure 5-28 - Photograph showing WFMT of showing WFMT of SOHIC damage SOHIC damage

Figure 5-29 - Figure 5-29 - Schematic of SSC Schematic of SSC damage of a hard damage of a hard weldweld

Affected MaterialsAffected Materials– Carbon steel and low alloy steelsCarbon steel and low alloy steels

Critical Factors Critical Factors – environmental conditions (pH, Henvironmental conditions (pH, H22S level, contaminants, S level, contaminants,

temperature) temperature)

– material properties (hardness, microstructure, strength) material properties (hardness, microstructure, strength)

– tensile stress level (applied or residual)tensile stress level (applied or residual)

Wet HWet H22S Damage S Damage (Blistering/HIC/SOHIC/SSC)(Blistering/HIC/SOHIC/SSC)

Critical Factors Critical Factors – pH - Hydrogen permeation or diffusion rates have been pH - Hydrogen permeation or diffusion rates have been

found to be minimal at pH 7 and increase atfound to be minimal at pH 7 and increase at both higher and both higher and lower pH's. The presence of hydrogen cyanide (HCN) in the lower pH's. The presence of hydrogen cyanide (HCN) in the water phase significantly increases permeation in alkaline water phase significantly increases permeation in alkaline (high pH) sour water (high pH) sour water

– HH22S - Hydrogen permeation increases with increasing HS - Hydrogen permeation increases with increasing H22S S

partial pressure due to a concurrent increase in the Hpartial pressure due to a concurrent increase in the H22S S

concentration in the water phase concentration in the water phase


Wet HWet H22S Damage S Damage (Blistering/HIC/SOHIC/SSC)(Blistering/HIC/SOHIC/SSC) Critical Factors Critical Factors

– Temperature:Temperature:» Blistering, HIC, and SOHIC damage have been found to Blistering, HIC, and SOHIC damage have been found to

occur between ambient and 300°F (150°C) or higheroccur between ambient and 300°F (150°C) or higher» SSC generally occurs below about 180°F (82°C)SSC generally occurs below about 180°F (82°C)

– Hardness:Hardness:» Typical low-strength carbon steels used in refinery Typical low-strength carbon steels used in refinery

applications should be controlled to produce weld applications should be controlled to produce weld hardness < 200 HB in accordance with NACE RP0472hardness < 200 HB in accordance with NACE RP0472.. These steels are not generally susceptible to SSC unless These steels are not generally susceptible to SSC unless localized zones of hardness above 237 HB are presentlocalized zones of hardness above 237 HB are present

» Blistering, HIC and SOHIC damage are not related to Blistering, HIC and SOHIC damage are not related to steel hardnesssteel hardness

Wet HWet H22S Damage S Damage (Blistering/HIC/SOHIC/SSC)(Blistering/HIC/SOHIC/SSC) Critical Factors Critical Factors

– Steelmaking:Steelmaking:» Blistering and HIC damage are strongly affected by the Blistering and HIC damage are strongly affected by the

presence of inclusions and laminations which provide presence of inclusions and laminations which provide sites for diffusing hydrogen to accumulatesites for diffusing hydrogen to accumulate

» Steel chemistry and manufacturing methods also affect Steel chemistry and manufacturing methods also affect susceptibility and can be tailored to produce the HIC susceptibility and can be tailored to produce the HIC resistant steels outlined in NACE Publication 8X194resistant steels outlined in NACE Publication 8X194

» Improving steel cleanliness and processing to minimize Improving steel cleanliness and processing to minimize blistering and HIC damage may still leave the steel blistering and HIC damage may still leave the steel susceptible to SOHICsusceptible to SOHIC

» The disadvantage is that an absence of visual blistering The disadvantage is that an absence of visual blistering may leave a false sense of security that Hmay leave a false sense of security that H22S damage is not S damage is not active yet subsurface SOHIC damage may be presentactive yet subsurface SOHIC damage may be present

Critical Factors Critical Factors – PWHT:PWHT:

» Blistering and HIC damage develop without applied or Blistering and HIC damage develop without applied or residual stress so that PWHT will not prevent them from residual stress so that PWHT will not prevent them from occurringoccurring

» High local stresses or notch-like discontinuities such as High local stresses or notch-like discontinuities such as shallow sulfide stress cracks can serve as initiation sites shallow sulfide stress cracks can serve as initiation sites for SOHICfor SOHIC

» PWHT is highly effective in preventing or eliminating PWHT is highly effective in preventing or eliminating SSC by reduction of both hardness and residual stressSSC by reduction of both hardness and residual stress

» SOHIC is driven by localized stresses so that PWHT is SOHIC is driven by localized stresses so that PWHT is also somewhat effective in reducing SOHIC damagealso somewhat effective in reducing SOHIC damage


Affected Units or Equipment Affected Units or Equipment – Blistering, HIC, SOHIC and SSC damage can occur throughout the Blistering, HIC, SOHIC and SSC damage can occur throughout the

refinery wherever there is a wet Hrefinery wherever there is a wet H22S environment presentS environment present– In hydroprocessing units, increasing concentration of ammonium bisulfide In hydroprocessing units, increasing concentration of ammonium bisulfide

above 2% increases the potential for blistering, HIC and SOHIC.above 2% increases the potential for blistering, HIC and SOHIC.– Cyanides significantly increase the probability and severity of blistering, Cyanides significantly increase the probability and severity of blistering,

HIC and SOHIC damage - especially for the vapor recovery sections of HIC and SOHIC damage - especially for the vapor recovery sections of the fluid catalytic cracking and delayed coking units. the fluid catalytic cracking and delayed coking units.

– Typical locations - fractionator overhead drums, fractionation towers, Typical locations - fractionator overhead drums, fractionation towers, absorber and stripper towers, compressor interstage separators and absorber and stripper towers, compressor interstage separators and knockout drums and various heat exchangers, condensers, and coolers. knockout drums and various heat exchangers, condensers, and coolers.

– Sour water stripper and amine regenerator overhead systems are Sour water stripper and amine regenerator overhead systems are especiallyespeciallyprone to wet Hprone to wet H22S damageS damage

– SSC is most likely found in hard weld and heat affected zones and in high SSC is most likely found in hard weld and heat affected zones and in high strength components including bolts, relief valve springs, 400 Series SS strength components including bolts, relief valve springs, 400 Series SS valve trim, compressor shafts, sleeves and springs valve trim, compressor shafts, sleeves and springs


Appearance or Morphology of Damage Appearance or Morphology of Damage – All four forms of wet HAll four forms of wet H22S damage are best illustrated though S damage are best illustrated though

the pictures and diagrams shown in Figure 5-21 through the pictures and diagrams shown in Figure 5-21 through Figure 5-30Figure 5-30

– Hydrogen blisters appear as bulges on the ID or OD surface Hydrogen blisters appear as bulges on the ID or OD surface of the steel and can be found anywhere in the shell plate or of the steel and can be found anywhere in the shell plate or head of a pressure vessel. Blistering has been found on rare head of a pressure vessel. Blistering has been found on rare occasions in pipe and very rarely in the middle of a weld occasions in pipe and very rarely in the middle of a weld

– HIC damage can occur wherever blistering or subsurface HIC damage can occur wherever blistering or subsurface laminations are presentlaminations are present

– In pressure-containing equipment, SOHIC and SSC damage In pressure-containing equipment, SOHIC and SSC damage is most often associated with the weldments. is most often associated with the weldments.

– SSC can also be found at any location where zones of high SSC can also be found at any location where zones of high hardness are found in vessels or in high strength steel hardness are found in vessels or in high strength steel components components


Figure 5-30 - Schematic showing morphology of Figure 5-30 - Schematic showing morphology of sulfide stress cracking in a hard heat affected zone sulfide stress cracking in a hard heat affected zone

Prevention/MitigationPrevention/Mitigation– Effective barriers that protect the surface of the steel from the wet HEffective barriers that protect the surface of the steel from the wet H22S S

environmentenvironment– Process changes that affect the pH of the water phase and/or ammonia or Process changes that affect the pH of the water phase and/or ammonia or

cyanide concentration can help to reduce damage. cyanide concentration can help to reduce damage. » Cyanides can be converted to harmless thiocyanates by injecting dilute Cyanides can be converted to harmless thiocyanates by injecting dilute

streams of ammonium polysulfides. Injection facilities require careful design.streams of ammonium polysulfides. Injection facilities require careful design.

– HIC-resistant steels can be used to minimize the susceptibility to HIC-resistant steels can be used to minimize the susceptibility to blistering and HIC damage. blistering and HIC damage.

– SSC can generally be prevented by limiting the hardness of welds and SSC can generally be prevented by limiting the hardness of welds and heat affected zones to 200 HB maximum through preheat, PWHT, weld heat affected zones to 200 HB maximum through preheat, PWHT, weld procedures and control of carbon equivalents. procedures and control of carbon equivalents.

» Depending on the service environment, small zones of hardness up to 22 Depending on the service environment, small zones of hardness up to 22 HRC should be resistant to SSCHRC should be resistant to SSC

– PWHT can also help to minimize susceptibility to SOHIC. PWHT can also help to minimize susceptibility to SOHIC. – Specialized corrosion inhibitors can be used.Specialized corrosion inhibitors can be used.


Inspection and MonitoringInspection and Monitoring– Process conditions should be evaluated by process engineers Process conditions should be evaluated by process engineers

and corrosion/ materials specialists to identify piping and and corrosion/ materials specialists to identify piping and equipment where conditions are most likely to promote wet Hequipment where conditions are most likely to promote wet H22S S damagedamage

– Although cracks may be seen visually, crack detection is best Although cracks may be seen visually, crack detection is best performed with WFMT, EC, RT or ACFM techniques. Surface performed with WFMT, EC, RT or ACFM techniques. Surface preparation by grit blasting, high pressure water blasting or preparation by grit blasting, high pressure water blasting or other methods is usually required for WFMT but not for ACFMother methods is usually required for WFMT but not for ACFM

– UT techniques including external SWUT can be used. SWUT is UT techniques including external SWUT can be used. SWUT is especially useful for volumetric inspection and crack sizingespecially useful for volumetric inspection and crack sizing

– Grinding out the crack or removal by thermal arc gouging is a Grinding out the crack or removal by thermal arc gouging is a viable method of crack depth determination.viable method of crack depth determination.

– AET can be used for monitoring crack growth. AET can be used for monitoring crack growth.


Related MechanismsRelated Mechanisms– SSC is a form of hydrogen stress cracking (hydrogen SSC is a form of hydrogen stress cracking (hydrogen

embrittlement)embrittlement)

– Amine cracking and carbonate cracking can also occur in Amine cracking and carbonate cracking can also occur in wet Hwet H22S environments, may be similar in appearance, and S environments, may be similar in appearance, and

are sometimes confused with the various forms of wet Hare sometimes confused with the various forms of wet H22S S

damage. damage.


Description of DamageDescription of Damage– The hydrogen reacts with carbides in steel to form methane The hydrogen reacts with carbides in steel to form methane

(CH(CH44) which cannot diffuse through the steel. The loss of ) which cannot diffuse through the steel. The loss of

carbide causes an overall loss in strengthcarbide causes an overall loss in strength

– Methane pressure builds up, forming bubbles or cavities, Methane pressure builds up, forming bubbles or cavities, microfissures and fissures that may combine to form cracksmicrofissures and fissures that may combine to form cracks

– Failure can occur when the cracks reduce the load carrying Failure can occur when the cracks reduce the load carrying ability of the pressure containing partability of the pressure containing part

Other Mechanisms Other Mechanisms High Temperature Hydrogen Attack (HTHA)High Temperature Hydrogen Attack (HTHA)

Affected Materials Affected Materials – C-0.5Mo, Mn-0.5Mo, 1Cr-0.5Mo, 1.25Cr-0.5Mo, 2.25Cr-1Mo, 2.25Cr-C-0.5Mo, Mn-0.5Mo, 1Cr-0.5Mo, 1.25Cr-0.5Mo, 2.25Cr-1Mo, 2.25Cr-

1Mo-V, 3Cr-1Mo, 5Cr-0.5Mo and similar steels1Mo-V, 3Cr-1Mo, 5Cr-0.5Mo and similar steels Critical Factors Critical Factors

– For a specific material, HTHA is dependent on temperature, hydrogen For a specific material, HTHA is dependent on temperature, hydrogen partial pressure, time and stresspartial pressure, time and stress

– HTHA is preceded by a period of time when no noticeable change in HTHA is preceded by a period of time when no noticeable change in properties is detectable by normal inspection techniques.properties is detectable by normal inspection techniques.

– The incubation period - time period during which enough damage has The incubation period - time period during which enough damage has occurred to be measured with available inspection techniques (vary from occurred to be measured with available inspection techniques (vary from hours at very severe conditions to many years)hours at very severe conditions to many years)

– Figure 5-35 contains curves that show a temperature/hydrogen partial Figure 5-35 contains curves that show a temperature/hydrogen partial pressure safe operating envelope for carbon and low alloy steelspressure safe operating envelope for carbon and low alloy steels

– The curves are reasonably conservative for carbon steel up to about The curves are reasonably conservative for carbon steel up to about 10,000 psi hydrogen partial pressure10,000 psi hydrogen partial pressure

High Temperature Hydrogen Attack (HTHA)High Temperature Hydrogen Attack (HTHA)

Recommended pressure and H2 partial pressure limits per API 941

Affected UnitsAffected Units– Hydroprocessing units, such as hydrotreaters (desulfurizers) Hydroprocessing units, such as hydrotreaters (desulfurizers)

and hydrocrackers, catalytic reformers, hydrogen producing and hydrocrackers, catalytic reformers, hydrogen producing units and hydrogen cleanup units, such as pressure swing units and hydrogen cleanup units, such as pressure swing absorption units, are all susceptible to HTHAabsorption units, are all susceptible to HTHA

– Boiler tubes in very high pressure steam serviceBoiler tubes in very high pressure steam service


Appearance or Morphology of Damage Appearance or Morphology of Damage – HTHA can be confirmed through the use of specialized techniques HTHA can be confirmed through the use of specialized techniques

including metallographic analysis of damaged areas as described below including metallographic analysis of damaged areas as described below (Figure 5-36).(Figure 5-36).

– In the early stages of HTHA, bubbles/cavities can be detected in In the early stages of HTHA, bubbles/cavities can be detected in samples by a scanning microscopesamples by a scanning microscope

– Early stages of HTHA can only be confirmed through advanced Early stages of HTHA can only be confirmed through advanced metallographic analysis of damaged areas (Figure 5-37).metallographic analysis of damaged areas (Figure 5-37).

– In later stages of damage, decarburization and/or fissures can be seen by In later stages of damage, decarburization and/or fissures can be seen by examining samples under a microscope and may sometimes be seen by examining samples under a microscope and may sometimes be seen by in-situ metallography (Figure 5-38).in-situ metallography (Figure 5-38).

– Cracking and fissuring are intergranular and occur adjacent to pearlite Cracking and fissuring are intergranular and occur adjacent to pearlite (iron carbide) areas in carbon steels(iron carbide) areas in carbon steels

– Some blistering may be visible to the naked eye, due to either molecular Some blistering may be visible to the naked eye, due to either molecular hydrogen or methane accumulating in laminations in the steelhydrogen or methane accumulating in laminations in the steel


Figure 5-37 - High Figure 5-37 - High magnification photomicrograph magnification photomicrograph showing microfissuring showing microfissuring

Figure 5-36 - Brittle Figure 5-36 - Brittle appearing failure of a pipe appearing failure of a pipe section due to HTHAsection due to HTHA

Prevention/MitigationPrevention/Mitigation– Use alloy steels with chromium and molybdenum to increase carbide Use alloy steels with chromium and molybdenum to increase carbide

stability thereby minimizingstability thereby minimizing methane formation. Other carbide methane formation. Other carbide stabilizing elements include tungsten and vanadium.stabilizing elements include tungsten and vanadium.

– C-0.5Mo carbide stability under HTHA conditions may be due at least C-0.5Mo carbide stability under HTHA conditions may be due at least in part to the different carbides formed during the various heat in part to the different carbides formed during the various heat treatments applied to the fabricated equipment.treatments applied to the fabricated equipment.

– As a result of the problems with the 0.5 Mo alloy steels, its curve has As a result of the problems with the 0.5 Mo alloy steels, its curve has been removed from the main set of curves and the material is not been removed from the main set of curves and the material is not recommended for new construction in hot hydrogen servicesrecommended for new construction in hot hydrogen services

– 300 Series SS overlay and/or roll bond clad material is used in hydrogen 300 Series SS overlay and/or roll bond clad material is used in hydrogen service where the base metal does not have adequate sulfidation service where the base metal does not have adequate sulfidation resistance. Although it is recognized that properly metallurgically resistance. Although it is recognized that properly metallurgically bonded austenitic overlay/clad will decrease the hydrogen partial bonded austenitic overlay/clad will decrease the hydrogen partial pressure seen by the underlying metalpressure seen by the underlying metal


Inspection and Monitoring Inspection and Monitoring – Damage may occur randomly in welds or weld heat affected zones as Damage may occur randomly in welds or weld heat affected zones as

well as the base metal, making monitoring and detection of HTHA in well as the base metal, making monitoring and detection of HTHA in susceptible materials extremely difficultsusceptible materials extremely difficult

– Ultrasonic techniques using a combination of velocity ratio and Ultrasonic techniques using a combination of velocity ratio and backscatter have been the most successful in finding fissuring and/or backscatter have been the most successful in finding fissuring and/or serious crackingserious cracking

– In-situ metallography can only detect microfissuring, fissuring and In-situ metallography can only detect microfissuring, fissuring and decarburization near the surfacedecarburization near the surface

– Visual inspection for blisters on the inside surface may indicate methane Visual inspection for blisters on the inside surface may indicate methane formation and potential HTHA(but HTHA may frequently occur without formation and potential HTHA(but HTHA may frequently occur without the formation of surface blisters)the formation of surface blisters)

– Other conventional forms of inspection, (WFMT and RT) are severely Other conventional forms of inspection, (WFMT and RT) are severely limited in their ability to detect anything except the advanced stages of limited in their ability to detect anything except the advanced stages of damage where cracking has already developeddamage where cracking has already developed

– AET is not a proven method for the detection of damage AET is not a proven method for the detection of damage


Related Mechanisms Related Mechanisms – A form of HTHA can occur in boiler tubes and is A form of HTHA can occur in boiler tubes and is

referred to by the fossil utility industry as hydrogen referred to by the fossil utility industry as hydrogen damage damage


Thank You For Thank You For Your AttentionYour Attention

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Damage Mechanisms Affecting Fixed Equipment in the Refining Industry