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INDUSTRIAL TRAINING PHASE- 1 AT LARSEN & TOUBRO LTD., HAZIRA COMPLEX HEAVY ENGINEERING DIVISION
A MINOR REPORT ON WELDING AND FABRICATION TECHNOLOGY ROYAL COLLEGE OF TECHNOLOGYINDORE,
PREPARED BY:
RAJNIKUMAR KOLADIYA ENR. NO: - 0836ME091019CERTIFICATE
This is to certify that MR. RAJNIKUMAR KOLADIYA . Enrolment no. 0836ME091019 of Dept. of Fabrication Technology has successfully completed his Minor report on WELDING during his training period of first phase 05/07/2012 to 20/07/2012 in L&T Hazira, Surat.
APPROVED BY: GUIDED BY :
Dr.SUJIT MEMON Dr.JAIRAJ GOHIL
(INCHARGE OF HFS-3A) (CO-ORDINATOR OF
HFS 3A)
Sr.NO. TOPIC
PAGE NO.1. Job Detail
42. P no. 5 Low Alloy Steel
63. Characteristics
64. Chemical composition
65. Effect of Chromium
66. Effect of Vanadium
77. Cr-Mo-V steels
78. Comparison
79. Comparison of reactor steels
810. Enhanced Tensile Strength
811. Creep
812. Temper Embrittlement
913. Hydrogen Embrittlement
914. Hydrogen Induced Overlay Disbonding1015. Weldability of Cr-Mo Steel
1016. Preheating
1117. Inter-Pass Temperature
1218. DHT (De-Hydrogenation Treatment) 12 19. Intermediate Stress Relieving (ISR) 1220. Why ISR??
13 21. ISR Requirement 1322. Critical Weldability issues 13 Reheat, or stress-relief cracking
Solidification, or hot cracking
Hydrogen-induced, or cold cracking
23. Welding Training 21 AIM: To investigation the slag inclusion in PETROBRAS job
JOB DETAILS:-
NAME OF JOB:- DIESEL HYDROTREATING REACTOR
PROJECT NO.:- 45537/2 CUSTOMER:
PETROLEO BRASILEIRO (PETROBRAS)
JOB DIMENSION:
4916 mm I.D., 23346 mm LENGTH, (150 mm THK+8 mm OVERLAY)
JOB MATERIAL:
FOR HEADS: SA 542M TYPE .D CL. 4a (Quenched + Tempered) + (SS 309 L+ SS 347 overlay - 8 mm THK.)
FOR NOZZLE: SA 336M GR. F22 V.
Y-RING : SA 336 GR. F22 V (Q+T)+(SS 309L +SS 347O/L-8THK).
MANHOLE: SA 542M TYPE .D CL. 4a (Quenched + Tempered)+(SS 309 L+ SS 347 overlay) BOLTING:SA193M Gr. B16/ SA 194 M Gr.4 GASKATE: SA182M Gr. F347 DESIGN TEMPERATURE (INT/EXT.)430/30 0C
DESIGN PRESSURE (KG/CM2)- INTERNAL: 134
- EXTERNAL: 1.05
SHELL: 9 shells + 2 D end. FABRICATED WEIGHT: - 560000 kg.
HYDRO TEST PRESSURE : 16.26 M pa horizontal
: 5.988 M pa vertical
HYDRO TEST TEMP. : 27 to 50 0C CHEMICAL COMPOSITION : Carbon 0.05 to 0.15
Manganese 0.30 t0 0.60
Phosphorus 0.035 max.
Sulphur 0.035 max.
Silicon 0.50
Chromium 2.00 to 2.50
Molybdenum 0.90 to1.10
CODE REFERENCE: ASME SEC: VIII, DIV: - 2 ED.-2007.P no. 5 Low Alloy SteelCharacteristics Used up to 650oC Operating Temp.
Resistance to H2 attack
Better creep ruptures properties and high temp. strength than carbon steels
Resist oxidation and sulphidation
High hardenability
Chemical composition A: 2.25Cr 1Mo SA 508 Gr. 22, CL. 3 Forgings SA 541 Gr. 22 CL.3 Forgings SA 542 TYPE B CL.4 Forgings
B: 2.25Cr 1 Mo -2.25V (LAS) SA 336 Gr. F22V Forgings SA 182 Gr. F22V Forgings
SA 541 Gr. 22V Forgings
SA 542 TYPE D CL.4a plates SA 832 Gr.22V plates. C: 3Cr 1Mo V-Ti-B (LAS) SA 182 Gr. F3V Forgings
SA 542 TP C CL. 4A Plates
SA 832 Gr.21V Plates
SA 541 Gr.3V Forgings SA 508 Gr.3V Forgings SA 336 Gr.F3V Forgings CODE:- ASME SEC.8, DIV.-2, PART:3, Material requirements part content table-3.18.Chromium Increases resistance to corrosion and oxidation
Increases hardenability
Adds some strength at high temperatures
Resist abrasion and wear (with high carbon)
Molybdenum Molybdenum is a potent hardenability agent and is a constituent of many heat treatable alloy steels.
It raises grain coarsening temperature of austenite
It retards softening at elevated temperatures and is therefore used in boiler and pressure vessel steels, as well as several grades of high speed and other tool steels. Vanadium Enhance tensile strength at elevated temperatures (above 400oC)
Enhance creep rupture strength
Improve resistance to in-service degradation like temper embittlement, high temp. hydrogen attack, hydrogen embrittlement, hydrogen induced overlay disbonding
Lower unit weight of the reactors at a comparable cost by increase of steel strength.
Cr-Mo-V steels 2.25Cr - 1Mo - 0.25V
ElementCMnPSSiCrMoV
% Composition0.11 0.150.30 0.600.0150.0100.102.00 2.500.90 1.100.25 0.35
Tensile StrengthYield StrengthElongation in 2Brinell hardness no.
585 780 MPa415 MPa18.0%174-237
ComparisonMaterialTensile StrengthYield StrengthElongation in 2
C.S (SA 516 Gr. 70)485 620 MPa260 MPa21.0%
SA 387 Gr. 11415 585 MPa242 MPa22.0%
SA 182 Gr. F22V585 780 MPa415 MPa18.0%
Comparison of reactor steels
Steel Grade2.25Cr-1Mo2.25Cr-1Mo-0.25V
Max. allowed temp. ASME VIII 2482oC482oC
Min. Tensile Strength517586
Min. Yield Strength 310414
Design Stress Intensity Value, ASME VIII-2At 454oC 150 MPaAt 454oC 169 MPa
At 482oC 117 MPaAt 482oC 163 MPa
Wall ThicknessAt 454oC 338mmAt 454oC 298mm
At 482oC 442mmAt 482oC 310mm
454oC Design Reactor Weight; Typical Cost1038MT
Rs 45.2x107916MT
Rs 44.0x107
482oC Design Reactor Weight; Typical Cost1359MT
Rs 59.1x107953MT
Rs 45.7x107
Enhanced Tensile Strength In service behavior of steels strongly depend on the type and morphology of carbide phase
Vanadium modification provides fine, vanadium rich carbides, evenly distributed in the metal matrix
Four types of carbides formed: M7C3, M23C6, M6C and M2C
All contained vanadium with differentiated amounts of Cr, Fe and Mo
Thermodynamic stability of carbides is much greater than V free precipitates Creep Creep is defined as the process by which plastic flow occurs when constant stresses are applied to metal for prolonged period of time at high temp.
It occurs at all stress levels at higher temp.
Creep rate with stress at given temp.
Effect of Vanadium on creep resistance Heat application leads to carbide growth
Coarse carbides distort the grains and lead to smaller grains
More Sliding & Dislocations in smaller grains
Vanadium resist carbide growth at elevated temperature
Temper Embittlement Caused by:
Grain boundary segregation of impurities and tramp elements
Watanable No. (J Factor)
To limit the impurity /tramp elements content in reactor steels
J factor = 104(P+Sn)(Mn+Si)
Resistance of steel to temper embrittlement will be sufficient when J factor is limited to a value of less than 100
Carbide formation is accompanied by microstructural and microchemical change.
The addition of Cr in steels enhances the impurities, such as P, Sn, Sb, and As, segregating to grain boundaries and induces temper embrittlement.
A delay in carbide formation, precipitation or thickening usually leads to delay in embrittlement
Hydrogen Embrittlement At typical hydro processing temperatures and hydrogen partial pressures, hydrogen diffuses easily through reactor walls
When reactor is cooled down rapidly, delayed hydrogen cracking may occur
Fine, evenly distributed vanadium rich carbides trap the diffusible hydrogen in steel
So lesser hydrogen is available at the tips of the crack
High Temperature Hydrogen Attack Diffused hydrogen reacts with carbides to form methane
Leads to decarburization of the material with formation of cavities, fissures or cracks
Higher thermodynamic stability of carbides leads to reduced methane pressure
Precipitation of vanadium rich carbides in the modified steel enhances the resistance to hydrogen attack.
Hydrogen Induced Overlay Disbonding Hydrogen reactors must be protected from high temperature sulphide corrosion caused by hydrogen sulphide present in processed steam.
Hydrogen concentration increases at the interface of both the steels.
Hydrogen is trapped in the fine vanadium containing carbides
So, Hydrogen has low diffusivity in vanadium steels
Weldability The capacity of a metal to be welded under the fabrication conditions imposed into a specific, suitably designed structure, and to perform satisfactorily in the intended service
Depends on,
- Composition of weld metal
- Circumstances in which weld freezes
Weldability of Cr-Mo Steel Hardened when Quenched from Austenitizing temperature
Sensitive
-Hydrogen Induced Cracking
-Solidification Cracking
To avoid Cracking
-Preheat Maintenance
-Use of appropriate Welding Consumables
-Heat Treated to improve Toughness
-Carbon Content of weld Metal Ultra High Strength material
Air Hardenable
Form Hard Martensite when quenched from Hardening temperature of around 1000 C
Hard Martensite will form unless proper Preheat and PWHT procedure is followed
HAZ portion Highly susceptible Under bead Cracking
To avoid Cracking: Proper Preheat is required
Preheat Temperature: above Ms temperature
Preheating Preheating promotes slow cooling of weld and HAZ
Slow cooling softens or prevents hardening of weld and HAZ
Soft material not prone to crack even in restrained condition
Removes moisture, oil, etc. Temp = 35 X [CE(1 + 0.5t) 0.25]^0.5
Where t = thickness
CE = carbon equivalent
CE = C + Mn/6 + (Cr+Mo+V)/5+ (Ni+Cu)/15 Width of preheating material should be equal to plate thickness or 75mm whichever is less on each side (but not less than 25mm)P-NUMBERS
PREHEATING TABLEMaterial/ P.No.Groove & Fillet (Preheat)
Base Metal Thickness (mm)
=100
C-MnP1 Gr 1& 220100125150
C-1/2 MoP3 Gr1 & 2100125150175
P3 Gr 1100150175200
11/4Cr-1/2MoP4 Gr1 & 2150200
21/4Cr-1 MoP5A Gr 1150200
5Cr-1/2 MoP5B Gr 1200
21/4Cr- 1Mo -1/4VP5C Gr 1200
Q & T SteelP11 AS150
Inter-Pass Temperature Control on inter pass temperature avoids over heating, there by
Refines the weld metal with fine grains
Improves the notch toughness properties
Minimize the loss of alloying elements in welds
Reduces the distortion
Inter-Pass required for Cr-Mo-V is about 250OcDHT (De-Hydrogenation Treatment) SMAW introduces hydrogen in weld metal
Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature
Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld
Material/ P.No.Groove (DHT)Fillet (DHT)
Base Metal Thickness (mm)Fillet Size
=100
C-MnP1 Gr 1& 2----------
C-1/2 MoP3 Gr1 & 2------300-350oC /3 hrs(>=50 CFW)
300-350oC /3 hrs
P3 Gr 1----300-350oC /3 hrs(>=35 CFW)
300-350oC /3 hrs
11/4Cr-1/2MoP4 Gr1 & 2----300-350oC /3 hrs(>=35 CFW)
300-350oC /3 hrs
21/4Cr-1 MoP5A Gr 1--350-400oC /4 hrs(>=15 CFW)
350-400oC /4 hrs
5Cr-1/2 MoP5B Gr 1--350-400oC /4 hrs(>=10 CFW)
350-400oC /4 hrs
21/4Cr- 1Mo -1/4VP5C Gr 1350-400oC /4 hrsALL
350-400oC /4 hrs
Intermediate Stress Relieving (ISR) Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness Applicable to
-Highly restrained air hardenable materialWhy ISR?? Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.
Cracks due to entrapped hydrogen and built in stress
Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone
ISR Requirement For 2.25Cr-1Mo-0.25V material,
all L/S & C/S having thickness >100 mm,
all nozzle # Shell/head welds and support ring/nub attachment to shells, shall undergo an ISR at 690oC for minimum 1hr or 650-670oC for 2hrs.
Critical Weldability issues Hydrogen-induced, or cold cracking
Reheat, or stress-relief cracking
Solidification, or hot crackingHydrogen-Induced Cracking (HIC) Hydrogen dissolved in molten weld pool (e.g., wet coatings, poor gas shield, grease/rust on component surface) high solubility in liquid
During rapid solidification of weld deposit, some hydrogen is trapped supersaturated condition
In Cr-Mo/Cr-Mo-V steels, greater hardenability increases the risk of lower bainite/martensite formation in the weld and HAZ
Hydrogen diffuses preferentially to these highly stressed regions of the weldment structure e.g., the coarse-grained HAZ increasing the risk of crackingNecessary Components for HIC to Occur Sufficient quantity of trapped hydrogen in weldment
-Total vs diffusible hydrogen (residual hydrogen remains)
Susceptible microstructure
-Structures with high internal stress/lower transformation products
Stress-Residual stresses, influence of stress concentrators
Temperature of susceptibility
-Limited range of susceptibility reflecting the influence of hydrogen mobility (must be high enough to allow concentration, but not so high to allow escape)
Potential Sources of Hydrogen in Weld Metal Welding consumable
-Coatings and fluxes (cellulosic vs basic)
Atmosphere
-High humidity
-Ineffective gas shield
Base metal
-Trapped hydrogen in heavy sections
-Surface moisture, grease, oil, etc.
-Rust, other surface corrosion productsSolubility of Hydrogen in Weld Metal
Typical Features of Hydrogen-Induced Cracking Can occur in weld metal or HAZ
Can occur at weld root, weld toe, sub-surface (underbead)
Can show features of intergranular, transgranular, or ductile fracture
Can occur hours after welding is complete controlled by diffusion rates
Exacerbated by restraint
Can propagate in service and lead to failure
Hydrogen-Induced Cracking In HAZ
Hydrogen-Induced Cracking in Weld Deposit
Prevention of HIC Minimize hydrogen in the weld metal
Low hydrogen electrodes (proper storage, baking)
Steel cleanliness
Preheat
Match temperature to alloy
Allow sufficient time for diffusion
Microstructure control
Isothermal transformation
Use austenitic or nickel base filler metal
Hydrogen sink & residual stress mitigationReheat Cracking Reheat Cracking is defined as cracking that occurs in the heat-affected zone (HAZ) or weld metal during the exposure of a welded assembly to PWHT or elevated temperature service.
Reheat cracking is also referred to PWHT cracking or stress-relief cracking.
Common in Cr-Mo steels containing less than 3%Cr.
Characteristics Of Reheat Cracking Low rupture ductility.
Intergranular fracture along prior austenite grain boundaries..
Heat-to-heat crack susceptibility varies ( dependent on residual elements
Bulk chemistry of a material may not be reliable predictor of cracking susceptibility
The time-to-failure exhibits a C-curve behavior as a function of temperature. Reheat Cracking --- C-Curve Behavior
Mechanism of Reheat Cracking A balance of intergranular and intragranular carbide precipitation controls the reheat cracking susceptibility.
Cracking can initiate at prior austenite grain boundaries by cavitation on incoherent, Fe-rich M3C carbides.
The grain matrix is resistant to plastic deformation due to precipitation strengthening by alloy carbides. Impurities have significant effect on susceptibility to reheat cracking.
Reheat Cracking Susceptibility Parameters G parameter:
- G = Cr + 3.3Mo + 8.1V 2
- If G > 0, the material is considered to be susceptible.
PSR parameter:
- PSR = Cr + Cu + 2Mo + 10V + 7Nb + 5 Ti 2
- If PSR > 0, the material is deemed to be susceptible
Effect of Cr and Mo According to G & PSR, Cr increases reheat cracking susceptibility.
According to Nakamura & Ito, steels containing >1.5Cr are not susceptible.
According to Tamaki, effect of Cr varies with Mo content (right figure)
Molybdenum:
Mo increases reheat cracking susceptibility
In early stage of tempering, Mo2C carbides precipitate first and cause hardening in grain matrix
In presence of V, Nb & Ti (more affinity for C than Mo), there exists a tendency to form more stable carbides.
Effect of Vanadium Vanadium
V increases reheat cracking susceptibility.
V forms uniform and fine V4C3 carbide in the matrix.
At temperatures of 930-1020 F, coherent precipitates of V4C3 occur in ferrite lattice similar to M2C formation.
z
Solidification Crack Cracking that forms during solidification of the molten weld pool hence the term hot cracking
Lack of sufficient feed of hot metal into the area of final solidification (e.g., crater cracking)
Unfavorable orientation of the final freezing zone relative to the direction of solidification
Factors Promoting Solidification Cracking Composition
Long freezing range
High levels of carbon, sulfur, phosphorus, etc.
Bead Shape
High depth : width ratio
Joint Profile
Root condition
Thickness mismatch
Influence of Composition on Solidification Cracking
Long freezing range:
The risk of cracking is a direct function of the magnitude of the difference in solidification temperature between the solvent-rich and solute-rich components of the molten weld metal
Stresses that develop during solidification due to contraction must be borne by the solute-rich metal that solidifies last
Elevated levels of impurities and some alloying elements:
Elements that promote low-melting eutectics, such as S, B, and Cb, increase the risk of solidification cracking
Differences in solubility of certain elements, such as sulfur, in austenite vs ferrite can have a potent effect on susceptibility: Carbon and other austenite formers that promote solidification as austenite increase the risk of solidification cracking
Role of carbon can be critical, particularly weld roots and when using high dilution processes, such as SAW
Bead Shape Depth:Width ratio affects solidification pattern
High depth:width ratio
promotes concentration of lowest melting material at the centerline (by heat extraction) of the weld deposit
Shape of the weld bead will be influenced by:
Welding current (lower current reduces depth:width ratio)
Welding speed (lower speed reduces depth:width ratio)
Polarity (dc positive vs ac/dc negative)
Reducing Susceptibility to Solidification Cracking Change bead shape (depth:width ratio) by reducing penetration
Reduce dilution, particularly in root pass (lower C and S)
Buttering of higher carbon steels
Reduce length of molten weld pool (easier fill of final solidification zone with hot metal), use backfill techniques
Control weld metal chemistry within specification
Reduce root gaps; maintain gap dimension along full length of long weldsWelding Training
Welding training includes the training given to welders, L&T Supervisor & Contractors Welding Engineer by Welding Engineering.
1. Welding parameter understanding
Preheating Temperature
Interpass Temperature
DHT Temperature & Time
Checking of Preheating on Base Metal
Checking of Interpass Temperature on Bead
Maintenance of preheat temperature until DHT
SMAW Welding Parameters: Current, Voltage, Bead Length
GTAW Welding parameters: Current, Voltage, Travel Speed
Temper Bead understanding
Interpass Cleaning
Understanding of Detrimental effect due to Arc Strike, Precautionary actions to avoid Arc-Strike on base metal.
Critically of Cr-Mo-V with respect to welding, handling, etc.
Practical Training: Before Starting on job- SMAW Bead on Practice to achieve required bead length in various positions.
Position of Curve Dependant on Alloy And Heat Chemistry.
PAGE 22
_1368963310.xlsSheet1
P-NUMBERSTypes of material
1Carbon-Manganese steel
2Carbon-1/2%Mo
31%Cr-0.5%Mo
42.25%Cr-1%M
5Ferritic stainless steel.
6Martensitic stainless steel.
7Austenitic stainless steel.
8Nickel steel.
9 to 11Quenched & Tempered steel
21-25Al & Al base alloys
31-35Cu & Cu base alloys
41-45Ni & Ni base alloys
51-53Ti & Ti base alloys
61-62Zr & Zr base alloys