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8/11/2019 BSR Inspection Case Study - Cyclone
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Case Study -2nd Regenerator Secondary Cyclones.
Prepared By
Mr. Tran Anh Vu
Deputy Technical Manager
1. Summary
2. Drawing3. History
4. Observation/ Findings
5. Root Cause Analysis
6. Recommendation
7. Repair Method
8. Lesson Learnt
CONTENTS
The RFCC unit was shut down for 2nd TA in 2014. During
inspection secondary cyclone CY-1504 E~H in the 2nd
regenerator D-1503 were found severe damaged. The carbon
steel portion in the cyclone barrel were replaced with SS-304H
material after detail analysis of root cause for damages by
performing NDT methods like UTM, Hardness test, replica etc.
Summary Drawing
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Drawing
refractory crack
refractory crack
History
In 1st TA, some crack were found in the refractory around the carbon steel
portion of cyclone barrel
BeforeHacking
AfterHackingBracingBowing
Observation/ Findings (TA 2014)
Picture 2
refractorycrack
BeforeHacking
refractorycrack
Observation/ Findings
Licenser Design Detail design & Actual
LicensorDesign Detail design &Actual
Dis-similar weld joint is slanting and near
to 2nd regenerator shell
Dis-similar weld joint is horizontal and
far away from 2nd regenerator shell
Have extrenal refractory to cover
dis-similar weld
125mm thick refractory outside the
carbon steel material
In cyclone barrel less carbon steel andmore SS material inside re-regenerator
In cyclone more carbon steel and lessSS material inside re-generator
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Dis-similar
weld joint
Observation/ Findings
Picture 4 shows degradation/metal flakes in cyclone barrel (Carbon
Steel portion). For all 4 cyclones same condition
Observation/ Findings
CycloneF
Dissimilar weld metal found crack in the heat affected zone of carbon steel
portion in two cyclones E &F.
CycloneE
Observation/ Findings
Picture 6b show horizontal Stiffener bracing found bend(Bowing) at
middle of bracing & Picture 6a show crack in one of the dipleg weld
metal
Picture 6a Picture 6b
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Philosophy
NDT inspection is carried out based on the API 579
Fitness for service philosophy.For Assessment of fire damage chapter 11 fig: 11.7.
NDT inspection are carried out step by step process
First perform Hardness test to evaluate the hardness
limit. If hardness limit is lower 240HB that means
the metal is good
If the hardness value is higher than 240 HB check the
microstructure and follow subsequent test as per flowchart.
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Philosophy
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Observation/ Findings
NDT- UTM ResultUTM result confirms there is no major thickness
reduction. From the dis-similar weld zone to about 0.6
meter in height towards Carbon Steel cannot measure the
thickness due to high flaking of material and above 0.6
meter For all four cyclones the similar condition.
Picture 1 shows the thickness near the dis-similar weld
seam is reduced about 3-4mm.
Picture 1
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Observation/ Findings
NDT- Hardness Result
Hardness test result confirms that from the dis-
similar weld zone to about 0.7-0.9 meter in heighttowards Carbon Steel the hardness value is very high
around 600HB and many locations cannot measure
hardness due to flaking. Above 0.9 meter the
hardness value is with in the acceptable range. All
four cyclones has the similar condition.
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Observation/ Findings
NDT- Replica Result
Replica result says that Carbon steel material in the
cyclone has undergone many damage mechanism like
creep voids, degraded microstructure, no carbide have
only ferrite, high temperature sulfidation, graphitation
and microstructure degradation due to high temperature
corrosion etc
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Observation/ Findings
NDT- Replica Result
Cyclone H replica result says the Carbon steel material about 0.7 m above dis-similar
weld joint has creep voids and degraded microstructure
Report 3
CY 1504-E
Cyclone E replica result by PVI and Vietnam Material Institute says the Carbon steel
material near the dis-similar weld zone is no carbide have only ferrite
Report 4
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H:
488
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Observation/ Findings
NDT- Replica Result
Cyclone E replica result says the Carbon steel material about 0.5 m above
dis-similar weld joint was damaged due to high temperature sulfidation, graphitation and
microstructure degradation. Even after remove 5mm of degraded carbon steel material the
replica result shows that the material microstructure structure is decomposed
Report 5
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Cyclone G replica result says the Carbon steel material about 0.6 m above
dis-similar weld joint was damaged due to high temperature sulfidation,
Report 6 CY 1504-F
Cyclone F replica result says the Carbon steel material about 0.3 m above
dis-similar weld joint was partially degraded microstructure due to high
temperature corrosion
Report 7
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Observation/ Findings
Metal Laboratory Analysis result
The flaking metal portion was detailed analyzed in the laboratory, the
results says that this is the corrosion product, which is iron oxide, a
product of metal oxidation at high temperature.
The laboratory report says the cause for corrosion at cyclone is due to the
damage refractory. Oxygen has contacted with metal surface through the
defect positions which led to chemical corrosion at high temperature.
The corrosion products are iron oxides under the form of magnetite
(Fe3O4) and hematite (-Fe2O3).
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Root Cause Analysis
Replica result for CY-1504H microstructure @400X shows the
isolated creep void.
API 571, clause 4.2.8.3 point a says the rate of creep deformation is
a function of the material, load, and temperature.
API 571, clause 4.2.8 Table 4-2 says Threshold Temperatures for
Creep for Carbon steel material is 370C
API 571, clause 4.2.8.3 point b says If the metal temperature exceeds
threshold temperature values, then creep damage and creep cracking
can occur
Creep Damage
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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Root Cause Analysis
JGC Heat Transfer Analysis
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RecommendationAPI 571 clause 4.2.8.6 point c says Creep damage is not reversible.
Once damage or cracking is detected much of the life of the
component has been used up and typically the options are to repair or
replace the damaged component.
ASM Volume 17 Table 2, creep classification table says for fewcavities of creep damage need to re-inspect after 20,000hrs (less than
3 years estimated next Turn around)
API 579 chapter 11 figure:11.7 says if hardness value high,
microstructure is unacceptable, decarburized the material need to be
replaced
The laboratory sample test reports shows the Carbon steel metal was degraded due to high
temperature oxidation. Referring to the above table (API-571) based on the current
operation temperature of D-1503 the corrosion rate will be severe above 48 mils/year or
1.21 mm/year. As per design the allowable corrosion allowance is 1.5 mm for CS and
0.75mm for SS. This corrosion allowance is calculated for 25mm thickness of cyclone
barrel CS material.
Root Cause Analysis
Key Factors Recommendation
6. Project specification 8474L-000-JSS-6300-001 Rev-2 Clause 7.4.1 mention
requirement for minimum weld distance is 100mm or 2T:
Recommendation for Repair method
Option 1: Replacement (Permanent repair) as licenser design
The SS304H material can withstand the high temperature corrosion like
sulfidation, graphitization, oxidation etc.
Key factors recommendation should be considered in this option 1.
Option 2: PatchingAPI 510 calls th is option 2 method as temporary method:Temporary repairs should be removed and replaced with suitable permanent repairs at
the next available maintenance opportunity.
Temporary repairs may remain in place for a longer period of time only if evaluated,
approved, and documented by the engineer and inspector.
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RecommendationOption 2: Patching
Limitation for fillet welding patch
Fillet-welded Patches
Fillet-welded patches may be used to make temporary repairs to damaged, corroded,
or eroded areas of pressure vessel components.
This type of patch cannot control crack during opportunity maintenance
As per ASME PCC-2 calls:
i. Differential thermal expansion between the cyclone shell and the reinforcing
lap band sleeve shall be considered in the design and application of sleeves.
ii. Fillet welded patch repair is allowed up to 345C only. So the refractory
work shall make sure the temperature of CS is not over 345C
iii. ASME PCC2 clause 3.5 call The fillet weld patch thickness should be 1.4
times the carrier steel
7/31/2014
Repair
After Cyclone barrel cutting New Cyclone barrel
7/31/2014
Repair
After new Cyclone barrel welding After completion of welding
When Carbon steel material is operating under creep range
for long period it undergoes multiple damage mechanisms.
Replica shall be done to analysis the microstructure. Fitness
for service should be followed to assess the damage.
The dis-similar welding should be monitored closely at the
every possible opportunity . When operating temperature is
high Nickel chrome filler wire should be used rather than
E-309 filler wire
7/31/2014
Lesson Learnt