1. Failure of Catalyst Tubes of Primary Reformer Presented By: S. M
Failure of Catalyst Tubes of Primary Reformer Presented By: S.M. Imran Bacha App-Engineer Batch 14th

2. HISTORY OF AMMONIA PLANT
Ammonia plant is Bechtel designed and of 1965 vintage with natural gas as feed stock.
Relocated to Bin Qasim, Karachi - Pakistan from Lake Charles, USA.
Re-commissioned and came into operation in 1998.
Ammonia plant had a name plate capacity of 1,270 MTPD.

3. ORIGINAL DESIGN OF PRIMARY REFORMER:
OEM: FWEL (Foster Wheeler Engineering Ltd)
Design Year: 1965, Type Terrace Wall
Radiant Section Contain Dual Chamber (North & South)
432 Catalyst Tubes placed in Staggered Arrangement
216 Catalyst Tubes Each Radiant Chamber
Convection Section Located at Top of Reformer
having following Tube Banks
Process Steam Superheat Coils
Air Preheat Coils
Feed Gas Coils
Power Steam Coils
Steam Generation & BFW Coils

4. DETAIL SKETCH Mixing manifold Convection Section NG FEED
Inlet manifold
Process Steam
Inlet Pigtail
Radiant Section
Catalyst Tubes
Burner
Process Gas
TO C-102
FUEL NG

5. DETAIL SKETCH

6. CATALYST TUBE CONFIGURATION
Component List:
1. Micro Alloy tubes.
2. 1¼" Sch.-160 Incoloy 800H outlet pigtail.
3. R-30 Octagonal SS-304 Gasket
4. R-30 Octagonal SS-304 Gasket
5. ½" x 5" Stud bolts B-16 with two hexagonal nuts.
6. ½" x 5" Stud bolts B-16 with two hexagonal nuts.
7. Top blind flange A-182 F-11.
8. Bottom blind flange A-182 –F-11
9. Catalyst support cone & sleeve SS-321 / HK-40.
10. Back up spacer ring.
11. Top seal Kaowool basket.
12. Cast pusher bar assembly
13. 1¼" Sch.-40 A-321(HK-40) inlet pigtail.
14. Insulation blanket for inlet pigtail.

7. CHANGES MADE IN ORIGINAL DESIGN:
Catalyst Tube
Catalyst tube material changed from HK-40 to Micro alloy in 2004 & 2006.
Catalyst tube thickness reduced from 14 mm to 8.1 mm.
Tubes weld joints reduced from 6 to 4.
Bottom flange material changed from Carbon Steel to Chrome Molly Steel (F-11).

8. HISTORY OF CATALYST TUBES
2004: All the catalyst tubes of north chamber were
replaced with modified material new
Micro alloy tubes provided by M/s Metal Tek, USA
due to excessive problem in old HK-40 tubes.
2006: All the catalyst tubes of south chamber were
Micro alloy tubes provided by M/s Schmidt- Clemens, Spain due to excessive problem in old HK-40 tubes.

9. PROBLEMS OBSERVED IN CATALYST TUBES
On 19-Aug-2008 a process gas fire was observed at the lower end of the catalyst tube #324.The tube was isolated from the reformer and inspection revealed joint crack failure found between bottom flange to tube at the weld toe along Cr-Mo side.New tube was not installed at its location.
OBSERVATIONS OF TA-09:
Grooving observed in Bottom flanges weld joints of primary reformer.
UT/Radiographic inspection carried out of the bottom flange to tube weld joints of catalyst tubes in north/south chamber.
Visual inspection revealed a distinct grooving (metal loss) along weld root in the F11 flange side.
Upon grinding of the groove, we found cracks in the welds (all in 4 tubes which attempted).

10. TA-2009 OBSERVATIONS Penetration test (from south cell)
Visual examination and penetration test did not show any cracks from the outside neither on tube nor on flange.

11. After cut (from South cell)
Catalyst tube
Flange
low alloy steel
Inner surface of the tubes showing the weld regions with failures and crack.
Crack starts from the wedge shaped groove in the weld root and passes towards the surface.

12. Penetration test
(from North cell)
This sample also didn't
show any indication of
cracks from the outer
surface

13. After cut (north cell)
Catalyst tube MA
Crack
Flange low alloy steel
Pictures shows crack at the weld zone. The crack start on the inner surface, and develops all the way to the outer surface.

14. SUMMARY OF INSPECTION RESULTS
Results of radiographic examination & ultrasonic inspection are as under:
Radiographic Examination
Ultrasonic Scanning
Description
Tubes
Full grooving 54
Groove greater than 1mm 23
Partial grooving 75
Groove range 0.5~1 mm
148
No grooving
114
Groove less than 0.5 mm
261
Total
243
432

15. IMMEDIATE CORRECTIVE ACTION TAKEN/TA-09
Repair by Welding:
It required removal of tubes, flange cutting ,buttering with inconnel,slow cooling under insulation, heat treatment, machining, RT , final welding with MA tube i.e. extensive job scope & time. Only one tube was attempted and it took 36 hrs, therefore, further job postponed.
Installation of Backup Sleeves:
Installed external backup sleeves of most affected Bottom weld joints i.e.54 tubes.
Tube manufacturer, equipment designer and an independent consultant consented it as a short-term measure only.
It was decided to thoroughly investigate the cause of failure involving different engineering companies.

16. ENGINEERING STUDIES STORK COOPER HEAT, UAE HALDOR TOPSOE A/S, DENMARK
METALTEK, USA
SCHMIDT-CLEMENS,
FOSTER-WHEELER

17. ROOT CAUSE FAILURE ANALYSIS BY STORK COOPER HEAT.
Two samples were shipped for root cause analysis to Cooper Heat having following details:
Post weld heat treatment was carried out at 725 o C for 2 hours for tubes provided by Schmidt-Clemens.
Sample
Tube no. in assembly
Origin
Chamber
Exposure life
Tube 1
Tube # 183
Schmidt & Clemens
South
2 years
Tube 2
Tube # 297
Metaltek International
North
4 years.

18. MAJOR OBSERVATIONS:
Degree of grooving was more severe for Schmidt-Clemens sample & cracks depth was greater for MetalTek sample.
Hydrogen embrittlement are susceptible if the weld HAZ hardness exceed 235 BHN. As per analysis the average hardness for Tube # 1 is 171 BHN & for Tube # 2 is 268 BHN.
Following mechanisms are the contributors in resulting grooving & cracking:
Galvanic Corrosion. ( Grooving)
Water condensate corrosion. (Grooving)
Dissimilar metal welds.( Cracking)
Hydrogen Cracking. (Cracking).

19. CONCLUSION: INTERIM SOLUTION RECOMMENDATION BY STORK COOPERHEAT
Maintaining flange temperature in excess of 110oC to avoid condensation.
Limiting number of shutdowns and start up and minimizing upset conditions during operation.
RECOMMENDATION BY STORK COOPERHEAT
Replacement of bottom flanges with Ni based alloy (Similar material that of tube).
Detailed inspection of top flanges.

20. RECOMMENDATIONS BY HALDOR TOPSOE
Material for filler and bottom flanges compatible for mentioned process conditions.
HTAS recommends the following PWHT procedures.
690°C , 1 hour at the weld regions of the flange and catalyst tube, to ensure the Vickers micro hardness falls below 250 HV in HAZ.
Repair of the existing weld can not be carried out, unless the whole weld is removed.

21. RECOMMENDATIONS BY METALTEK
Change of flange material—selection of fully austenitic grade of material.
Reduce hardness in HAZ—hardness of martensitic phase makes material more susceptible to chemical attack.
Prevent exposure to process gas.

22. ROOT CAUSE FAILURE ANALYSIS BY SCHMIDT-CLEMENS
OBSERVATIONS:
Continuous carbide layer b/w flange and the weld material.
Material loss due to carbonic acid attack and/or galvanic corrosion (dissimilar materials).
Carbonic acid formed from co2 and water.
Carbonic acid promotes stress corrosion cracking (SCC) especially in the most stressed area of the flange.

23. Contd….
Most stressed area of the flange is the interface b/w the flange and the weld material because of the inherent difference in the thermal expansion coefficient of the weld (austenitic) and the flange alloys (ferritic).
Reason for cracking—stress concentration formed due to differences in thermal coefficients, enhanced by SCC phenomenon.

24. Recommendations by Schmidt-Clemens
Replace the Cr-Mo flanges to stainless Steel flanges, because :
No thermal stress will be caused, since the thermal expansion coefficients are similar (both alloys would be austenitic).
stainless Steel will not be sensitive to carbonic acid SCC.
No carbide will be precipitated in the interface b/w the weld and the flange.
No need of heat treatment thus decrease cost and lower shut down time.

25. COMPARISON OF ALL ENGINEERING ANALYSIS
CONSULTANT
RECOMMENDATION
STORK COOPER HEAT
Replacement of bottom flanges with Ni based alloy (Similar material that of tube).
Detailed inspection of top flanges.
HALDOR TOPSOE
HTAS recommends the following PWHT procedures.
690°C , 1 hour at the weld regions of the flange and catalyst tube, to ensure the Vickers micro hardness falls below 250 HV in HAZ.
Based on past experience HTAS, periodic condensation will increase the risk of SCC in present system in case of SS-304H flanges.
METALTEK INTERNATIONAL
Change of flange material—selection of fully austenitic grade of material.
Reduce hardness in HAZ—hardness of martensitic phase makes material more susceptible to chemical attack.

26. COTD------- CONSULTANT RECOMMENDATION SCHMIDT-CLEMENS
Replace the Cr-Mo flanges to stainless Steel flanges.
FOSTER-WHEELER
Report still awaited..Recommendations

27. FINAL APPROVED DECISION
To replace all the 432 nos. bottom Cr-Mo flanges with appropriate metallurgy ( Still to be finalized) in the forth coming TA scheduled in Jan-Feb 2010.
F-101 is presently running with 425 catalyst tubes. Order placed to Schmidt-Clemens for 20 catalyst tubes with SS- 304H flange (bottom) and F-11 (upper).

28. FEASIBLE OPTIONS
Multiple options has been worked out which are as follows:
Complete replacement in yard.
Complete replacement in situ.
Partial replacement in yard & insitu ( 216 EA)
Feasible option:
Advantages:
Minimum time required for job execution.
Improved weld quality by having enough space for welders.
Ease in cutting / beveling because of enough space.

29. RESEARCH & DEVELOPMENT
MOCK UP:
Mock up for various options and results.

30. THANK YOU