F-101 CATALYSTS TUBE WELD JOINT FAILURE Presented by: Asad Abdullah AMMONIA/Operations

ROAD MAP Introduction Incident TA-2009 Observations Vendor Study Conclusion Recommendations

Introduction Primary Reformer:

Incident On August 19, 2008 at about 0730 hours, a process gas fire was observed in the mid section of north side outlet manifold section of Primary Reformer.

Observations: 1. Fire proof cloth around catalyst tubes was found badly burnt / damaged. 2. Severe heat caused distortion in beams. Observations after pulling out Catalyst Tube # 324:

1.Bottom flange to tube butt weld was found cracked . 2. Crack appeared at the location where a weld repair was carried out. 3. In addition, repair of bottom flange to tube welds of three more tubes had been carried out. 4. As precaution, bottom flange of catalyst tubes nos. 312 thru 331 were also checked.

TA-2009 OBSERVATIONS Radiography of all identified repaired catalyst tubes was performed which indicated (lack of fusion/crack) along the fusion line. A narrow dark band was also noticed on flange side indicating some metal loss toward bottom flange weld.

Bottom flanges of some catalyst tubes were removed and visual inspection revealed a distinct grooving (metal loss up to 2.1 mm deep) along bottom flange side. Radiography of randomly selected south chamber catalyst tubes were also performed. Ultrasonic flaw detection of all north and south chamber tube to bottom flange weld was performed.

Estimated depth of indication North East cell North West cell South East cell South West cell <0.5 mm 56% 79% 51% B/w 0.5~1.0 37% 20% 41% 39% >1.0 mm 6% 1% 4% 10%

Based on RT & UT results two tubes found having crack 4mm deep. Due to presence of crack, it was decided to scan as many tubes by radiography. Estimated depth of indication North East cell North West cell South East cell South West cell OK 11% 50% 8% 10% Grooved at partial periphery 4% 29% 5% Grooved at full periphery 19% Nil 0.9%

REMEDIAL ACTIONS TAKEN Temporary box-up sleeve arrangement of SS 304 H. In order to carry out detailed investigation, samples were sent to Vendors.

VENDOR STUDY METAL TEK STROK COOPER HEAT SCHMIDT-CLEMENS HALDOR TOPSOE

TUBE ANALYSIS VISUAL EXAMINATIONS DPT CHEMICAL ANALYSIS X RAY OF RESIDUE MACROSTRUCTURAL INSPECTION HARDNESS FEG-SEM-EDX MICROSCOPIC INSPECTION

Visual Examination Crack

Visual Examination

DPT

CHEMICAL ANALYSIS No deviations were found in the chemical composition of the different samples and alloys that were examined.

XRF of Residue

Macrostructural Inspection

VERTICAL VIEW

HARDNESS

FEG-SEM-EDX Microscopic Inspection

CONCLUSION METAL TEK Schmit Clemens The failure was initiated by the deposition of a carbonaceous buildup. The catalyst tube was sufficiently alloyed to resist the attack. The interface between the weld material and the flange was developing brittle areas. The flange has been selectively corroded very likely to have happened by the formation of carbonic acid Moreover, the two alloys are dissimilar thus their thermal expansion coefficients are different.

CONCLUSION HALDOR TOPSOE STROK COOPER HEAT Similar Cracking pattern was observed in both the tubes from North and South cell. Crack starts from the groove in the weld root and propagates along the fusion line. Insufficient PWHT is considered to be the most probable cause for the catalyst tubes failure. The possibility of condensation of CO2 containing water and corrosion phenomenon has probably occurred after crack formation, and therefore has played secondary role in the failure process. Cracks within the flange metal are associated with the groove area and propagated along the fusion boundary, from the inner surface. The weld metal dilution was greatest for the Metaltek manufactured tubes. The hardness of the flange material was greater than that of the tube material. The premature degradation mechanisms were found to be the combination of hydrogen and dissimilar metal weld cracking and the combination of water condensate corrosion.

RECOMENDATIONS METAL TEK SCHMIT CLEMENS Change of flange material. Reduce the hardness.(PWHT) Prevent exposure to process gas.(Design) S+C recommends not to use Cr-Mo materials for this flanges. Use a material which has same thermal coefficient expansion as that of tube material and is resistant to carbonic acid. S+C strongly recommends the upgrade of material by changing the current selected alloy, as well as improving the operation by a higher corrosion resistance to SCC.

RECOMENDATIONS HALDOR TOPSOE STROK COOPER HEAT Material selected for filler and for bottom flanges appears to be compatible. HTAS recommends the use of appropriate PWHT procedures. Repair of the existing weld can not be carried out, unless the whole weld is removed. Replace all the bottom flanges, with flanges manufactured from a Ni-based alloy (i.e. material similar to that of the remainder of the tube). Monitor the top flange-to-tube weld for cracks. In the interim (before all the bottom flanges are replaced) the significance of condensation and galvanic corrosion can be mitigated by limiting the number of stop-starts and minimizing upset conditions during operation.

FUTURE PLAN

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