Mixed Sour Gas Manifold-Weld-O-Let Cracks
Problem Summary
Anomaly Description:
Axial-orientated cracks were found in one butt-weld and one fillet-weld on a 2” pipe with RT on the U300 Mixing Manifold.
Root causes:
Probable cause for the defect is the availability of wet chlorides causing stainless steel chloride cracking.
Integrity concerns:
There was a high risk that the known defect could continue growing further and it is not improbable that further defects may develop.
Technical Details
Line Diameter:
Design Pressure:
Operating Pressure:
Design Temperature:
Operating Temperature:
Material:
Line Class:
20 to2”
85 BAR
66.7 BAR
190°C
95°C
SA-358
900P21
The Beruseal Solution
Clamp Design:
An analysis of an on-line leak sealing clamp for a sour gas line was made for the cracked weld-o-let. The intention of the design was firstly to seal the whole area to prevent leakage without putting any additional stress into the already cracked weld. The second intention was to support the drain should the weld crack through completely. The Beruseal design department designed a strong-back clamp and used FEA (Finite element analyses) technology to determine stress levels that would be imposed on the clamp in the event of catastrophic failure of the weld. The design was made according to ASME PCC2 and underwent stringent analysis by Client Engineering House Department and found to be acceptable.
Seal:
The on-line leak sealing clamp was a multi-medium system where the use of PTFE based compound was injected into a precut groove around the clamp and bores of the large diameter pipe to create an outer seal. Surface preparation was made to the 20” line and the inside of the clamp to ensure adhesiveness of the resin, the clamp was then filled with a two-part high temperature epoxy resin. The resin is resistant to hydrocarbon attack and highly adhesive which also acted as additional support for the cracked weld.
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