Large through-wall defect on a 36” Sulphur Degassing Unit
Problem Summary
Anomaly Description:
Visual inspection found through-wall damage on a section of the line. Damage was located near tie-in 6” nozzle attachment weld of exhaust gasses line from Sulphur Degassing Unit. UT scanning was performed to determine the condition of the area of damage and 6” nozzle. In accordance with inspection results, wall residual thickness in the area of damage was ≈4.7mm, in the adjacent areas. Т-min was 5.0mm, nominal thickness was 7.9 mm. Wall residual thickness of 6” nozzle was 5.8mm, nominal thickness was 7.11 mm.
Root causes:
The probable cause of this damage was occurrence of wet acid corrosion mechanism due to missing of heat tracing on 6” nozzle tie-in of exhaust gasses line from Sulphur Degassing Unit.
Integrity concerns:
The length of through wall damage was ≈200mm and consists approximately ⅓ of nozzle attachment weld length, and may result in catastrophic failure of the nozzle.
Technical Details
Line Diameter:
Design Pressure:
Operating Pressure:
Design Temperature:
Operating Temperature:
Material:
Line Class:
36” to 6”
14.5 BAR
1 BAR
100°C
90°C
A671 – CC60
The Beruseal Solution
Clamp Design:
A T-clamp was designed according to the ASME PCC2 specifications with a strong back system to hold the 6” Nozzle in place in the case of catastrophic failure occurring. In the process of the clamp design a lead patch was installed over the hole in the pipe and set down with BELZONA1111 to stop the H2S leak while the clamp is being manufactured.
Seal:
The clamp was a multi-medium system where the use of PTFE based-compound was injected into a pre-cut groove around the clamp and bores of the large diameter pipe to create an outer seal.
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