Failure of Carbon Steel Piping due to Methanol Stress Corrosion Cracking

After approximately 18 months in service, a pinhole leak was observed on a carbon steel line from the methanol storage vessels to methanol transfer pumps. Further examination revealed multiple leaks and weeps at various locations throughout the low-pressure carbon steel bunkering, storage and transfer piping. All of the leaks and weeps were due to cracking associated with welds.

Although the welds were mechanically sound and had passed QC inspections, it is suspected that there may have been some deviation from the weld procedure, which resulted in individual welds having high residual stresses.