During a visual inspection of a product storage tank, a trace of solidified product was identified, indicating a crack along the drip ring and the annular bottom plate. The tank specification called for the steel to have a minimum design metal temperature (MDMT) of -40 C but the material became brittle at lower temperatures (-15 C and below), resulting in a crack.
The supplier substituted a higher quality steel product not knowing that it had a different MDMT.
A risk assessment using an international standard, such as API 650 Welded Tanks for Oil Storage, was not performed.
The tank material vendors and internal company supply chain both assumed the appropriate tests were conducted, and specifications were met.
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