The last years Statoil has replaced some of our seabed mooring chain segments. Some of these chains have corrosion pits caused by Microbiologically Influenced Corrosion (MIC).
In 2016 and 2017 one full length of a seabed chain segment, including anchor, was retrieved from a SEMI at approximately 300m water depth in the North Sea. The chain has been 20 years on the seabed. The corrosion on the chain was carefully documented, and showed significant levels of MIC. The extent of the MIC showed a strong dependency on seabed contact and how well the chain was buried in the sediments. The observed MIC is caused by Sulphate Reducing Bacteria (SRB). After corrosion identification, the chain has also been subject to full scale fatigue testing.
This paper presents the technical condition of the seabed mooring chain, describing the different levels of MIC, typical SRB corrosion attacks, and the results from the fatigue testing.