Gas release due to the failure of an incorrect seal ring material installed on a Clamp Connector resulting in galvanic corrosion

A gas release occurred on a normally unmanned installation (NUI). On investigation the release was coming from a proprietary size 52 clamp connector joint between the lower master valve and spacer spool on one of the platforms gas condensate producing wells.

It is believed the seal ring was installed as a carbon steel material specification approximately 15 years previously during a well work-over program in 2002. The seal ring lost a significant amount of material thickness due to internal CO2 and galvanic corrosion at the carbon steel to stainless steel interfaces, resulting in a perforation of the ring and gas release from the Christmas tree.

The adjacent downstream clamp connector between the spacer spool and upper master valve was inspected and found to have a correct martensitic stainless steel material seal ring.