Metallurgical examination of gas pipeline reassures Shell

An area of the riser being prepared for replication

Riser area being prepared for replication

An on-site metallurgical examination of a gas pipeline carried out at short notice for Industrial Member, Shell Expro, has assured the company that a pipeline riser with suspected cracking will not have to be replaced.

The Shell BT platform in the southern North Sea takes gas from other wells in the field, compresses it and sends it ashore via a 30inch diameter 25mm wall thickness pipeline.

During the shut-down for maintenance, Shell located some crack-like indications on the surface of three 90° pipe bends at the top of a riser. They were concerned that cracking may have occurred during service which would have necessitated a prolonged and costly shut-down of the platform to repair or replace the riser bends. Specialists from TWI's Materials Department were therefore called in to assess the situation.

TWI investigated the bends using a replication technique which enables microstructures and/or cracks to be examined on-site without damaging the component or fabrication. Fortunately, the 'cracks' were shown to be surface flaws introduced during forming, and not service cracking.