What is this standard about?
This is a new British Standard on how to test for corrosion and environmentally assisted cracking in oil and gas pipelines. It is a revision of HSE guidance document OTI 95 635 which is referenced in ISO 15156, the flagship document for upstream material selection for sour service.
Who is this standard for?
It will be used by the manufacturers of pipelines that are designed to transport petroleum, petrochemicals and natural gas products.
Why should you use this standard?
Sour service cracking problems in pipeline steels are caused by the presence of wet hydrogen sulphide (H2S). This standard provides a protocol for ensuring such pipelines are properly tested to avoid environmental damage from pipeline failure.
The test method determines the susceptibility of pipeline steels, bands, flanges and fittings including all associated welds. It details an industry-proven technique for assessing pipeline steels by stressing a full ring specimen in a sour environment using mechanical means to deform the pipe by ovalization.
The test exerts a known stress level at two regions of a full ring section of pipe steel. The pipe specimen is then exposed internally to a sour test solution, although some cases require the sour media externally.
Ultrasonic monitoring and hydrogen permeation measurements are then conducted regularly during the exposure period. Both crack initiation and propagation can therefore be monitored. Finally a metallographic study of indications is undertaken to classify any defects found by the ultrasonic survey.
