March 2017, Vol. 244, No. 3

TechNotes

New Standard for Corrosion Testing Published

Business standards company BSI has published the new standard for corrosion testing in pipelines used in the oil and gas industry. BS 8701 Full ring ovalization test for determining the susceptibility to cracking of linepipe steels in sour service – test method enables measurement of corrosion and environmentally assisted cracking of pipelines.

The issue of pipeline stability and integrity has always been of great importance to the oil and gas industry for the safe transportation of petroleum and natural gas products. Not least because of the damage that can be caused if a pipeline fails and spills product into the local environment.

This standard updates the 1996 HSE Guidance document OTI 95 635 which features the protocol for ensuring pipelines are properly tested to avoid environmental damage from pipeline failure and which is referenced in ISO15156, the flagship document for upstream material selection for sour service.

Different factors have to be taken into account when testing pipes: such as environments, age of pipeline, materials used, coatings etc. In addition to this, the types of corrosion must be accounted for too, such as sweet corrosion, (wet carbon dioxide, CO-2) and sour corrosion (wet hydrogen sulphide, H2S). Both scenarios exist in pipelines.

Prior to testing materials and weldments for pipelines, basic parameters need to be established such as what was the pipeline designed for, what is the environment inside or outside, whether the internal environment is sweet or sour etc. In the case of testing the influence of the sour environment, previous guidance is not up to date. However, BS 8701 rectifies this and looks at the cracking problems that can occur in pipelines.

One of the best ways of assessing the susceptibility to cracking is through testing a full ring specimen of the linepipe in a sour environment where a stress level is applied at two regions on the specimen. Both during and following exposure of the specimen to the sour test solution, ultrasonic monitoring can define crack initiation and propagation, and a metallographic study made post-test, to classify any defects found by the ultrasonic survey.

“Whenever an oil tanker spills its cargo we hear a great deal about the environmental impacts of such an incident, but less about one of the major causes of it. The condition of pipelines that transport oil and gas is crucial in preventing an environmental event,” said David Fatscher, head of Market Development for Sustainability & Energy at BSI. “Ensuring pipelines are unaffected by corrosion from the marine environment, can help avoid these scenarios.

BS 8701 is of importance to manufacturers of pipelines designed for the transport of petroleum and natural gas products. It was developed using a collaborative consensus-based approach with input from industry experts within the petroleum, petrochemical and natural gas industries.

“Having a test method such as BS 8701 in place allows the correct tests for identifying the damaging levels of corrosive hydrogen sulphide gas, to be carried out. It can act as an early warning system that offers reassurance that everything is being done to safeguard the environment,” Fatscher said.