Operating in extreme environments means that pipelines are subject to unprecedented conditions, with varying hydrogen sulfide and carbon dioxide levels, colder temperatures and higher pressure all affecting pipe material corrosion rates. This creates enormous industry-wide challenges in predicting and preventing potential pipeline cracking and failure.
The answers to these problems are being sought through materials technology. Fracture toughness testing is one of the most important methods of evaluating the mechanical properties of pipeline materials. It measures how a weld containing small defects resists fracture during installation and operations, which is a vital property in pipe materials, as the occurrence of flaws during these process cannot be completely avoided. Therefore, methods such as Single-Edge Notched Beam (SENB), Single-Edge Notched Tensile (SENT), Compact Tension (CT) and Crack Tip Opening Displacement (CTOD) testing are necessary to determine the allowable level of defects in pipelines used for exploration and production.
Data gathered from these tests is input directly into the engineering critical assessment (ECA) of an offshore structure’s integrity, applied increasingly to pipeline laying, reeling and operation in subsea environments. The data is not only needed to calculate fracture points at different parts of the pipe, including the weld join cap and Heat-Affected Zone (HAZ), but also to develop testing techniques for validating the ECA output.
As everyone knows, it is no longer easy to find or extract the world’s oil and gas, and if materials testing is to continue to lead the way in technology advancements for exploration and production, fracture toughness testing of pipelines will play a key role in this.
Crack Tip Opening Displacement (CTOD)
Crack Tip Opening Displacement is a measure of the physical opening of the fatigue crack tip at the point of failure. It is typically used to measure the toughness of materials that tear before failure.
All CTOD tests can be carried out from -129ºC (-200ºF) to 200ºC ( 400ºF)