Video
Threat Awareness: Circumferential Stress Corrosion Cracking
Circumferential stress corrosion cracking (CSCC) is a type of stress corrosion cracking (SCC) in which a corrosive environment combined with circumferentially-oriented tensile stress causes circumferential cracks to form around a pipeline. In this video, members of our Integrity Engineering Solutions team dive into the subject, share causes of CSCC and explain how TDW leverages our MDS™ Platform to help operators prioritize potential CSCC locations for investigation and remediation.
Transcript
Today, we're going to be talking about circumferential stress corrosion cracking, or CSCC.
Why should operators be aware of CSCC?
This is something that can occur both in liquid and natural gas pipelines, and is not as easily detectable as axial SCC.
What is Stress Corrosion Cracking (SCC)?
SCC is a form of environmentally-assisted cracking produced by the combined application of a corrosive environment, a tensile stress, either residual or applied, on a steel that is susceptible to SCC.
SCC is typically characterized by small individual cracks adjacent to one another in an array or colony. If the cracks continue to grow, they overlap and coalesce and become equivalent to a large single crack And so we must treat them as such when we evaluate their effect on pipeline and carrying capacity. Cracks can eventually develop large enough to cause the pipeline to leak or rupture.
What makes CSCC different from SCC?
Most of the time when we talk about SCC, we're thinking about cracks that grow in the axial direction along the length of the pipe.
CSCC is similar, but grows in a circumferential or helical direction, making it harder to detect. Because most SCC and cracks on pipelines in general are axially oriented, the majority of the crack detection tools are designed to detect these axially oriented anomalies. The same SCC triangle conditions cause CSCC as well. The difference is that the predominant stress has been shifted to be circumferentially oriented. Picture your pipeline as a pool noodle. When the primary stress is only caused by internal pressure, the SCC forms axially.
But, if you bend your pipeline, the SCC starts to form circumferentially.
Changes in pipeline conditions such as extreme weather events, geo hazards and line settling are things that can introduce bending strain, so operators of assets and environments where these are more prevalent need to be especially wary.
How do we prioritize potential CSCC threats?
Our Integrity Engineering Solutions team uses the MDS platform to collect multiple data sets in a single run. Bending strain analysis, line movement assessment, SpirALL MFL, high-field axial MFL, and low-field axial MFL are all utilized in input into our CSCC prioritization model.
Even data from prior MDS runs can be examined for CSCC. Using our original model, we've been able to show a 75 percent true positive success rate, and the model is continuing to be improved. If you're looking for more information on CSCC, the Integrity Engineering Solutions team here at TDW is here to help and provide ongoing advice and support.