Challenges of Circumferential Stress-Corrosion Cracking (C-SCC) in Pipelines
Pipeline operators are increasingly concerned about cracks that form around the circumference of pipes, especially those caused by circumferential stress-corrosion cracking (C-SCC). C-SCC has become a growing concern for pipeline operators and is particularly problematic in pipeline applications with geohazards. The ground movement can cause significant axial loading, leading to the formation and rapid growth of circumferential cracks.
Unlike axial stress-corrosion cracking (SCC), where failure is often related to circumferential loading (hoop stresses), the load-carrying capacity of pipelines with C-SCC is not as well understood.
While there has been a lot of progress in testing and understanding cracks that run along the length of the pipe, there is still a lack of knowledge about how these circumferential cracks affect the pipe’s strength. Pipeline operators are looking to manage cracks along the circumference of pipes found during inspections.
To address this knowledge gap, the industry is working to better understand the mechanisms behind C-SCC, improve assessment accuracy, and select effective repair methods. However, more full-scale testing is needed to fully understand how pipes with C-SCC flaws behave under real-world conditions.
Industry came together in a Joint Industry Project (JIP) to help improve the industry’s ability to manage and reduce the risks associated with circumferential cracks in pipelines. During Phase-2, the JIP had 10 members from Canadian pipeline operators.
Joint Industry Project Overview
JIP Benefits
Increased knowledge of C-SCC’s effect on pipe’s strength will inform:
- Decisions about where to dig
- Planning ways to fix issues
- Deciding on monitoring actions
- Predicting pipe failures
In 2019, a Joint Industry Project (JIP) was launched to study the performance of circumferential crack-like flaws. The insights gained from this project are expected to aid in decision-making related to excavation site selection, mitigation planning, monitoring requirements, and failure load prediction.
Phase one of the JIP identified the need for full-scale validation testing for circumferentially orientated crack-like features in pipe body material.
Full-scale Testing with Artificial and Natural Circumferential Cracks
During phase two of this project, 10 pipeline operators participated in extensive testing of pipes with both artificial and natural circumferential cracks from donated pipe sections. The testing focused on understanding how these cracks affect the pipe’s strength when it is under both internal pressure and axial load. They looked at the impact of the size of the cracks, the internal pressure, and compared natural cracks to artificial ones.
Testing of Vintage Pipes
Phase 2 Completed
- Loading: combination of axial tension and internal pressure
- Four specimens with CSCC Colonies
- Main findings:
- Higher than expected failure load
- More vintage pipe tests needed to evaluate stress- and strain-based models
Tests of Modern Pipes
Phase 2 Completed
- Tested 12 new pipes with machined flaws
- Established data trends between failure load and key variables to evaluate models
- FFS model evaluation focused on API579/BS7910
Manage Your Circumferential Cracking More Effectively - Join Phase 3
Phase three of this JIP will support the assessment of the load-carrying capacity of pipelines with C-SCC features. This includes testing vintage pipes with flaws of medium depth, expanding assessment tools to strain-based applications.
Main Activities
Experimental Testing
Testing vintage pipes with CSCC or machined flaws
Strain-based Assessment
Expanding assessment tools to strain-based applications
Pipeline Integrity
Expanding evaluation range of stress-based fit-for-service (FFS) procedures to vintage pipes
Future testing may include other evaluation tests such as long-term testing and bend testing. The JIP will support other integrity management priories for pipeline operators such as:
- Estimating stress/strain demands from operational and environmental loads
- Projecting CSCC growth rates
- Developing guidelines for model application
Leverage C-FER's Experience & Third-party Perspective
For over 40 years, C-FER Technologies has been bringing pipeline operators together to tackle challenges related to pipeline integrity management through Joint Industry Projects (JIPs) such as:
Drawing on our experience with pipeline integrity management and structural testing, this Joint Industry Project will tap into existing infrastructure and testing facilities.
C-FER’s third-party perspective ensures non-biased results.
Contributor
Brian Wagg, MSc, PEng.
Director, Testing Services
With over 35 years with C-FER, Brian Wagg’s current focus is on applying C-FER’s analytical and full-scale testing capabilities to projects in clean energy including CCUS, hydrogen, geothermal and small modular nuclear reactors.
