Strain-based design (SBD) method has evolved over the years for use in the construction of large-diameter, high pressure gas and liquid transmission pipelines. It has not been widely materialized for major construction projects because of the technical complexity which requires multidisciplinary expertise including, but not limited to, pipeline material properties, welding processes, mechanical testing, field construction, and weld inspection. The industry has been showing more interest in using this methodology for strain capacity assessment of in-service stress-based pipelines, especially those that are subjected to ground movement. The strain capacity assessment of the stress-based pipelines is essential to ensure structural integrity and operational safety of the pipeline. This has become more apparent due to recent incidents in pipeline industry caused by geotechnical hazards.
This paper provides a case study of assessing the tensile strain capacity (TSC) of existing modern linepipes manufactured through thermomechanical controlled process (TMCP). The TSC was predicted using two main methodologies in the public domain: the CSA Z662-11 Annex C approach and the PRCI-CRES TSC model. Actual pipeline information and construction data are used to perform TSC assessment when possible. This includes pipe material properties, welding procedures qualified on the project pipe, and test weld properties.
The predicted TSC and the estimated strain demand will allow for effective remediation decisions. This work helps to enhance pipeline strain management systems in response to the geotechnical and hydrotechnical issues and therefore fills the gaps in present day’s pipeline threat management programs in addition to crack, corrosion and mechanical damage threats. Through such a program, prevention, monitoring and mitigation strategies can be deployed to existing stress-based pipelines, especially in areas where pipeline strain is identified as a potential risk.