At least 10 girth weld incidents in newly constructed pipelines are known to have occurred.  The main contributing factors to the incidents are: (1) weld strength undermatching, (2) heat-affected zone softening, (3) weld bevel geometries of manual stick welding processes that favor plastic straining along the softened HAZ, and (4) elevated stresses/strains from normal settlement and other loads.  In addition to the girth weld incidents, there are some indications that some features of modern linepipe steels may lead to under-performance in comparison with vintage steels when anomalies are present in pipelines.  

This paper covers the development of improved linepipe specifications aimed at reducing the risk of similar girth weld incidents in newly constructed pipelines and to increase the long-term resilience of the pipelines to anomalies such as mechanical damage, corrosion, etc.  A companion paper covers possible improvements to welding processes to reduce the risk of similar incidents. 

The linepipe specifications have been developed through extensive work in the following areas: 

Reviewing the characteristics of the linepipes involved in the girth weld incidents, 

Reviewing the history and trends of linepipe properties and comparing them with the properties of the linepipes involved in the incidents, 

Correlating failure processes with characteristics of linepipes through numerical analysis and experimental testing, 

Understanding the evolution of metallurgical and material properties of linepipe steels when subjected to welding thermal cycles, and 

Understanding the interaction between linepipes and pipeline service conditions. 

The improved specifications include (1) limiting the upper-bound strength for a given pipe grade, (2) having optional testing of longitudinal tensile properties, (3) alternative tensile test methods, (4) alternative definitions of yield strength, (5) the need to maintain a certain level of strain hardening, and (6) potential ways to quantify a linepipe steel’s susceptibility to HAZ softening.  The linepipe specifications were developed with a full account of current practices and the history associated with the practices.   

The improved specifications are expected to be adopted by pipeline operators in stages that are most suitable to their circumstances.  The specifications are written in a tiered structure meant for different stages of a pipeline construction project.   


Improved Linepipe Specifications and Welding Practice for Resilent Pipelines

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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