In recent years, the girth weld cracking and leakage accidents in onshore pipelines have become an increasing trend. Most accidents are concentrated in modern, high-grade pipeline steel (such as X70 / X80). According to the analysis of girth weld failure accidents, the failure mechanism mainly involves three aspects, namely:
- external load resulting mainly from geological disasters and construction activities,
- pipeline welding defects, and
- the undermatch effect of high-strength steel and welding materials.
The China-Myanmar natural gas pipeline uses X70 / X80 high-strength steel and its route crosses mountainous areas, where there are frequent geological disasters which have resulted in two severe failure incidents at circumferential welds. Therefore, there is an urgent need for reliable technical means to investigate the risks of girth welds to ensure the safe operation of the pipeline. Axial strain inspection is a newly developed in-line inspection technology that can measure the elastic axial strain of the pipe. Combined with IMU bending strain measurement technology, it can identify the external load of the pipeline caused by geological hazards or construction related events.
This paper introduces a case study of the application of the combined high-resolution MFL, AXISS™ axial strain and IMU bending strain inspection technology developed by Baker Hughes, in the inspection of the 206km NPS 40 pipeline Duyun - Hechi section of the China-Myanmar pipeline, and combines a girth weld threat assessment model to prioritize, investigate and mitigate the risk of girth weld failure in the pipeline.
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