With the increasing demand for energy, long-distance oil and gas pipeline has become the main mode of transportation of oil and gas resources. High pressure, inflammable and explosive medium, complex and changeable route environment and other factors make the safe transportation of pipeline concerned. The girth welds of oil and gas pipeline have always been the weak part of the pipeline due to the technical level during the construction, on-site welding practices and operation environment, and the girth weld cracking is one of the main failure forms of oil and gas pipeline. It is an effective way to ensure the safety of pipeline to adopt various advanced and targeted inspection to identify pipeline defects, judge the types of defects, and then carry out safety evaluation and maintenance. This paper analyzes the main failure factors of girth weld of oil and gas pipeline, and systematically summarizes the content and methods of various in-line inspection on girth weld in view of these failure factors, so as to provide reference for the development and application of in-line inspection technology on girth weld of oil and gas pipeline.

Long-distance oil and gas pipelines buried in permafrost areas will inevitably encounter typical geological disasters, such as frost heave and thaw settlement and sliding, which easily cause pipeline displacement, bending, or deformation. When there are certain defects in the pipeline, additional complex, external stress will further lead to the failure of the pipeline or weld and can even lead to serious accidents such as pipeline leakage, pipe burst, or fracture. This paper introduces in detail the typical defects and risks of buried pipelines in permafrost areas and summarizes the in-line inspection technologies, off-line inspection technologies, and integrated monitoring systems for pipelines in the pipeline industry. Regarding pipelines in permafrost areas, in-line inspection methods may be employed. These include magnetic flux leakage, electromagnetic eddy current, ultrasonic, IMU, and electromagnetic acoustic transducer inspections. Off-line inspection is also one of the important means of inspecting a pipeline in a permafrost area. Indirect inspection is combined with verification by direct inspection to check and evaluate the integrity of the anticorrosive coating and the effectiveness of the cathodic protection for the pipeline. Meanwhile, considering the external environment of a pipeline in a permafrost area, a monitoring system should be developed and established. This paper discusses and projects the future development of related technologies, which provides reference for the construction and operation of pipelines in permafrost areas.

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