Perforation failure analysis of pipeline elbow at a receiving station.

• Pipeline elbow made of 304L stainless steel at a natural gas receiving station suffered a perforation failure after 6 years of service. • Standard failure analysis methods such as physical and chemical properties are used to analyze the root cause of failure. • The thinning of elbow wall and perforation failure are mainly caused by high pressure erosion. During the daily inspection process at a natural gas receiving station, ice was found to be present at the elbow of the pipeline, with a fog emerging from the elbow itself. This elbow was suspected of leaking. After investigation, it was found that the outer arc side of the elbow contained perforations resulting in the leaking of combustible gas. In this work, the causes for failure of such a low-temperature 304L stainless steel pipe elbow are analyzed and discussed. Macromorphological analysis, nondestructive testing analysis, chemical composition analysis, Charpy impact test, hardness test and microstructural analysis were performed to determine the root cause of the failure. The field investigation shows that the perforated failure pipe section is located downstream of the flow-limiting orifice plate, and that the pipe medium can contain small particles. Macroscopic observation reveals that the perforation defect is located at 3 points on the outer arc side, and the defect takes the shape of a bowl, with a perforation aperture diameter of approximately 0.7 mm. Microscopic observation reveals that the defective area has a honeycomb shape with tiny spheres on the surface, with many slip lines observed in the metallographic structure near the defect, indicating that the small deformation was caused by a large impact load. Based on the evidence of failure, the formation of the perforation defect is attributed to the excessive flow rate generated by the high pressure difference between the front and back sides of the single-stage orifice plate, which leads to the intensification of erosion. Moreover, when combined with the actual situation, it is found that the fine solid particles mixed in the medium can aggravate the thinning of the pipe wall section. [ABSTRACT FROM AUTHOR]