The Crack Defect Analysis Of High Grade Natural Gas Pipeline

Oil and gas pipeline has become one of the most economical and convenient means of transportation all over the world’s. However, with the growing demand for oil and gas of residents and industry, the previous low pressure, small diameter and low strength oil and gas pipeline cannot have satisfied the requirements of the times.Therefore, high pressure, large diameter, high strength pipeline arises at the right moment. In order to ensure the safety of high grade pipeline in daily operation, not only to guarantee the quality of pipeline material, the security status of pipe welding joint is also important, because the vast majority of pipeline leak from the weld joint.This article described the present situation of oil and natural gas pipeline、development trend and the significance of the paper. In this thesis, the type of crack、the reasons and damages of appearing the crack defects of welding joint with the temperature change in welding process will be studied, and some prevention measurements will be proposed from the theoretical perspective based on the carrier of X70 and X80 pipeline steel. These crack defects can reduce the strength of weldment structure, the most important reason is that the structure of these defects reduce the effective cross-sectional area of load, while the surrounding defects produced a stress concentration region, resulting in the use of welded pieces of performance and life have a negative impact. In order to ensure the quality of pipe welding joint, it is necessary to carry out the routine testing, to be able to detect problems and take appropriate measures to reduce unnecessary losses. Ultrasonic inspection technique because of its convenient operation, testing speed, reliable data and the advantages of lower cost in-service pipeline defects become a major means of detection.By using digital ultrasonic flaw detector detect the homemade natural defect simulation test block from the experimental perspective. Through practice detection, analyzes and summarizes the influence of the ultrasonic detection probe parameters(frequency, K value, the die size)、coupling agents and the scanning ways on the detection sensitivity, and proposed how to use the probe、coupling agent and the scanning ways. After detecting indicated defect length、indicated defect height and the distance from the defect to the weld centerline, compared with the embedded theoretical size, find that the error of three kinds of practical detection data of nearly 90 percent is within 9%,and validate that the ultrasonic inspection technique is accurate and reliable in high grade pipeline weld crack defect detection.