Pipeline failure and maintenance-17

Release time:

2024-05-11

What are the causes and maintenance methods of old pipeline accidents?

A: Although the development history of China's pipeline industry is not long, there are many old pipelines in service, which are widely distributed and have certain characteristics, and the safety problems are prominent, especially the safety problems of welds. Based on the understanding of the actual situation, this paper puts forward the measures to ensure the safe and lasting operation of the old oil and gas pipelines in service in China, establishes and improves the integrity management system of the old oil and gas pipelines in service in combination with the engineering practice, speeds up the research and development of the detection technology and equipment inside and outside the pipelines, and ensures the smooth development of the integrity management.

Accident cause analysis:

1) At that time, due to the backward pipe making and welding technology, as well as historical reasons, there were serious defects such as lack of penetration, lack of fusion, inclusions, nozzles and staggered edges. The defect itself not only reduces the load-bearing section, causes serious stress concentration, greatly reduces the mechanical properties of the weld, but also tends to become the crack origin and the crack opening position.

2) The spiral submerged arc welded pipe has high forming and welding residual stress near the weld and heat affected zone, and the internal surface shows high residual tensile stress. In addition, the additional bending tensile stress caused by defects such as weld "nozzle" and the membrane stress generated by internal pressure are superposed, and the stress concentration is increased, which promotes stress corrosion, especially under the environment conditions such as h, s, etc., stress corrosion will be more severe Heavy.

3) The pipeline suffers from the effects of fatigue, dynamic load, pressure and temperature frequent fluctuations in operation, which makes the defects at the weld germinate and crack, and expand to cause cracks.

In conclusion, the weld defect of pipeline is the biggest problem that affects the safety of old oil and gas pipeline in service in China. A large number of cases show that weld fracture is usually caused by several types of defects. Due to the difference of the actual defects, the severity and the internal pressure of the defects, the conventional method of analyzing and evaluating the pressure bearing capacity of the whole channel through limited observation and limited strength test has lost its practical significance. It can be seen that the safety of welding seam is the key problem of safe operation of old pipelines in normal service period or delay period.

Maintenance measures for old pipelines: in particular, it is necessary to increase the research and development of quantitative non-destructive testing method and testing system for pipe body, especially for the detection of weld defects of old pipelines. In order to improve the safety and maintain the normal operation of the pipeline, it is necessary to excavate the pipe section with serious defects and accurately locate and quantify the defects.