A Study On The Law And Assessment Method Of High Grade Pipeline Steels

Stress corrosion cracking(SCC) on pipeline steel is a significant aspect in line pipe safe operation area. The west-east natural gas transmission project had already successfully went into operation, with the X80 grade steel and 1219 mm diameter pie. The soil survey result shows that potential near-neutral p H line pipe focus on Shaanxi-Gansu-Ningxia junction part and Hubei province and Jiangxi province, the length of line is 1328.745 km, 30% of the main line length. Together with the 0.8 design factor experimental west-east natural gas transmission line’s completion, present a big challenge to the safe operation and monitoring of gas linepipe.This piece of work summarized research status on pipeline near-neutral p H SCC. Using X80、X90 grade steel as test material, operated electrochemical test、slow strain rate test、stress ring constant load test、wedge-shape open loaded pre-crack teat and high load micro-stress fluctuation SCC test. In the last, based on the SCC growth rate data, calculated a simulated pipe with SCC defect remained strength, proposed a proper evaluation method. It is carried out SCC risk assessment of the experimental third west-east natural gas transmission line.Tests’ results show: under over protection potential、high stress level and low stress ratio, increases the X80 grade steel SCC susceptibility, welding part higher than the base metal. In the constant load condition, as design factor raise, the X90 steel SCC susceptibility increases higher than the X80 steel. At present, the risk assessment shows that the experimental third west-east natural gas transmission line SCC risk is low.