Research On Welding Procedure And Stress Corrosion Of 12Cr Pipeline

Stress corrosion is the most common form of the environmental factrue, and it is a spontaneous process, which generally occurs when metal or alloy suffers the combined effects of the specific environment and a centain stress. 12Cr pipeline as riser of offshore oil field, mainly delivering oil and gas, is served under the seawater, so the influences from the environment are serious and complicated. And under the stress simultaneously, the structures tend to occur stress corrosion, determining the service life of the welded structures. That requires that 12Cr pipeline not only has well mechanical properties and fracture toughness, but also excellent stress-corrosion resistance.The research on mechanical properties and fracture toughness of 12Cr pipeline is carried out through mechanical test and CTOD test, based on the standards API 1104 and BS7448. And the research on stress corrosion of 12Cr pipeline are carried out through four-point bent-beam stress-corrosion test, based on the standard ASTM G39. The stress-corrosion tests are composed of CO₂ stress-corrosion test and HIC stress-corrosion test. The tests are carried out at 50℃, and CO₂ partial pressure of 10KPa, The test solution used is an aqueous mixture of 10% NaCl with 0.5% CH3COOH, and the pH maintained at 4.5. The applied stress is equivalent to 90% SMYS. In the HIC stress-corrosion test, the specimens are polarized at -1150 and at -850mV during the exposure period.The results suggest that 12Cr pipeline not only have well mechanical properties and fracture toughness, but also excellent CO₂ stress-corrosion resistance and Hydrogen-Include Cracking(HIC) resistance.