Study On Sulfide Stress Corrosion Cracking Of X100 Pipeline Steel Weld Heat Affected Zone Based On Thermal Simulation Technology

Welding is an essential process in the pipeline laying.The welding joint,especially the heat affected zone(HAZ),is the weakest link of the whole pipeline due to the welding residual stress and the uneven microstructure.Sulfide stress corrosion cracking(SSCC)is a common problem in the heat affected zone(HAZ)of welded joints under acidic conditions with hydrogen sulfide.Therefore,it is of great theoretical significance and engineering value to design a reasonable welding process to ensure that the heat affected zone(HAZ)of welding has excellent stress corrosion resistance.In this paper,X100 pipeline steel is taken as the research object.By using thermal simulation technology,the microstructures of HAZ under different welding heat input under the action of primary and secondary thermal cycles are obtained.The SSCC resistance of different microstructures was studied by slow strain rate tension.Finally,the optimized welding heat input is calculated by Rykalin heat conduction mathematical model,which provides scientific basis for the formulation of welding process.The main research contents of this paper are as follows:(1)After the initial thermal cycle,the coarse grain heat affected zone(CGHAZ)resistance to SSCC performance at different cooling rates is deteriorated.When T_8/5 is 30s,the simulated CGHAZ has the best anti-SSCC performance,and the sensitivity of SSCC was the lowest at 76.4%.After the subsequent thermal cycle,the inter-critically reheated coarse grain heat affected area(ICCGHAZ)resistance to SSCC performance is deteriorated.Moreover,the larger the thermal input,the worse the anti-SSCC performance.(2)Comparing the electrochemical corrosion of CGHAZ under different heat input,hydrogen embrittlement(HE)sensitivity,SSCC sensitivity and fracture morphology,it is found that SSCC is mainly caused by HE,and anode dissolution plays a secondary role.(3)In order to obtain the optimal resistance to SSCC in the HAZ,this study gives the following recommendations for the welding process.When backing welding,the welding heat input should be selected around 28.5kJ/cm to reduce the SSCC sensitivity of the CGHAZ.When welding the second weld,the low heat input shall be selected to avoid the formation of coarse"chain"M/A component at the boundary of the prior austenite grain boundary.