| Along with the recently development of oil and gas pipelines, there are a lot of pipeline damage examples which caused by H2S corrosion both home and abroad. Due to little re-search, it is urgent to develop pipeline steel of resistant H2S. The work of this dssertation aims at X70pipeline steel of resistant H2S in technics and structure property, acid X70pipeline steel is developed by TMCP technology. It not only has excellent mechanical properties but also good corrosion resistance. The main research contents are carried out as follows:(1) Transformation behavior With and without deformation was reserached. The conti-nuous cooling transformation(CCT)diagrams were conducted by using thermal dilation me-thod combined with microstructure observation. The Results of CCT without deformation:As cooling rate more than5℃/s, microstructure are Acicular ferrite and a few granular bainite; As cooling rate more than25℃/s, microstructure is s more fine and uniform and bainite lath width decereases. The Results of CCT with deformation:As cooling rate more than5℃/s, microstructure are Acicular ferrite and a few granular bainite; Acicular ferrite is more refined and the percentage is up as increase of cooling rate.(2) Hot rolling test and Research of Mechanical and microstructure properties results re-vealed that the X70pipeline steel of hot plate satisfied the good comprehensive mechanics performance can be obtained by controlling of heating temperature inl200℃, two regions rolling, finish rolling temperature in800℃～820℃, final cooling temperature in500℃～550℃and cooling rate in20～25℃/s. The acicular ferrite and granular bainite would be mainly ob-tained.(3) According to NACE Standard TM0284-2003and NACE Standard TM0177-2005Standard, pipeline corrosion tests are carried out. The principle of hydrogen induced cracking Firstly bubbling hydrogen appear on the surface of sample, Those cracks gradually extended from the sample surfaceto the internal, after propagating and joining, joining, finally formed step-like crack. Many MnS and aluminum oxides existed at crack tip.(4) Testing HIC performance of acid corrosion-resistant X70pipeline,All meet the requirement, and factors of inclusion and microstructure on HIC are researched to result that Fine grain, dense, homogeneous acicular ferrite own high density of dislocations and disloca-tion pinning precipitates which Can hinder crack propagationan and enhance HIC perfor-mance. By reducing the content of S and controlling inclusion morphology, improving the HIC resistance properties.(5)Experimental steel electrochemical corrosion test results show that the self-corrosion current of the4#sample with ferrite and pearlite is large and the self-corrosion current of the5#sample with uniform and fine acicular ferrite and granular bainite is small. Those results are basically consistent with HIC. Corrosion resistance of the pipeline decreased significantly at corrosive environment.(6) To solve the problem that the traditional stress corrosion device can not provide sta-ble stress and reduce the high cost of device, a portable precision spring stress corrosion de-vice is to be developed. The results of X70pipeline SSC test by using the stress corrosion de-vice show that can do it but there is still need for improvement. |
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