Study On H₂S Stress Corrosion Of Buried Pipeline Material

Pipeline transportation is the most convenient,economical and reliable way totransport natural gas,the overall tendency of natural gas transporting development isto increase transmission pressure of natural gas and adopt high strength steel pipe.The X70 high strength steel pipe was adopted in the West-to-East Natural GasTransportation Project in China,while X60 grade pipeline was used in other naturalgas applied engineering. For the transportation system of Nanjing City Natural GasUsing Engineering X60 spiral welded pipe is employed. But,the existence of H2Sand water in pipeline transporting natural gas is inevitable, and sometimes thecontaining of H2S is too high,it is possible to happen stress corrosion cracking (SCC).The possibility is more with the increasing of strength grade of pipeline steel. So thesusceptibility of stress corrosion cracking of pipeline steel became higher and thismay lead to SCC. This dissertation focused on the research on SCC of X60 spiralwelded pipe, the research contents and results were as follows:(1)Through the physical,and chemical properties test of X60 spiral weldedpipeline adopted in Nanjing city Natural Gas Using Engineering,the results show thatthe used X60 spiral welded pipeline material come up with the standard of X60 gradepipeline steel. The hardness value of the material is lower than HRC22, and meets therecommended value in《The recommended method to prevent the failure of pressurevessel in wet H2S environment》and standard of NACE-MR-01-75:the hardness valueshould be no higher than HRC22 in acid wet H2S environment.(2)The four-point bending specimens were designed. Susceptibility tests ofstress corrosion cracking of material were carried out in the H2S solution of differentconcentration and under different stress level. After susceptibility tests of stresscorrosion cracking of X60 material for 1600 hours,cracks in the four-point bendingspecimens were not appeared,data of cracking time were not gotten,it is clear that thesusceptibility of stress corrosion cracking of X60 material without defects was nothigh. i(3)The H2S SSC resistance of X60 pipeline steel in laboratory condition wascarried out by four-point bending method. The results show that used X60 spiralwelded pipeline material displays a better resistance to H2S SSC.(4)A reforming WOL specimen was designed, and stress corrosion tests forpre-cracked wedge-open loading specimens (WOL specimens) were carried out. TheKISCC and da dt of X60 pipeline steel were gotten in 1000ppm and 500 ppm H2Ssolution .(5)An estimation of safety and predication of life of stress corrosion cracking ofX60 pipeline steel in wet H2S environment were made .