Research And Development Of X80 Grade Hydrogen Sulfide (H ₂ S) Corrosion Pipeline Steel

Hydrogen sulfide corrosion is one of main reasons which caused corrosion of pipeline. In order to ensure the safety of pipeline transportation, hydrogen sulfide corrosion resistance performance has become an important property of pipeline steel. This study was supported by National Science-technology Support Plan Projects "production technology of high strength and corrosion resistance pipeline steel applying in oil and gas gathering and transportation".In this paper, two types of X80 grade hydrogen sulfide corrosion resistant pipeline steel (17# and27#) and X80 grade industrial acid-resistance pipeline steel (8#) were investigated. To confirm the effects of different microstructure (polygon ferrite, acicular ferrite, martensite and granular bainite structure) on the HIC properties of pipeline steel, the microstructures of the experimental steel on different heat treatment were studied by optical metallographic microscope(OM), scanning electron microscope (SEM) and energy dispersive x-ray analysis (EDAX). Phase transition behaviors of X80 grade hydrogen sulfide corrosion resistant pipeline steel (8#) during continuous cooling were studied by Formastor-f II automatic test instrument division and Gleeble-1500D thermal simulation testing machine. The transformation rules of X80 grade hydrogen sulfide corrosion resistant pipeline steel (8#) were also researched. Furthermore, the CCT curves were given. Based on the previous research, the control rolling and control cooling process of X80 grade hydrogen sulfide corrosion resistant pipeline steel was determined, which provided scientific basis for production. HIC performance of three kinds of grade X80 pipeline steel was evaluated by A standard solutions which come from "HIC assessment of pipeline steel and pressure vessel steel" of NACE TM0284. Through OM, SEM, EDAX, transmission electron microscope (TEM) and inductively coupled plasma mass spectrum analyzer (icp-ms), the reason of hydrogen induced cracking was found, and which one possess of good HIC property among this three kinds of pipeline steel was determined. The relationship between the hydrogen charging current density and the hydrogen content was researched by means of electrochemical charging and Thermal Desorption Spectrometry (TDS). Moreover, the forming and expanding regularity of HIC was obtained. In all, this paper thoroughly researched the effect of hydrogen content on mechanical property of grade X80 pipeline steel.The experimental results show that acicular ferrite structure possessed the largest HIC sensitivity, HIC sensitive of polygonal ferrite structure was less than the former, what is more the HIC sensitive of bainite and martensite were the least. The uniformity of the microstructure had a great influence on anti-HIC sensitivity of the materials. Specifically, the more uniformity of the structure owned, the finer the grain size was, so that the anti-HIC sensitivity of material was stronger. In addition, HIC was expending along high-angle grain boundaries, nevertheless, low angle boundaries had a certain function to crack arrest.The static phase transformation CCT curves of X80 grade hydrogen sulfide corrosion resistant pipeline steel (17#) illustrated that phase change temperature mainly occurred between 450-780℃. Trough controlled rolling and controlled cooling test, the mechanical properties of X80 pipeline steel were investigated. That is deformation temperature for 830±15℃, the cooling speed of 15℃/s, and coiling temperature for 400±15℃.One cause of nonconformity for HIC performance was elements segregation of C、Mn、S、Si, and so on. The source of crack initiation was inclusions and massive MA with inclusions. Based on research, it was found that the highest properties of HIC resistance was X80 grade hydrogen sulfide corrosion resistant pipeline steel (17#).For X80 pipeline steel, the crack began to grow when the diffusion hydrogen content was 1.86 PPM. When the diffusion hydrogen content was 1 PPM, elongation of sample decreased 24.3%. Furthermore, the tensile fracture appeared to be a dimple pattern in whole. However, the more diffusible hydrogen content was, the smaller and shallower the dimple had, and the hole will become larger, which lead to quasi-cleavage fracture on the edge of the hole. There was almost no change with impact energies of sample while the diffusion hydrogen content was about 1 PPM, nevertheless, impact energies was down 4.9% when the diffusion hydrogen content was 1.86 PPM. The crack began to initiation and propagation if the diffusion hydrogen content further increase, meanwhile, the fracture morphology was changed and even appeared wavy quasi-cleavage fracture.