Study Of Welding Technology On Repairing Pressure Pipe With H₂S

With the development of oil and natural gas industry, the number of pipeline in service was increased rapidly. The pipe wall thinning or failure of oil and gas pipeline in the transport process often occurs due to pipeline corrosion medium such as H2S or other causes with the use time of pipe. Therefore, the repair work of transmission medium pressure pipeline is not only huge, but also difficult welding and high rework rate because the welding of pipeline with medium H2S is easy to produce solidification cracking and stress corrosion cracking. It has been a problem need to solve in the late stage of maintenance for natural gas pipeline.The relationships among the welding, microstructure and properties of pipeline were studied systematically by testing the material composition, heat treatment and welding test for two kinds of pipeline with H2S medium in this paper.Firstly, the corrosion products on the pipeline were characterized by XRD analysis. It was showed that the pipe wall was corroded mainly by the H2S, so the pipe joint before welding for950-1000℃heat treatment was useful for removal of sulfur compounds and improving the properties of materials. Secondly, through the characterization of microstructure and properties of welded joints, the relationship between welding technology and microstructure and properties of welded joints for transport H2S medium pressure pipeline was established. A small heat input of welding is critical to ensure the quality of welded joints. The welding residual stress, which was easy to produce stress corrosion cracking under H2S corrosion environment, can be reduced effectively after650℃x1h heat treatment. The comprehensive evaluation of welded joints in the transmission medium H2S service pipe was conducted through a series of welding experiments. Finally the welding technology parameters for H2S medium pressure transmission pipeline maintenance were determined.Through this systematic study, the heat treatment technology and welding technology for transmission medium H2S service pipe were formed. It provides a theoretical foundation and scientific basis for repair welding of transport H2S medium service pipeline in China.