Mechanical and Metallurgical Properties of Heavy Wall Grade X80 High Strain Line Pipe Steel

摘要

Mechanical and metallurgical properties of a 27mm thick Grade X80 steel plate and its UOE pipe are described in this paper. The steel is economically designed for its chemical compositions. Steel plates were produced by Thermal-mechanical processing (TMCP) with attentive reduction control during hot rolling stage. The microstructure is composed of multi-phases in which polygonal ferrite and granular bainite are the principal constituents. Line pipes of 1219mm outer diameter, which has strain based design for long distance natural gas transportation over the permafrost and seismic areas, were manufactured by the UOE process under a 0.8% expanding ratio on the pipe. Mechanical properties of the pipe and in the girth weld joints comply well with the pipeline construction requirement. Precipitation behaviors were analyzed in the steel materials, and a strengthening contribution at about 45.6 MPa is disclosed. Dislocation hardening in the pipe base materials after the simulating coating gives rise to 44.9 MPa.