This paper provides description of deep-sea JCOE process of longitudinal submerged-arc welded pipe.The test methods including optical microscopy and tensile,toughness,drop weight tear are applied, the microstructure and properties of deep-sea pipeline steel and deep longitudinal submerged arc welded pipe with thick wall are studied. The results indicates that pipeline steel of substrate organization to acicular ferrite mainly and deep with longitudinal submerged-arc welded thick wall pipe welding HAZ of rough crystal area and fine crystal area respectively main for granular bainite and associate polygon ferrite organization; Deep-sea LSAW steel pipe has reasonable control parameters for process, and its performance meets DNV-OS-F101:2007 specification and user project technology conditions,used for materiels of pipeline steel for China deep-sea oil and gas pipeline project.
