The Use of High Temperature Processing(HTP) Steel for High Strength Oil and Gas Transmission Pipeline Applications

摘要

The trend toward higher operating pressures in gas and oil transmission pipelines over the past 10 years has resulted in an increased demand for higher strength steels such as API X70 and X80 with good low temperature toughness. The current alloy design for API X70 transmission pipeline projects with higher toughness requirements over a variety of different temperature ranges utilizes either a low C-Mn HSLA chemistry resulting in a ferrite/pearlite microstructure or a low C-Mn-Mo HSLA chemistry resulting in a ferrite/acicular fertile microstructure. The current alloy design for API X80 transmission pipeline projects with improved toughness over a variety of temperature ranges utilizes a traditional ferrite/acicular ferrite microstructure generated with low C-Mn-Mo based chemistry. This alloy design has been well documented as a viable approach for high strength oil and gas pipelines with reasonable toughness over a variety of temperature ranges. Recently, an alternative low C-Mn HSLA chemistry utilizing a high niobium level, that develops a ferrite/acicular ferrite microstructure, has been successfully utilized to produce an API X80 transmission pipeline project. This chemistry is unique in that it has the ability to produce the strengths and pipe body impact toughness required for an API X70 or X80 transmission pipeline projects utilizing higher than normal processing temperatures during rolling than the traditional low C-Mn-Mo based design. In addition, the ability to produce the desired microstructure, strength and toughness without the use of molybdenum has a positive effect in keeping the hardness in the pipe body, HAZ, and weld below 260 HvlO. This alloy design's ability to utilize high temperature processing (HTP) improves productivity and alleviates issues in rolling (mill loads, shape, etc.) associated with the lower temperatures required to process the traditional low C-Mn-Mo alloy design. This paper describes the development and implementation of the first large scale commercial production of an API X80 gas transmission pipeline project utilizing the high temperature processing (HTP) low C-Mn (Nb-only) steel alloy design.