Discussion on equal inner diameter technology for onshore high-grade large-diameter natural gas pipelines

Abstract

The equal outer diameter design(the inner-tapered bevel design) of onshore high-grade large-diameter natural gas pipelines has effectively improved the quality problems of welding at place of pipeline with unequal wall thickness.However, the problems, including the staggered platform at the unequal wall thickness inside the pipeline and its effects on pigging, pipeline loss, and maximum transportation capacity, remain unsolved fundamentally. In order to completely eliminate the adverse effects of unequal wall thickness in equal outer diameter design, the feasibility of equal inner diameter design method for onshore high-grade large-diameter natural gas pipelines were discussed through four aspects, which are the comparison of standards and specifications at home and abroad, the numerical simulation on stress concentration at girth welds of pipelines, the influence of steel pipeline production and onsite construction, and the analysis on the construction cost and the economy of operation and maintenance. According to the results, it is technically feasible to adopt the equal inner diameter design in view of design, material and construction. Besides, in terms of the construction cost and the economy of operation and maintenance, the construction cost and full life cycle cost of equal inner diameter design is basically balanced with that of the equal outer diameter design in the calculation of a specific scenario model.In general, the research results could provide reference to the equal inner diameter design in natural gas pipeline projects.

Keywords

• natural gas pipelines
• high-grade steel
• large diameter
• equal inner diameter
• pipe manufacturing
• welding
• gas transportation capacity