Design of Parallel Pipelines in Second West-East Natural Gas Pipeline Project

Abstract

The Second West-East Gas Pipeline (2nd WEP) Project, consisting of one trunk line and eight branches, has a total length of 8,704 km and a designed annual transportation capacity of 30 billion cubic meters. The outside diameter of trunk line is 1,219 mm (48″). According to the plan, 2nd WEP will parallel with several existing or planning pipelines in long distance, some will even be located in rocky area. However, there are neither requirements of separation distance nor other related provisions of parallel pipelines in current domestic regulation and codes in China. It is an urgent critical problem to reasonably design, construct and operate multiple pipelines in same corridor. In order to design 2nd WEP in parallel with other existing and planning pipelines, a series of technical studies were carried out. This paper describes the main work. First of all is the literature review, including regulation, standards, codes etc. and similar work on parallel pipelines and applicable practices in other countries. Second, for the primary concern-separation distance, the main factors are considered. Then, the computational results of some 2nd WEP paralleling with other pipelines based on the impact of the failure of natural gas pipeline to adjacent pipelines are introduced. Third, the experiments and some related researches in rocky areas where 2nd WEP parallels with existing pipelines are introduced. Forth, analysis of Direct Current (DC) stray current interference resulted from Cathodic Protection (CP) Systems located along each parallel pipeline is briefly introduced. Then is the mitigation and monitoring requirements for unbounded (separate) CP system. According to the works above together with engineering practices as well as experiences, the design guideline of parallel pipelines is established. When 2nd WEP parallels with other pipelines not locating in rocky areas, the reasonable separation distance is based on integrated considerations of adjacent pipeline’s survival in the event of failure of gas transmission pipeline, easiness to construct, less CP interferences, adequate space requirements for maintenance and repair. For other paralleling cases, engineering requirements are established separately. This guideline has been applied in design of parallel pipelines and provides management requirements for future operation in 2nd WEP project.