Principles of and tips for nitrogen displacement in gas pipeline commissioning

Since the West-to-East Pipeline I was put into production, operators have made many attempts and accumulated valuable experiences in gas pipeline commissioning. However, there are still some problems. For example, the injected nitrogen quantity was determined only by experience rather than by quantitative calculation formula; there are some unnecessary steps in the nitrogen displacement process. Therefore, the authors summarized experiences from various scenarios at home and abroad over the past decade, and introduced some innovative practices in the preparation of pipeline commissioning schemes. Particularly, the calculation formula was first developed for the required nitrogen quantity in the commissioning process; the in-turn nitrogen displacement was replaced by the simultaneous way in the paralleling pipes at the stations; nitrogen displacement was abolished in vent and drainage lines; and several other tips were concluded for the nitrogen displacement process. Supported by scientific evidences, previous commissioning experiences and data, the above innovative practices help not only simplify the on-site operation on the premise of safe production but also shorten the nitrogen displacement time greatly, and save a large quantity of nitrogen gas, as a result, the economic benefit is significantly enhanced.