With the pipeline industry's increased focus on pipeline safety and integrity, more frequent and complex pipeline outages are required to perform this safety work. How can dead-end, single feed natural gas systems be taken out of service to perform safety work while maintaining service to customers? It has become increasingly necessary to support customers using portable natural gas (PNG) in compressed (CNG) or liquefied (LNG) form. Pacific Gas & Electric Company (PG&E) has relied on PNG support during pipeline outages more frequently in recent years and recently undertook two separate projects that were unprecedented in scope and volume - in Santa Cruz and Redding, California.
PG&E's Gas System Planning (GSP) department performed complex hydraulic analysis and operational support for the 2 major pipeline safety projects, each of which required more than 40,000+ customers to be supported solely with PNG for up to 4 weeks. In Redding, 130 tankers carried 110 mmscf of LNG to be injected into the pipeline, plus additional equipment provided 13 mmscf of CNG. Personnel traveled over 135,000 miles to support the project. In Santa Cruz, 119 loads of LNG injected a volume of 81 mmscf with personnel traveling 83,300 miles over the course of the outage.
This paper presents the analysis and tools used to perform extensive and complex gas system planning analysis. In the initial phases of the project, GSP provided input on the project schedule, how to phase the work to minimize customer impacts and maintain system reliability, and what additional PNG equipment would be needed to support the entire project. As we moved into the project design phase, GSP calculated total daily volumes and peak hourly flow rates, as well as found hydraulically feasible injection site locations and pressures for each tap off of the pipeline. Finally, during the outages, GSP provided real-time flow monitoring and operational support for field personnel.