The Department of Transportation (DOT) has granted waivers to three proposed or relatively new interstate natural gas pipelines that would allow them to operate at a higher maximum allowable operating pressure (MAOP) in low-density areas along their routes — a move that would clear the way for more gas to flow through the systems.

The DOT’s Pipeline and Hazardous Materials Safety Administration (PHMSA) gave a waiver to the proposed Rockies Express Pipeline to operate at pressure levels of up to 80% of specified minimum yield strength (SMYS) in Class 1 (low-density) locations along the entire route of the proposed 1,323-mile, 42-inch diameter pipeline from the Rocky Mountains to gas markets in the Midwest and East. The project is sponsored by Kinder Morgan Energy Partners LP, Sempra Pipelines & Storage and ConocoPhillips.

It also gave the green light for Alliance Pipeline to increase its stress level to 80% SMYS from 72% SMYS on the 874-mile U.S. leg of the pipeline from the Canadian border to the inlet of the Aux Sable Delivery Meter Station near Chicago, IL. The Alliance line went into service in late 2000. Maritimes & Northeast Pipeline LLC won similar approval to operate at stress levels of 80% in low-density areas on a 100-mile portion of its system that is jointly owned with Portland Natural Gas Transmission System. The joint facilities extend from Westbrook, ME, to Dracut, MA.

The PHMSA earlier this year said it was mulling the possibility of adjusting the MAOP for certain natural gas pipelines that satisfy increased design and construction standards (see Daily GPI, March 16). The Pipeline Research Council International had found that pipelines can be operated safely and reliably at pressure levels of up to 80% of SMYS if the pipe has well-established metallurgical properties and can be managed to protect it against known threats, such as corrosion and mechanical damage, according to the PHMSA.

Current pipeline regulations in the United States generally restrict operating pressure to 72% of the SMYS of the pipeline. However, some U.S. pipelines that were in place prior to this standard currently operate at a higher pressure. The MAOP in Canada is 80% of SMYS, and a number of other countries are considering operating at higher levels than 72% SMYS, according to PHMSA.

The DOT agency has said three categories of gas pipelines would see an “immediate benefit” from a rise in operating pressure: the proposed Alaska gas pipeline from the North Slope to the Lower 48 states; new gas pipelines that are being certificated by the Federal Energy Regulatory Commission; and gas pipelines constructed since 1980 with line pipe of known metallurgical and mechanical properties.

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