Interstate natural gas pipelines have eked out economic and transportation efficiencies on their systems over the years despite challenges on the financial, regulatory and legislative fronts, according to a white paper released Wednesday by the Interstate Natural Gas Association of America (INGAA).

"Pipeline companies have used increasingly larger diameter pipeline and higher pressures to improve the hydraulic efficiency of the system. Since 1940, maximum line pipe diameters of newly built pipelines have doubled from 24 inches to 48 inches, while the MAOP [maximum allowable operating pressure] has more than doubled from 720 psig (pounds per square inch, gauge pressure) to 1750 psig or higher" in 2009, according to the 60-plus page white paper.

"This has been achieved through the development of economic, high strength steels, enabling pipelines to be built economically and safely operated at higher pressure/stress levels." In fact new advances have allowed the operating pressure of some new pipe installations to increase to 80% of its specified maximum yield strength (SMYS) from 72% of its SMYS, the INGAA paper said.

INGAA defines pipeline efficiency in two ways -- economic efficiency and transportation efficiency. "Economic efficiency measures the delivered cost to customers compared to the cost of the natural gas, taking into account both the fuel cost and transportation rates. The overall system transportation efficiency is a measure of the fuel and/or electric energy used to transport natural gas and is a function of the overall system design (hydraulic efficiency)," it noted.

"Basic economics may limit a pipeline company's ability to maximize the pipeline's overall transportation efficiency, such as when an efficiency improvement, particularly one with limited efficiency gains, cannot cost justified or the cost recovery period is too long or too uncertain," the paper said.

INGAA noted that regulations can compromise pipeline efficiency. It cited the Environmental Protection Agency's proposal rule establishing national emissions standards for hazardous air pollutants for reciprocating internal combustion engines as an example. The proposed rule would limit the carbon monoxide and formaldehyde emissions from engines commonly used at natural gas compressor stations.

"The only way to assure compliance with the proposed limits would be to install post-combustion catalytic control equipment. The equipment degrades engine efficiency by requiring the engine to operate at a higher fuel-to-air ratio, causing the engine to burn moire fuel than necessary and thus operate less efficiency," INGAA said.

In addition, it said the uncertainty over the timing and content of pending and proposed climate change legislation and regulation has deterred investment in efficiency improvements aimed at reducing greenhouse gas emissions.

And the increased use of renewable energy sources may affect pipeline operations, according to the white paper. Industry analysts anticipate that gas-powered electric generators will be called upon to fill the gap created by the intermittent nature of solar and wind power and the current lack of commercialized methods to store electricity from these sources. "This, in turn, could create a new demand for natural gas transportation and storage services that can respond quickly and reliably in providing intermittent fuel for these gas-powered electric generators."

As of 2008, there were 217,000 miles of interstate pipelines in the United States and Canada, with a capacity of 183 Bcf/d.

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