Line pack is natural gas that is stored within the pipes of a gas transmission or distribution system. Line pack is used by gas system operators as a means of balancing the system or meeting customer demand even when supply delivered to the system on a given day does not match consumption. System operators continually manage the amount of gas in their pipes to ensure customer demands can be met while not exceeding safe pressure levels.
The amount of line pack is adjusted by allowing the system to pack or draft. Packing is putting more gas into a pipe than is being withdrawn. This raises the pressure of the pipe segment allowing it to hold more gas. Alternatively, drafting is allowing more gas to be withdrawn from the pipe than is being supplied. This reduces the amount of gas stored in the pipe and results in a pressure drop.
An example of how system operators use line pack to manage a potential mismatch between supply and demand is operation in anticipation of a cold snap. In this case, the system operator can pack the system, meaning put more gas in than customers are using, in anticipation of the colder days when more gas will be needed than is available upstream to satisfy all the heating demand. Of course, the system operator must do this while at the same timing not exceeding the maximum allowable operating pressure of the pipeline. The operator must also maintain a minimum pressure or risk customer devices not working properly.
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