*This is the last article in a two-part series on the transportation of natural gas.
As natural gas use increases, so does the need to have transportation infrastructure in place to supply the increased demand. This means that pipeline companies are constantly assessing the flow of natural gas, and building pipelines to allow transportation of natural gas to those areas that are under served.
Installing a pipeline is much like an assembly line process, with sections of the pipeline being completed in stages. First, the path of the pipeline is cleared of all removable impediments, including trees, boulders, brush, and anything else that may prohibit the construction. Once the pipeline’s path has been cleared sufficiently to allow construction equipment to gain access, sections of pipes are laid out along the intended path, a process called ‘stringing’ the pipe. These pipe sections are commonly from 40 to 80 feet long, and are specific to their destination. That is, certain areas have different requirements for coating material and pipe thickness.
Once the pipe is in place, trenches are dug alongside the laid out pipe. These trenches are typically 5 to 6 feet deep, as the regulations require the pipe to be at least 30 inches below the surface. In certain areas, however, including road crossings and bodies of water, the pipe is buried even deeper. Once the trenches are dug, the pipe is assembled and contoured. This includes welding the sections of pipe together into one continuous pipeline, and bending it slightly, if needed, to fit the contour of the pipelines path.
Coating is applied to the ends of the pipes (the coating applied at a coating mill typically leaves the ends of the pipe clean, so as not to interfere with welding), and the entire coating of the pipe is inspected to ensure that it is free from defects.
Once the pipe is welded, bent, and coated, it can be lowered into the previously dug trenches. This is done with specialized tracked construction equipment acting in tandem to lift the pipe relatively uniformly and lower it into the trench. Once lowered into the ground, the trench is filled in carefully, to ensure that the pipe and its coating do not incur damage. The last step in pipeline construction is the hydrostatic test. This consists of running water, at pressures higher than will be needed for natural gas transportation, through the entire length of the pipe. This serves as a test to ensure that the pipeline is strong enough, and absent of any leaks of fissures, before natural gas is pumped through the pipeline.
Laying pipe across streams or rivers can be accomplished in one of two ways. Open cut crossing involves the digging of trenches on the floor of the river to house the pipe. When this is done, the pipe itself is usually fitted with a concrete casing, which both ensures that the pipe stays on the bottom of the river, and add an extra protective coating to prevent any natural gas leaks into the water. Alternately, a form of directional drilling may be employed, in which a sort of ‘tunnel’ is drilled under the river through which the pipe may be passed. The same techniques are used for road crossings – either an open trench is dug up across the road and replaced once the pipe is installed, or a tunnel may be drilled underneath the road.
Once the pipeline has been installed, and covered up, extensive efforts are taken to restore the pipeline’s pathway to its original state, or to mitigate for any environmental or other impacts that may have occurred during the construction process. This often includes replacing topsoil, fences, irrigation canals, and anything else that may have been removed or upset during the construction process.
While large interstate natural gas pipelines transport natural gas from the processing regions to the consuming regions and may serve large wholesale users like industrial or power generation customers directly, it is the distribution system that actually delivers natural gas to most retail customers, including residential natural gas users.
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