Hydrostatic testing makes pipelines run better and safer

Just as the sun welcomes the day, hydrostatic testing is required by federal and state regulation before new and reactivated pipelines transport crude oil, natural gas or liquid natural gas (LNG).

Pipe delivered to the site is required to undergo hydrostatic
testing to comply with the U.S. Code of Federal Regulations.

The U.S. Code of Federal Regulations (CFR) specifies the requirement, along with applicable American Petroleum Institute and American Society of Mechanical Engineers standards
Hydrostatic testing occurs whether or not there's a leak. Colored water -- even fluorescent dyes -- are sometimes used to help identify a leak, but the primary method of determining a leak is the ability of the pressurized pipe to retain its pressure. Existing pipelines can also benefit from hydrostatic testing to ensure safety and strength of the structure.
When a pressure drop occurs during hydrostatic testing of an existing pipeline, the cause is usually a leak due to a defective weld or corrosion. Damage to new pipe, such as a puncture, can have occurred during transport, storage, or placement of the pipe. While line pipe is often tested in individual segments, pipe can be tested as well in multiple segments of welded pipe.
Before the testing takes place, two steps are needed:

1. The construction of a temporary launcher and receiver to run pigging.
2. Establishing a pumping system into the line.

Once the ends of the pipe have been sealed, fluid -- usually water, because it is nearly incompressible and is easily available -- is introduced into the pipeline segment and is pressured (pumped up) for four continuous hours to 125 percent of the maximum allowable operating pressure (MAOP) for the particular type of pipe, as specified by the applicable CFR. If the line cannot be visually inspected for leakage during the test, the regulation requires an additional four continuous hours of pressurization at 110 percent of the MAOP. In beginning the initial test, a batching pig is driven ahead of, and by, the water to remove any air and provide an effective seal. With an eye on the environment, water is let out of the pipe and reused to test the next segment. Once the testing of a section of pipe is completed, the water is removed, sometimes by draining, but usually with the use of a dewatering pig. The water is captured and sent to a wastewater treatment facility.
“When dealing with crude oil, the dewater pig is usually sufficient,” said Wes Millett, vice president of engineering for Decisive Pipeline Corporation. "There's often a little bit of water in the oil anyway. If the line is to be used for transporting certain petrochemicals, however, extra care must be taken to ensure all the water has been removed to avoid a reaction when the product is introduced, which typically means flushing the line with an inert gas, such as nitrogen.”
While hydrostatic testing is mandated by federal regulation, the owner and operator of the pipeline can take comfort knowing that the line is safe and the environment is protected from the possibility of contamination, even under roads, wetlands, and waterways.
In other words, one less thing to worry about in the oil business is always welcome.