Which type of piping tightness test may be mandated by codes if piping is installed and operational?

The hydrostatic piping tightness test is often mandated by codes when piping is installed and operational. This type of testing involves filling the piping system with water at a specified pressure to check for leaks. The hydrostatic test is favored because water is generally non-hazardous, and it allows for a thorough examination of the system's integrity under pressure conditions comparable to its normal operating environment.

During the test, any drop in pressure would indicate potential leaks, ensuring that the system is secure before it becomes operational. Regulatory bodies typically require this robust method to verify the safety and functionality of underground storage tank systems, as it provides clear and measurable results about the tightness of the piping.

In contrast, the other testing methods mentioned may not fit the specific requirements for regulatory compliance in certain situations. Pneumatic testing uses air or gas and can be risky if not done under controlled conditions, electrical testing examines the integrity of sensors or electrical systems rather than the physical piping, and vacuum testing checks for leaks in systems designed to operate under a vacuum, which is not as commonly used for standard underground storage tank installations.