Underground Tape Wrapping & Holiday Testing
Underground tape was first introduced into the pipeline oil and gas industry in the early 1950s for the purpose of providing long lasting in-ground corrosion protection.
Corrosion protection is required to maintain the integrity of a buried pipeline system and coatings are the primary protection for a pipeline. As a buried pipeline is subject to corrosive attack if it is in contact with a wet environment, coating the pipeline to isolate it from this corrosive environment is an obvious approach to corrosion control.
Most countries have regulations that require pipelines to be coated and in general stipulate that a coating possess
the following properties:
1) Electrically isolate the external surfaces of the pipeline from its environment.
2) Have sufficient adhesion to resist under-film migration of electrolyte.
3) Be sufficiently ductile to resist cracking.
4) Resist damage due to soil stress and normal handling.
5) Be compatible with cathodic protection.
6) Resist deterioration due to the environment and service temperature.
Holiday testing is a non-destructive test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids. The test involves checking an electric circuit to see if current flows to complete the circuit. This testing is used to find coating film discontinuities that are not readily visible.
The testing is usually performed on tank interiors, chemical storage vessels and buried structures because of the importance of maintaining adequate coating protection in aggressive service environments. Holiday testing is also known as continuity testing.