HOLIDAY DETECTION (HT)

Holiday testing is a non-destructive test method applied on protective coatings to detect unacceptable discontinuities such as pinholes and voids. A Holiday test or Continuity test is performed by applying voltage (connected in series with an LED or noise-producing component such as a piezoelectric speaker) across the chosen path. The testing is usually performed on transmission pipelines, tank interiors, chemical storage vessels and buried structures because of the importance of maintaining adequate coating protection in aggressive service environments.

NDTL provides a range of units to perform Low Voltage holiday detection on thin film coatings and High Voltage holiday detectors for thicker coating applications.

VACUUM BOX TESTING (VB)

Vacuum box testing is a non-destructive examination used when trying to locate through thickness leaks on seam welds and adjacent sheeting material. A vacuum box and a vacuum pump create a high or low pressure vacuum while a bubble forming solution is applied to the test area. The bubbles indicate leaks visible within the created pressure envelope.

Items tested are as follows:

• Lap welds, butt welds, and shell to annular welds

• Piping systems and pressure vessels

• Tank bottoms

• Objects on which a pressure differential can be created across the area to be examined