General

This NACE standard provides a nondestructive test method for the detection of holidays in a nonconductive coating film that has been applied to the inner wall (bore) of oilfield tubular goods. The apparatus and the recommended procedure for conducting the test are described, as are methods of reporting the test data.

The test method applies to coatings that have a specified dry-film thickness of 250 to 760 µm (10 to 30 mils). It is valid only for coatings that have not been in service or previously tested with a salt solution. When holiday testing is performed on coatings that have been in service or that have been previously tested for holidays with a salt solution, there is a possibility of misleading results arising from surface contamination or salt bridging. The coating surface shall be free of materials that give added electrical insulation or that can mechanically damage the coating during the test.

A "holiday" is defined as a discontinuity in a protective coating that exposes unprotected surface to the environment. For this test method, it means an area in an applied nonconductive coating that exhibits electrical conductivity when exposed to a known impressed voltage.

The voltage range for holiday detection is 4 to 12 V (DC) per µm (100 to 300 V [DC] per mil) of dry-film thickness. The test voltage is determined by the type of probe, the maximum specified dry-film thickness, the type of coating application, and the customer. The voltage shall be measured between the probe and the pipe.

Several internal tubular coatings have specified thickness ranges of 200 to 330 µm (8 to 13 mils). These coatings shall be tested with a wet sponge at 67.5 V (DC) and 80,000 ohms (±10%) resistance.1

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