4.1 The widespread use of glassed-steel equipment in highly corrosive chemical processes has made it necessary to detect weak spots in the coating and repair them before catastrophic failure occurs in service. This test is intended to detect discontinuities and thin areas in a glass coating on metal to ensure that the coating is defect free and has sufficient thickness to withstand the prescribed service conditions. A test voltage may be selected at any desired value up to 20k V, thus making the test applicable to a wide range of thickness requirements. When, because of bubbles or defects, the thickness of glass at any spot is less than enough to withstand the applied voltage, a puncture results with an accompanying indication of a defect. Remedial action is then required to repair the defect before the equipment can be used for corrosive service. (When such defects are found before the equipment leaves the manufacturer's plant another application of glass can usually be applied and fired to become an integral part of the coating.)

1.1 This test method covers the determination of the reliability of glass coating on metal and is intended for use by manufacturers of equipment that is designed to withstand highly corrosive conditions where a failure of the coating in service would cause extreme damage to the exposed metal. Its use outside the manufacturer's plant is discouraged because improper or indiscriminate testing can cause punctures that are difficult to repair without returning the equipment to the manufacturer's plant. This test method detects not only existing discontinuities in the glass coating, but also areas where the glass may be thin enough to be likely to result in premature failure in service.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see Section 7.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.