ASTM G8-2019 pdf free download

ASTM G8-2019 pdf free download.Standard Test Methods for Cathodic Disbonding of Pipeline Coatings
1. Scope
1.1 These test methods cover accelerated procedures for simultaneously determining comparative characteristics of in- sulating coating systems applied to steel pipe exterior for the purpose ofpreventing or mitigating corrosion that may occur in underground service where the pipe will be in contact with inland soils and may or may not receive cathodic protection. They are intended for use with samples of coated pipe taken from commercial production and are applicable to such samples when the coating is characterized by function as an electrical barrier. 1.2 This test method is intended for testing coatings sub- merged or immersed in the test solution at room temperature. When it is impractical to submerge or immerse the test specimen, Test Method G95 may be considered where the test cell is cemented to the surface of the coated pipe specimen. If higher temperatures are required, see Test Method G42. If a specific test method is required with no options, see Test Method G80. 1.3 The values stated in SI units to 3 significant decimals are to be regarded as the standard. The values given in parentheses are for information only. 1.4 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Summary of Test Method
3.1 Both of the two test methods described subject the coating on the test specimen to electrical stress in a highly conductive, alkaline electrolyte. Electrical stress is obtained either by means of a sacrificial magnesium anode or from an impressed current system. The coating is perforated before starting the test. 3.1.1 In Method A, a magnesium anode is used with no electrical monitoring during the test period. The results are determined by physical examination after the test period is concluded. 3.1.2 In Method B, either a magnesium anode or an im- pressed current system may be used. Electrical instrumentation is provided for measuring the current in the cell circuit. The electrical potential is also measured, and upon conclusion of the test period, the test specimen is physically examined. 3.1.3 In both test methods physical examination is con- ducted by comparing the extent of loosened or disbonded coating at the perforations in the immersed area with extent of loosened or disbonded coating at a new test hole in the coating made in an area that was not immersed.
4. Significance and Use
4.1 Breaks or holidays in pipe coatings may expose the pipe to possible corrosion, since after a pipe has been installed underground, the surrounding earth will be more or less moisture-bearing and it constitutes an effective electrolyte. Damage to pipe coating is almost unavoidable during trans- portation and construction. Normal soil potentials as well as applied cathodic protection potentials may cause loosening of the coating, beginning at holiday edges, in some cases increas- ing the apparent size of the holiday. Holidays may also be caused by such potentials. While apparently loosened coating and cathodic holidays may not result in corrosion, this test provides accelerated conditions for loosening to occur and therefore gives a measure of resistance of coatings to this type of action. 4.2 The effects of the test may be evaluated by either physical examination or monitoring the current drawn by the test specimen and both of these two. Usually there is no correlation between the two methods of evaluation but both methods are significant. Physical examination consists of assessing the effective contact of the coating with the metal surface in terms ofobserved differences in the relative adhesive bond. It is usually found that the electrically stressed area propagates from the holiday to a boundary where the loosened coating leaves off for the more effective contact or bond attributed to an original condition throughout the specimen before electrical stressing was applied. Assumptions associated with test results include the following: 4.2.1 Attempting to loosen or disbond the coating at a new test hole made in the coating in an area that was not immersed represents maximum adhesion or bond as measured by the lifting technique used, and that the same lifting technique can be used at a test hole that was immersed thereby providing a means of comparing relative resistance to lifting.