Význam a účel

4.1 Poškození povlaků potrubí je během přepravy a stavby téměř nevyhnutelné. A break or breach in the pipe coating may expose the pipe to corrosion because after the pipe is installed underground, the surrounding soil will contain moisture and constitute effective electrolytes. The cathodic protection potential applied may cause the coating to loosen, starting from the holiday edge. Spontaneous holidays may also be caused by such potentials. This test method provides an accelerated condition for the occurrence of cathodic stripping and provides a measurement of the resistance of the coating to such actions.

4.2 The test effect shall be evaluated by physical inspection and monitoring the current consumed by the specimen. Usually there is no correlation between these two evaluation methods, but both methods are significant. The physical examination consists of assessing the effective contact of the coating with the metal surface based on the observed relative adhesion differences. It is often found that the cathodic stripping region extends from the region where adhesion is zero to the region where adhesion reaches the original level. There may also be intermediate regions of reduced adhesion.

4.3 Assumptions related to the test results include:

4.3.1 Maximum adhesion or bonding is found in the coating not immersed in the test liquid, a

4.3.2 The decreased adhesion in the immersion test area is the result of cathode stripping.

ASTM G42-11-2019 Standard Test Method for Cathodic Stripping of Pipeline Coatings at High Temperatures

4.4 Peel resistance is a desirable quality on a comparative basis, but peel in this test method is not necessarily an unfavourable indicator of coating performance. The advantage of this test method is that all the dielectric type coatings now commonly used peel off to some extent, thus providing a way to compare one coating with another.

4.5 The current density in this test method is much higher than the current density usually required for cathodic protection in natural environment.

4.6 Any relatively small bonding area is caused by the combination of electrical stress with high and/or low temperatures and not due to anomalies in the application process. Relatively speaking, peel resistance is a professional quality, but most insulation materials will undergo some degree of peel under the accelerated conditions of this test. Bond strength is more important for proper functioning of some coatings than others, and the same measured peeling of two different coating systems may not represent an equivalent loss of corrosion protection.

4.6.1 The current flow through the test battery may be a relative indicator of the area to be protected against corrosion; nicméně, the current densities present in this test are much greater than those normally required for cathodes protection in natural inland soil environments.

ASTM G42-11-2019 Standard Test Method for Cathodic Stripping of Pipeline Coatings at High Temperatures

4.6.2 Test voltages higher than the recommended values may result in chlorine formation. Subsequent chemical effects on the coating may cast doubt on the interpretation of the test results.

Pohled do

1.1 This test method describes an accelerated procedure for determining the comparative characteristics of an insulating coating system applied to the exterior of a steel pipe with the aim of preventing or mitigating corrosion that may occur in underground service where the pipe is exposed to high temperatures and under cathode-protection. The test method is intended for use on coated pipe samples obtained from commercial production and is applicable to samples where the coating has an electrical barrier function.

1.2 This test method is used to test coatings immersed or submerged in test solution at high temperature. When it is impractical to submerge or immerse the specimen, the use of test method G95, in which the test unit is bonded to the surface of the coated pipe specimen, may be considered. If room temperature is required, viz zkušební metoda G8. If you need a specific test method without options, see Test Method G80.

1.3 The value of three valid decimals retained in SI units shall prevail. Hodnoty uvedené v závorkách jsou pouze orientační.

1.4 Warnings – Mercury has been designated by the EPA and many state agencies as a hazardous substance that can cause damage to the central nervous system, kidney, and liver. Mercury or its vapors may be hazardous to health and corrodes materials. Care should be taken when handling mercury and products containing mercury. For more information, please refer to the applicable Product Material Safety Data Sheets (MSDS) and for additional information, please refer to the EPA website (epa.gov/mercury/faq.htm). Users should be aware that in your state, state laws may prohibit the sale of mercury or mercury-containing products, nebo oboje.

ASTM G42-11-2019 Standard Test Method for Cathodic Stripping of Pipeline Coatings at High Temperatures

1.5 Tato norma není určena k řešení všech bezpečnostních problémů, jestli nějaký, spojené s jeho užíváním. Je odpovědností uživatelů této normy zajistit odpovídající bezpečnost, zdravotní a environmentální postupy a určit použitelnost regulačních omezení před použitím.

1.6 This international Standard has been developed in accordance with the internationally accepted standardization principles established in the decisions of the Technical Barriers to Trade (TBT) Committee of the World Trade Organization on the Formulation of International standards, pokyny a doporučené zásady.