Chloride Testing / Bresle Bresle Patch Method
The most of the coating specification requires that chloride testing ( Bresle Bresle patch Method) being performed before sandblasting i.e. SSPC-SP 5 White Metal Cleaning, SSPC-SP 10 Near-White Metal Cleaning, etc. The chlorides are the salts of HCL acid; the CL gets one electron to form anion Cl-. It is substantial to measure the amount of contaminants such as chloride salt before application of sandblasting.
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The chloride testing is covered in the I4I Academy API Source Inspector Course. The material degradation caused by the premature failure of the coating system is covered in the I4I Academy API RP 571 Corrosion and Material Course.
The sandblasting not only does not remove soluble salt contamination but also cause the contamination of the "sands" that might be used for another job and consequently might contaminate other equipment which is subjected to sandblasting.
If chloride salt remains on the surface can draw moisture through the paint and cause corrosion in metal surface and subsequently cause paint failure. The chloride salt if stays between coating layers similarly absorb moisture through osmotic action and cause disbondment and cause paint failure.
Measure Chloride Amount by Bresle Patch Chloride Testing
The Bresle Patch Method is most common test method to measure chloride content. This chloride testing is done based on the requirements of the ISO 8502-6 and ISO/DIS 8502-9. Select a test area on the equipment surface and make sure the selected area is dry and there is no loose mill scale or rust.
Follow the Bresle Patch manufacturer instruction and remove the cover and adhere the patch to the selected area. Fill the syringe with the 5-milliliter solution and inject to the spongy foam of patch, subsequently fill the syringe with 3-milliliter reagent water and inject to the patch. Gently massage the patch and ensure the solution is in contact with the metal surface. The solution should be in contact for almost 15 seconds and then fill back syringe with patch solution and use a Kitagawa tubes to measure chloride amount. The coating specification requires one test being performed on each 100 square ft.
Permisible Amount of the Chloride
The permissible amount of chloride is different from one specification to another one, and still, there is no particular standard or code to determine the allowable amount. In most cases, the customers require being less than 10μg/cm² or sometimes required by ppm amount.
However, if the test indicated that chloride level is higher than this amount (or specified amount) the surface shall be subjected to solvent cleaning and the test shall be repeated. If after solvent cleaning, chloride content still is higher than the specified value, the surface is subjected to the high-pressure water jetting. Similarly, the test is repeated and if fell below the permissible level, then can be proceeded to the sandblasting process.