Soluble Salt testing is becoming the latest inclusion into EPCM specifications for quality requirements.
What are Soluble Salts and Sulphates?
Soluble Salts and Sulphates are the most dangerous forms of contaminants for paints and coatings. When they are painted over they have the power to draw moisture through Osmosis and cause blistering, detachment and accelerate corrosion of the underlying metal. When steel is repainted, rough or pitted areas are visible after dry abrasive blast cleaning. These may contain soluble salt contamination, especially in the base of the pits. Dry abrasive blasting does not remove these salts. It is wise to check for the presence of soluble salts with specially designed field test kits before painting and if they are present in detrimental amounts, to take additional cleaning steps to remove the salts.
How can you test for Soluble Salts?
The common tools used to test for soluable salts are the Chloride Iron Test Kit for Surfaces. This test looks for remaining chloride levels on a sub-straight prior to painting. The second tool is a Salt contamination Meter. This tests for soluble salts on the substrate surface prior to painting by absorbing distilled water soaked filter paper and then testing it.
How do Soluble Salts Occur?
There are many ways your steel can be exposed to soluble salts and sulphates. The most common way is through transportation. Pipe and steel travelling at sea can accumulate contaminants during travel to the fabricators. The other method is when trucking materials during the winter. Road salts can easily be distributed on to steel during the transportation process.
Is checking for Soluble salts necessary?
Soluble salts became an additional test required and recommended by Nace. As engineers attempt to cover off as many concerns with their specifications as possible, it is becoming a popular addition. The method of testing and the frequency required by this code make production volume of pipe spooling and steel testing costly and difficult. Most pipe from mill come with mill varnish helping protect the surface during travel. New steel will generally not be pitted, where a good sandblast profile will easily eliminate any surface contaminants. There are situations where you are on an oil platform, recoating old steel, in the middle of the ocean where this specification is highly advisable but for most steel processing this is considered over processing. The short answer is where required.
Soluble Salt in relation to rubber lining.
Generally speaking in a rubber lining application, the internal liner will fail far sooner than the steel or coating will deteriorate. Rubber lined product is generally considered a wear product. Warranties are difficult as process flow, materials configurations are always changing. Unless adamantly specified this specification should be avoided.