Coating Inspections: Inspection of Steel Surface Preparation, Part 7 Massimo Cornago NACE International Certified Coating Inspector, NACE CIP PEER Reviewer firstname.lastname@example.org
ur series of articles about the inspection of surface preparation operations on steel and the tests this requires continues with the
presentation of other tests related to surface contamination after the surface preparation phase itself. In this article, we will deal with soluble test contamination, grease and oil contamination, and dust. Again, in these cases, the international standards normally used are NACE, SSPC, ISO, ASTM, and so on.
Amount of soluble salt contaminants on steel surfaces After surface preparation, the Inspector may be required to check that surfaces are free of soluble salt contamination. This test is normally performed after steel has been prepared by blast cleaning. However, if a long interval occurs between the application of two coating layers (i.e. full top coating of a shop-applied primer), it may be advisable to check for contaminants on the existing layer to be overcoated. Contamination of otherwise visually clean steel surfaces can have very serious effects on the coatings applied over them. These adverse effects include as follows:
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• Osmotic blistering of coatings. • Acceleration of corrosion.
• Nature and amount of contamination.
• Interference with the action of chemical corrosion inhibitors, such as
• Generic type and design of the coating system.
chromates (particularly with chloride contamination).
• Coating thickness.
There are numerous sources of soluble salt contamination, including the
The international standard NACE5/SSPC-SP12 defines three levels of
soluble salt contamination as follows:
• Atmospheric contamination from ocean spray, combustion of fuel
1. Condition SC-1: An SC-1 surface shall be free of all detectable levels
(sulphates), and chemical processes.
of contaminants as determined using available field test equipment with
• Exposition to and direct contact with seawater.
sensitivity approximating laboratory test equipment. For purposes of
• De-icing salts on highways and bridges, especially in the winter season.
this standard, contaminants are water-soluble chlorides, iron-soluble
• Contaminated abrasive.
salts, and sulphates. 2. Condition SC-2: An SC-2 surface shall have less than 7 µg/cm2 chloride
Chlorides and sulphates being the most common soluble salt
contaminants, less than 10 µg/cm2 of soluble ferrous ion levels, and
contaminants, their effects on coating performance depend on as
less than 17 µg/cm2 of sulphate contaminants, as verified by field or
laboratory analysis using reliable, reproducible test equipment.
• Service environment.
3. Condition SC-3: An SC-3 surface shall have less than 50 µg/cm2
N. 42 - 2022 JUNE - ipcm® Protective Coatings