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December 13 - December 19, 2010

The literature indicates that UHP waterjetting does produce a profile on steel, although of a micro nature. Is this sufficient roughness for good adhesion of thin film primers (e.g. < 2 mils dft)?


Selected Answers

From Adrian Granda of n/a on January 11, 2011:
I agree with Barry Barman: waterjetting does not provide a "profile" and will not remove mill scale on new steel. You can use the pre-existing profile, however, after old coatings have been removed by waterjetting. The adhesion is no only issue with the pre-existing profile. It depends on both coating type and waterjetting level (WJ1, WJ2, WJ3 or WJ4). all this information must be addressed by the coating manufacturer.

From David Grove of Shaw Nuclear Power Services on December 28, 2010:
Seems no one asked the question, "What is the surface condition of the steel?" If it is new and has milscale on it, then no. If it was previously prepped where milscale had been removed, or had been allowed to rust so no milscale remained, then possibly, depending upon the coating type and the service. Ask the coating tech service representative for the specifics.

From greg sprinkle of certified coating inspections inc on December 27, 2010:
I think the very first question by far is the service environment. If it is to be mild atmospheric, power washing to UHP is more than accepted by many coating manufacturers that offer very surface-tolerant primers.

From Barry Barman of Barry Barman & Associates on December 16, 2010:
The short answer is no.According to the Joint Surface Preparation Standard SSPC-SP 12/NACE No. 5, waterjetting does not provide the primary anchor pattern on steel known to the coatings industry as “profile.” We use waterjetting primarily for recoating or relining projects in which there is an adequate pre-existing profile. The fact that the intended primer is thin (<2 mils)does not negate the need for a proper anchor profile. Consider that the primer is just one coat of the specified paint system and that profile depth should be approximately 25% of the total coating thickness. If there are concerns that a thin prime coat will produce pinpoint rusting when applied over a profiled surface, remember that coating thickness is measured as the thickness "above the peaks" - determined by subtracting the BMR (Base Metal Reading) from the measured coating thickness as described in SSPC-PA 2. In this manner there will be a nominal dry film thickness of 2 mils above the peaks. Regardless, the primed-only steel should not be left untopcoated for an extended period of time.

From David hennerbichler of Imperial Oil on December 15, 2010:
It really depends on the level of detail in the manufacturer's data sheet

From Adam Backhaut of Diamond Vogel Paints on December 14, 2010:
It will depend on the type of primer being used. Are you using an etch, epoxy, or 2k polyurethane primer? Make sure the primer “system” is designed for a direct-to-metal application. I would test one small area for adhesion with the current surface profile using the ASTM method (bear claw cross hatch). Also, don’t be afraid to call your paint supplier for assistance; they will be there to help you with technical support.

From Muhammad Iqbal of ENI Indonesia on December 14, 2010:
Philip A. Schweitzer in his book titled,"Paint and Coatings: Applications and Corrosion Resistance," wrote that profile depth should be approximately 25% of the total coating thickness. On the basis of a 6-mil coating thickness, the profile depth should be 1.5 mils; hence,if what Philip wrote is applicable and acceptable, then it is sufficient.

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