KTA-Tator, Inc.

Original Photo, unmagnified

After SSPC-SP5 Blast, unmagnified

Challenge 1 is a microphotograph (50x, taken in the KTA laboratory with a state of the art, digital microscope) of a new hot rolled carbon steel surface that was subjected to a quick pass with an abrasive blast cleaning nozzle. Compare the appearance of the Challenge photo with the second microphotograph above. The second microphotograph also represents a blast cleaned surface at 50x, but the difference is that the cleaning was very thorough, to SSPC-SP5, White Metal. In the SP5 photograph, the surface exhibits a dense, continuous surface profile (surface roughness) with no evidence of any rust or mill scale remaining. The Challenge photo shows non-uniform roughening with many flat areas in between the random pock marks created by the abrasive. The flat areas are mill scale remaining on the surface. A few pinpoints of corrosion are also visible.

The difference between the degrees of cleaning can also be seen when examining the photograph of the two surfaces side by side without magnification. Note that the SSPC surface preparation specifications require that the inspection be made without magnification, so this is the type of view that would be seen when inspecting work in the shop or field, rather than the microscopic view of the Challenge. It is clear from this photograph that the surface used in the Challenge is not cleaned as thoroughly as the comparison sample, but this does not necessarily mean that the degree of cleaning is inadequate for coatings performance. This depends on the coating system being applied and the service environment. Further, the degree of cleaning may or may not meet the contractual requirements. The project specifications will typically stipulate the degree of cleaning and roughening required. If this information is not included in the specifications, it can be found in the coating manufacturer's product data sheets.

Blast cleaning inspections are an integral part of the contractor's Quality Control inspections on a project in order to verify that the cleaning meets the requirements of the specification. KTA distributes the written SSPC surface preparation standards and the SSPC visual standards that depict the appearance of various degrees of abrasive blast cleaning. SSPC-VIS1, Guide and Reference Photographs for Steel Surfaces Prepared by Dry Abrasive Blast Cleaning, is an excellent reference standard that shows the appearance of both coated and uncoated steel prepared to degrees of cleaning ranging from SSPC-SP7, Brush off to SSPC-SP5, White Metal. KTA also distributes a variety of instruments for determining the depth of the surface profile created by abrasive blast cleaning.

The Winner: The responses included blast cleaned steel, aluminum and wrought iron substrates, abrasive embedment, acid etching, wet blast cleaning, salt crystals, copper sulfate testing, and the back side of failing paint chips. While the majority of the responses recognized that the Challenge was a microscopic view of a blast cleaned steel surface, only two people noted that traces of mill scale were present. By luck of the draw, the winner is Kyle Hough of G.C. Zarnas Company.