Monday, August 19, 2019; 11:00 AM - 12:00 PM Eastern
Coating specifications commonly contain requirements to generate a surface profile to anchor the coating system to the steel surface. The resulting profile or anchor pattern is quantified/semi-quantified according to the three methods described in ASTM D4417 or according to the method described in ASTM D7127. The frequency and acceptability of the acquired measurements is described in SSPC PA 17.
Selection of an abrasive that is too small or too large that results in an insufficient or excessive surface profile depth, removal of an existing coating system that reveals an existing surface profile that exceeds the specification or extensive pitting of the existing steel that overtakes any surface profile created by an abrasive can result in specification deviations, non-conformities and/or project delays. It was unknown whether follow-up blast cleaning of a profiled surface (whether pre-existing or newly formed) with a smaller or larger abrasive (or different abrasive shape) would effectively and uniformly change the surface profile depth or texture across the prepared surface. Further, attempts to reduce a surface profile by holding the nozzle parallel to the surface was suspected to simply “roll-over” the peaks (rather than generate the specified depth) and decrease the peak density, thereby reducing the surface area. The net effect could be to cause potential coating detachment and lower the coating system’s resistance to undercutting when it becomes damaged in service.
A research project was conducted that consisted of preparing steel panels with small and large abrasives (to produce surface profiles that are too deep and too shallow), re-preparing the surfaces using smaller/larger abrasives in an attempt to bring the surface profiles “into conformance,” then characterizing the surface according to ASTM D4417, methods B and C, peak density measurements using special replica tape and a replica tape reader, as well as the two surface characterizations described in ASTM D7127 (Rt and Rpc). The change in the shape of the surface profile was examined using 3D microscopy together with digital microphotographs of the surfaces. This webinar will describe the potential impact of insufficient/excessive surface profile on production and quality as well as present the results of the research initiative.
• Describe the process of generating a surface profile;
• Recognize the impact of insufficient or excessive surface profile on coating performance;
• Describe the process of increasing or decreasing surface profile; and
• Recognize the impact of reducing surface profile on peak density/count.