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KTA-TATOR, INC.
Corporate Headquarters
115 Technology Drive
Pittsburgh, PA 15275
Phone: 412.788.1300
Fax: 412.788.1306
E-mail: info@kta.com

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1-800-KTA-GAGE
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KTA Challenge #9
Answer - Testex Tape


Photograph 1 - Challenge microphotograph at 50x	Photograph 2 - Testex Tape at 20x	Photograph 3 - Testex Tape on blast cleaned surface

Challenge 9 (Photograph 1) is a digital microphotograph (50x) of Testex Tape that has been to measure surface profile. Photograph 2, at 20x shows a larger portion of the tape.

The measuring area of the tape (the area within the circle) consists of an emulsion of microscopic bubbles attached to a 2 mil thick film of clear Mylar. The tape is placed on the blast cleaned surface, emulsion side down, and the Mylar is rubbed with a burnishing tool until the area within the circle turns uniformly gray (see Photograph 3). The gray is caused by the peaks of the surface profile breaking through the bubbles of the emulsion and coming into contact with the clear Mylar. When removed from the surface, the emulsion retains the shape of the surface profile, creating a reverse replica that is attached to the Mylar. The total thickness of the tape is measured with a spring micrometer. The 2 mil thickness of the Mylar, which does not compress, is subtracted from the total thickness to determine the maximum average surface profile depth. The tape can be stored with inspection reports, serving as a permanent record of the surface profile achieved during blast cleaning.

Replica tape and two other methods for measuring surface profile (visual comparator and depth micrometer) are described in ASTM D4417, Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel.

The surface profile required for the coating system can be found in the coating manufacturer's product data sheets or in the project specification. A number of factors influence the depth and shape of the surface profile achieved, but the two most common are the abrasive being used (type, size, and hardness) and the hardness of the material being cleaned.

KTA can provide all of the instrumentation necessary for measuring surface profile, and can also provide technical assistance and problem solving in the field of surface preparation.

Nearly one-third of the responses were correct. Some of the incorrect responses were overspray, oil contamination beneath a coating, a non-continuous coating film applied to concrete, embedded blast media, zinc primer, metallizing, and blast cleaned steel with rust and mill scale remaining on the surface. The winner by random drawing of the correct answers is Dan Flickinger.