ASTM D7087-05a An Imaging Technique to Measure Rust Creepage at Scribe

Scope:

Rust creepage areas at scribe on painted/coated on flat test panels caused by corrosive environment are measured using the ASTM D7087-05a standard test method. This method covers procedures involving the use of visual imaging software for identifying the area damaged by rust creepage at the scribe. ASTM D7087-05a is a simple and easy-to-use method. The results are quite accurate but not as exact as those obtained from advanced digital imaging.

Test Procedure:

In ASTM D7087-05a the scribed specimens are prepared. Then the rust creepage area is traced and the test specimen is marked using a ruler. Once area tracing is done, a transparent plastic sheet is placed. The traced creepage is placed on the glass of the scanner.  The scanned image is saved on the computer as a .xxx file. The next step in the procedure is imaging and integrating the creepage area.

Specimen size:

Measure the width of the scribe in mm. Preferably 50 mm to 100 mm. A length suitable to trace using a ruler.

Data:

The mean creepage (Including Area of Original Scribe Line) is calculated by the equation,
C = Aijlk/(2L)
Where,
C = mean creepage in mm,
Aijlk = integrated area inside the boundary of ijlk by tracing and imaging, and
L = length of scribe line from which creepage (or under-cutting) is extended and area is integrated.

Calculating the Net Mean Creepage (Excluding Area of Original Scribe Line),
Cnet = (Aijlk-A0)/(2L)
Where,
Cnet = net mean creepage in mm,
Aijlk = integrated area inside the boundary of ijlk by tracing and imaging,
A0 = integrated area of scribe line before exposure, and
L = length of scribe line from which creepage (or undercutting) is extended and area is integrated.