Evaluation using the rating number is employed as an evaluation method for the results of corrosion resistance tests such as salt spray tests.

(1) Checking test piece

On the test piece after the corrosion resistance test, corrosions in the form of pit, stain from corrosions in the base material, scale-like peels, lumpy corrosions, dendritical corrosions, swollenness, cracks on the plating film, etc. are observed.The test is to check if these corrosion products are properly removed.

(2) Surfaces subjected to evaluation

As shown in [Fig. 1], the surface with the specified sections removed from the test piece edge is subjected to the test.

(3) Evaluation using rating number standard drawings

Evaluate the degree of corrosion by visually checking the surface against the rating number standard drawings as shown in [Fig. 2].

(4) Evaluation by actual measurement of corroded area

If the shapes of corrosion are too complex to check it against the standard drawings, actually measure the corrosion areas to determine the rating number in the following manner:

1. Use a magnifying lens with magnification power of 10 times or more to look for the corrosion section larger than 0.1mm in shorter diameter and measure the longer diameter (d1) and shorter diameter (d2). Then calculate the corroded area by the formula: (d1 x d2 x π)/4
2. Divide the total of corroded area calculated in step 1 by the area of the surface subjected to evaluation to determine the ratio of all corrosion area.
3. Determine the rating number from the ratio of all corrosion area using [Table].