1. Surface preparation

1) Polish the valve surface and remove all the burrs, grease and other pollutant.

2) The surface process should be processed on temperature higher than dew point temperature, relative humidity 80％.

3) After the shoot-blasting process the casting surface should be free of any rust or iron oxide scale.

4) The valve casting’s coating should be finished within 3 hours after the cleaning process, or the cleaning process should be done again for castings left for more than 3 hours.

2. General coating thickness requirement

The minimum coating thickness for non-machining surface should be larger than 150 microns.

3. Inspection

1) Surface finish should be smooth, bright and uniform in color. No wrinkling, blistery, dust, scratch or chloride should be allowed.

2) Thickness inspection will be carried out for 3 times for each batch of the valve. Every time 4 points on the valve body will be measured with the thickness gauge. The average data for the 4 points should be larger than the minimum coating thickness requirement.

3) Adhesive test： Use knife to carve 2X15mm cut onto the coating. The 2 cuts should be deep enough to the metal part with 30 degree angle “X” shape. Peel off the coating from the cross position of the “X”. If the peeled off part exceed the 2mm limits of the “X” cuts, or the peeled off parts are easily broken, the coating should be taken as unqualified.

  4) Sample test frequency: according to GB/T2828 Common inspection frequency.

  5) Inspection record should be kept every day by the inspector.