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Inspection Standard for Galvanized Seamless Pipe

Date:2022-11-04    keywords: galvanized seamless steel pipe, galvanizing process
The galvanizing method of seamless pipe (SMLS) shall be hot-dip galvanizing. Size, shape, surface, mechanical properties and process performance inspection should be carried out before galvanizing.

Surface quality requirements of galvanized layer:

The galvanized layer on the inner and outer surfaces of the seamless steel pipe should be complete, no black spots and air bubbles without zinc plating are allowed, and small rough surfaces and local zinc tumors are allowed. The surface of the steel pipe can be passivated after galvanizing.


 galvanized seamless steel pipe


Weight determination of galvanized coating:


For galvanized steel pipes, the weight of the zinc layer shall be measured. The total weight per unit area of the galvanized layer on the inner and outer surfaces of the steel pipe shall not be less than 300g/m2.
According to the requirements of the buyer, the supplier can supply galvanized steel pipes with the total weight per unit area of the galvanized layer on the inner and outer surfaces not less than 500g/m2 after negotiation between the supplier and the buyer and indicate in the contract. When the total weight of the galvanized layer per unit area is 500g/m2, the total weight of the galvanized layer of one of the samples is allowed to be less than 500g/m2, but not less than 480g/m2.

Zinc coating uniformity test:

The galvanized steel pipe shall be subjected to the uniformity test of the zinc layer. During the test, the sample (except for the weld) should not be red (copper-plated color) after being continuously immersed in copper sulfate solution for 5 times.

Adhesion test of galvanized layer:

GB/T 3091

After galvanizing steel pipes with an outer diameter of not more than 60.3mm, a bending test shall be used to test the adhesion of the galvanized layer. During the test, the bending sample shall be without filler, the bending radius shall be 8 times the outer diameter of the steel pipe, the bending angle shall be 90°, and the weld shall be located on the outer side of the bending direction. After the test, the sample is not allowed to peel off the zinc layer.

According to the requirements of the buyer, after negotiation between the supplier and the buyer, and it is indicated in the contract, the flattening test can be used to test the adhesion of the galvanized layer after the steel pipe with an outer diameter greater than 60.3mm is galvanized. The length of the flattened specimen shall not be less than 64mm. During the test, when the distance between the two flat plates is 3/4 of the outer diameter of the steel pipe, the zinc layer is not allowed to peel off on the sample.

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