How to discriminate stainless steel pipe fittings

- Apr 08, 2018 -

1. Test magnetism

The simplest way to distinguish the annealed austenitic stainless steel pipe and ferritic stainless steel pipe is to enter the magnetic inspection. Generally pure chromium and low alloy steel are super magnetic, and austenitic stainless steel belongs to non magnetic steel, but austenitic stainless steel pipe will have a little bit of magnetism if it is cold processed at atmospheric pressure.

Two. Test nitric acid point

It has strong corrosion resistance for concentrated nitric acid and dilute nitric acid. This is the most notable feature of stainless steel pipe fittings. This special property can be easily distinguished from most metals and alloys. But only high carbon steel 440 and 420 steel will be slightly corroded when conducting nitric acid test, however, when non-ferrous metals are encountered in concentrated nitric acid, they will be immediately corroded. Concentrated nitric acid is particularly corrosive to carbon steel pipes.

Three. Test cupric sulphate point

The simplest and quickest way to distinguish common carbon steel pipes from all types of stainless steel pipes is that the concentration of copper sulphate solution used in the test of copper nitrate point test should be kept between 5% and 10%. Before the copper nitrate test is carried out, the various impurities and oils of the test area should be cleared. The specific method is to polish the test area with a soft cloth, and then drop the copper sulfate solution in a drop bottle to the ordinary carbon steel pipe in the test area or iron in a few seconds to form a layer of metal copper. This phenomenon will not happen on the surface of stainless steel pipes.

Four. Test sulfuric acid

Using sulfuric acid to immerse stainless steel pipes, we can distinguish 302 from 304 and 304 to 317. The cutting edge of the test sample should be fine grinding, cleaning and passivating at the temperature of 60-66 degrees and the volume concentration in the nitric acid solution of 20%-30%. The time is controlled for half an hour. If the concentration of the solution of the nitric acid test reaches 10%, then the solution is heated, when the temperature rises to 71 degrees Celsius, the 302 and 304 steel will be put into this solution, and the steel will be corroded rapidly, and a large number of bubbles will be produced. In these minutes, the sample will be quickly blackened; but 316 and 317 steel are carried out. In the same test, the specimen will not be corroded or corroded very slowly, nor will it produce bubbles. It will not change color in 10 to 15 minutes. If we want to make the experiment more accurate, we can carry out the simultaneous test while doing the contrast.


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