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Magnetic test is the simplest method to distinguish annealed austenitic stainless steel from ferritic stainless steel

brand stores: water pipes

I. magnetic test

magnetic test is the simplest way to distinguish annealed austenitic stainless steel from ferritic stainless steel. Austenitic stainless steel is non-magnetic steel, but it will have slight magnetism after cold working under high pressure; Pure chromium steel and low alloy steel are strong magnetic steel

II. Nitric acid point test

a remarkable feature of stainless steel pipe is its inherent corrosion resistance to concentrated nitric acid and dilute nitric acid. This property makes it easy to distinguish from most other metals or alloys. However, high carbon 420 and 440 steels are slightly corroded during nitric acid point test, and non-ferrous metals will be corroded immediately when encountering concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel

III. copper sulfate point test

copper sulfate point test is the simplest method to quickly distinguish ordinary carbon steel from all types of stainless steel. The concentration of copper sulfate solution used is 5-10%. Before the spot test, the test area should be completely cleaned of grease or various impurities, and a small area should be polished with a soft abrasive cloth, and then drip copper sulfate solution into the cleaned area with a dropping bottle. Ordinary carbon steel or iron will form a layer of surface metal copper in a few seconds, while the surface of stainless steel will not produce copper precipitation or show the color of copper

IV. sulfuric acid test

sulfuric acid immersion stainless steel pipe test can distinguish 302 and 304 from 316 and 317. The cut edge of the sample shall be finely ground, and then cleaned and passivated in nitric acid (specific gravity 1.42) with volume concentration of 20~30% and temperature of 60~66 ℃ for half an hour. The volume concentration of sulfuric acid test solution is 10%, when heated to 71 ℃ When 302 and 304 steels are immersed in this hot solution, they are rapidly corroded and produce a large number of bubbles, and the samples turn black in a few minutes; While the samples of 316 and 317 steel are not corroded or react very slowly (without bubbles), and the samples do not change color within 10-15 minutes. If samples with known components are tested at the same time for approximate comparison, the test can be more accurate

link: Qijia expert teaching: selection and classification of water pipe materials




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