SHINESTAR STEEL GROUP CO., LTD

盛仕达钢铁股份有限公司

How to identify stainless steel pipe?

1Magnetic test

Magnetic test is the simplest method 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.

2Nitric 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 they encounter concentrated nitric acid. Dilute nitric acid has strong corrosivity to carbon steel.

3Copper 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 shall be completely cleaned of grease or various impurities, and a small area shall be polished with a soft abrasive cloth, and then copper sulfate solution shall be injected 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.

4Sulfuric acid test

The sulfuric acid immersion stainless steel tube 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. 

When the volume concentration of sulfuric acid test solution is 10% and heated to 71 , when. 302 and 304 steel are immersed in this hot solution, they are rapidly corroded and produce a large number of bubbles, and the sample turns black in a few minutes; 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 the samples with known composition are tested at the same time for approximate comparison, the test can be more accurate.


Post time: Dec-30-2021

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