First, magnetic test
The magnetic test is the simplest way to distinguish annealed austenitic stainless steel pipes from ferrite stainless steel pipes. Austenitic stainless steel pipes are non-magnetic steels, but they will have a slight magnetism after being cold worked under heavy pressure; pure chromium steel and low alloy steel are both strongly magnetic steels.
Second, the nitric acid point test
A notable feature of stainless steel pipes is their inherent corrosion resistance to concentrated nitric acid and dilute nitric acid. This property makes it easy to distinguish them from most other metals or alloys. However, high-carbon 420 and 440 pipes are slightly corroded when subjected to nitric acid point tests, and non-ferrous metals corrode immediately when they encounter concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel.
Third, copper sulfate point test
The copper sulfate point test is the simplest way to quickly distinguish ordinary carbon steel from all types of stainless steel pipes. The concentration of the copper sulfate solution used is 5~10%. Before conducting the point test, the test area should be thoroughly cleaned of grease or various impurities, and a small area should be polished with a soft abrasive cloth, and then the copper sulfate solution should be dripped into the cleaned area with a dropper. Ordinary carbon steel or iron will form a layer of surface metallic copper within a few seconds, while the surface of the stainless steel tube will not produce copper precipitation or show the color of copper.
Fourth, the sulfuric acid test
The sulfuric acid immersion test can distinguish 302 and 304 from 316 and 317. The cut edges of the sample should be finely ground, then cleaned and passivated in nitric acid (specific gravity 1.42) with a volume concentration of 20~30% and a temperature of 60~66℃ for half an hour. The volume concentration of the sulfuric acid test solution is 10%, heated to 71℃. When 302 and 304 steel are immersed in this hot solution, they rapidly corrode and produce a large number of bubbles. The sample turns black within a few minutes; while the samples of 316 and 317 steel are not corroded or react very slowly (no bubbles are produced), and the sample does not change color within 10~15 minutes. If a sample with a known composition is tested simultaneously for approximate comparison, the test can be made more accurate.
Fifth, hydrochloric acid test
The hydrochloric acid test can be used to distinguish low-chromium 403, 410, 416, and 420 pipes of steel from 430, 431, 440, and 416 pipes of steel with higher chromium content. Dissolve equal weights of sample cuttings in a 50% volume concentration hydrochloric acid solution and compare the color intensity of the solution. The steel with higher chromium content has a darker green color. Put a few grams of sample cuttings in each test tube, and then inject an equal amount of 40-50% volume concentration hydrochloric acid solution into each test tube; after 3 minutes, the solution changes as follows.
1.302 reacts quite quickly, and the solution color is light green-blue.
2.303 (se) will emit a garlic smell, and the solution color is light amber.
3.410 reacts strongly, and the solution color is darker than the 302 solution.
4.416 reacts quickly and emits an odor similar to rotten eggs, and the solution color is dark turbid green. 301, 304, 310, 316, and 347 steel react to acid solution similarly to 302 steel, slowly showing a light green-blue color, but without the garlic smell.
Post time: Jun-17-2024