Physical and chemical identification of stainless steel pipes
The physical point of view：
From a physical point of view, magnetic testing is the easiest way to identify annealed austenitic stainless steel and ferrite stainless steel. Austenitic stainless steel is a kind of non-magnetic stainless steel, but after cold work under big pressure have mild magnetic, but pure chromium stainless steel and low alloy steel has strong magnetism. It can be distinguished by magnetism.
Sulfuric acid test
The test of stainless steel pipes through sulfuric acid can distinguish between 302 and 304 stainless steel and 316 and 317 stainless steel. Stainless steel pipe sample trimming needs after fine grinding, then is 20-30% in volume concentration, temperature is 60-66 ℃ (specific gravity of 1.42) of nitric acid cleaning and passivation in half an hour.
Sulfuric acid test solution volume concentration is 10%, when heated to 71 ℃ when the 302 and 304 stainless steel in such a hot, rapid corrosion and generate a large number of air bubbles, sample in a few minutes will turn black; However, the samples of 316 and 317 stainless steel are not corroded or slow to react (no bubble formation), and the sample is not discoloured in 10-15 minutes. The experiment is more accurate if it is approximated by the test samples with known components.
Nitrate point test
One of the obvious features of the stainless steel pipe is the inherent corrosion resistance of the nitric acid and the dilute nitrate. Such properties make it easy to distinguish from most other metals or alloys. However, the high-carbon 420 and 440 stainless steel were slightly corroded in the nitric acid test, and the non-ferrous metals were immediately corroded when the nitric acid was encountered. But the nitric acid is more corrosive to carbon steel.
Copper sulfate test
The copper sulfate test is the easiest way to quickly distinguish between ordinary carbon steel and all types of stainless steel. The concentration of copper sulfate was 5-10%.
Before the points test, test area should be thoroughly remove grease or all kinds of material, using a soft grinding, and polishing a small area, then use to clean up after dropping bottle regional drip copper sulfate solution. Ordinary carbon steel or iron will form a surface metal in a matter of seconds, while the stainless steel surface does not produce copper deposits or the color of copper.
Through such physical and chemical experiment method, can clearly distinguish the different kinds of stainless steel pipes, then on the basis of its performance, choose the appropriate use occasions, such conducing to the safety of the production and living.
Identification Tests for Stainless Steels
- magnet testing
- spark testing
- hardness testing
- acid testing
|AISI Type||Grade||Group||Magnet Test||Spark Test||Hardness Test||Sulfuric Acid Test||Hydrochloric Acid Test|
|Few forks – short, reddish||>165 Brinell after heated to 1800oF and water quench||Strong attack – green crystals and dark surface||Rapid reaction – pale blue-green solution|
|303||Spoiled egg odor – heavy black smudge|
|304||Strong attack – green crystals and dark surface||Fast attack – gas formation|
|308||Full red without many forks|
|316||Few forks – short, reddish||Slow attack – tan surface turns brown||Very slow attack|
|321||Fast attack – gas formation|
|410||Chromium||Martensitic||Magnetic||Long white with few forks||> 280 Brinellafter heated to 1800oF and water quench||Rapid reaction – dark green solution|
|416||Spoiled egg odor – heavy black smudge|
|420||Long white-red with burst|
|431||Long white with few forks|
|440 A, B, C||Long white-red with burst|
|430||Ferritic||Long white with few forks||180 – 250 Brinell after heated to 1800oF and water quench|
|430F||Spoiled egg odor – heavy black smudge|
|446||Full red without many forks|
Source: China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)
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