Several chemical identification methods of stainless steel flanges

Stainless steel flange is a disc-shaped part, which is the most common in pipeline engineering. Stainless steel flanges are used in pairs and with matching flanges on valves. In pipeline engineering, flanges are mainly used for the connection of pipelines. Then let's introduce some chemical identification methods!
1. Magnetic test method: The magnetic test method is a simple and common method to distinguish austenitic stainless steel from ferritic stainless steel. Austenitic stainless steel is non-magnetic steel, but it will have mild magnetic properties after cold working under large pressure, while Pure chrome steels and low alloy steels are strong magnetic steels.
3. Copper sulfate spot test method: Copper sulfate spot test is the easiest way to quickly distinguish ordinary carbon steel from all types of stainless steel. The concentration of copper sulfate solution used is 5%-10%. The test area should be thoroughly cleaned of oil or other impurities, and a small area should be polished with a grinder or a soft abrasive cloth, and then the test liquid should be dropped to the grinding place. Ordinary carbon steel or iron will form a layer of surface metal within a few seconds. copper, while the surface of the spot-tested stainless steel did not produce copper precipitation or show copper color.
2. Nitric acid spot test method: A notable feature of stainless steel flanges is their inherent corrosion resistance to concentrated and dilute nitric acid, a property that makes it easy to distinguish from most other metals or alloys, but high Carbon type 420 and 440 steels are slightly corroded during nitric acid spot test, non-ferrous metals are corroded immediately when they encounter concentrated nitric acid, and dilute nitric acid is strongly corrosive to carbon steel.
4. Sulfuric acid test method: Sulfuric acid immersion stainless steel can distinguish 302 and 304 from 316 and 317. The cut edge of the sample should be finely ground, then cleaned and passivated in sulfuric acid with a volume concentration of 20%~30% and a temperature of 60~66℃ for half an hour. The volume concentration of the sulfuric acid solution is 10%, and heated to 71℃ When 302 and 304 are immersed in the solution, the steel is rapidly corroded and a large number of bubbles are generated, and the sample turns black within a few minutes, while the samples of 316 and 317 steel are not corroded or corroded very slowly (no bubbles are generated), The test does not change color within 10 to 15 minutes. Testing can be made more accurate if approximate comparisons are made by simultaneously testing samples of known composition.