Method for identifying the authenticity of stainless steel elbows

 1. Magnetic test: Magnetic test is a simple method to distinguish between annealed austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is a non-magnetic steel, but it will have mild magnetism after cold working under high pressure; And pure chromium steel and low alloy steel are both strong magnetic steels.

　　2. Nitric acid point test: One obvious feature of stainless steel elbows is their inherent resistance to corrosion of concentrated and dilute nitric acid. This performance makes it easy to distinguish from most other metals or alloys. However, high carbon 420 and 440 steels are slightly corroded during the nitric acid point test, and non-ferrous metals immediately corrode when they encounter concentrated nitric acid. Dilute nitric acid has strong corrosiveness to carbon steel.

　　3. Sulfuric acid test: The sulfuric acid immersion stainless steel elbow test can distinguish 302 and 304 from 316 and 317. The cut edges of the sample should be finely ground, and then cleaned and passivated for half an hour in nitric acid (with a specific gravity of 1.42) with a volume concentration of 20-30% and a temperature of 60-66 ℃. The volume concentration of the sulfuric acid test solution is 10%, and it is heated to 71 ℃. When 302 and 304 steel are immersed in this hot solution, they are corroded and generate a large number of bubbles, causing the sample to turn black within a few minutes; The samples of 316 and 317 steel are not corroded or react slowly (without bubbles), and the samples do not change color within 10-15 minutes. If samples with known composition are tested simultaneously for approximate comparison, it can make the test more accurate.

　　4. Copper sulfate spot test: The copper sulfate spot test is a convenient method to quickly distinguish between ordinary carbon steel and all types of stainless steel. The concentration of the copper sulfate solution used is 5-10%. Before conducting point tests, the test area should be coated with grease or various impurities, and a small area should be polished with a soft abrasive cloth. Then, a copper sulfate solution should be dripped into the cleaned area using a drip bottle. Ordinary carbon steel or iron will form a layer of surface metal copper within a few seconds, while the surface of stainless steel will not produce copper precipitation or display the color of copper.