Four identification methods for the authenticity of stainless steel elbow

I. Nitric Acid Point Test A notable feature of stainless steel elbows is their 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, the high carbon type 420 and 440 steels are slightly corroded when subjected to the nitric acid point test, and the non-ferrous metals are immediately corroded when they encounter concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel.

2. Sulfuric Acid Test The sulfuric acid immersion stainless steel elbow test can distinguish 302 and 304 from 316 and 317. The cut edge of the sample should be finely ground and then cleaned and passivated for half an hour in nitric acid (specific gravity 1.42) at a concentration of 20 to 30% and a temperature of 60 to 66 °C. The sulfuric acid test solution has a volume concentration of 10% and is heated to 71 ° C. When the .302 and 304 steels are immersed in this hot solution, they are rapidly corroded and generate a large number of bubbles, and the sample turns black in a few minutes; while the 316 and 317 steels The sample is not corroded or the reaction is very slow (no bubbles are generated), and the sample does not change color within 10 to 15 minutes. The test can be made accurate if a similar sample is tested simultaneously for approximate comparison.

III. Copper Sulfate Point Test The copper sulfate point test is a convenient method for quickly distinguishing ordinary carbon steel from all types of stainless steel. The concentration of the copper sulfate solution used is 5 to 10%. Before the point test, the test area should be grease or various impurities, and a small area should be polished with a soft cloth, and then the copper sulfate solution should be dripped into the cleaned area with a drop bottle. Ordinary carbon steel or iron forms a layer of surface metallic copper in a few seconds, while stainless steel surfaces do not produce copper deposits or show copper color.

4. Magnetic test The magnetic test is a simple method to distinguish between austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is non-magnetic steel, but will have mild magnetic properties after cold working under large pressure; pure chrome steel and low alloy steel are strong magnetic steel.