1. Magnetic Test: Magnetic test is a simple method to distinguish annealed austenitic stainless steel from ferritic stainless steel. Austenitic stainless steel is non-magnetic steel, but it will have a slight magnetism after cold pressing. After annealing, the magnetism of stainless steel elbows will be greatly reduced, while low-alloy steel elbows are all highly magnetic. Therefore, austenitic stainless steel and carbon steel materials can be distinguished by magnetic particle testing.

2. Nitric Acid Spot Test: An obvious feature of stainless steel elbows is that they are inherently not afraid of corrosion by 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 steels are slightly corroded during nitric acid spot tests, and non-ferrous metals will be corroded immediately when they encounter concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel.

3. Sulfuric acid test: The sulfuric acid immersion test can distinguish 302 stainless steel elbows and 304 stainless steel elbows from 316 stainless steel elbows and 317 stainless steel elbows. The cut edges of the specimen 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 degree for half an hour. The volume concentration of the sulfuric acid test solution is 10%, heated to about 71 degree . When 302 and 304 stainless steels are immersed in this hot solution, they will be corroded and produce a large number of bubbles, and the specimens will turn black within a few minutes; while 316 and 317 steel specimens will not be corroded or react very slowly (no bubbles are produced), and the specimens will not change color within 10~15 minutes.

4. Copper sulfate spot test: The copper sulfate spot test is a simple method to quickly distinguish ordinary carbon steel from all types of stainless steel. The concentration of the copper sulfate solution used is 5~10%. Before conducting the spot test, the test area should be free 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 stainless steel will not produce copper precipitation or show the color of copper.