Sulfuric acid immersion stainless steel elbow test can put 302 and 304 and 316 and 317 distinguished. The sample cutting edge through fine grinding, and then the concentration of 20~30%, temperature of 60~66 nitrate (accounted for 1.42) in the cleaning and passivation for half an hour. Concentration of sulfuric acid test solution was 10%, heated to 71 degrees when.302 and 304 stainless steel elbow is immersed in the hot solution, rapid corrosion and a large number of bubbles, sample within a few minutes of black; and 316 and 317 steel bend specimen is not subject to corrosion or reaction is very slow (bubble) sample in 10 to 15 minutes do not change color. At the same time, if the test sample with known composition to approximate comparison, can make the test more accurate.
Copper sulfate test is fast to distinguish between ordinary carbon steel elbow and all types of stainless steel elbow is the most simple method. The use of copper sulfate solution concentration is 5~10%. Before the test, the test area should be thoroughly cleaned of oil or various impurities, and polishing cloth polishing a small region, then dropping to clean up after the regional drop note copper sulfate solution. Ordinary carbon steel elbow or iron elbow in a few seconds will form a layer on the surface of copper, and the surface of the stainless steel elbow does not produce copper precipitation or copper color.
The magnetic test is the easiest way to distinguish the annealing of stainless steel elbow and ferritic stainless steel elbow. Austenitic stainless steel elbow is non-magnetic steel elbow, but the high pressure after cold working with mild magnetic; and pure chrome steel elbow and low alloy steel elbow are strong magnetic steel elbow.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)