How to identify the material of
stainless steel tube? there are some ways to state:
1, Nitric acid point test: a significant feature of stainless steel tube is concentrated nitric acid and dilute nitric acid has inherent corrosion resistance. This performance makes it easy to distinguish from most other metals or alloys. But the high carbon type 420 and 440 steel in the nitric acid point test is slightly corroded, non-ferrous metals encountered concentrated nitric acid will be corroded immediately. The dilute nitric acid on the carbon steel has a strong corrosive.
2, Magnetic test: magnetic test is the difference between annealing
austenitic stainless steel and ferritic stainless steel tube of the most simple method. Austenitic stainless steel is non-magnetic steel, but by the cold down after cold processing will have a mild magnetic; and pure chrome steel and low alloy steel are strong magnetic steel.
3, Sulfuric acid test: sulfuric acid immersed stainless steel tube test can 302 and 304 and 316 and 317 distinguish. The trimming of the sample shall be finely ground and then washed and passivated for half an hour in nitric acid (specific gravity 1.42) at a volume concentration of 20 to 30% and at a temperature of 60 to 66 ° C. Sulfuric acid test solution volume concentration of 10%, heated to 71 ° C when .302 and
304 steel immersed in this hot solution, the rapid corrosion and produce a large number of bubbles, the sample in a few minutes black; and 316 and 317 steel of the sample is not subject to corrosion or reaction is very slow (no bubbles), the sample does not change color within 10 to 15 minutes. The test can be made more accurate by comparing the samples with the known composition at the same time.
4, Copper sulfate point test: copper sulfate point test is a quick distinction between ordinary carbon steel and all types of stainless steel tube the most simple way. The concentration of the copper sulfate solution used is 5 to 10%. Before conducting the point test, the test area should thoroughly remove grease or various impurities, and polish a small area with a soft grind, and then use a drop bottle to clean the area after the infusion of copper sulfate solution. Ordinary carbon steel or iron in a few seconds will form a layer of surface copper, while the surface of stainless steel does not produce copper precipitation or show the color of copper.
