Methods for Identifying Stainless Steel Pipes

 

Methods for Identifying Stainless Steel Pipes

1. Magnetic Test

The magnetic test offers a straightforward way to differentiate between annealed austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel, typically non-magnetic, may become slightly magnetic after cold working under high pressure. In contrast, pure chromium steel and low alloy steel exhibit high magnetic properties.Stainless Steel Pipes

2. Nitric Acid Point Test

Stainless steel pipes possess inherent corrosion resistance to concentrated and dilute nitric acid, a characteristic setting them apart from most other metals or alloys. Notably, high-carbon 420 and 440 steels may experience slight corrosion during nitric acid point tests, while non-ferrous metals corrode immediately when exposed to concentrated nitric acid. Dilute nitric acid also exhibits high corrosiveness to carbon steel.

3. Copper Sulfate Point Test

The copper sulfate point test stands as the simplest method to differentiate between ordinary carbon steel and all types of stainless steel. Using a 5-10% concentration of copper sulfate solution, the test area should be meticulously cleaned of grease or impurities. Upon dripping copper sulfate solution onto the cleaned area, ordinary carbon steel will form a layer of metallic copper within seconds, whereas stainless steel surfaces will remain unchanged.

4. Sulfuric Acid Test

The sulfuric acid immersion test distinguishes between 302 and 304 stainless steel and 316 and 317 stainless steel. After finely grinding and cleaning the sample's cut edge, it should be passivated in nitric acid (specific gravity 1.42) for half an hour at 20-30% concentration and a temperature of 60-66°C.

The sulfuric acid test solution, heated to 71°C with a 10% concentration, reveals distinct reactions. When immersed, 302 and 304 steel rapidly corrode, generating bubbles and turning black within minutes. In contrast, 316 and 317 steel either exhibit minimal or no corrosion, with no discoloration occurring within 10 to 15 minutes. Conducting tests on samples with known compositions simultaneously aids in achieving more accurate results through approximate comparison.

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