How to identify stainless steel seamless pipes

Identification of Stainless Steel Seamless Pipes

I. Magnetic Test

The magnetic test is the simplest method to distinguish annealed austenitic stainless steel from ferritic stainless steel. Austenitic stainless steel is non-magnetic material, but after cold processing under atmospheric pressure, it will acquire a slight magnetism on its own. However, pure chromium stainless steel and low alloy stainless steel are all highly magnetic steel.

II. Nitric Acid Spot Test

One notable feature of stainless steel pipes is their inherent resistance to corrosion in concentrated nitric acid and dilute nitric acid. This characteristic makes it easy to distinguish them from most other metals or alloys. However, high-carbon grades 420 and 440 base pipes in production nitric acid spot tests are slightly corroded. Colored metal enterprises will be corroded immediately when encountering concentrated nitric acid. Thin-walled stainless steel has a strong corrosive effect on carbon steel.

III. Copper Sulfate Spot Test

The copper sulfate spot test is a simple and convenient method for quickly distinguishing ordinary carbon steel from all types of double flange steel expansion joints. The concentration of the copper sulfate solution used is 5 - 10%.

Before conducting the spot test, the test area should be thoroughly and effectively cleaned of grease or various impurities on the concrete surface of the 304 stainless steel pipe, and polished with a soft abrasive cloth in one or a small area. Then, we will control the dripping of copper sulfate solution onto the cleaned area using a dropper. Ordinary carbon steel or iron forms a layer of metallic copper within a few seconds, while the surface of the double flange steel expansion joint does not produce copper deposits or show copper color.

The effect of the solution treatment of stainless steel seamless pipes

1. Make the arrangement and composition of stainless steel seamless pipes uniform and consistent

This is particularly important for raw materials, as the rolling temperature and cooling speed of each section of hot-rolled pipes are different, resulting in inconsistent structures. During high temperatures, atomic economic activities intensify, and the chemical composition tends to be uniform. After rapid cooling, a more uniform single-phase arrangement is achieved.

2. Eliminate work hardening to facilitate further cold processing.

Through solution treatment, the distorted lattice structure is restored, elongated and broken grains start to recrystallize, internal stress is eliminated, and the tensile strength of the wire decreases, while the elongation gradually increases.

3. Restore the inherent corrosion resistance of stainless steel pipes.

Because during the cold processing process, the formation of carbides and their segregation cause a decrease in the corrosion resistance of stainless steel pipes. After solution treatment, the corrosion resistance of the stainless steel seamless pipes returns to the optimal state.