Stainless steel pipes are used in a wide range of industries/markets, due to their overall corrosion resistance and good machinability. Pipes are generally considered passageways for liquids, and measured by inside diameter or ID. Some industry examples include marine, chemical & petrochemical, oil & gas, and renewable energy. Here are some test methods for identifying stainless steel pipe:
First, the magnetic test
The magnetic test is the simplest way to distinguish between annealed austenitic stainless steel and ferritic stainless steel. 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.
Second, nitric acid point test
One of the salient features of stainless steel welded pipes is the inherent corrosion resistance of concentrated nitric acid and dilute nitric acid. 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.
Third, the copper sulfate point test
The copper sulfate point test is the easiest way to quickly distinguish between ordinary carbon steel and all types of stainless steel. 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 drop the bottle into the clean area after the dripping 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.
Fourth, sulfuric acid test
Sulfuric acid immersed stainless steel welded pipe test can distinguish 302 and 304 from 316 and 317. The trimming of the sample should 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.