How can one distinguish the quality of 304 stainless steel pipes

I. Several Points to Consider When Judging the Quality of Stainless Steel Pipes

1. Longitudinal Cracks

Longitudinal cracks refer to the longitudinal cracks that appear on the surface of the steel ingot. They usually occur in the upper part and corners. The longitudinal cracks that appear on the top will be deeper. 

2. Cross Cracking

The phenomenon of cross cracking is relatively easy to understand. It refers to the occurrence of transverse cracks on the surface of the stainless steel welded pipe. This usually happens during the forging process of the steel ingot, but most of the cracks are of relatively shallow depth. 

3. Scabbing

As mentioned earlier, longitudinal cracks may occur at the upper part or corners and recesses of the stainless steel industrial welded pipes. Sometimes, in the lower part area, there may also be crust-like or tumor-like metal splashes and deposits, which look like a scab has formed. This is why it is called scabbing. However, this problem rarely occurs. 

4. Surface pores

The concept of pores is quite easy to understand. On the surface of stainless steel welded pipes, there are numerous tiny pores that can be seen with the naked eye. These pores are mostly shallow and resemble cross-cracks. 

5. Shrinkage Cavity

A shrinkage cavity occurs when the molten stainless steel liquid contracts within the mold. Sometimes, it may be affected by environmental factors such as air and temperature, resulting in the formation of such cavities. In professional terms, it is called a shrinkage cavity. 

II. Simple methods for identifying stainless steel pipes are as follows:

1. Using a magnet for identification

This is a common method. Magnets can basically distinguish between two types of stainless steel. Because chromium stainless steel can be attracted by magnets in any state, chromium-nickel stainless steel is generally non-magnetic in the annealed state, and after cold processing, some may have magnetic properties, but high manganese steel is non-magnetic. The magnetic properties of chromium-nickel-nitrogen stainless steel are more complex: some are non-magnetic, some are magnetic, and some have no magnetic property on the longitudinal surface but have magnetic property on the cross-sectional surface. Therefore, although magnets can basically distinguish chromium stainless steel and chromium-nickel stainless steel, they cannot correctly distinguish some special types of steel, let alone specific steel grades. 

2. Nitric Acid Spot Test

The notable feature of stainless steel pipes is their inherent resistance to corrosion by concentrated and dilute nitric acid. This characteristic enables them to be easily distinguished from most other metals or alloys. However, high-carbon 420 and 440 steels will experience slight corrosion during the nitric acid spot test due to the influence. will be immediately corroded when exposed to concentrated nitric acid treatment. Dilute nitric acid has a strong corrosive effect on carbon steel. 

3. Copper Sulfate Spot Test

The copper sulfate spot test is the simplest method for quickly distinguishing ordinary carbon steel pipes from various stainless steel pipes. The concentration of the copper sulfate solution used is 5-10%.