How to Deal with the Black Surface of Stainless Steel Pipes?

  • By:Iris Liang
  • Date:2021/10/12

Stainless steel polished pipe has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, and good hot workability such as stamping and bending.

It is widely used in seawater equipment, chemistry, dyes, papermaking, oxalic acid, fertilizer and other production equipment. However, the problem is how to deal with the black surface of the polished stainless steel pipe. Below, Hangao Tech (SEKO Machinery) sorted out some reasons for the blackening of the polished stainless steel pipe surface and its treatment methods:   

Generally speaking, good stainless steel polished pipe products will not have this situation. If the surface of the tube appears black during long-term use, it is because the stainless steel polished tube produces an oxide film under the action of air. The oxide film prevents the metal in the stainless steel from being oxidized. This oxide film does not need to be specially oxidized. Wipe it off and there is no damage to the tube. Stainless steel polished tubes of different materials have some differences in element content, so the color of the oxidized film will also be different, but all have no effect on the tube. If you feel that this is not beautiful, you can do polishing.

If the surface of polished stainless steel pipe becomes black after welding, this is caused by insufficient welding gas purity or high temperature oxidation. The following three methods teach you how to avoid such things from happening.

1. Increase the purity of the argon used in the welding of stainless steel polished tubes to pure argon. From the outer surface of the tube, pure argon is significantly brighter than ordinary argon welding.

2. The backside should be protected by argon gas. The important stainless steel polished pipe should be backside protected after welding. Otherwise, high temperature oxidation will cause the welding layer passing through the backside to oxidize and produce defects. Polishing the backside weld is like slag. After protection, it can effectively prevent back oxidation.

3. You can apply a back protection agent on the back, which can save argon protection. Just apply a thickness of about 1 mm. Then when the front is soldered, a thin film is formed on the back to form a protective layer.

4. Perform bright solution treatment on the steel pipe. Our online bright solution annealing furnace can be used online without preheating. The predetermined heating temperature can be reached after 10-15 seconds after starting up, which greatly saves energy consumption. A fully enclosed water-cooled tunnel is used, and the pipe is cooled under a protective gas atmosphere to prevent the heated pipe from oxidizing with the oxygen in the air.

5. If you have found that the weld marks of the stainless steel polished pipe are black, you can use pickling passivation paste to clean it. It is to use acid to corrode the black oxide layer on the surface, and then rinse it with clean water.

The above is the reason for the black surface of the stainless steel polished pipe and the treatment method. I hope it will be helpful to you. If you need more information about the stainless steel industrial welded pipe making machinery, please keep paying attention to us.

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