To Improve Stainless Steel Pipe's Corrosion Resistance, What Should Be Noticed When Welding?

  • By:Iris Liang
  • Date:2021/12/17

As the excellent properties of stainless steel pipes are becoming more and more widely known, stainless steel pipes have been more and more widely used in various industries. However, due to the production cost, stainless steel welded pipes have performance comparable to seamless stainless steel pipes and are widely welcomed. Hangao Tech (SEKO Machinery), who has 20 years of experience in manufacturing bright annealing industrial stainless steel pipe weld bead rolling machine manufacturer,  today we introduce the precautions for welding operations, so that you can obtain better corrosion resistance of stainless steel pipes.

 

Part One 

1. Never ignite the arc randomly on the surface of the stainless steel strip, otherwise it will cause local burns on the surface of the pipe. Local burns on the pipe surface are the source of corrosion, especially for stainless steel tube production line that needs to be used in industries that require high corrosion resistance, such as beverages, medicines, oil and gas, and so on.

2. Pay attention to adjusting the working speed of the production line. If you blindly pursue high speed and ignore the welding quality, the welding effect will be unsatisfactory.

3. The welding rod used for tack welding should be the same as the welding rod used during welding, and it is absolutely not allowed to replace it with carbon steel welding rod arbitrarily.

4. Before the stainless steel strip is formed and welded, or after being formed into a tube, there must be no nicks, arc marks, stains, and slag crust after welding on the surface. Otherwise, this will increase the corrosion of the stainless steel surface, which should be paid attention to. We can install an introductory leveling device at the front end of the forming section. This small structure can help remove the burrs on the strip edges, and at the same time make the strip smoother and easier to shape.

5. For industrial welded pipes with relatively high process requirements, qualified manufacturers can consider equipping online bright annealing equipment. The stainless steel tube after bright annealing can not only eliminate the intergranular stress. After annealing, a dense and uniform oxide film can be formed on the surface of the steel pipe to protect the internal metal from oxidation and corrosion.

  

Part Two

6. When welding is finished or interrupted, in order to avoid arc craters or cracks, the arc craters should be filled.

7. When welding, the weldment should be in close contact with the ground wire to avoid poor contact between the weldment and the ground wire, resulting in arc burns on the surface of the stainless steel and affecting its corrosion resistance.

8. In order to prevent carbon or other impurities from being mixed into the weld during welding and affecting the corrosion resistance of stainless steel weldments, it is best to clean the steel strip within 20~30mm on both sides before welding. You can choose to install a deburring introduction device at the front end of the forming welding section.

9. When storing or transporting stainless steel strip, it is not advisable to stack it with ordinary steel to avoid being contaminated by other oxides such as rust and other impurities.

10. Avoid scratches or scratches on the surface of stainless steel welded pipes when they are in the industrial pipe equipment for processing. A softer cushioning protective layer can be wrapped on the unloading rack.

  

Part Three

11. When the stainless steel pipe is straightened, it is forbidden to directly hammer it with a hammer to avoid dents on the surface of the pipe. Otherwise, its corrosion resistance will be greatly affected.

12. It is best to use cold pressing to form the seal head and other parts of the container, rather than hot pressing. If hot press forming is necessary, changes in corrosion resistance should be checked and corresponding heat treatment should be carried out.

14. When the stainless steel is subjected to post-weld heat treatment, it is not suitable to leave oil and other dirt on the surface of the steel before heating. It must be cleaned up to avoid carburization during heating. Otherwise, it will not only affect the annealing effect, but also shorten the equipment life of the annealing furnace and increase the maintenance cost. Consider adding a cleaning and drying device before the annealing process. The device uses hot water to clean the surface of the pipe, and then quickly air-dry the pipe with an air knife to keep the surface of the pipe clean and dry. The heating temperature must be uniform. When performing stress relief treatment above 800~900℃, the temperature should be raised slowly below 850℃. However, when the temperature reaches 850°C or higher, the temperature rise should be rapid to avoid the tendency of crystal grains to increase.

15. The surface treatment of stainless steel pipes such as flattening, polishing, pickling and passivation needs to be taken seriously. The treatment process must comply with the operating procedures. The standard is that the surface of the steel is uniformly silvery white.

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