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What kind of stainless steel welded pipe is good?

Edit:Shaanxi Tonghui Steel Co., Ltd.UpDate:2020-03-30

There are good and bad things in stainless steel welded pipes in the world, and the same is true for stainless steel welded pipes. There are grades. Only stainless steel that meets certain quality standards can be graded steel. The state has formulated a set of stainless steel pipe grade standards in this regard. A thorough understanding of these standards can help us select and identify better steel products. Today let us understand the quality standards of stainless steel welded pipes to grade steel.

Stainless steel welded pipe

1. Stainless steel welded pipe products must meet the requirements of GB / T17395-2008: outer diameter: 70 ± 0.3mm, wall thickness tolerance: 2.2 ± 0.2mm, length tolerance: 4060-0 / + 5mm;

2. The bending degree meets the E3 standard (the full-length bending degree is 0.1%);

3. The ovality meets NR2 (the ovality is not more than 5% of the allowable deviation of the outer diameter);

4, polished outer wall Ra≤0.8 (or Ra≤0.1); stainless steel industrial welded pipe

5. After welding of Xi'an stainless steel welded pipe, the surface should be cleaned in time. Stainless steel welded pipe manufacturers

6. After the surface treatment of stainless steel pipe is finished, care should be taken to protect the finished product, to avoid touching by personnel, and to avoid secondary pollution such as oil, dust and the like.

What factors affect the quality of stainless steel welded pipe

1) Stainless steel tube blanks are supplied with molten steel from an electric arc furnace or an intermediate frequency furnace and refined in an AOD furnace. In the AOD furnace, decarburization and boiling are carried out by oxygen blowing, so that the gas inclusions in the molten steel float to the slag layer. In actual operation, sometimes more oxygen is blown, and then reduced by adding ferrosilicon, but more silica inclusions are generated.

2) The stainless steel seamless tube uses round tube blanks for two-roll oblique rolling perforation. The metal flows outwards during oblique rolling to form holes. When the speed of the roll is too fast, the hole forming speed exceeds the billet forward speed, causing internal holes and core rod Disengage without contact, the inner hole is not compressed during the perforation deformation process, and the inner hole crack is easy to occur.

3) Stainless steel seamless tubes are cold-drawn and cold-rolled to change the outer diameter and wall thickness. The work hardening after cold-drawing and cold-rolling needs to be eliminated by solid solution; in order to avoid bending of steel tubes, some factories slowly cool the steel tubes after solid solution. The carbides are not dissolved in the austenite grains and precipitate at the grain boundaries. When the metal is deformed again, the hard carbides precipitated become resistance to deformation, and cracks are likely to occur during cold drawing and cold rolling again.

4) Stainless steel welded pipe The stainless steel continuous casting slab is hot rolled into a medium-thick plate, and after bending and longitudinal welding, it becomes a stainless steel welded pipe. The temperature is too high during welding, and layered welding is not used when the wall is thick. The wet seam and heat-affected zone are slowly cooled from high temperature after welding, and the carbides in austenite precipitate to the weld and heat influence. In the grain boundaries of the zone, the toughness of the weld and the heat affected zone is greatly reduced, and welding cracks are generated accordingly. When the steel pipe is butt welded, welding cracks will occur.