Some stainless steel welded pipes are directly polished and straightened after welding and leveling, and then taken offline and stored in the warehouse. After a period of use, corrosion was found on the surface, and even cracking occurred in severe cases.

Why is this happening? It is because a very important step was overlooked during the production process of welded pipes.

This step is called annealing.

Composition of stainless steel

In the smelting production of steel, we will adjust the elemental formula to achieve the desired characteristics of the produced steel, such as Cu, Cr, Ni, N, Nb, Ti, Mn, Mo, Si, and other elements.

One of the properties we need to improve is the high corrosion resistance of steel, which is what we call stainless steel.

The corrosion resistance of stainless steel comes from an element contained in the formula - Cr (chromium).

When the content of chromium reaches a certain peak, the corrosion resistance of steel will be greatly improved.

Generally, the Cr content of stainless steel should be at least around 10.5%.


Common types of corrosion

Now that we have figured out the key to corrosion resistance of stainless steel, let's take a look at the common types of corrosion - intergranular corrosion and stress corrosion.

Intergranular corrosion, in simple terms, refers to the reaction of internal elements in the weld seam and adjacent materials caused by high temperature during the welding process of welded pipes. The carbon and chromium elements in the steel form a carbon chromium compound (Cr23C6), which causes chromium depletion in the grain boundary area and ultimately leads to the occurrence of intergranular corrosion.


Stress corrosion originates from the reaction force generated when the steel strip undergoes deformation under external pressure during the forming and welding process, which will remain inside the welded pipe after the welding is finalized. If not eliminated, the welded pipe will have a particularly high hardness, making it difficult to proceed with the next step of processing.

On the other hand, if there are problems with welding quality, over time, stress will gradually cause tearing of the weld seam, ultimately leading to cracking of the welded pipe and affecting its use.

To address these two quality hazards, the use of Hangao's bright solid solution equipment can achieve a thorough solution.

Functional characteristics of Hangao Bright Solid Solution Equipment:

1. Refine grain size, uniform structure and composition of pipes

2. Eliminating internal stress in pipes and preventing deformation and cracking

3. Reduce the hardness of pipes and improve plasticity to facilitate subsequent processing.