Tips for Welding Square Tubes: Avoid Cracks | MachineMFG

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Tips for Welding Square Tubes: Avoid Cracks


There are some welding problems when you use square and rectangular tubes.

The welding process of square and rectangular tubes has always been a difficult step in the process flow of square and rectangular tubes. Pay attention to welding!

If the cooling speed is too fast during welding, cracks are likely to occur, so avoid being wet by rain and welding at the tuyere during welding;

When welding medium/high carbon steel or alloy steel, it is necessary to take heating and insulation measures according to the composition and characteristics of raw materials before welding.

Cracks may also be caused by too fast heat dissipation due to low ambient temperature or too good heat dissipation conditions such as tuyere during the welding operation.

The welding rod used for welding square and rectangular pipe is also easy to produce cracks in the welds with high sulfur, phosphorus and carbon content;

Sulfur and phosphorus are harmful elements. Welds with high sulfur content have thermal brittleness, while welds with high phosphorus content have cold brittleness.

The sulfur and phosphorus content of welding rods must be controlled below 0.0035.

At present, square and rectangular tubes have such problems, most of which are related to the welding method and the temperature during welding.

This phenomenon can also be caused by low welding environment temperature and too fast cooling speed;

In addition, no matter straight rectangular tubes are formed at one time, or square tubes are formed from round to square, square tubes will generate internal stress during the forming process.

In the high temperature season, the existence of internal stress will not cause too much trouble.

In the low temperature winter, the existence of internal stress is more obvious. For example, cracks may occur during loading, unloading and welding. 

The best solution is to heat treat the produced square and rectangular tubes (that is, the heating and insulation measures mentioned above);

For the heat treatment process of square and rectangular tubes, first take the square and rectangular tubes for testing to understand the mechanical properties (yield, tensile strength, etc.) of the square and rectangular tubes.

After the test results are obtained, set the heat treatment time and temperature in the furnace, and put the square and rectangular tubes into the trolley type furnace.

The furnace temperature changes according to the specified heating system.

Heating – constant temperature – heat preservation – cooling in the furnace can eliminate the internal stress of the steel tubes after heat treatment, greatly reducing the probability of cracking.


Do not rush to weld when the temperature is very low;

Preheat the position to be welded with flame or other methods before welding, which will greatly reduce cracks (for example, if you pour boiling water directly into a cold glass in cold winter, the cup may crack due to too large temperature difference.

If you pour warm water into the cup first to raise the temperature of the cup, then pour boiling water into the cup, will the cracking be greatly reduced?)

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