Causes and Control Methods of Welding Deformation of Steel Structure

Causes and Control Methods of Welding Deformation of Steel Structure

The type of deformation

1.Linear deformation

Longitudinal deformation: is caused by longitudinal contraction of weld;

Causes and Control Methods of Welding Deformation of Steel Structure
Causes and Control Methods of Welding Deformation of Steel Structure

Transverse deformation: is caused by transverse contraction of weld;

2.Angular distortion

The upper layer of fillet weld has a large amount of welding and a large amount of shrinkage, so the fillet deformation is mainly caused by the uneven transverse shrinkage of the weld in its height direction.

3.Bending deformation

For a t-shaped section, the contraction of the weld has an eccentricity to the center of gravity, thus bending the section upward, so the bending deformation is caused by the longitudinal contraction of the eccentricity weld.

4.Reverse the distortion

In the welding process of steel structure, some special structural forms will appear wave-shaped or spiral-shaped deformation, which is called torsional deformation.

Influence factors of welding deformation

The main cause of welding deformation is the local non-uniform heating of the welding parts during the welding process, and the subsequent non-uniform cooling effect and the rigid restraint effect of the structure itself or the external force, temperature, microstructure and other factors, resulting in non-uniform shrinkage deformation in the welded joint area.

1)Material factor

It is mainly due to the physical properties of the material itself, especially the Coefficient of thermal expansion, yield limit and elastic modulus of the material. The greater the coefficient of expansion, the greater the welding deformation of the material, the welding deformation decreases with the increase of elastic modulus, while the deformation increases with the increase of high residual stress. The expansion coefficient of stainless steel is greater than that of carbon steel, so the trend of welding deformation of stainless steel with the same thickness is greater than that of carbon steel.

2) Structural factors

The general principle is that with the increase of restraint degree, the welding residual stress increases, and the welding deformation decreases accordingly.
1.Structural stiffness is the ability of resisting tensile and bending deformation, which mainly depends on the shape and size of the cross-section of the structure.

2.When the rigidity of steel structure is small, the welding line is symmetrical in the structure, the welding procedure is reasonable, only linear shrinkage will occur, and when the welding line is asymmetrical, the bending deformation will occur If the welding procedure is reasonable, only linear shortening will occur when the barycenter of the weld section is at the same position as the barycenter of the joint section, and angular deformation will occur when the barycenter of the weld section deviates from the barycenter of the joint section.

3) Process factors

The main influencing factors are welding method, welding heat input (current and voltage) , component positioning or fixing method, welding sequence, welding fixture use. The most important factor is the welding sequence.

  • Large welding current, thick electrode diameter and slow welding speed will result in large welding deformation;
  • The deformation of automatic welding is smaller than that of manual welding, but the deformation of automatic welding is larger than that of manual welding.
  • In multi-layer welding, the shrinkage of the first layer is the largest, and the shrinkage of the second layer and the third layer is 20% and 5 ~ 10% of the first layer, respectively.
  • The shrinkage of intermittent welds is less than that of continuous welds.
  • The transverse shrinkage of butt weld is 2 ~ 4 times larger than the longitudinal shrinkage.
  • Welding sequence is not appropriate or not first welded parts, and then the total assembly welding, are easy to produce larger welding deformation.
  • Welding methods such as submerged arc welding, shielded metal arc welding and CO2 Gas metal arc welding produce different amounts of heat and deformation.

Control of welding deformation

  • reasonable selection of welding size and form
  • reasonable selection of weld length and quantity
  • reasonable arrangement of weld position

Technical measures

Causes and Control Methods of Welding Deformation of Steel Structure-2
Causes and Control Methods of Welding Deformation of Steel Structure-2
  • anti-deformation method
  • residual method
  • rigid fixation method
  • choose reasonable assembly welding sequence
  • welding technology measures

Welding deformation correction method

When the degree of bending and twisting deformation of members exceeds the current specifications and design requirements of steel structures, they must be corrected by mechanical correction, flame correction and hybrid correction. During construction, it can be selected reasonably according to the actual situation, and the following principles should be observed when rectifying: first overall, after local; first main, after secondary; first lower, after upper; first main parts, after accessories.

  • mechanical rectification method
  • flame rectification method
  • hammering method
  • strong electromagnetic pulse rectification method (electromagnetic hammer method)

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