Steel structures fabricated by welding are to be hot-dip galvanized after fabrication, are subject to warping and distortion of the material due to the heating and cooling incidental to the galvanizing operation, particularly when it is necessary for the parts to be dipped more than once to cover the entire surface.
There can also be an issue if you combine light and heavy sections. These will be dipped at 450 C and will cool down at different rates. This may cause them to pull against one another.
Most Frequent reasons for Warping and Distortion
Figure 1 Warping
- One of the most commonly distorted and warped members of assemblies is that of sheets or plates up to 6 mm in thickness which are assembled by welding.
- Warping also happens by the use of non-symmetrical sections such as channels. Regardless of size, channels require straightening after galvanizing. This is not true of an I-beam, pipe, H-column, or any other section that is symmetrical about both its major axes.
Channels and other non-symmetrical sections should be avoided whenever it is possible to use symmetrical shapes or sections.
3. Certain welding practices, weld sizes and configurations, and thickness differences between welded components can introduce imbalanced stresses into the welds. If these stresses are combined with other stresses during hot-dip galvanizing, the stress relieving effect of galvanizing may permit distortion to occur.
How to Avoid Warping and Distortion
Figure 2 Distortion
- Use symmetrically rolled sections wherever possible, in preference to angle or channel frames. I-beams are preferred to angles or channels.
- All edges of tightly contacting surfaces should be completely sealed by welding unless the area exceeds the recommended size.
- The sheet steel should not be welded to the angle steel frame prior to galvanizing if the galvanizing kettle is not of sufficient size to permit the total immersion in one dip
- Unequal thickness of metal should be avoided wherever possible due to the different rates of heating and cooling during the galvanizing operation and the effect of unequal expansion and contraction.
- Arranging weld seams symmetrically. The size of weld seams should be kept to a minimum.
- Use temporary bracing or reinforcing on thin-walled and asymmetrical designs.
Novelty Steel engineering has vast experience with hot dip galvanization of the steel fabrications. Potential distortion and warping risks are identified in the steel detailing phase in order to prevent unpleasant surprises after hot dip galvanization. Feel free to contact Novelty Steel team for a free review of your project and risk analysis.