There is a perception that distortion of fabricated steel items is a significant problem, however, in reality, distortion occurs in only a very small number of instances. Distortion has become a rare occurrence as bath sizes and handling facilities have improved. Galvanizing will not generally cause distortion provided that design and fabrication principles are correct. When steel fabrications do distort during galvanizing, the reasons have usually been ‘built-in’ at an earlier stage. Distortion almost always arises from the relief of stresses as the steel is heated to the galvanizing temperature (usually 445-465℃). Although such stresses may be inherent in the steel and may vary from batch to batch, they are more commonly caused during fabrication. Distortion may also occur if steels of significantly different thicknesses are joined together in a fabrication. Only very rarely is it caused by handling in the galvanizing plant.
Basic design rules for avoiding distortion:
Maximise the uniformity of heat transfer into and out of the steel. Minimise the effect of stresses while the article is in the molten zinc. Use symmetrically rolled sections in preference to angle or channel frames. I-beams are preferred to angles or channels. Ensure assembly and welding techniques minimise stresses in components making up the article. Avoid designs that require double dipping. It is preferable to build assemblies and sub-assemblies in suitable modules allowing for quick immersion and galvanized in a single dip so the entire article can expand and contract uniformly. Ensure the structural design of the item is sufficient to support its own weight at 50% of the steel’s specified yield strength. Avoid using large areas of thin (under 8mm), unbraced flat plate. Use temporary bracing or reinforcing on thin-walled and asymmetrical designs. For more information, download our Advisory Note on Distortion and our Design Guide from our Technical Publications page.