It is NOT always possible to control distortion within acceptable limits, especially when dealing with a new type of fabrication for the first time, and in certain cases it is either more practical or more economic to allow distortion to occur and to correct it after welding.   Also, there are bound to be instances where intolerable distortion occurs in spite of the thought and planning put into the job before work is started.   In such circumstances, it is usually possible to rectify the distortion by one of the following methods, provided that the product has not shrunk so much that it will be too small to meet the dimensional requirements.

Parts of a fabrication, which have buckled or otherwise changed their shape, may be corrected by mechanical means or hammering.   Sometimes an entire fabrication, which has bowed can be straightened on a press; in this case packers must be inserted between the fabrication and the platens, Fig. 1.
Fig.1 Use of press to correct bowing
Flat fabrications that have become distorted may sometimes be corrected by clamping them to a heavy base plate or some other strong structure with a flat surface, and stress relieving the fabrication while it is clamped.   It is important to make sure that the base plate is strong enough to hold the fabrication flat.   For stress relieving low carbon steel the fabrication should be heated slowly to approximate 650ºC, and maintained at that temperature for a period of 1hr/25mm of thickness of the material.   It should then be allowed to cool, free from draughts (in furnace atmosphere at less than 300ºC).