technical case study
welding can be costly and technically difficult. Mechanical straightening may damage the surface, while thermal correction must be carefully controlled to avoid further distortion, metallurgical changes, residual stress or impaired corrosion performance. The strongest result is therefore achieved before the first arc is struck. By calculating the weld volume, predicting the likely direction of contraction and designing the welding sequence around that movement, fabricators can improve dimensional control, reduce rework and produce more consistent stainless steel assemblies. Stainless steel will always expand and contract beneath the welding arc. The fabricator’s advantage lies in knowing where that movement is likely to go, and planning the job so that the finished component ends up exactly where it should.
introduce bending as well as shortening. Similarly, a series of unbalanced welds on one side of a fabrication can create cumulative distortion even when the movement associated with each individual weld appears relatively small. Long seams should therefore be assessed as part of the complete structure rather than considered in isolation. Plan the weld before the metal moves The most effective distortion control begins before welding. The fabricator should confirm the joint type, plate thickness, groove angle, root gap, root face, welding process, heat input and anticipated number of passes before deciding how the assembly should be restrained and sequenced. Depending on the design and application, practical control measures can include: • Reducing unnecessary weld-metal volume • Using double-V joints on thicker sections where both sides are accessible • Presetting components opposite to the expected movement • Applying balanced or symmetrical welding sequences • Using back-step, skip or block welding techniques where appropriate • Alternating welds around the neutral axis • Controlling heat input and interpass temperature • Using correctly positioned tack welds and strongbacks • Welding smaller subassemblies before completing the main structure • Conducting a representative trial before repeat production The correct approach will vary from one fabrication to another. Thin sheet may be particularly vulnerable to buckling, while thick and highly restrained sections may retain significant residual stress even when visible distortion is limited. From calculation to workshop control Shrinkage calculations do not guarantee a final dimension. Their value lies in providing a rational starting point for the fabrication plan. Once the likely direction and scale of movement have been estimated, the fabricator can decide whether the joint requires a modified root opening, preset, alternative sequence, different fixturing arrangement or representative trial. Production results should also be recorded. Measuring the actual movement from the first completed fabrication creates valuable workshop data that can be used to refine allowances for subsequent units produced with the same material, joint configuration, welding procedure and restraint. This turns distortion control from a reactive correction process into an increasingly accurate production system. Correcting a distorted stainless steel assembly after
22
Issue 3 – 2026
Made with FlippingBook - professional solution for displaying marketing and sales documents online