Multi-pass welding technique
Multi-pass technique is a welding process technique where multiple passes are stacked and welded to manage large wall thicknesses and improve grain refinement. Each new pass partially anneals the underlying one.
Physico-Chemical Mechanism of Action
Multi-pass technique uses the principle of layer formation and thermal cycles to create a stable and fine-structured weld. Each time a new layer is welded, the underlying metal surface partially tempers and rearranges, leading to a homogeneous structure.
Metallurgical Relevance & Welding Risks
This technique is especially useful for thick sections or materials with high stress buildup. Wrong application can, however, lead to structural irregularities and increased crack risk if layers are not properly overlaid.
Workshop Practice & Action Instructions
For successful multi-pass welding, follow these steps:
1. Material preparation: Make sure the parts to be welded are clean and free of dirt.
2. Layer formation: Overlap the layers, with each new layer slightly overlapping the previous one.
3. Welding: Use a suitable welding method (e.g. TIG welding) to weld each layer. Make sure temperature and time are correctly set for each welding cycle.
4. Cooling: Let the finished weld cool down slowly to ensure a homogeneous structure formation.