Spiral welding is a welding process in which a continuous, full-penetration metal inert gas (MIG) weld overlay is applied in a spiral pattern onto a cylindrical component. The process is used to rebuild damage caused by wear, erosion, corrosion, or cracking, or to increase the dimensions of a component to match a mating part.
Process
In spiral welding, the workpiece (typically a cylindrical object such as a shaft or pipe) is rotated on a rotary turntable while a welding torch deposits a continuous weld bead along the surface in a helical (spiral) pattern. The process is carried out in an inert argon gas atmosphere to prevent oxidation during welding. Each successive layer of weld and its associated heat-affected zone is tempered by subsequent overlapping passes, which refines the grain structure and reduces residual stresses.
Advantages
Spiral welding is a low-energy-input process that eliminates the possible distortion of the component caused by unbalanced stresses that can occur with conventional welding methods. It can be more cost-effective than manufacturing a new component and often results in faster turnaround times. Depending on the choice of overlay material, the repaired component can achieve higher strength or improved performance compared to the original.
Applications
Spiral welding is commonly used in remanufacturing and repair of industrial components, particularly pipework, manufacturing shafts, and other cylindrical parts. It is also used in the production of spiral welded pipe (also known as spiral seam pipe), where a steel strip is continuously wound into a spiral and the edges are welded together—typically using submerged arc welding (SAW)—to form a pipe. Spiral welded pipes are used in applications such as water distribution, structural piling, and oil and gas transport, and are available in diameters ranging from approximately 24 inches to 144 inches.
Materials
The overlay material can be selected to match the parent material or to provide enhanced resistance against corrosion, erosion, or wear. Considerations include the coefficient of thermal expansion, strength and ductility of the materials, and the potential for galvanic corrosion. Pre- and post-weld heat treatment is typically applied to control hydrogen cracking and to manage the transformation of the substrate microstructure.
