CLADDING TECHNOLOGY SHANXI CO., LTDReduction of Residual Stress in Welded Joints by Internal Surface Overlay Welding of Nozzles
Literature Overview and Background
The paper "Research on Reduction of Residual Stress in Welded Joints by Internal Surface Overlay Welding of Nozzles" addresses a critical issue in pressure vessel fabrication: the management of residual stresses in nozzle-to-shell weld joints. Nozzle welds are among the most highly stressed regions in a pressure vessel, subjecting to combined effects of internal pressure, thermal cycling, mechanical loading, and residual stresses from fabrication. High residual stresses in these regions can significantly reduce the fatigue life of the vessel and increase the risk of stress corrosion cracking (SCC) and hydrogen-induced cracking (HIC), particularly in vessels operating under corrosive or hydrogen-containing environments.
This study investigates the use of internal surface overlay welding on nozzle weld joints as a method to reduce residual stresses and improve the fatigue performance of the welded assembly. The approach involves depositing a carefully designed overlay layer on the internal surface of the nozzle weld, which acts as a counter-stress layer that partially compensates for the tensile residual stresses generated during the original welding process.
Residual Stress Distribution in Nozzle Weld Joints
Residual stresses in nozzle weld joints are generated during the welding process due to the non-uniform heating and cooling of the material. The stress distribution is complex and three-dimensional, with the highest tensile stresses typically occurring at the weld toe and the root of the weld. The following table summarizes the typical residual stress distribution in a nozzle weld joint:
| Location | Residual Stress (MPa) | Stress Type | Remarks |
|---|---|---|---|
| Weld toe (external) | 200–350 | Tensile | Highest stress concentration |
| Weld toe (internal) | 150–280 | Tensile | Subject to overlay |
| Weld root | 100–200 | Tensile | Near penetration point |
| HAZ (base metal) | 50–150 | Tensile | Gradual decrease from weld |
| Base metal (far field) | 0–50 | Compressive or zero | Equilibrium region |
These residual stresses are superimposed on the operating stresses (pressure, thermal, and mechanical), and the combination can lead to premature fatigue failure or cracking, particularly in the weld toe region where the stress concentration is highest.
Principle of Internal Surface Overlay for Residual Stress Reduction
The principle behind using internal surface overlay welding to reduce residual stresses is based on the concept of counter-stress induction.