CLADDING TECHNOLOGY SHANXI CO., LTDSimulation of Welding Deformation in Central Overlay Welds Under Different Constraints
Literature Overview
This study published in 2009 by researchers from the School of Materials Science and Engineering at Hefei University of Technology investigates the welding deformation behavior of central overlay welds on test plates subjected to various constraint conditions. The work appears in the journal "Hot Working Technology" and addresses a fundamental problem encountered in the fabrication of clad-plate pressure vessels and bimetallic components: the prediction and control of residual deformation during weld overlay processes.
Core Technical Content
The central challenge addressed is the geometric distortion that occurs when a weld overlay is deposited onto a flat test plate, particularly when the overlay is applied at the center of the plate. Welding deformation is governed by the thermal gradients, material properties, restraint conditions, and welding sequence. The researchers employed finite element simulation methods to model the thermomechanical behavior of the overlay weld under different constraint scenarios.
Constraint Conditions Analyzed
| Constraint Type | Description | Deformation Characteristic |
|---|---|---|
| Free (unconstrained) | Plate is fully free to deform | Maximum angular distortion and warping |
| Partially restrained | Edges fixed, center free | Intermediate distortion with local buckling |
| Fully restrained | All edges rigidly clamped | Compressive residual stresses, potential cracking |
| Symmetric multi-pass | Sequential symmetric passes | Reduced net distortion through self-compensation |
Key Technical Parameters
The simulation typically considers the following critical parameters:
- Heat input range: 15–45 kJ/cm depending on process (SAW overlay typically 25–40 kJ/cm)
- Plate thickness: 10–50 mm for clad plate applications
- Overlay thickness: 3–15 mm depending on corrosion resistance requirements
- Base material: carbon steel (Q345R / 16MnR equivalent)
- Overlay material: austenitic stainless steel (304/316L equivalent) or nickel-based alloy
Engineering Practice Integration
In pressure vessel fabrication per GB/T 150 and NB/T 47002, welding deformation directly impacts dimensional accuracy, fit-up tolerance, and the feasibility of subsequent machining operations. For clad-plate vessels where the overlay layer serves as the corrosion-resistant lining, angular distortion can cause:
- Excessive out-of-flatness requiring costly flame straightening or mechanical correction
- Tensile stresses in the overlay layer that compromise corrosion resistance
- Cracking in the overlay layer due to high restraint stresses when deformation is fully suppressed
- Non-conformance with ASME VIII Div.1 dimensional tolerances
Practical Countermeasures Derived from Simulation
The simulation results inform several practical strategies:
- Multi-pass symmetric welding: Depositing overlay layers in a symmetric sequence around the centerline allows thermal stresses to partially self-cancel, reducing net angular distortion by 40–60% compared to single-direction welding.
- Controlled backing: Using compressible backing bars instead of rigid fixtures allows some plastic deformation while maintaining root geometry.
- Pre-bending compensation: Pre-setting the plate with a controlled camber opposite to the predicted deformation direction can achieve near-zero final distortion.
- Intermittent restraint: Applying moderate restraint at mid-span rather than at edges distributes stress more uniformly and avoids localized cracking.
Key Reflections
The most valuable insight from this study is the quantitative relationship between restraint level and both deformation and residual stress. In engineering practice, there is a fundamental trade-off: high restraint minimizes visible deformation but maximizes residual stress, which can lead to overlay cracking, hydrogen-induced cracking in susceptible base metals, and premature fatigue failure. The optimal design point typically lies in the partially restrained regime where deformation is acceptable for subsequent machining while residual stresses remain below the threshold for cracking.
For hydrogenation reactors and high-pressure vessels where overlay thicknesses of 10–20 mm are common, the cumulative deformation from multiple overlay layers compounds significantly. The simulation approach provides a rational basis for sequencing overlay passes, selecting appropriate welding procedures, and setting post-weld machining allowances. This work reinforces the principle that welding deformation is not merely a fabrication nuisance but a design parameter that must be addressed in the welding procedure specification (WPS) development phase.