Dynamic Simulation of Stress Field in Weld Overlay Process Based on ANSYS

Literature Overview

This study employs finite element analysis using ANSYS to model the thermal-mechanical coupled behavior during multi-pass weld overlay cladding processes. The research focuses on predicting residual stress distribution, deformation patterns, and crack susceptibility in thick weld overlay builds used for corrosion-resistant and wear-resistant surface treatments on pressure vessels, heat exchangers, and large structural components. The work bridges the gap between theoretical welding metallurgy and practical process optimization by providing quantitative predictions that guide welding sequence design and preheat strategies.

Core Technical Methodology

The simulation adopts a sequential coupled approach where the thermal analysis is solved first, followed by the mechanical analysis using the computed temperature field as a body load. The heat source is modeled as a moving double-ellipsoidal Goldak heat source that captures the asymmetric heat distribution characteristic of arc welding processes.

The material properties are defined as temperature-dependent functions covering the full range from room temperature to above the solidus temperature. Phase transformation effects are incorporated through the Koistinen-Marburger equation for martensitic transformation and the JMA equation for austenite decomposition.

Key Simulation Results

Residual Stress Distribution

The simulation reveals that peak longitudinal residual stresses reach 350-480 MPa in the weld metal and heat-affected zone of carbon steel and low-alloy steel substrates, while transverse stresses are typically 20-40% lower. The stress field shows a characteristic pattern: compressive stresses exist in the region ahead of the weld, while tensile stresses develop in the trailing region.

Deformation Patterns

For multi-pass overlay builds on thick plates (20-50 mm), the simulation predicts total weld-induced deformation of 2-5 mm per 100 mm length, with angular distortion being the dominant mode. The first pass causes the largest incremental deformation, while subsequent passes produce diminishing returns due to the thermal history of previously deposited layers.

Effect of Welding Sequence

The study compares several welding sequences including sequential, symmetric, and skip-welding patterns. The symmetric welding sequence from the center outward reduces angular distortion by 40-60% compared to sequential welding from one edge. The skip-welding pattern, where every other weld is deposited first, further reduces distortion by an additional 15-25%.

Process Optimization Based on Simulation Results

Preheat Temperature Effects

The simulation demonstrates that preheating the substrate from 20 degrees Celsius to 200 degrees Celsius reduces peak residual stresses by approximately 80-120 MPa. This is attributed to the reduction in thermal gradient and the onset of stress relief during welding. However, excessive preheating above 350 degrees Celsius can promote grain coarsening in the HAZ, which is detrimental to toughness.

Interpass Temperature Control

Maintaining interpass temperatures between 100-250 degrees Celsius for low-alloy steels is critical. The simulation shows that interpass temperatures above 300 degrees Celsius result in a 20-30% increase in residual stress due to the accumulation of thermal strain without adequate stress relief.

Welding Speed and Heat Input

Higher welding speeds reduce heat input and consequently reduce residual stresses, but excessively high speeds may lead to inadequate fusion and increased porosity. The optimal welding speed for overlay applications is typically in the range of 200-400 mm/min for SAW processes and 50-150 mm/min for GMAW processes.

Integration with Engineering Practice

In the fabrication of clad-plate pressure vessels and hydrogenation reactors, the residual stress levels predicted by simulation directly inform the requirement for post-weld heat treatment (PWHT). For example, if the simulation predicts residual stresses exceeding 200 MPa in the overlay layer of a vessel operating at elevated temperatures, PWHT becomes mandatory to prevent stress corrosion cracking and fatigue failure. The simulation also guides the design of welding sequences for large overlay areas, such as the interior cladding of a 6-meter diameter reactor shell, where the welding sequence can be optimized to minimize distortion that would otherwise compromise dimensional accuracy.

Case Study: Hydrogenation Reactor Shell Overlay

A hydrogenation reactor shell with a 25 mm carbon steel base plate and a 6 mm 316L stainless steel overlay was analyzed using the simulation methodology. The predicted residual stresses in the overlay layer reached 420 MPa without PWHT, which exceeded the threshold for stress corrosion cracking in the presence of hydrogen. After optimizing the welding sequence and applying PWHT at 620 degrees Celsius for 4 hours, the residual stresses were reduced to below 150 MPa, well within acceptable limits per GB/T 150.

Key Reflections

The study demonstrates that finite element simulation is an indispensable tool for weld overlay process design, particularly for large and complex components where trial-and-error approaches are prohibitively expensive. However, the accuracy of simulation results depends critically on the quality of material property data, heat source characterization, and boundary condition assumptions. Engineers must validate simulation predictions against experimental measurements such as neutron diffraction or hole-drilling residual stress measurements before relying on them for critical applications. The simulation should be viewed as a decision-support tool rather than a definitive predictor, and its outputs should be integrated with weld procedure qualification results to ensure comprehensive process control.