CLADDING TECHNOLOGY SHANXI CO., LTDDeformation Simulation and Control of Large Diameter Tube Sheet Cladding
Literature Overview
This paper by Du Jintao, Pan Xiujian, Wang Ziwei, and Zhang Jianxiao from Lanzhou Lanchi Heavy Equipment Co., Ltd. and the Gansu Provincial Key Laboratory for Special Materials Welding in Pressure Vessels addresses one of the most persistent engineering challenges in pressure vessel fabrication: controlling angular and bow deformation during weld overlay cladding of large-diameter tube sheets. Published in the journal "Petrochemical Equipment" in 2016, the work targets the specific problem encountered in hydrogenation reactor and heat exchanger manufacturing where tube sheets with diameters exceeding 1000 mm are clad with stainless steel or nickel-based alloy layers.
Core Technical Problem
Large tube sheets present a unique deformation challenge because the cladding weld passes generate extremely high residual stresses that accumulate asymmetrically across the plate thickness and diameter. The cladding layer, typically composed of austenitic stainless steel such as 304, 316L, or nickel-based alloys like Inconel 625, has a coefficient of thermal expansion significantly different from the base carbon or low-alloy steel substrate. This mismatch causes the cladding side to contract more rapidly during cooling, producing angular distortion and potential bowing.
The paper applies finite element method (FEM) simulation to predict deformation patterns and proposes corrective strategies including pre-bending, back-heat treatment, and optimized welding sequence planning. The simulation approach models the thermal-mechanical coupling during multi-pass cladding, accounting for the transient temperature field and the resulting plastic deformation accumulation.
Deformation Mechanism Analysis
The primary deformation modes observed in large tube sheet cladding include:
- Angular distortion: The most common mode, caused by differential contraction between the cladding layer and the base metal, producing a wedge-shaped angular deviation.
- Bow deformation: Longitudinal curvature arising from non-uniform heat input distribution across the width of the tube sheet.
- Twist deformation: Asymmetric accumulation when the welding sequence is not properly balanced, particularly in multi-layer multi-pass operations.
- Diameter shrinkage: Circumferential contraction of the tube sheet outer diameter due to the cumulative effect of multiple cladding passes.
| Deformation Parameter | Typical Acceptable Limit | Common Exceedance Cause |
|---|---|---|
| Angular distortion | ≤ 1:100 of plate width | Excessive heat input per pass |
| Bow deformation | ≤ 1:1000 of length | Unbalanced welding sequence |
| Diameter change | ≤ 0.5% of nominal | Insufficient pre-heat, high cooling rate |
| Flatness | ≤ 1.5 mm/m | Inadequate back-heat treatment |
Control Strategies
The authors propose a multi-faceted control approach:
- Welding sequence optimization: Using a symmetric, balanced welding pattern that starts from the center and progresses outward in both directions, or employing a spiral pattern that minimizes cumulative asymmetry.
- Pre-bending compensation: Introducing a deliberate pre-bend in the opposite direction of expected distortion based on simulation predictions, typically 1.2 to 1.5 times the predicted angular deviation.
- Back-heat treatment: Applying controlled heating (typically 200–300 °C) to the non-clad side during welding to reduce the temperature gradient through the plate thickness.
- Heat input management: Limiting the linear energy input per pass to 15–25 kJ/mm for submerged arc welding (SAW) or 10–18 kJ/mm for gas metal arc welding (GMAW) to minimize thermal expansion differential.
- Multi-layer strategy: Distributing the total cladding thickness across multiple layers with intermediate stress relief steps to prevent excessive residual stress accumulation.
Engineering Practice Integration
In actual production at Lanzhou Lanchi Heavy Equipment, these simulation-based control strategies have been applied to hydrogenation reactor tube sheets with diameters ranging from 1200 mm to 2000 mm. The practical experience confirms that combining pre-bending with optimized welding sequence can reduce final angular distortion to within 0.3–0.5 mm/m, well within the acceptance criteria specified by GB/T 150 and NB/T 47002.
The key practical insight is that simulation alone is insufficient; the model parameters must be calibrated against actual production data from previous similar jobs. The thermal conductivity and yield strength values used in the simulation must reflect the actual material conditions, including the effect of pre-heat temperature on the base metal's mechanical response.
Reflections and Key Insights
The most valuable contribution of this work is the demonstration that numerical simulation can be effectively coupled with practical manufacturing experience to achieve predictable deformation control. The approach of using FEM to establish baseline predictions and then refining through iterative production feedback represents a mature engineering methodology. However, the paper could benefit from more detailed discussion of the interpass temperature control strategy and its quantitative effect on residual stress levels, which directly impacts the risk of hydrogen-induced cracking in the cladding layer. For engineers working on similar projects, the recommended approach is to always validate simulation predictions against actual post-weld measurement data before committing to full production runs.