Deformation Prevention Measures for Large Diameter Overlay Welded Tube Plates

Literature Overview

This paper by Han Quanyong from Offshore Oil Engineering Co., Ltd. Huizhou Branch addresses the significant engineering challenge of controlling distortion during overlay welding of large diameter tube plates used in petrochemical heat exchange equipment. Published in Guangdong Chemical Engineering (Volume 43, Issue 12, 2016), the study focuses on a common but critical problem: the management of welding-induced deformation in large, thin-walled plate structures that require stainless steel overlay for corrosion protection.

Core Technical Challenge

Large diameter tube plates in petrochemical heat exchangers typically have diameters exceeding 1500 mm with thicknesses of 30–80 mm. The overlay welding of stainless steel on these plates introduces substantial thermal stresses that can cause significant distortion, including:

Warping: Out-of-plane deformation causing the plate to curve or twist.
Bowing: In-plane bending resulting in loss of flatness.
Local buckling: Compressive stresses in the overlay layer causing localized instability.
Dimensional drift: Overall dimensional changes affecting assembly and sealing.

The deformation is particularly problematic because tube plates must maintain precise flatness to ensure proper sealing at the tube-to-tube-plate joints and at the shell-to-tube-plate connection.

Root Cause Analysis of Deformation

The deformation mechanisms in large diameter overlay welded tube plates can be understood through the following analysis:

Deformation Type	Primary Cause	Contributing Factors	Severity
Warping	Asymmetric heat input from one-sided welding	Welding sequence; plate thickness; material thermal expansion mismatch	High
Bowing	Compressive stresses in overlay layer	Overlay thickness; base material yield strength;拘束 conditions	Moderate
Local buckling	High compressive stresses in thin overlay	Overlay thickness; interpass temperature;拘束 rigidity	Moderate
Dimensional drift	Cumulative thermal expansion and contraction	Total heat input;拘束 conditions; cooling rate	Low to Moderate

The fundamental cause of all deformation types is the thermal stress induced by the welding process. When stainless steel is deposited on a carbon steel base, the thermal expansion coefficient mismatch (stainless steel: ~17.3 × 10⁻⁶/°C vs. carbon steel: ~12.2 × 10⁻⁶/°C) creates additional stresses during cooling.

Deformation Prevention Measures

The paper proposes several deformation control strategies that can be categorized as follows:

Pre-Welding Measures

Mechanical restraint: Use of heavy backing plates, clamping fixtures, or temporary stiffening ribs to restrict plate movement during welding.
Pre-heating: Uniform pre-heating of the entire plate to 100–150°C to reduce the thermal gradient and minimize differential expansion.
Symmetric design: Designing the welding sequence to ensure symmetric heat input distribution around the plate diameter.

During Welding Measures

Symmetric welding sequence: Welding in a balanced pattern—typically starting from the center and working outward in concentric rings, or using a back-and-forth pattern from opposite edges.
Reduced heat input: Using lower welding currents and higher travel speeds to minimize the heat-affected zone and reduce thermal distortion.
Multi-pass thin layers: Depositing multiple thin layers rather than fewer thick layers to reduce peak temperatures and thermal gradients.
Interpass temperature control: Maintaining interpass temperatures below 150°C to prevent excessive cumulative heat input.

Post-Welding Measures

Mechanical straightening: Cold straightening or hot straightening to correct residual deformation within acceptable limits.
Stress relief annealing: Heat treatment at 550–650°C for 2–4 hours to reduce residual stresses and improve dimensional stability.
Vibration stress relief: Application of controlled vibration to reduce residual stresses without thermal treatment.

Process Parameter Optimization

The following table summarizes the recommended welding parameters for large diameter tube plate overlay welding:

Parameter	Recommended Range	Rationale
Welding current	180–250 A (SMAW); 250–350 A (FCAW)	Reduced heat input to minimize distortion
Travel speed	150–250 mm/min	Higher speed reduces heat input per unit length
Layer thickness	2–3 mm per pass	Thin layers reduce peak temperature and thermal gradient
Interpass temperature	< 150°C	Prevents excessive cumulative heat input
Pre-heat temperature	100–150°C	Reduces thermal gradient and cracking susceptibility
Post-weld stress relief	550–650°C for 2–4 hours	Reduces residual stresses and improves dimensional stability

Engineering Practice Implications

For offshore and petrochemical applications, the deformation control of overlay welded tube plates is particularly critical because:

Tube plates are often large and thin, making them susceptible to buckling and warping.
The overlay welding is typically performed on one side only, creating asymmetric thermal stresses.
The service environment involves cyclic thermal loading, which can exacerbate any initial deformation.
Assembly tolerances are tight, requiring precise dimensional control.

The paper's emphasis on a comprehensive approach—combining pre-welding, during-welding, and post-welding measures—reflects the practical reality that no single measure is sufficient to control deformation in large diameter tube plates.

Key Questions and Reflections

Several important questions arise from this study:

How does the deformation behavior change with increasing plate diameter and decreasing thickness ratio?
What is the optimal welding sequence for circular plates versus rectangular plates?
How does the choice of overlay material (304 vs. 316 vs. duplex) affect the deformation tendency?
Can advanced welding technologies such as laser cladding or friction stir welding reduce deformation compared to conventional arc welding?

The systematic approach to deformation control presented in this paper is directly applicable to many other large plate overlay welding applications in the petrochemical and offshore industries.

Summary and Study Insights

This paper provides a practical and comprehensive framework for deformation control in large diameter overlay welded tube plates. The emphasis on a multi-faceted approach—combining mechanical restraint, symmetric welding sequences, reduced heat input, and post-weld stress relief—reflects the practical engineering reality that deformation control requires a holistic strategy. For engineers working on similar projects, the key takeaway is that deformation prevention must be planned from the design stage through to post-weld inspection, and that no single measure is sufficient to achieve acceptable dimensional control. The systematic approach presented here can serve as a template for developing deformation control procedures for other large plate overlay welding applications.