Measurement of Thinning Elongation and Overlay Welding Shrinkage in Hot-Wall Hydrogenation Reactor Shell Rolling

Literature Overview

The paper by Fei Yuetao and Yu Yifeng, published in 1990 in the journal Petrochemical Equipment, addresses a critical manufacturing challenge encountered during the fabrication of hot-wall hydrogenation reactor shells. These large-diameter pressure vessels, typically constructed from thick carbon steel or low-alloy steel plates, undergo hot rolling and straightening operations during shell forming, followed by overlay welding of corrosion-resistant alloy cladding layers. The authors present a systematic methodology for measuring and calculating the wall thinning and circumferential elongation that occur during medium-temperature rolling, and further demonstrate that the overlay welding shrinkage can be effectively compensated by the elongation produced during the rolling process.

Core Technical Points

Thinning and Elongation During Medium-Temperature Rolling

During the hot rolling of thick steel plates into cylindrical shells, the material experiences significant plastic deformation. The inner surface of the shell is compressed and elongated, while the outer surface is stretched and thinned. The degree of thinning depends on the plate thickness, the rolling radius, the number of rolling passes, and the temperature at which rolling is performed. For typical hot-wall hydrogenation reactor shells with wall thicknesses ranging from 80 mm to 200 mm and diameters exceeding 3000 mm, the thinning can reach 2% to 5% of the original wall thickness.

Overlay Welding Shrinkage Compensation

The overlay welding process, typically performed using submerged arc welding (SAW) with corrosion-resistant alloy consumables such as 309L/316L or duplex steel fillers, introduces significant shrinkage in the weld deposit. This shrinkage reduces the effective wall thickness on the overlay side. The authors' key finding is that the circumferential elongation produced during rolling approximately equals the shrinkage produced during overlay welding, thereby achieving a natural compensation effect. This means that the net wall thickness change from both processes can be minimized when the rolling parameters are properly selected.

Calculation Methodology

The authors propose a calculation framework based on plastic deformation theory and thermal contraction analysis:

1. The thinning amount is calculated using the volume constancy principle during plastic deformation, relating the circumferential strain to the radial thinning through the relationship ε_t = -ε_r (assuming ε_θ is the dominant strain component).
2. The elongation amount is derived from the difference between the arc length of the rolled shell and the original plate length.
3. The overlay welding shrinkage is estimated from the thermal contraction coefficient of the weld metal and the heat input per unit length.

Standards and Engineering Practice Context

Hot-wall hydrogenation reactors are governed by standards such as GB/T 150, TSG 21, ASME Section VIII Division 1, and specific petrochemical industry standards. The shell forming process must ensure that the final wall thickness after all manufacturing steps—including rolling, overlay welding, and post-weld heat treatment—meets the minimum required thickness specified by design calculations. The compensation principle described in this paper is particularly relevant when the design margin is tight, as is common in high-pressure hydrogen service where wall thickness directly impacts structural integrity.

In engineering practice, the following considerations are essential:

• The rolling temperature must be controlled to avoid excessive grain growth or phase transformation in low-alloy steels such as 15CrMo or 20MnMo.
• The overlay welding procedure must be qualified under applicable codes (ASME Section IX or NB/T 47014) to ensure weld quality.
• Post-weld heat treatment (PWHT) temperatures and holding times must be coordinated with the overlay alloy to prevent sensitization or softening.

Key Reflections and Implications

This paper, though published in 1990, presents a practical engineering insight that remains highly relevant today. The concept of using rolling elongation to compensate for overlay welding shrinkage is an elegant solution to a persistent manufacturing challenge. In modern practice, this principle is often implemented through finite element simulation during the process planning stage, allowing engineers to predict the final wall thickness with greater accuracy. However, the fundamental physical understanding presented by Fei and Yu remains the foundation upon which these simulations are built.

One area for further investigation is the interaction between the residual stresses introduced during rolling and those generated during overlay welding. While the paper focuses on dimensional changes, the stress state of the shell after both processes can significantly affect the long-term performance of the reactor under cyclic thermal and pressure loading. Understanding this interaction could lead to improved process windows that simultaneously control dimensions and residual stress levels.

The practical value of this work lies in its simplicity and direct applicability. Engineers involved in the fabrication of large pressure vessels should incorporate this compensation principle into their process planning, particularly when working with thick-wall components where dimensional tolerances are critical. By carefully selecting rolling parameters to produce a target elongation that matches the expected overlay welding shrinkage, manufacturers can achieve tighter dimensional control and reduce the need for additional machining or rework operations.