Study Note on Shaped Cladding Technology in Pressure Vessel Manufacturing

Literature Overview

This study examines the application of shaped cladding (form cladding) technology in pressure vessel manufacturing, where weld overlay is applied directly to formed (curved) components rather than flat plates. Shaped cladding is a critical technology in the fabrication of pressure vessels for the chemical, petrochemical, and nuclear industries, where corrosion-resistant overlay layers must be applied to curved geometries such as dished heads, cylindrical shells, and nozzles. The challenge lies in maintaining consistent cladding quality, bond strength, and mechanical properties on curved surfaces where welding parameters, heat input distribution, and residual stress patterns differ significantly from flat-plate cladding.

Core Technical Approach

Shaped cladding involves the application of a corrosion-resistant overlay layer to a formed pressure vessel component, typically after the component has been shaped (rolled, formed, or forged) but before final assembly and welding. The cladding can be applied using various welding processes, including submerged arc welding (SAW), gas metal arc welding (GMAW), plasma arc welding (PAW), or laser cladding, depending on the component geometry, cladding thickness, and production requirements.

Shaped Cladding Process Parameters

Cladding on Curved Surfaces: Geometric Considerations

The curvature of shaped components introduces several challenges compared to flat-plate cladding:

1. Heat input distribution: On a convex surface (outside of a cylinder or dished head), the heat input per unit length is concentrated on the outer surface, potentially causing excessive dilution and distortion. On a concave surface (inside of a cylinder), the heat input is distributed over a larger area, which may require higher heat input to achieve complete fusion.
2. Welding position: Shaped cladding may involve welding in various positions, including flat, horizontal, vertical, and overhead, depending on the component orientation and the welding equipment available.
3. Distortion control: Curved components are more susceptible to distortion during welding than flat plates, particularly thin-walled components with large radii. Welding sequence and clamping strategy are critical to minimize distortion.
4. Gas shielding: For GMAW and PAW cladding on curved surfaces, maintaining consistent gas shielding can be challenging, particularly on vertical and overhead surfaces where gas flow patterns are affected by gravity and buoyancy.

Standards and Code Requirements

Shaped cladding of pressure vessels is governed by several national and international codes and standards, which specify the requirements for materials, welding procedures, inspection, and testing.