Nickel-based Surfacing Process for Valve Sealing Surface Performance Enhancement

Literature Overview

The paper by Lin Lizong, Liu Yichong, Liu Xiaolei, and Zhang Xiaojin from East China University of Science and Technology, published in Welding in 2006 (Issue 4, pages 29-32), describes a nickel-based surfacing process for improving the sealing surface performance of rotating check valves. The work is classified under TG455 and addresses a specific industrial challenge in valve manufacturing where sealing surface integrity directly impacts valve reliability and service life.

Core Technical Content

Rotating check valves are critical components in fluid handling systems where reliable sealing is essential to prevent backflow and maintain system integrity. The sealing surface of these valves is subject to erosive wear, galling, and corrosion during operation, leading to premature failure. The study proposes a nickel-based alloy surfacing approach using gas metal arc welding (GMAW) with a specialized process design tailored to the three-dimensional curved geometry of the valve sealing surface.

Process Design and Equipment Development

The key innovation in this study is the development of a specialized welding process and corresponding equipment to accommodate the three-dimensional curved geometry of the rotating check valve sealing surface. The process involves:

1. Uniform deposition: Achieving consistent surfacing thickness across the curved sealing surface requires precise control of the welding torch trajectory, travel speed, and wire feed rate.
2. Specialized execution mechanism: A custom-designed execution mechanism and control system was developed to accurately follow the three-dimensional surface contour during the surfacing operation.
3. GMAW process parameters: The gas metal arc welding process was selected for its versatility, controllability, and compatibility with nickel-based alloy wires.

Performance Objectives and Results

The nickel-based alloy overlay provides superior wear resistance, corrosion resistance, and galling resistance compared to the base valve material. The uniform deposition across the curved surface ensures consistent sealing performance throughout the valve's operating cycle.

Engineering Practice Integration

The application of nickel-based surfacing to valve sealing surfaces offers several practical advantages:

1. Remanufacturing capability: Worn valve sealing surfaces can be restored through surfacing rather than requiring complete valve replacement, reducing maintenance costs and downtime.
2. Performance enhancement: New valve manufacturing can incorporate nickel-based surfacing as a standard feature to extend service life and improve sealing reliability.
3. Process automation potential: The specialized execution mechanism and control system developed in this study demonstrate the feasibility of automated surfacing for complex geometries, which can improve consistency and reduce operator dependency.
4. Material selection: The selection of nickel-based alloys for valve sealing surface surfacing is well-established in industry, with alloys such as Stellite 6, Inconel 625, and various nickel-chromium-iron compositions offering excellent combinations of hardness, corrosion resistance, and thermal stability.

Key Questions and Reflections

The paper raises an important question about the long-term durability of the nickel-based surfacing layer under cyclic loading conditions. Valve sealing surfaces experience repeated contact and separation during valve opening and closing cycles, creating cyclic stress and potential fatigue initiation sites at the weld interface. The fatigue resistance of the surfacing layer and its bond to the substrate should be evaluated through cyclic loading tests to ensure long-term reliability.

Another practical consideration is the interaction between the nickel-based surfacing layer and the valve seat material during sealing. If the valve seat is made of a different material (such as carbon steel or stainless steel), the tribological compatibility between the surfacing layer and the seat material must be verified to prevent galling, adhesion, or accelerated wear of either surface.

Study Insights and Implications

This paper demonstrates that nickel-based GMAW surfacing, when combined with a purpose-designed execution mechanism and control system, can effectively address the challenging three-dimensional geometry of rotating check valve sealing surfaces. The approach offers a practical solution for both new valve manufacturing and valve remanufacturing applications. For valve manufacturers and maintenance engineers, the study highlights the importance of process-equipment integration when surfacing complex geometries, and underscores the value of nickel-based alloys as a versatile surfacing material for sealing surface applications. The specialized control system developed in this study represents a meaningful engineering contribution to the automation of surfacing processes for non-planar surfaces, with potential applicability to other valve types and similar curved-surface applications in the process industry.