Nickel-Based Overlay Welding Process for Valve Body Sealing Surfaces

Literature Overview

This paper by Lin Lizong, Liu Yichong, Liu Xiaolei, and Zhang Xiaojin from East China University of Science and Technology (2006, Welding, No. 4, pp. 29-32) presents a specialized nickel-based overlay welding process developed for improving the sealing surface performance of rotary check valves. The work addresses a specific engineering challenge: achieving uniform, high-quality nickel-based alloy deposition on three-dimensional curved sealing surfaces where conventional welding techniques struggle to produce consistent results.

Engineering Problem Statement

Rotary check valves in pipeline systems are critical safety components that prevent backflow in pumping stations, compressor stations, and process piping systems. The sealing surface of these valves is subjected to:

• Repeated impact loading during valve closure events
• Erosion from high-velocity fluid flow containing suspended particles
• Corrosive attack from process fluids
• Temperature cycling between process and ambient conditions

Conventional valve body materials (typically carbon steel or low-alloy steel per ASTM A216 WCB/WCC) offer insufficient surface hardness, corrosion resistance, and erosion resistance for the sealing surface under these combined degradation mechanisms. Overlay welding a nickel-based alloy onto the sealing surface provides a cost-effective solution that extends valve life without requiring complete valve replacement.

Process Design and Innovation

The authors developed a specialized process using Gas Metal Arc Welding (GMAW) with nickel-based alloy wire to deposit a uniform wear-resistant layer on the valve sealing surface. The key innovation lies in the process design adapted to the three-dimensional curved geometry of the sealing surface.

Three-Dimensional Surface Adaptation Strategy

The primary technical challenge is maintaining consistent bead profile and penetration on a rotating three-dimensional sealing surface. The authors addressed this through:

1. Specialized welding torch positioning: The torch holder was designed to maintain constant distance and angle from the curved surface throughout the rotation cycle.
2. Custom execution mechanism: A mechanical fixture synchronized with the valve body rotation ensured uniform deposition rate around the circumference.
3. Controlled system integration: The welding parameters were linked to the rotational position, enabling compensation for geometric variations.
4. Multi-pass strategy: Multiple thin passes were used to achieve the required overlay thickness while maintaining low dilution and minimal residual stress.

Quality Control Considerations

For valve sealing surfaces, the quality requirements are extremely stringent:

• Surface finish: Typically Ra 0.8-1.6 μm required for proper sealing against valve seats
• Flatness: Deviation from design geometry must not exceed 0.05-0.1 mm
• Overlay thickness: Typically 3-6 mm for sealing surfaces
• Dilution control: Must be minimized to preserve nickel alloy properties at the surface
• Crack freedom: Zero tolerance for longitudinal or transverse cracking
• Porosity: Must not exceed ASME Section IX qualification limits

Nickel-Based Alloy Selection

The nickel-based alloy selected for this application typically contains:

• Nickel balance (70-75%)
• Chromium 15-20%
• Molybdenum 5-8%
• Iron balance

This composition provides:

• Excellent corrosion resistance in acidic and chloride-containing environments
• High hardness (HRC 35-45) for erosion resistance
• Good thermal shock resistance
• Low thermal conductivity reducing heat input to base metal
• Compatibility with carbon steel base metals

Engineering Practice Integration

This work is particularly relevant to engineers in the following industries:

• Oil and gas: Rotary check valves in pipeline systems handling sour crude or natural gas
• Pulp and paper: Valve sealing surfaces exposed to corrosive pulping chemicals
• Chemical processing: Valve components in aggressive chemical service
• Power generation: Steam and condensate system valves

The process development approach described in this paper follows a systematic methodology that can be adapted to other valve types and sealing surface geometries. The key principle is that the welding process must be tailored to the specific geometry rather than attempting to apply standard welding procedures to non-standard configurations.

Key Questions and Reflections

While the paper demonstrates successful implementation of the process, several aspects merit further discussion. The long-term durability of the overlay under repeated valve actuation cycles is critical but not extensively addressed. Each valve closure event represents an impact loading event, and thousands of cycles may occur during valve service life. Fatigue cracking at the overlay-base metal interface under cyclic loading is a potential concern that requires systematic evaluation.

Additionally, the paper does not provide detailed information on the post-weld machining requirements. For sealing surfaces, the overlay is typically machined after deposition to achieve final dimensional accuracy and surface finish. The machinability of the nickel-based overlay and its effect on residual stress relief through machining should be considered in the overall process design.

Study Conclusions

This paper demonstrates a practical and effective approach to overlay welding nickel-based alloys onto complex three-dimensional valve sealing surfaces. The combination of specialized equipment design, controlled GMAW parameters, and multi-pass deposition strategy achieves the required quality standards for critical sealing applications. The methodology is particularly valuable for valve maintenance and repair operations where overlay welding can extend component life by 3-5 times compared to bare steel sealing surfaces. Engineers responsible for valve maintenance specifications should consider this approach as a cost-effective alternative to complete component replacement.