Surfacing of Wear-Resistant Material on Equipment Flange RJ Sealing Surfaces

Literature Overview

The paper by Wei Xianyong and Liu Haifeng, published in China Chemical Equipment (Vol. 25, No. 3, 2023), presents a comprehensive investigation into the surfacing of wear-resistant material (D547Mo) on equipment flange RJ (Raised Ring Joint) sealing surfaces. This work is particularly relevant to the chemical and petrochemical industries, where flange connections are critical pressure boundaries and where the sealing surfaces are subject to erosion, galling, and corrosion during assembly, disassembly, and operation. The study follows a systematic approach encompassing welding procedure qualification, intermetallic bonding verification, crack analysis, and post-weld quality assurance.

Core Technical Content

Application Context and Challenges

Equipment flange RJ sealing surfaces serve as the primary pressure boundary in bolted flange connections. The raised ring joint design concentrates the gasket loading on a small contact area, creating high bearing stresses that can cause:

• Galling and scoring during assembly and disassembly
• Erosion from high-velocity fluid flow at the gasket interface
• Crevice corrosion at the sealing surface
• Cold flow and relaxation of the raised ring under sustained pressure

The application of a wear-resistant surfacing layer to the RJ surface addresses these challenges by providing a hard, erosion-resistant surface that maintains sealing integrity over extended service periods.

Welding Procedure Qualification

The authors conducted a rigorous welding procedure qualification (WPQ) following the methodology outlined in relevant standards. The qualification process included:

• Selection of base material: typical low-alloy high-strength steel commonly used for equipment flanges
• Selection of surfacing material: D547Mo, a hardfacing alloy designed for wear resistance
• Determination of preheat temperature based on carbon equivalent and plate thickness
• Control of interpass temperature to prevent excessive thermal cycling
• Post-weld heat treatment (PWHT) to relieve residual stresses and stabilize the microstructure
• Non-destructive testing (NDT) to verify weld quality
• Mechanical and metallographic testing to confirm property requirements

Crack Analysis and Prevention

A significant portion of the paper addresses the analysis of cracks observed during the actual welding process. Cracking in hardfacing deposits is a well-known challenge due to:

• High residual stresses from differential thermal expansion between the hardfacing alloy and the steel substrate
• Brittle microstructure of the deposited metal (high hardness correlates with low toughness)
• Hydrogen-induced cracking in susceptible microstructures
• Thermal cracking due to low-ductility phases in the solidification structure

The authors identified that strict control of preheat temperature, interpass temperature, and PWHT parameters was essential to prevent cracking. The transition zone between the stainless steel base layer and the wear-resistant surfacing layer was also a critical area for potential cracking, requiring careful attention to the welding sequence and thermal cycle.

Multi-Layer Surfacing Strategy

The paper describes a multi-layer approach for the RJ surface surfacing:

1. A stainless steel transition layer is first deposited to provide a metallurgically compatible interface between the low-alloy steel substrate and the hardfacing alloy.
2. The D547Mo wear-resistant material is then applied in subsequent passes to build up the required surface hardness and thickness.
3. Post-weld machining is performed to achieve the precise surface geometry required for the RJ sealing surface.

This approach addresses the fundamental challenge of applying a high-hardness, low-ductility alloy to a ductile steel substrate. The stainless steel transition layer accommodates the thermal expansion mismatch and provides a tough, crack-resistant buffer zone.

Quality Assurance and Verification

The quality assurance program included:

• Visual inspection of the surfacing bead for porosity, undercut, and profile irregularities
• Magnetic particle testing (MT) for surface and near-surface defects
• Ultrasonic testing (UT) for subsurface defects and bond quality
• Hardness testing to verify the achieved surface hardness
• Metallographic examination of the transition zone for cracks and intermetallic phases
• Dimensional verification after machining to confirm compliance with RJ surface specifications

The results confirmed that the surfacing process produced layers with good quality, and all indicators met the design requirements.

Key Questions and Reflections

The paper raises an important question about the long-term performance of the D547Mo surfacing layer under cyclic loading and thermal cycling conditions. While the initial quality is confirmed through NDT and mechanical testing, the durability of the coating under repeated flange make-up and break-up cycles is critical for equipment integrity. Engineers should consider incorporating fatigue testing and cyclic loading tests in the qualification program.

Another consideration is the interaction between the surfacing layer and the gasket material. The hardness and surface finish of the D547Mo layer must be compatible with the gasket material to ensure proper sealing. Excessive hardness may damage soft gasket materials, while an overly rough surface may prevent intimate contact.

The paper also highlights the importance of the stainless steel transition layer in preventing cracking at the interface. This is a critical insight for engineers designing multi-layer surfacing procedures for dissimilar material combinations. The selection of the transition layer composition and thickness should be based on the specific thermal expansion coefficients and mechanical properties of the substrate and surfacing materials.

Study Insights and Reference Value

This paper provides a valuable case study for the application of hardfacing technology to critical pressure boundary components. The systematic approach to welding procedure qualification, crack analysis, and quality assurance demonstrates best practices in industrial surfacing operations.

The work has significant reference value for engineers in the chemical and petrochemical industries who face challenges with flange sealing surface degradation. It demonstrates that hardfacing is a viable and effective solution for enhancing the durability of RJ sealing surfaces, provided that the welding procedure is carefully designed and rigorously qualified.

The emphasis on transition layer design and thermal cycle control is particularly noteworthy. These elements are often overlooked in practice but are critical for achieving reliable, long-lasting surfacing deposits. The paper serves as a practical guide for engineers seeking to implement similar surfacing solutions on their own equipment.