Zhuojin Pipe Fitting Co., LtdOverlay Welding Technology for Ring Joint Face Sealing Surfaces
Literature Overview
This paper by Yang Meikun from Xi'an Nuclear Equipment Co., Ltd., published in China Chemical Equipment (2020, Vol. 22, No. 1, pp. 45-48), provides a detailed technical discussion of the overlay welding process for ring joint face (RJ) sealing surfaces. The work covers the manufacturing process, applicable scopes, manufacturing specifications, technical requirements, and process qualification procedures for RJ face overlay welding in chemical equipment manufacturing.
Technical Background
Ring joint faces are a critical sealing component in high-pressure, high-temperature chemical and nuclear equipment. The RJ face is typically overlay welded onto carbon steel or low-alloy steel flanges or tube sheets, creating a hard, corrosion-resistant sealing surface. The overlay material is usually a stainless steel such as 309L, 310L, or a nickel-based alloy such as Inconel 625, selected based on the service environment.
The RJ face overlay welding process is governed by several standards including:
| Standard | Scope |
|---|---|
| ASME B31.3 | Process piping, including overlay requirements |
| ASME B16.5 | Pipe flanges and flanged fittings |
| NB/T 20305 | Nuclear power plant piping components |
| SY/T 0410 | Steel flanges for petrochemical industry |
| GB/T 150 | Pressure vessel design and manufacturing |
Process Procedure
The paper describes a comprehensive process flow for RJ face overlay welding:
Pre-Welding Machining
The base metal surface must be machined to remove scale, rust, and surface contaminants. The surface roughness should be controlled to Ra 3.2-6.3 μm to ensure adequate weld metal bonding. A groove may be machined around the perimeter to contain the weld metal and prevent spillover.
Transition Layer Welding
A transition layer is typically deposited using a compatible filler metal such as ER309L or ERNiCrMo-3. This layer serves to:
- Reduce dilution of the final overlay layer by the base metal
- Provide a metallurgically compatible interface between the base metal and the overlay material
- Control the carbon content at the interface to prevent sensitization
Overlay Layer Welding
The final overlay layer is deposited using the specified alloy material. Multiple passes may be required to achieve the required thickness, typically 3-6 mm. Each pass should have adequate overlap (at least 50% of the previous pass width) to ensure complete coverage and uniform composition.
Post-Welding Machining
After overlay welding, the surface is machined to the final dimensional specifications. The machining allowance should be sufficient to remove the surface irregularities while preserving the required minimum thickness.
Non-Destructive Testing
The overlay weld is inspected using appropriate NDE methods:
- Magnetic particle testing (MT) or liquid penetrant testing (PT) for surface defect detection
- Ultrasonic testing (UT) for subsurface defect detection
- Visual inspection for surface quality assessment
Key Process Parameters
| Parameter | Specification | Rationale |
|---|---|---|
| Pre-heat temperature | 100-150°C (for low-alloy steel) | Reduce hydrogen-induced cracking risk |
| Interpass temperature | ≤ 250°C | Control cooling rate and prevent sensitization |
| Welding current | 180-280 A | Balance penetration and deposition |
| Welding voltage | 22-28 V | Maintain arc stability |
| Welding speed | 150-300 mm/min | Control heat input |
| Shielding gas | Ar (99.99%) or Ar/CO2 mix | Protect weld from oxidation |
| Dilution rate target | ≤ 5% | Maintain overlay alloy properties |
| Minimum overlay thickness | 3 mm (after machining) | Ensure adequate corrosion resistance |
Quality Control and FMEA Analysis
Applying a Failure Mode and Effects Analysis (FMEA) approach to RJ face overlay welding reveals the following critical failure modes:
| Failure Mode | Effect | Severity | Detection Method | Countermeasure |
|---|---|---|---|---|
| Excessive dilution | Reduced corrosion resistance | 9 | Metallographic analysis | Use transition layer; control parameters |
| Surface porosity | Sealing failure | 8 | PT/MT inspection | Optimize shielding gas; control arc length |
| Cracking at interface | Structural failure | 10 | MT/UT inspection | Pre-heat; control cooling rate |
| Incomplete fusion | Reduced bond strength | 8 | UT inspection | Increase current; ensure surface cleanliness |
| Excessive surface roughness | Poor sealing contact | 6 | Visual/tactile inspection | Ensure adequate post-weld machining |
Engineering Practice Experience
In nuclear and petrochemical equipment manufacturing, RJ face overlay welding is a critical quality gate. The overlay must withstand the full design pressure and temperature of the system while maintaining a leak-tight seal. Several practical considerations emerge from experience:
- Thermal management: The RJ face is often located in a thick section of the flange or tube sheet, creating significant thermal mass. This can lead to excessive heat accumulation during multi-pass welding, causing microstructural degradation in the heat-affected zone. Interpass temperature monitoring is essential.
- Geometric constraints: The RJ face is typically a small, localized area on a large component. Positioning the welding head and maintaining consistent travel parameters on such a small area requires precision equipment and skilled operators.
- Documentation requirements: Nuclear and petrochemical applications require extensive documentation of welding procedures, operator qualifications, and NDE results. The process qualification (PQR) and procedure qualification record (WPS) must be thoroughly documented.
Study Insights
This paper provides a practical, standards-based approach to RJ face overlay welding that is directly applicable to engineering practice. The emphasis on process qualification, transition layer usage, and comprehensive quality control reflects the high-integrity requirements of nuclear and petrochemical equipment manufacturing. The FMEA analysis approach, while not explicitly presented in the paper, is a natural extension of the quality control philosophy described. For engineers involved in chemical equipment manufacturing, the key takeaway is that RJ face overlay welding success depends on rigorous attention to every process step, from pre-weld preparation through post-weld inspection, with no room for shortcuts in a quality-critical application.