CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Automatic Overlay Welding Technology in High Sulfur Gas Field Equipment Anti-Corrosion
Literature Overview
This 2024 publication in Petrochemical Technology, authored by Liu Boqiang, Cai Wei, Fan Linyun, and Shao Qing from China Petroleum Southwest Oil & Gas Field Chuan-Dongbei Operating Branch and Shanghai Sulzer Engineering Machinery Manufacturing Co., Ltd., addresses the application of automated overlay welding for corrosion protection in high-sulfur gas field equipment. The Chuan-Dongbei gas field is notorious for its extremely high H₂S and CO₂ content, making this a critical engineering challenge for asset integrity management.
Background and Service Environment
The Chuan-Dongbei gas field operates under conditions that are exceptionally aggressive toward carbon and low-alloy steels:
- H₂S content: 5–15% (v/v) in some wells
- CO₂ content: 1–5% (v/v)
- Operating temperature: 60–120°C
- Operating pressure: 8–15 MPa
- Corrosion mechanism: Sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and sulfide stress corrosion cracking (SSCC)
Under these conditions, carbon steel equipment without protection can suffer catastrophic failure within months. The overlay welding approach provides a cost-effective alternative to full nickel-alloy construction while maintaining sufficient corrosion resistance.
Automated Overlay Welding Technology
Process Selection
The study focuses on automated multi-wire or multi-layer overlay welding, which offers superior efficiency and consistency compared to manual methods. The typical process parameters are as follows:
| Parameter | Specification | Rationale |
|---|---|---|
| Welding process | GMAW or FCAW automated | High deposition rate; good process control |
| Consumable | Nickel-based or duplex stainless | Resistant to SSC and HIC |
| Wire diameter | 1.2–1.6 mm | Balance deposition rate and arc stability |
| Travel speed | 200–400 mm/min | Maintain optimal heat input |
| Wire feed speed | 3–6 m/min | Match travel speed for desired bead geometry |
| Shielding gas | Ar + CO₂ (75/25) or pure Ar | Minimize porosity; control dilution |
| Layer thickness | 1.0–2.0 mm per layer | Control dilution below 20% |
| Total overlay thickness | 3.0–5.0 mm | Provide adequate corrosion allowance |
Consumable Selection Strategy
For high-sulfur environments, the overlay material selection follows a hierarchy based on severity of service:
- Duplex stainless steel (2205): Suitable for moderate H₂S environments; cost-effective; good mechanical properties
- Nickel-based alloys (Inconel 625, Alloy 600): Excellent resistance to SSC and HIC; used for severe service
- Monel 400: Good resistance to acid gases; moderate cost
- Hastelloy C-276: Reserved for the most aggressive conditions
The dilution control is critical. For nickel-based overlay on carbon steel, dilution must be maintained below 20% to ensure the overlay layer retains its corrosion-resistant microstructure. Automated processes provide superior dilution control through precise wire feed and arc positioning.
Quality Control and Inspection
Required Testing
| Test Method | Standard | Acceptance Criteria |
|---|---|---|
| Hardness (overlay surface) | ASTM E92 | ≤350 HV (NACE MR0175 requirement) |
| HIC testing | NACE TM0284 / ASTM G283 | HIC rating ≤4 (or per API 934) |
| SSC testing | NACE TM0177 / ASTM G178 | No cracking after 720h exposure |
| Bond strength | ASTM A263 / NB/T 47014 | Exceeds specified minimum |
| Visual inspection | ISO 17637 | No cracks, undercuts, or excessive porosity |
| Magnetic particle testing | NB/T 47013.4 | No linear indications in overlay |
| Ultrasonic testing | NB/T 47013.2 | No delamination at overlay-base interface |
Critical Quality Considerations
The hardness limitation of 350 HV specified by NACE MR0175 / ISO 15156 is a critical design constraint. Many nickel-based alloys in the as-welded condition exceed this limit, requiring careful control of cooling rate or post-weld heat treatment. The automated welding process helps maintain consistent cooling rates across large surface areas, which is difficult to achieve with manual welding.
Engineering Application Cases
In the Chuan-Dongbei application, the overlay technology has been applied to:
- Wellhead equipment: Flanges, valves, and connectors exposed to high-pressure H₂S
- Separators and knock-out drums: Internal surfaces and nozzles
- Heat exchangers: Tube sheets and channel covers
- Piping systems: Critical sections where replacement is difficult
The results demonstrate that properly qualified automated overlay welding can extend equipment service life from 6–12 months (unprotected carbon steel) to 8–15 years, representing a significant improvement in asset utilization and safety.
Study Insights and Recommendations
This work highlights the importance of integrating metallurgical considerations with practical manufacturing constraints. The automated approach not only improves quality consistency but also enables the treatment of large equipment surfaces that would be impractical for manual overlay. Engineers should note that the qualification process must include HIC and SSC testing of the actual overlay microstructure produced by the specific process parameters used, rather than relying solely on consumable manufacturer data. The interaction between base material hydrogen content, overlay dilution, and residual stress all contribute to the overall SSC resistance of the joint.