**Abstract:**
Due to the strong corrosive nature of hydrogen sulfide, equipment and materials used in sulfur-bearing oil and gas fields must possess excellent resistance to hydrogen sulfide corrosion. To evaluate the performance of cast-in-place wellhead valves in sulfur-containing fields in western Sichuan, a disassembly inspection was conducted. The inspected components included the handwheel, stem copper nut, bearing seat, thrust ball bearing, packing gland, packing rings, seal rings, valve stem, bonnet, valve plate, valve body, bolts, and nuts. The results revealed that certain design flaws and inappropriate material choices reduced the valves' resistance to hydrogen sulfide corrosion. Based on these findings, preliminary recommendations for improvement were proposed.
**Keywords:** Wellhead valve; anti-corrosion inspection; sulfur-containing oil field
With the rapid growth of China’s economy, domestic energy demand has surged significantly. As one of the key energy sources, the imbalance between supply and demand has become increasingly apparent. Therefore, accelerating the development of comprehensive technologies for high-sulfur oil and gas fields is not only essential but also urgent for China National Petroleum Corporation. In such environments, due to the intense corrosion caused by hydrogen sulfide, all equipment and materials must be designed with corrosion resistance in mind.
To this end, we carried out a demolition inspection on several cast-in-place wellhead valves commonly used in sulfur-containing oil and gas fields in western Sichuan. Two valves were dismantled and analyzed. The first valve showed significant corrosion on the valve body, bonnet, and bearing seat, while the second valve had flange paint peeling and visible rust on the bearing. Both valves exhibited signs of early degradation, indicating that their service life was shorter than expected.
Based on the inspection, several issues were identified, and suggestions for improvement were made. For instance:
- **Handwheel:** The mating surface with the bronze nut showed excessive wear, suggesting a need for improved design. It was recommended to modify the inner hole to an internal conical shape for better assembly and disassembly.
- **Stem Copper Nut:** Although the trapezoidal thread remained intact, the outer surface was severely worn, causing assembly difficulties. Reducing the length of the copper nut could improve efficiency and reduce material usage.
- **Bearing Seat:** Some areas showed black corrosion products, likely due to trace hydrogen sulfide leakage. The current design of the bearing positioning screws was found to be problematic, as they are prone to rust and can cause disassembly issues.
- **Thrust Ball Bearings:** These bearings showed varying degrees of corrosion, even though they were supposed to be isolated from the hydrogen sulfide medium. This suggested a design flaw in the sealing system.
- **Packing Gland:** Corrosion was more severe here, affecting the ability to regulate the packing seal. Replacing the gland with stainless steel was recommended.
- **Packing Rings and Seals:** While PTFE seals performed well, rubber seals showed signs of aging and deformation. It was suggested to use more stable materials like fluorine rubber for long-term reliability.
- **Valve Stem:** The stem itself showed minimal corrosion, but stress concentration at the root of the trapezoidal thread raised concerns about potential stress corrosion cracking. Improvements in design and material selection were recommended.
- **Bonnet:** Although the bonnet was mostly intact, its hardness exceeded standard specifications, which could lead to early failure under hydrogen sulfide exposure. Recommendations included increasing the radius of fillets to reduce stress concentration and ensuring proper heat treatment.
In conclusion, the inspection highlighted critical design and material issues in the wellhead valves, emphasizing the need for further research and improvements to enhance their durability in sulfur-rich environments. Future studies should involve a larger sample size and more detailed analysis to ensure reliable and safe operation in high-sulfur oil and gas fields.
**Keywords:** Sulfur-containing oil field; casting wellhead valve; demolition inspection; corrosion resistance
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