**Abstract:**
Due to the strong corrosive nature of hydrogen sulfide, equipment and materials used in sulfur-bearing oil and gas fields must be designed with high resistance to hydrogen sulfide corrosion. To evaluate the performance of wellhead valves in such environments, a disassembly inspection was conducted on cast-in-place wellhead valves from sulfur-containing fields in western Sichuan. The dismantled 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 material choices reduced the valves’ overall resistance to hydrogen sulfide corrosion. Based on these findings, preliminary suggestions for improvement were proposed to enhance the durability and safety of these critical components.
**Keywords:** Wellhead valve; anti-corrosion inspection; sulfur-containing oil field; casting valve; structural design
With the rapid growth of China’s economy, energy demand has surged, intensifying the supply-demand gap. As an essential energy source, the development of high-sulfur oil and gas fields has become a strategic priority for CNPC. However, the presence of hydrogen sulfide poses significant challenges, as it can severely corrode equipment and materials. Therefore, conducting detailed inspections of wellhead valves is crucial to ensure their long-term reliability and safety.
In this study, two wellhead valves from sulfur-containing fields in western Sichuan were dismantled and examined. The first valve showed severe external corrosion on the valve body and bonnet, while the second exhibited similar issues, including flange paint loss and rusting. The inspection also identified several problematic areas, such as the handwheel, stem copper nut, bearing assembly, and packing gland, which required further analysis.
The handwheel, made of cast steel, was in relatively good condition, but the mating surface with the bronze nut showed numerous scratches. This suggests that the design may not be optimal for preventing damage during installation. It is recommended that the inner hole of the handwheel be redesigned as a conical shape to improve ease of assembly and reduce wear.
The stem copper nut, though intact in terms of thread structure, had a severely worn keyway, leading to assembly difficulties. Shortening the length of the copper nut could reduce material usage and improve functionality. However, the exposed copper makes it vulnerable to mechanical damage, so protective measures should be considered.
The bearing housing showed some black corrosion products, possibly due to trace hydrogen sulfide leakage. The bearing positioning screws were found to be prone to rust, making disassembly difficult. A redesign of the bearing system would help improve accessibility and prevent corrosion-related failures.
Thrust ball bearings displayed varying degrees of corrosion, even in areas that were supposed to be isolated from the hydrogen sulfide medium. This indicates potential design flaws in sealing mechanisms. Improving the sealing of these components would significantly enhance their longevity.
The packing gland suffered from serious corrosion, reducing its ability to regulate the packing seal. Replacing it with stainless steel could improve corrosion resistance and ensure better sealing performance.
PTFE packing rings performed well under hydrogen sulfide conditions, while rubber seals showed signs of aging and deformation. It is recommended to use more stable materials like fluorine rubber for flexible seals in future designs.
The valve stem was generally intact, but minor surface corrosion and pitting were observed. While the material selection seems adequate, stress concentration at the working slot root could lead to stress corrosion cracking. Adjusting the root radius of the trapezoidal thread and improving the stem design would help mitigate this risk.
The valve cover showed signs of corrosion but remained largely intact. The material used (45 steel) met chemical standards, but its hardness exceeded the recommended range, increasing the risk of stress corrosion cracking. It is advised to use forged parts instead and optimize the design to avoid sharp corners that could lead to stress concentration.
Overall, this inspection highlights the need for improved material selection, structural design, and corrosion protection measures in sulfur-bearing oil and gas fields. Further research and large-scale data collection are necessary to validate and refine these recommendations.
**Keywords:** Sulfur-containing oil field; Casting wellhead valve; Demolition inspection; Anti-corrosion design; Structural optimization
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