Requirements for degreasing and degreasing of low temperature check valves for natural gas transportation

I. Necessity of degreasing and degreasing
‌Safety risk control‌
Natural gas is a flammable and explosive medium. Residual oil and oxygen contact may cause violent oxidation reaction, resulting in seal failure or safety accidents‌12.
In low temperature environment (such as LNG system), grease may solidify or adhere to the surface of the valve disc, causing valve jamming or poor sealing‌45.
‌Sealing performance guarantee‌
Oil will reduce the bonding strength of the metal sealing surface, accelerate the aging of the sealing material, and increase the risk of natural gas leakage‌12.
The cryogenic treatment process of Low Temperature Check Valves must be carried out after degreasing, otherwise the residual grease may affect the low temperature toughness of the material‌46.
II. Degreasing and degreasing operation specifications
‌Treatment process‌
‌Chemical cleaning‌: Use organic solvents such as carbon tetrachloride to soak or wipe key components such as valve body and valve disc to thoroughly remove residual grease from processing‌37.
‌Mechanical cleaning‌: Ultrasonic cleaning is used for complex structural parts (such as spring chamber) to ensure no dead corner cleaning‌14. ‌Acceptance criteria‌

After cleaning, a white cloth wiping test is required. There is no visible oil stain and the solvent residue must comply with ASTM G93 standard‌13.
The degreased valve must be vacuum packed or nitrogen sealed to avoid secondary contamination‌45.
III. Special working conditions requirements
‌LNG system adaptation‌

LNG cryogenic check valves must be deacidified, dehydrated and degreased during the manufacturing stage to meet the anti-brittle fracture performance in a deep cold environment of -196℃‌45.
The valve body material is preferably 304/316L stainless steel or nickel-based alloy, and the Stellite alloy sealing surface is welded to enhance corrosion resistance‌46.
‌Maintenance precautions‌

It is prohibited to use grease-containing tools during installation and maintenance, and operators must wear oil-free gloves‌14.
Regularly check the wear of the sealing surface. If the thickness of the weld layer is <0.5mm, it should be returned to the factory for re-degreasing‌45.
Conclusion
When low-temperature check valves are used for natural gas transportation, they must be degreased and deoiled to eliminate the risk of explosion and ensure sealing reliability. Operations must strictly follow the chemical cleaning process and acceptance standards, and at the same time combine material selection and maintenance specifications to achieve long-term safe operation.