Selection of valve leakage rating
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According to GB/T13927, the leakage levels are classified into grades A, AA, B, C, CC, D, E, EE, F, and G. Is there a GB standard for selecting valve leakage levels? For example, with flammable gases such as natural gas and propylene, operating at a pressure of 6 kilograms and used in workshops, how should the valve leakage rating be selected? Thank you all
These grades are derived from ISO 5208, and now API 6D also follows ISO. For gases at moderate temperatures, a soft seal can be used, achieving an A or AA rating. Metal seal, generally corresponding to D; a special design of type C can also achieve this, but at a higher cost.
Flammable gases require valves with zero leakage; if they are electric or pneumatic, they must also be explosion-proof. Therefore, soft seals are used at temperatures below 120°C, while double-eyeball or triple-eyeball hard seals with zero leakage are chosen when frequent opening and closing is required, as soft seals are not wear-resistant
A represents zero leakage, but in reality there is a slight amount of leakage; AA is the control level established for that ‘slight’ amount of leakage. The allowable leakage amount per ISO standard is proportional to the diameter.
This is a condition involving a Class 1 hazard source; the highest level of leakage control is required. For soft-sealed valves, grade VI is required, while for hard-sealed valves, grade V is required
Check the specifications for API 598 and 6D.
If you need more specific information, check the paper written by Yang Xingyou from Shanghai Petrochemical on leaks. Worth a look