Is there a concept of leakage rating for shut-off valves?

Cut-off valves also have requirements regarding leakage levels; generally, the leakage level for emergency cut-off valves is ≥ Class V.

HGT 20507-2014 Specification for the Selection and Design of Automated Instruments

The leakage class of the shut-off valve is an important factor in selection; refer to the specifications frequently. Standards such as GB/T4213 or ANSI/FCI 70-2 also have relevant requirements.

1Q053 How to select the leakage class of valves? A: Generally, the leakage class for control valves is IV, while it is V for on/off valves. Specifically, according to 11.2.3 in HGT20507, valve types with different leakage classes are selected based on the requirements regarding leakage levels in the process. The minimum leakage rating for the leakage control valve of straight-through single-seat valves is ANSI IV, while for double-seat valves, it is ANSI III or ANSI II. 11.3.2 The leakage class of the on-off valve should be ANSI V; ANSI VI can be selected when tight shut-off (TSO) is required. In SHT3005, 10.1.6: The selection of the allowable leakage level for control valves shall comply with the following provisions: a) The selection of the allowable leakage level for control valves should be carried out in accordance with the GB/T4213 or ANSI/FCI70-2 standards; b) Unless there are special requirements from the process, the allowable leakage level for control valves should preferably be at level IV as specified by the GB/T4213 or ANSI/FCI70-2 standards ； c) When the process requires tight shut-off (TSO) of the control valve or involves emergency shut-off interlocks, the allowable leakage class for the control valve should be selected as Class V or higher as specified in the GB/T4213 or ANSI/FCI70-2 standards ； d) The process requires that the control valves of TSO use non-metallic or composite materials for their seat, provided that the temperature, pressure, and material requirements are met. When fire protection requirements are also applicable in the process, the material and design of the valve seat must comply with those fire protection standards. 10.3.1.4 The allowable leakage rate of the switch valve shall comply with the provisions of GBT13927 (2016 Industrial Valves – Pressure Testing), GBT26480 (2011 Inspection and Testing of Valves), or API598. In GBT4213, except for Class I, the leakage grade of control valves in 5.6.2 is determined by the manufacturer itself. However, the leakage class of control valves with a single-seat valve structure must not be lower than Class IV ； The leakage class of control valves with a two-seat valve structure shall not be lower than Class II. Note: Under hard-seal conditions for valves, the leakage class VI costs 1.5 to 2.5 times as much as class V

Ball valves or butterfly valves are generally used as cut-off valves, with a leakage rating of at least level 5.

The scope of application for FCI 70-2 is control valves, including the shut-off valves mentioned by the questioner; it can be used as a reference. In my humble opinion, there’s no need to worry about what level of leakage it is; it’s simply a basic requirement for valves at the time of manufacturing. In practice, it still depends on the actual conditions on site.

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This post was last edited by feng*aosa on 2022-11-25 at 16:22. Regardless of the type of valve, the requirements (standards) regarding leakage levels are the same. Industrial valves → Control valves → Pneumatic control valves. Main standards: GB/T 13927 \"Industrial valves – Pressure testing\", GB/T 17213.4 \"Industrial process control valves – Part 4: Inspection and routine testing\", ASME B16.104 \"Standards for seat leakage of control valves\"