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ISO 5208: Valve seat leakage rate

The internal tightness of valves is an essential safety requirement in pressurized systems. Leaks can be a danger to people and the environment or have an impact on processes. As there is no such thing as absolute tightness, technical tightness is defined by leakage rates. The necessary leakage rate must be determined by the operator or manufacturer as part of a risk analysis or there are legal requirements for the system operator. Leakage rates can be defined between the ordering party and the valve manufacturer, for which they can refer to test standards or the product standard itself contains tightness requirements.

The internal tightness is defined by the seat tightness (or often also called closure test). Usually one side (valve inlet) shall be subjected to the test pressure and amount of leak shall be measured on the opposite side of the valve to atmosphere.

ISO 5208 is listed as a reference in the following valve product standards: ASME B16.34, API SPEC 6D, ISO 13942.

The following standard is a test standard containing test conditions and graded leakage rates.

ISO 5208 Leakage rate test for valves

ISO 5208 is intended to be applied in conjunction with the specific requirements of a valve product standard to the extent cited by the product standard as a normative reference.

Where requirements of a product standard differ from those given in ISO 5208, the requirements of the product standard apply.

ISO 5208 specifies examinations and tests that a valve manufacturer needs to act upon in order metallic valve and to verify the degree of valve closure tightness and the structural adequacy of its closure mechanism.

General closure test requirements

  1. Test fluids to be used
    • Water, that may contain a corrosion inhibitor, kerosene or other appropriate liquid having a viscosity not greater than that of water. The valve chamber under test shall be essentially free of air. Pressure testing valves with shell components of austenitic stainless steel, using water as the test fluid, requires that the chloride content of the water shall not exceed 100 × 10-6 (100 ppm).
    • Air or other suitable gas
    • Temperature of the test fluid: 5 °C < Tfluid ≤ 40°C
  2. Timing of test
    The closure test is to be performed after successful completion of valve shell test
  3. Closure test pressure
    • Test fluid is a gas: the closure test pressure shall be 1,1 times the CWPa or 6 bar ± 1 bar;
    • Test fluid is a liquid: the closure test pressure shall be minimum 1,1 times the CWPa;
    • For valves, including combination non-return types fitted with manual or power actuated torque multiplying devices, the required high-pressure closure test shall be performed at 110 % of the obturator design differential pressure used to size the device.
  4. Duration for closure tests:
DNMinimum duration closure test
Isolation valve
Minimum duration closure test
Check valve
DN ≤ 5015 s60 s
65 < DN ≤ 15060 s60 s
200 < DN ≤ 300120 s120 s
DN > 350120 s120 s
Duration closure tests

a CWP is the maximum fluid pressure assigned to a valve for operation at a fluid temperature of −20 °C to 38 °C.

A. Prescribed Gas LOW pressure closure test

DNPNGate
valve
Globe valvePlug valveCheck valveFloating ball valveDiaphragm valveEccentric butterfly valveTrunnion mounted ball valveConcentric butterfly valve
DN ≤ 100PN ≤ 250RequiredOptionalRequiredOptionalRequiredRequiredRequiredRequiredOptional
PN > 250OptionalOptionalOptionalOptionalRequiredRequiredOptionalOptional
DN > 100PN ≤ 100RequiredOptionalOptionalOptionalRequiredRequiredRequiredRequiredOptional
PN > 100OptionalOptionalOptionalOptionalOptionalOptionalOptionalOptional
Note 1: Successful completion of an optional test does not relief the manufacturer from also successfully completing the require test.
Exceptions:
Valves specified as double block and bleed valve, a sign pressure closure test is required and a low pressure test is an option.
For plug valves that rely on a sealing compound to effect a closure seal:
– a high-pressure closure test is required and the low-pressure test is an option;
– may be closure tested with the compound installed

B. Prescribed Liquid HIGH pressure closure test

DNPNGate
valve
Globe valvePlug valve 1Check valveFloating ball valveDiaphragm valveEccentric butterfly valveTrunnion mounted ball valveConcentric butterfly valve
DN ≤ 100PN ≤ 250OptionalRequiredOptionalRequiredOptionalOptionalOptionalOptionalRequired
PN > 250RequiredRequiredRequiredRequiredOptionalOptionalRequiredRequired
DN > 100PN ≤ 100OptionalRequiredOptionalRequiredOptionalOptionalOptionalOptionalRequired
PN > 100RequiredRequiredRequiredRequiredOptionalOptionalRequiredRequired
Note 1: Successful completion of an optional test does not relief the manufacturer from also successfully completing the require test.
Exceptions:
Valves specified as double block and bleed valve, a sign pressure closure test is required and a low pressure test is an option.
1For plug valves that rely on a sealing compound to effect a closure seal:
– a high-pressure closure test is required and the low-pressure test is an option;
– may be closure tested with the compound installed

C. Prescribed Gas HIGH pressure closure test

For all DN and PN and all valve type, the gas high pressure closure test is an OPTION.

Leakage rates

a) ISO 5208 Leckage rate if the test fluid is gas:

Unit
Rate ARate AARate BRate CRate CCRate DRate ERate EERate FRate G
mm3/s0 10,18×DN0,3×DN3×DN22,3×DN30×DN300xDN470xDN3000xDN6000xDN
bubbles/ s0 10,003×DN0,0046×DN0,0458×DN0,3407×DN0,4584×DN4,5837×DN7,1293×DN45,837×DN91,673×DN
1 No visually detectable leakage for the duration of the test

b) ISO 5208 Leckage rate if the test fluid is liquid:

Unit
Rate ARate AARate BRate CRate CCRate DRate ERate EERate FRate G
mm3/s0 10,006×DN0,01×DN0,03×DN0,08×DN0,1×DN0,3×DN0,39×DN1×DN2×DN
Drops/ s0 10,0001×DN0,00016×DN0,0005×DN0,0013×DN0,0016×DN0,0048×DN0,0062×DN0,016×DN0,032×DN
1 No visually detectable leakage for the duration of the test

Read More

Valve seat test – Standards for leakage acceptance

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