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 < T_fluid ≤ 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 CWP^a or 6 bar ± 1 bar;
   • Test fluid is a liquid: the closure test pressure shall be minimum 1,1 times the CWP^a;
   • 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:

DN	Minimum duration closure test Isolation valve	Minimum duration closure test Check valve
DN ≤ 50	15 s	60 s
65 < DN ≤ 150	60 s	60 s
200 < DN ≤ 300	120 s	120 s
DN > 350	120 s	120 s

^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

DN	PN	Gate valve	Globe valve	Plug valve	Check valve	Floating ball valve	Diaphragm valve	Eccentric butterfly valve	Trunnion mounted ball valve	Concentric butterfly valve
DN ≤ 100	PN ≤ 250	Required	Optional	Required	Optional	Required	Required	Required	Required	Optional
	PN > 250	Optional	Optional	Optional	Optional	Required	Required	Optional	Optional	–
DN > 100	PN ≤ 100	Required	Optional	Optional	Optional	Required	Required	Required	Required	Optional
	PN > 100	Optional	Optional	Optional	Optional	Optional	Optional	Optional	Optional	–

B. Prescribed Liquid HIGH pressure closure test

DN	PN	Gate valve	Globe valve	Plug valve 1	Check valve	Floating ball valve	Diaphragm valve	Eccentric butterfly valve	Trunnion mounted ball valve	Concentric butterfly valve
DN ≤ 100	PN ≤ 250	Optional	Required	Optional	Required	Optional	Optional	Optional	Optional	Required
	PN > 250	Required	Required	Required	Required	Optional	Optional	Required	Required	–
DN > 100	PN ≤ 100	Optional	Required	Optional	Required	Optional	Optional	Optional	Optional	Required
	PN > 100	Required	Required	Required	Required	Optional	Optional	Required	Required	–

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 A	Rate AA	Rate B	Rate C	Rate CC	Rate D	Rate E	Rate EE	Rate F	Rate G
mm3/s	0 1	0,18×DN	0,3×DN	3×DN	22,3×DN	30×DN	300xDN	470xDN	3000xDN	6000xDN
bubbles/ s	0 1	0,003×DN	0,0046×DN	0,0458×DN	0,3407×DN	0,4584×DN	4,5837×DN	7,1293×DN	45,837×DN	91,673×DN

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

Unit	Rate A	Rate AA	Rate B	Rate C	Rate CC	Rate D	Rate E	Rate EE	Rate F	Rate G
mm3/s	0 1	0,006×DN	0,01×DN	0,03×DN	0,08×DN	0,1×DN	0,3×DN	0,39×DN	1×DN	2×DN
Drops/ s	0 1	0,0001×DN	0,00016×DN	0,0005×DN	0,0013×DN	0,0016×DN	0,0048×DN	0,0062×DN	0,016×DN	0,032×DN

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