HERMETICITY OF VALVES

CONTENT Page
1 Introduction 1-3
2 ISO 5208 4-5
3 API 598 6-7
4 FCI 70-2 8-9
5 EN 12266-1 10
6 MSS SP-61 11
7 BS 6364 (cryogenic valves) 12

1. Introduction
The request of hermeticity of valves is often confusing and create wrong expectations to the user.
In this paper the most common hermeticity test for valves are described and a comparison between
the different test standards is intended. A real comparison is very difficult to provide because the
different standards test under different conditions, which very often are not comparable.

From an engineering point of view, almost all valves leak by some measure. A “zero leakage” do not
exist, since small amounts of material may indeed cross the seat, especially if helium or hydrogen or
other small molecule gases are used. Soft seated valves are commonly defined as “bubble tight”, while
most metal seated valves larger than DN 50 (NPS 2”) have an allowable leakage rate (according to API
598 or API 6D). In the ISO 5208 standard there are special zero leakage classes also for metal seated
valves.

It should be noted in the engineering design that API 600-2001 (ISO 10434–1998) specifies that the
sealing performance of the valve is tested in accordance with ISO 5208, but the leakage in tables 17
and 18 is equivalent to API 598–1996, not ISO 5208. Therefore, when API 600 and its sealing
performance test API 598 standard are selected for the engineering design, the version of the standard
must be clarified to ensure the uniformity of the standard content.

The relevant guidelines of API 6D (ISO 14313) for valve leakage are: “soft seated valves and oil-seal
plug valves shall not exceed ISO 5208 A (no visible leakage), metal seat valves shall not exceed ISO
5208(1993) D unless otherwise specified.” Note in the standard: “special applications may require
leakage less than ISO 5208(1993) class D. Therefore, leakage requirements higher than the standard
shall be given in the order contract.

The standard ANSI / FCI 70-2 are normally used for control valves but can also be defined by the user
for on-off valves.

This description is not intended to replace the norms, the test standards in its last version, selected by
the user, must be followed when testing a valve.

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Not all hermeticity classes described in the norms are possible at all type of valves, the manufacturer
must verify from case to case which class is possible and under which conditions.

The hermeticity test is done under laboratory conditions on a test rig. Leakages under process
conditions are not defined. Leakages after a long use of a valve depend on the process conditions and
cannot be guaranteed by the manufacturer of the valve.

Test standards for common vale types are:

Stell ball, gate, globe and check valves ISO 5208 / API 598 / EN 12266-1
Cast iron gate valves API 598 / MSS SP-70
Bronze gate, globe and check valves MSS SP-80
Steel gate, globe and check valves larger than ASME B16.34
NPS 24” (DN 600)
Pressure seal gate, globe and check valves ASME B16.34
Pipeline valves (API 6D) ISO 5208
Steel ball valves API 598
Steel butterfly valves API 598
Cryogenic valves API 598 / BS 6364
Control valves FCI 70-2 / EN 60534-4
Pressure relief valves API 527 / ASME PTC 25

In this description only the standards and procedures for on-off valves are described.
Procedures for control and pressure relief valves are included.

Which test, and under which procedures the valve must be tested can be defined by
• the user
• norms like API (used in the USA), EN 12266-1 (used in Europe) or other local regulations

The norms refer to a specific test procedure like

Norm Applicable for Test procedures

EN 12266-1 On-off valves ISO 5208
API 6D Ball, check, gate and plug valves used in pipelines ISO 5208
API 608 Ball valves for industrial service API 598
API 609 Butterfly valves API 598
API 602 Gate, globe and check valves in dimensions < ND 100 (4”) API 598
EN 1349 Control valves EN 60534-4
API 6D Control valves ANSI / FCI 70-2

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Measuring units used for the test

Leakage flow measurement with gas:

1 bubble/min = 60 bubbles/sec = 0,15 ml/min = 2,5 mm3/sec

1 bubble/sec = 0,0166 bubble/min = 9 ml/min = 150 mm3/sec
1 ml/min = 6,66667 bubbles = 400 bubbles/sec = 16,66667 mm3/sec
1 mm3/sec = 0,06 ml/min = 0,4 bubbles/min = 24 bubbles/sec

Leakage flow measurement with water

1 drop/min = 60 drops/sec = 0,0625 ml/min = 1,042 mm3/sec

1 drop/sec = 0,0165 drops/min = 3,75 ml/min = 62,4 mm3/sec
1 ml/min = 16 drops/min = 960 drops/sec = 16,66667 mm3/sec
1 mm3/sec = 0,06 ml/min = 0,96 drops/min = 57,60 drops/sec

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 2. ISO 5208 – 2015
International Organization for Standardization ISO 5208 specifies examinations and tests that a valve
manufacturer needs to act upon in order to establish the integrity of the pressure boundary of an
industrial metallic valve and to verify the degree of valve closure tightness and the structural adequacy
of its closure mechanism.

There are 10 leakage rates specified in ISO 5208: A, AA, A, B, C, CC, D, E, EE, F, G and the rate A is the
highest grades. There is a loosely defined correspondence between the leakage rate acceptance values
of API 598 and leakage value rate A as applied to DN 50, rate CC-liquid for other than metal-seated
check valves and for check valves rate EE-gas and rate G-liquid. Rate A, B, C, D, F and G correspond to
values in EN 12266-1.

Required hermeticity test

The ISO 5208 do not define different conditions for soft seated or metal seated valves. The
requirements are the same independent of the material that provides the sealing.
The ISO 5208 standard can be used for all type of on-off valves, it is not used for control valves.

The testing requirements for industrial steel valves are:

Temperature of Test with water Test with gas

test fluid 5°C to 40°C 5°C to 40°C
DN ≤ 50 15 sec (60 for check 15 sec (60 for check valves)
(NPS ≤ 2”) valves)
DN 65 to 150 60 sec 60 sec
Minimum test (NPS 2.5” to 6”)
duration DN 200 to 300 120 sec 120 sec
(NPS 8” to 12”)
DN ≥ 350 120 sec 120 sec
(NPS ≥ 14”)
Minimum test 1.1 x nominal pressure 1.1 x nominal pressure of the
pressure of the valve valve or 6 ± 1 bar

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Acceptance criteria

No visible leakage for DN ≤ 50 (NPS ≤ 2”). Allowable leakage rates as per below table.

Test fluid Unit Rate A Rate AA Rate B Rate C Rate CC

mm3/sec No visually 0,006 x DN 0,01 x DN 0,03 x DN 0,08 x DN
Liquid detectable
drops/sec 0,0001 x DN 0,00016 x DN 0,0005 x DN 0,0013 x DN
leakage for the
mm3/sec 0,18 x DN 0,3 x DN 3 x DN 22,3 x DN
Gas duration of the
bubbles/sec test 0,003 x DN 0,0046 x DN 0,0458 x DN 0,3407 x DN

Test fluid Unit Rate D Rate E Rate EE Rate F Rate G

mm3/sec 0,1 x DN 0,3 x DN 0,39 x DN 1 x DN 2 x DN
Liquid
drops/sec 0,0016 x DN 0,0048 x DN 0,0062 x DN 0,016 x DN 0,032 x DN
mm3/sec 30 x DN 300 x DN 470 x DN 3000 x DN 6000 x DN
Gas
bubbles/sec 0,4584 x DN 4,5837 x DN 7,129 x DN 45,837 x DN 91,673 x DN

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 3. API 598 (2009)
This standard cover inspection, examination, supplementary examinations and pressure test
requirements for soft seated, non-metallic seated (e.g. ceramic) and metal-to-metal seated valves of
the gate, globe, ball, check and butterfly types.
This standard supplements the API Standards, but it may also be applied to other type of valves by
agreement between the user and the manufacturer

Test required

The test listed in the following table shall be performed in accordance with written procedures that
comply with the standard

Valve type
Test Butterfly and trunnion
gate globe plug check Floating ball
guided ball
Low
optional optional optional optional required optional
pressure
High
required required required required optional required
pressure
When an optional test is specified by the user, the test shall be performed in addition to the required
test.
A high pressure test is required for all valves specified to be double block and bleed valves.

Testing requirements

Sizes Test with water Test with gas

Temperature of 5°C to 50°C 5°C to 50°C
test fluid
DN ≤ 50 15 sec (60 for check 15 sec (60 for check
(NPS ≤ 2”) valves) valves)
DN 65 to 150 60 sec 60 sec
Minimum test (NPS 2.5” to 6”)
duration DN 200 to 300 120 sec 120 sec
(NPS 8” to 12”)
DN ≥ 350 300 sec 120 sec
(NPS ≥ 14”)
Minimum test 1.1 x nominal pressure 4 to 7 bar
pressure of the valve

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Acceptance criteria

No visible leakage for soft seated valves. Allowable leakage rates as per below table for metal seated
valves.

Size Metal seated valves except check valves Metal seated check valves
DN NPS Test with Test with Test with Test with Test with Test with
liquid in liquid in gas in gas in gas in m3/h gas in
drops/min ml/min bubbles/min ml/min ml/min
≤ 50 ≤ 2” 0 6 0 0 0,08 1333
65 2 ½” 5 7,5 10 1,5 0,11 1833
80 3” 6 9 12 1,8 0,13 2167
100 4” 8 12 16 2,4 0,17 2833
125 5” 10 15 20 3,0 0,21 3500
150 6” 12 18 24 3,6 0,25 4167
200 8” 16 24 32 4,8 0,34 5667
250 10” 20 30 40 6 0,42 7000
300 12” 24 36 48 7,2 0,50 8333
350 14” 28 42 56 8,4 0,59 9833
400 16” 32 48 64 9,6 0,67 11167
450 18” 36 54 72 10,8 0,76 12667
500 20” 40 60 80 12 0,84 14000
600 24” 48 72 96 14,4 1,01 16833
650 26” 52 78 104 15,6 1,09 18167
700 28” 56 84 112 16,8 1,18 19667
750 30” 60 90 120 18,0 1,26 21000
800 32” 64 96 128 19,2 1,34 22333
900 36” 72 108 144 21,6 1,51 25167
1000 40” 80 120 160 24,0 1,68 28000
1050 42” 84 126 168 25,2 1,7 28333
1200 48” 96 144 192 28,8 2,02 33667

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 4. FCI 70-2 (2013)
American national standards/American instrument association standards ANSI/FCI 70-2 (ASME
B16.104) is applicable to the control valve seal grade requirements. Metal-elastic seal or metal seal
should be selected in engineering design according to the characteristics of the medium and the
opening frequency of the valve. Metal seated valve seal grades should be stipulated in the order
contract. The rates I, II, III are used less only when lower level are acceptable, generally the rate IV is
used at least or V and VI for higher requirements.

In the classes I till V the test can be done with water or gas, in the highest class VI only with gas.

Class IV is normally specified for metal to metal sealings (e.g. in the API 6D).

Class V is practically not used anymore and refers to the Class IV but with defined leakage rates.

Class Vl is used at soft seated valves. Soft seated valves are those where the seat or shut-off disc or
both are made from resilient material such as Teflon or similar elastomer.

For the Class I there are no test requirements defined but can be agreed between the user and the
manufacturer.

For class II till IV the test can be done with water or gas (air or nitrogen).
The ambient temperature during the test must be between 10°C and 50°C.
The pressure during the test must be between 3 and 4 bar or 5% of the maximal differential pressure
during operation, whichever is smaller.

Acceptance criteria

Acceptable leakage for the Class II: 0,5% of the maximum flow (e.g. 12100 ml/min for a 2” valve)
Acceptable leakage for the Class III: 0,1% of the maximum flow (e.g. 2420 ml/min for a 2” valve)
Acceptable leakage for the Class IV: 0,01% of the maximum flow (e.g. 242 ml/min for a 2” valve)

For the Class V the test is done with water.

The ambient temperature during the test must be between 10°C and 50°C.
The pressure during the test must the maximum differential pressure during operation, not to exceed
the ANSI body rating.

Acceptable leakage: 0,0005 ml/min per inch of the valve nominal diameter per psi of differential
pressure.

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Hermeticity class VI
Test made with gas (air or nitrogen).
The ambient temperature during the test must be between 10°C and 50°C.
The pressure during the test must be between 3 and 4 bar or 5% of the maximal differential pressure
during operation, whichever is smaller.
Acceptable leakage according to following table:

Diameter
Leakage in ml/min Leakage in bubbles/min
ND NPS
≤25 ≤1” 0,15 1
32 1,5” 0,30 2
50 2” 0,45 3
65 2,5” 0,60 4
80 3” 0,90 6
100 4” 1,70 11
150 6” 4,00 27
200 8” 6,75 45
250 10” 11,10 74
300 12” 16,00 107
350 14” 21,60 144
400 16” 28,40 189
For larger diameters, the allowed leakages are not defined in the norm.

Valid for all leakage classes is

• The leakage is measured once the valve has stabilized at the test pressure
• The nominal diameter is the one of the valve.

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 5. EN 12266-1 (2012)
This standard specifies the pressure tests, test methods and acceptance criteria – mandatory
requirements. It meets the requirements of ISO 5208 for seal classification but lacks AA, CC and EE
ratings.

Test with gas

Temperature of 5°C to 40°C
test fluid
DN ≤ 50 15 sec (60 for check valves)
(NPS ≤ 2”)
DN 65 to 150 60 sec
Minimum test (NPS 2.5” to 6”)
duration DN 200 to 300 120 sec
(NPS 8” to 12”)
DN ≥ 350 120 sec
(NPS ≥ 14”)
Minimum test 1.1 x nominal pressure of the valve
pressure or 6 ± 1 bar

Acceptance criteria

Test fluid Unit Rate A Rate B Rate C Rate D

mm3/sec No visually 0,01 x DN 0,03 x DN 0,1 x DN
Liquid detectable
drops/sec 0,00016 x DN 0,0005 x DN 0,0016 x DN
leakage for the
mm3/sec 0,3 x DN 3 x DN 30 x DN
Gas duration of the
bubbles/sec test 0,0046 x DN 0,0458 x DN 0,4584 x DN

Test fluid Unit Rate E Rate F Rate G

mm3/sec 0,3 x DN 1 x DN 2 x DN
Liquid
drops/sec 0,0048 x DN 0,016 x DN 0,032 x DN
mm3/sec 300 x DN 3000 x DN 6000 x DN
Gas
bubbles/sec 4,5837 x DN 45,837 x DN 91,673 x DN

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 6. MSS SP-61 (Manufacturers Standardization Society)
This standard has a section which describes the permissible leakage of ball, globe, gate and butterfly
valves.

It should be noted that SP 61 is often used for inspection of “fully open” and “fully closed” steel valves,
but not for control valves. MSS SP61 is not usually used for testing industrial valves.
For valve with soft seats, the hermeticity requirement is the same as the API 598, as well as the shell
pressure test.

Acceptance criteria

For metal seated valves the permissible leakage is 10 ml/hr (0,166 ml/min or 2,766 mm3/sec) per inch
of nominal diameter.

NPS 1” 1,5” 2” 2,5” 3” 4” 6” 8” 10” 12” 14” 16”

DN 25 40 50 65 80 100 150 200 250 300 350 400
Leakage
in 2,76 3,32 5,53 6,91 8,30 11,07 16.60 22,13 27,66 33,20 38,73 44,26
mm3/sec

For gate valve with metal seats, the value is 40 ml/min per inch of diameter at a pressure of 40 psi (3
bar)
The leakage allowed by the check valve can be increased by 4 times

The hermeticity test must be done with water at 1.1 the nominal pressure of the valve.

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 7. Testing of cryogenic valves – BS 6364
The test of cryogenic valves, defining the cryogenic service for a temperature < -60°C.

Valves cryogenic tests are performed in dedicated chambers that are filled with liquid nitrogen to reach
the desired temperature. According to the requirements, the test must be conducted by
submerging the valve body into liquid nitrogen, at a temperature of ca -196°C.

The hermeticity test is done in several steps:

Step 1 – at ambient temperature

Test done with nitrogen (N2) at a pressure of 6,9 bar
Test done with helium (He) at a pressure of the nominal pressure of the class.
The test duration is of 0,25 min for diameters up to DN 50 (2”), of 0,5 min for diameters up to DN 200
(8”) and of 1,0 min for larger diameters.

The acceptance criteria are:

For the test done with nitrogen apply the criteria of ISO 5208 Rate A
For the test done with helium the acceptable leakage is ≤ 1000 mm3/sec x DN

Step 2 – test at the specified temperature (till -196°C)

Test done with helium (He) at a pressure of the nominal pressure of the class.
The test duration is of 0,25 min for diameters up to DN 50 (2”), of 0,5 min for diameters up to DN 200
(8”) and of 1,0 min for larger diameters.
The acceptance criteria is: ≤ 1000 mm3/sec x DN
The valve must be actuated 20 times, and the required actuation torque should be measured at the
first and last cycle.

Step 3 – test with the valve at room temperature (the cooling must be done in still air)
Test done with helium (He) at a pressure of the nominal pressure of the class.
The test duration is of 0,25 min for diameters up to DN 50 (2”), of 0,5 min for diameters up to DN 200
(8”) and of 1,0 min for larger diameters.
The acceptance criteria is: ≤ 1000 mm3/sec x DN
The required actuation torque should be measured again.

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