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For shell and backseat tests, no visible leakage is
permitted. If the fluid is a liquid, there shall be no visible evidence
of drops or wetting of the external surfaces (no visible leakage through
the body, body liner, if any, and body-to-bonnet joint and no structural
damage). If the test fluid is air or gas, no leakage shall be revealed
by the established detection method. For both the low-pressure closure
test and the high-pressure closure test, visual evidence of leakage
through the disk, behind the seat rings, or past the shaft seals
(of valves that have this feature) is not permitted (Plastic deformation
of resilient seats and seals is not considered structural damage).
The allowable rate for leakage of test fluid past the seats, for the
duration of the tests, is listed in the following table: |
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MAXIMUM ALLOWABLE LEAKAGE RATES FOR CLOSURE TESTS:
| Valve
Size (NPS) |
All Resilient-Seated
Valves
|
All Metal-Seated Valves
(except Check Valves)
|
Metal-Seated Check
Valves
|
|
Liquid Test
|
Gas Test
|
Liquid Test
|
Gas Test
|
|
(drops/min.)
|
(bubbles/min.
|
(drops/min.)
|
(bubbles/min.)
|
| <= 2" |
0 |
0 (b) |
0 (b) |
(c) |
(d) |
| 2.5 - 6" |
0 |
12 |
24 |
(c) |
(d) |
| 8 - 12" |
0 |
20 |
40 |
(c) |
(d) |
| >= 14" |
0 |
28 |
56 |
(c) |
(d) |
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(a) For the liquid
test, 1 millimeter is considered equivalent to 16 drops. |
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(b) There shall
be no leakage for the minimum specified test duration. For liquid
test, 0 drop means no visible leakage per minimum specified test duration.
For gas test, 0 bubble means less then 1 bubble per minimum specified
test duration. |
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(c) The maximum
permissible leakage rate shall be 0.18 cubic inch (3 cubic centimeters)
per minute per inch of nominal pipe size. |
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(d) The maximum
permissible leakage rates shall be 1.5 standard cubic feet (0.042
cubic meter) of gas per hour per inch of nominal pipe size. |
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(e) For check
valves larger than NPS 24, the allowable leakage rate shall be per
agreement between purchaser and manufacturer |
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The allowable leakage rates for valves tested to MSS
SP-61, 1999 are as follows: |
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GATE, GLOBE, BALL VALVES: 10 cc/hr per inch of nominal
pipe diameter. (Example: A 4” globe valve is allowed to leak 40 cc/hr
in a test) |
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CHECK VALVES: 40 cc/hr per inch of nominal pipe diameter. |
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All shutoff or isolation valves specified to MSS SP-61
must pass the above standards. The seat closure test must be performed
at a fluid (liquid or gas) pressure no less than 1.1 times the 1000°F
(380°C) rating rounded to the next 5 psi (0.5 bar). |
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