MIL-STD-202H.pdf - 第84页
MI L - S TD - 202 - 112 4 . GENERAL REQUI R e ME N T S 4.1 . Test co nditions . 4.1 .1 Sel ectio n . Ther e ar e s i x t es t c on di t i on s ( A , B , C , D , E , and F ) i n t hi s m e t hod . T es t c onditions A and…
MIL-STD-202-112
METHOD 112
SEAL
1. SCOPE
1.1 Purpose. The purpose of this test method is to determine the effectiveness of the seal of a component part
which has an internal cavity which is either evacuated or contains air or gas. A defect in any portion of the surface
area of a sealed part can permit entrance of damaging contaminants which will reduce its effective life. This test will
detect leaks due to the use of inferior sealing materials, or to the manufacturing processes used to form the seal.
The degree of completeness of the seal can be verified by testing in the "as received" condition or after submission to
other environmental or physical-characteristics tests, such as thermal shock, physical shock, or vibration. This test
method does not include the many existing versions of lesser-sensitivity seal tests now appearing in some
specifications, which verify such requirements as "water tightness", "moisture proofness", etc. In those
lesser-sensitivity seal tests, parts are submerged to various depth in water, heated water, water or alcohol with a
vacuum, water with a wetting agent, etc; all these tests depend on observation of bubbles as the criterion for failure.
2. APPLICABLE DOCUMENTS
This section not applicable to this standard.
3. DEFINTIONS
3.1 Standard leak rate. Standard leak rate is defined as the quantity of dry air at 25°C in atmospheric cubic
centimeters flowing through a leak or multiple leak paths per second when the high-pressure side is at 1
atmosphere (760 mm Hg absolute) and the low-pressure side is at a pressure of not greater than 1 mm Hg
absolute. Standard leak rate shall be expressed in units of atmospheric cubic centimeters per second (atm
cm
3
/s).
3.2 Measured leak rate. Measured leak rate (R
1
) is defined as the leak rate of a given package as measured
under specified conditions and employing a specified test medium. Measured leak rate shall be expressed in
units of atmospheric cubic centimeters per second (atm cm
3
/s). For the purpose of comparison with rates
determined by other methods of testing, the measured leak rates must be converted to equivalent standard
leak rate.
3.3 Equivalent standard leak rate. The equivalent standard leak (L) rate of a given package, with a measured leak
rate (R
1
), is defined as the leak rate of the same package with the same leak geometry, which would exist
under the standard conditions of 1.1a. The formula (does not apply to procedure IIIb) in 4.4.4.3.2.3 represents
the L/R
1
ratio and gives the equivalent standard leak rate (L) of the package with a measured leak rate (R
1
)
where the package volume and leak test conditioning parameters influence the measured value of (R
1
). The
equivalent standard leak rate shall be expressed in units of atmospheric cubic centimeters per second (atm
cm
3
/s).
3.4 Sensitivity. (Minimum detectable leak rate). Sensitivity is the smallest leak rate that an instrument, method, or
system is capable of measuring or detecting under specified conditions. To compare sensitivities of two or
more different test conditions, the sensitivity should be converted to sensitivity under standard conditions by
using the appropriate conversion factors.
3.5 Ambient background. For a scintillation-crystal counting station, ambient background is the oscillatory reading
obtained on the meter readout due to electrical noise plus the reading in counts per minute due to cosmic
radiation that penetrates the lead shielding of the closed crystal system. This value must be determined just
before device counting.
1
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MIL-STD-202-112
4. GENERAL REQUIReMENTS
4.1. Test conditions.
4.1.1 Selection. There are six test conditions (A, B, C, D, E, and F) in this method. Test conditions A and B utilize
oil as a means to detect gross leaks by the observation of bubbles. Both of these tests will detect leaks of a nominal
value of 10
-5
atm cm
3
/s. Test condition B is used to test parts which will not withstand the temperature required in
test condition A. Test condition C detects fine leaks by using a tracer gas and apparatus to measure a leakage rate
(R
1
) to a nominal of 10
-8
atm cm
3
/s. The apparatus can be calibrated for any leakage rate within its range. Test
condition D utilizes a fluorocarbon liquid at 125°C ±5°C (257°F ±9°F) at ambient pressure and detects gross leaks by
the observation of bubbles. This latter test condition provides an alternate gross leak test to test condition A. Test
condition E utilizes two fluorocarbon liquids; one under pressure followed by the other at 125°C ±5°C (257°F ±9°F) at
room ambient pressure and detects gross leaks by the observation of bubbles. This test condition provides a
measure of leakage rate of a nominal value of 10
-5
atm cm
3
/s. Test condition F utilizes a fluorocarbon liquid and a
fluorocarbon vapor detector to detect gross leaks. Test condition F provides a measure of leakage rate of a nominal
value of 10
-5
atm cm
3
/s. Both test conditions C and F require more expensive commercial equipment and trained
personnel, but the equipment provides automatic and quantitative readings. The selection of a test condition to
perform the seal test depends on the state of the art of component part manufacturing, the leakage rate which can be
tolerated for the desired reliability, the frequency of testing, range of test conditions, cavity size, and whether the
testing is to be on a 100 percent production or on a periodic basis. The individual specification shall specify the test
condition letter required. When test condition C is specified, the procedure number (see 4.4.4) and the degree of
leakage rate sensitivity required shall be included. The following is included as a sensitivity and applicability guide:
Test condition A (bubble test - mineral oil or peanut oil at 125°C ±3°C (257°F ±6°F)). Use when a nominal
sensitivity of 10
-5
atm cm
3
/s is sufficient.
Test condition B (bubble test - silicone oil at room ambient temperature 25°C ±2°C (77°F ±3.6°F), with a vacuum
resulting in an absolute pressure of not greater than 1.5 inches of mercury (not greater than 38.1 torr). Use to
test parts which cannot withstand the temperature of test condition A, and when a nominal sensitivity of 10
-5
atm
cm
3
/s is sufficient.
Test condition C (tracer gas test). Use when a nominal sensitivity of 10
-8
atm cm
3
/s is sufficient.
Procedure I - (For parts having an evacuation tube which is unsealed and is to be connected to the leak
detector for test purposes.)
Leak from outside of part to inside. Check the seal of evacuation tube by backfilling with
air or gas. Then subject to procedure IIIa, IIIb, IIIc or IV.
Procedure II - (For parts having an evacuation tube which is unsealed to permit pressurizing with a
tracer gas.)
Leak from inside of part to outside. Check the seal of evacuation tube by backfilling with
air or gas. Then subject to procedure IIIa, IIIb, IIIc, or IV.
Procedure III - (For parts which are to be tested without breaking their seals.)
Fixed method (IIIa) - Part not filled with tracer gas. Force gas into leaks, then detect its
escape. Then subject to test condition A, B or D (see 4.4.4.3.2.1 permitting use of water),
as applicable, to check for gross leaks.
IIIb - Part not filled with tracer gas. Force radioactive gas into leaks, then use a
radioactivity counter to determine gas that has entered part. Then subject to test condition
A, B, or D (see 4.4.4.3.2.2.4 permitting use of water), as applicable, to check for gross
leaks.
2
北测（上海）电子科技有限公司
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MIL-STD-202-112
Flexible method (IIIc). Part not filled with tracer gas. Force gas into leaks then detect its
escape. Then subject to test condition A, B or D (see 4.4.4.3.2.3 permitting use of water),
as applicable, to check for gross leaks.
Procedure IV - (For parts which are to be tested without breaking their seals.) Parts backfilled with tracer
gas as normally supplied.
Leak from inside of part to outside, then subject to test condition A, B or D (see 4.4.4.4
permitting use of water), as applicable, to check for gross leaks.
Test condition D (gross leak bubble test - Fluorocarbon liquid at 125°C ±5°C (257°F ±9°F). Use as an
alternate when test condition A is specified as a gross leak test.
Test condition E (bubble test - two fluorocarbon liquids - one at pressure followed by immersion in a second
liquid at 125°C ±5°C (257° ±9°F). Use when a nominal sensitivity of 10
-5
atm cm
3
/s is sufficient.
Test condition F (fluorocarbon vapor detection test). Use when a nominal sensitivity of 10
-5
atm cm
3
/s is
sufficient.
4.1.2 Substitution. The individual specification should specify the lowest sensitivity test condition which is
practical; a higher sensitivity test which can be calibrated shall be permitted, i.e., if a test is specified such as test
condition A requiring a sensitivity of 10
-5
atm cm
3
/s, test condition C may be used since it can be calibrated to read
this leakage rate. Substitution of test condition B or C should be made to test condition A when parts are rated at a
temperature lower than 130°C (266°F). Test condition D may be substituted for test condition A.
4.2. Test condition A.
4.2.1 Materials.
4.2.1.1 Mineral oil or peanut oil. The oil used for the bath shall be clear mineral oil or peanut oil having a universal
Saybolt viscosity of 175 to 190 seconds when tested at 38°C (100°F).
4.2.2 Apparatus.
4.2.2.1 Heated oil container. The container for the oil bath shall be of sufficient depth to immerse the uppermost
portion of the enclosure or seal to be tested to a depth of 1 inch (25.4 mm) below the surface of the bath. The
container shall be capable of maintaining the oil at the required temperature.
4.2.3 Precautions. This condition shall not be used for parts rated at a temperature lower than 130°C (266°F). It
shall not be used for parts which contain seals made of materials which will outgas due to the temperature of the
bath.
4.2.4 Preparation of specimens. Immediately before immersion it shall be determined that the specimen is at room
ambient temperature and free of any foreign (including labels) matter. If applicable, the critical side of the specimen
shall be determined. The critical side is defined as the side having the greatest number of seals or length of seal.
4.2.5 Procedure. This test consists of one immersion of the specimen or groups of specimens into a bath of clear
mineral oil or peanut oil (see 4.2.1.1) maintained at a temperature of 125°C ±3°C (257°F ±6°F). The specimen shall
be placed in the oil bath with the critical side (or side of special interest) in a horizontal position facing up. If the
specimen has no critical side, it shall be placed in the bath with its major axis in a horizontal position. The specimen
shall be completely submerged in the bath, with the uppermost portion of the enclosure or seal at a depth of 1 inch
(25.4 mm), and left in that position for a minimum duration of 1 minute. The specimen shall be carefully observed
during the entire duration of the immersion for indication of a poor seal as evidenced by a continuous stream of
bubbles emanating from the specimen. After the test is completed, the specimen shall be cleaned in a suitable
degreaser and permitted to dry thoroughly before any additional tests are performed.
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