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MIL-STD 202 Seal Testing

This test helps determine the effectiveness seals on component parts which have internal cavities that are either evacuated or contain air or gas. A defect could allow enclosure ingress of damaging contaminants. This test will detect leaks resulting from inferior sealing materials, the manufacturing processes. The degree of completeness of the seal is verified by testing “as received” or after thermal shock, physical shock, or vibration.

This test method does not include the existing versions of lesser-sensitivity seal tests. In those lesser-sensitivity seal tests, parts experience immersion ingress at various depths and in various liquids. All these tests depend on observation of bubbles as the criterion for failure.

Keystone Compliance is an ingress protection lab with significant understanding of MIL-STD-202 seal testing. Our test engineers are experts in MIL-STD 202H seal testing and MIL-STD 202G seal testing. Below is outlined the requirements of water enclosure testing for seals. The following information is technical in nature, derived from MIL-202H seal and MIL-202G seal sections.

What Definitions are Need to Understand this Method of IP Code Testing?

Standard leak rate is the quantity of dry air at 25°C in atmospheric cubic centimeters, flowing through a leak path per second. This is when the high-pressure side is at 1 atmosphere and the low-pressure side is at a pressure of no more than 1 mm Hg absolute.

Measured leak rate (R1) is the leak rate of a given package, measured under specific conditions and employing a specified test medium.

The equivalent standard leak (L) rate of a package, is the leak rate of the same package with the same leak geometry, which would exist under standard conditions.

Sensitivity or minimum detectable leak rate,  is the smallest leak rate that an instrument, method, or system can measure or detect under specified conditions.

Ambient background, for a scintillation-crystal counting station, is the oscillatory reading obtained on the meter readout due to electrical noise. It also includes the reading in counts per minute due to cosmic radiation that penetrates the lead shielding of the closed crystal system.

What are the Test Conditions for Water Ingress Testing for Seals?

There are six test conditions in this method. Test conditions A and B utilize oil as a means to detect gross leaks by the observation of bubbles. Test condition C detects fine leaks by using a tracer gas and apparatus to measure a leakage rate (R1). The apparatus can be calibrated for any leakage rate within its range.

Test condition D utilizes a fluorocarbon liquid at 125°C +5°C at ambient pressure and detects gross leaks by bubbles. Test condition E utilizes two fluorocarbon liquids. One under pressure followed by the other at 125°C plus or minus 5°C at room ambient pressure. It detects gross leaks by the observation of bubbles.

Test condition F utilizes a fluorocarbon liquid and a fluorocarbon vapor detector to detect gross leaks. Both test conditions C and F require more expensive commercial equipment and trained personnel. All testing should be done in a seal testing lab.

The selection of a test condition depends on the state of the art of component part manufacturing, and on the leakage rate. Other factors include the frequency of testing, range of test conditions, cavity size, and if testing is needed on a periodic basis. The individual material specification will specify the test condition letter required.

Test Condition A

Clear mineral or peanut oil with a universal Saybolt viscosity of 175 – 190 seconds, when tested at 38°C, is used for the bath. The container for the oil bath must be deep enough to immerse the seal 1 inch below the surface of the bath. The container must be capable of maintaining the oil at the required temperature.

Test Condition B

Clear silicone oil with viscosity of 20 centistokes at 25°C, is typically used for this bath. The vessel for the oil bath must be deep enough to immerse the seal 1 inch below the surface of the bath. Over this can be drawn a vacuum resulting in an absolute pressure of no more than 1.5 inches of mercury. The vacuum pump must be able to evacuate and hold a vacuum at absolute pressure for at least 1 minute.

The silicone oil must be degassed, and cannot be poured from one container to another without first being degassed again before testing. This is done by placing it in the test fixture and attaining a pressure of 1 inch of mercury or less until it degases. Degassing is complete when there is no further bubbling or frothing. Components are gently lowered in the fluid to prevent aeration of the fluid.

Test Condition C

When performing tests in accordance with several procedures of this condition, tracer gases are used. These may include helium, argon, or other rare gas, or a mixture of a gas with nitrogen. The apparatus for this condition, excluding the pressurization equipment, is calibrated with a diffusion type calibrated standard leak at least once each working shift.

Enclosure testing lab equipment for this procedure includes mass-spectrometer-type leak detectors, chambers, pumps, and radioactive-gas detection apparatus. The mass-spectrometer-type leak detector is used to measure the leakage rate of gas through a faulty seal. Another instrument may be used if it is shown that it is properly calibrated to read tracer-gas content, and has the required leakage-detection sensitivity.

Test Condition D

Fluorocarbon liquid in a Pyrex glass container is used for this test condition. The container must hold the test specimen in the fluid and maintain a temperature of 125°C plus or minus 5°C. A filter is used which is capable of removing particles greater than 1 micron in size from the fluid. A 3X minimum magnifier or a stereo zoom microscope is used to observe bubbles emanating from the immersed test specimens.

Test Condition E

Fluorocarbon detector and indicator fluids, in a Pyrex glass container are used for this method. The container must be able to hold the test item in the fluid and maintain a temperature of 125°C + 5°C. A filter is  used which is capable of removing particles greater than 1 micron in size from the fluid. A magnifier with a range between 3X to 30X is used to observe bubbles from devices immersed in the indicator fluid.

A vacuum/pressure chamber is used for the evacuation and subsequent pressure bombing of devices up to 75 lbf/in2 up to 10 hours. A lighting source capable of producing at least 15,000 foot candles in air at a distance equal to that of  the most distant device in the bath is needed. Suitably calibrated instruments indicate the test temperature pressures and times. Suitable fixtures hold the device(s) in the indicator fluid.

Test Condition F

Fluorocarbon detector fluid, filtered through a system able to remove particles greater than 1 micron in size, is used. This condition requires a vacuum/pressure chamber able to evacuate, pressure bomb of devices up to 75 psi, and maintain pressure for 12.5 hours.

Also needed is a fluorocarbon vapor detection system with a nominal sensitivity of 10-5 atm cm3/s. The sensitivity of the detector must be better than 14 micrograms of FC84 or D/80. The detector should have a linear response to 280 micrograms and a response time of better than 1 second.

This test also requires suitably calibrated instruments to indicate that test, pressure times and temperatures are as specified. The detection system should be calibrated using a calibration source of fluorocarbon to an accuracy of at least ±15 percent. Calibration should happen at least once each shift .

Which Enclosure Testing Lab Will Provide the Best Seal Testing for my Product?

Keystone Compliance has been recognized as one of the best seal labs in the country. We employ experienced test engineers to provide quality seal compliance testing. Our seal laboratory is fully equipped to meet all the required test conditions to provide seal certifications for a variety of products.

Are you looking for ingress protection testing for your product? Keystone compliance is capable of providing IP Code Certification for commercial, military, and aerospace products. Contact us to learn why so many manufacturers rely on Keystone Compliance to meet their compliance testing needs.