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MIL-STD-750 Method 1011.1 Immersion Testing

The MIL-STD 750 immersion testing is performed to determine the effectiveness of the seal of component parts. The testing requires immersion of the part under evaluation into liquid. The liquid is at widely different temperatures, which subjects the part to thermal and mechanical stresses. These stresses readily detect a defective terminal assembly, or a partially closed seam or molded enclosure.

These types of defects can result from faulty construction or from mechanical damage. These results are similar to those that might be produced during physical or environmental tests. The immersion test is generally performed immediately following such tests because it will tend to aggravate any incipient defects in seals, seams, and bushings, which might otherwise escape notice. The MIL-STD 750 testing standard is a good guide for completing case testing and enclosure testing.

The MIL-STD 750 immersion test is essentially a laboratory test condition. This particular test procedure is intended only as a measurement of the effectiveness of the seal following this test. The immersion test lab can apply fresh or salt water as a test liquid. The decision should be dependent on the nature of the component part under test. Using salt solution instead of fresh water will facilitate detection of moisture penetration. This occurs when electrical measurements are made after immersion cycling to obtain evidence of leakage through seals.

This test provides a simple and ready means of detection of the migration of liquids. Effects noted can include lowered insulation resistance, corrosion of internal parts, and appearance of salt crystals. The test described is not intended as a thermal shock or corrosion test, although it may incidentally reveal inadequacies in these respects.

The test procedure of this ingress protection testing, consists of successive cycles of immersions, each cycle consisting of immersion in a hot bath of fresh (tap) water at a temperature of 65° +5°, -0 °C (149° +9°, -0 °F). This is followed by immersion in a cold bath. The number of cycles, duration of each immersion, and the nature and temperature of the cold bath shall be as indicated in the applicable test condition listed in the table below.

Test ConditionNumber of CyclesDuration of Each ImmersionImmersion BathTemperature of Cold Bath
A215Fresh or Tap Water25⁰ C (+10,-5)
B215Saturated Solution of Sodium Chloride and Water25⁰ C (+10,-5)
C560Saturated Solution of Sodium Chloride and Water0⁰ C +3

The transfer of specimens from one bath to another shall be accomplished as rapidly as practicable. After completion of the final cycle, specimens shall be thoroughly and quickly washed and all surfaces wiped or air-blasted clean and dry.

Unless otherwise specified, measurements shall be made at least four hours, but not more than 24 hours, after completion of the final cycle. Measurements shall be made as specified. The following details are to be specified in the individual specification. First, there should be a test condition letter. Next, the time after the final cycle allowed for measurements. Lastly, the measurements after the final cycle should be thoroughly noted.

As a leader in ingress protection testing, Keystone Compliance is the chosen MIL-STD 750 immersion testing lab of many manufacturers. We have comprehensive capabilities with ingress protection and all other mechanical / environmental testing. Contact us to request a quote and realize firsthand why so many companies trust Keystone Compliance as their immersion test lab.