Why test the seal before the drop in a Military Supply Case inspection?

Answer: Pressure hold and immersion are non-destructive, so the sample survives. A dropped case already carries damage, so a later seal failure could not be traced.

Is a sample of 13 enough?

Answer: Enough to accept or reject a lot at AQL 2.5, not to diagnose a process. To locate drift, sample one cavity over three lots.

What pressure decay is acceptable?

Answer: 1 kPa after 60 seconds at 20 kPa. Decay scales with volume, so large cases need their own limit.

Is cold conditioning mandatory?

Answer: For anything stored below freezing, yes. A room-temperature drop proves structure only, while most cracks appear at minus 18 °C.

Can appearance defects be reworked?

Answer: Only away from the sealing face. Sink marks and flash elsewhere can be trimmed and rechecked; one on the sealing face cannot be repaired without disturbing flatness.

Military Supply Case Inspection: Appearance, Seal and Drop Tests

Quick answer: A Military Supply Case is accepted on three tests. Appearance covers sink marks, flash, colour and wall, read with a depth gauge and an ultrasonic meter. Seal covers pressure hold, immersion and IP rating, read by decay and bubbles. Drop covers corner, edge and face, read by height and count.

Inspection Items and Sampling
Appearance Checks
Seal Checks
Drop Checks
Judgement and Disposition
FAQ

1. Inspection Items and Sampling

Sampling comes before gauges. At inspection level II, a lot of 51 to 90 pieces draws 13 samples, a lot of 91 to 150 draws 20. Appearance runs at AQL 2.5, seal and drop at AQL 1.0, because a failure in either cannot be recovered downstream.

Samples are also split by cavity. Each cavity supplies half the sample, so drift cannot hide inside an average. One lot means one grade, one colour, one cavity and 24 hours of output.

Lot size	Samples	Appearance AQL	Seal and drop AQL
26 to 50	8	2.5	1.0
51 to 90	13	2.5	1.0
91 to 150	20	2.5	1.0

2. Appearance Checks

Appearance needs instruments; a visual pass is no verdict. Sink marks are measured with a depth gauge: none on a sealing face, up to 0.3 mm elsewhere. Flash above 0.15 mm at the parting line fails, since it props the gasket open and lets a pressure test pass falsely.

Colour difference is read under D65 and held to 1.2 within a lot. Wall thickness is checked by ultrasound at 2.8 mm plus or minus 0.15 mm, at eight points per case, four on long sides and two each at corners and rib roots.

Item	Gauge	Accept line
Sink mark	depth gauge	0 on sealing faces, else 0.3 mm
Flash	feeler gauge	0.15 mm maximum
Colour	spectrophotometer, D65	1.2 maximum
Wall	ultrasonic, 8 points	2.8 mm plus or minus 0.15

3. Seal Checks

Seal is the easiest item to fake, so the order is fixed: pressure hold, immersion, then IP rating if required. The case is charged to 20 kPa, valve closed, for 60 seconds; decay above 1 kPa fails.

Immersion is the cross-check: 100 mm under water for 30 seconds, seams watched for continuous bubbles. One bubble can be trapped air, a stream means a channel. IPX7 then runs one metre for 30 minutes.

Method	Parameter	Pass criterion
Pressure hold	20 kPa, 60 seconds	decay 1 kPa maximum
Immersion	100 mm, 30 seconds	no continuous bubbles
IP rating	IPX7, 1 metre, 30 minutes	no visible water

4. Drop Checks

Drop order is corner, edge, face, since a corner concentrates the most energy. Ballasted to rated load, the case drops 1.2 m on each of three bottom corners, 1.0 m on three bottom edges and 0.9 m once on the base, opened for inspection after every drop.

Cold conditioning is often skipped. Four hours at minus 18 °C and a drop within five minutes define a cold drop; impact strength there is roughly half the room value.

Attitude	Height	Count	Pass criterion
Corner	1.2 m	one per bottom corner	no through-crack
Edge	1.0 m	one per bottom edge	no hinge set
Face	0.9 m	one on the base	sealing face intact

5. Judgement and Disposition

The three verdicts belong on one sheet of four columns: item, point, reading, verdict. One row per case. When a row fails, the first question is whether failures cluster in one cavity.

Disposition has three levels. Cosmetic defects are reworked and rechecked; seal failures trigger a top-up of 20 pieces, then rejection; a through-crack stops the cavity, since the crack usually sits on a weld line or cooling blind spot. Readings are recorded as numbers, never as the word pass.

Conclusion

Inspection of a Military Supply Case reduces to three actions: gauges for appearance, decay and bubbles for seal, height and attitude for drop. Sampling decides whether the sample speaks for the lot; disposition decides whether a failed unit returns. Fixed in that order, a Military Supply Case inspection stops depending on who is on shift.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.