Do Sea Freight Cases always need a vacuum bag?

Answer: Above 60 L and 35 days, yes; the bag holds residual air under 8% so the 20 g/m³ dose applies instead of triple.

Is 20 g/m³ based on case or box volume?

Answer: Case interior. A 65 m³ hold would need 1.3 kg, and that is the bar figure, not the sachet.

Can the 18-layer stack stay on Sea Freight Cases?

Answer: At 12 layers with honeycomb sheets, bottom load drops from 400 kg to 260 kg and gasket squeeze holds at 30%.

How is pallet moisture checked?

Answer: A pin meter, three points, highest reading wins. Over 20%, swap or dry the pallet.

Does white rust on Sea Freight Cases need action?

Answer: Clean it and keep the part; red rust means replacement. The 304 upgrade costs USD 0.14 a case.

Sea Freight Cases: Three Moisture Failure Points

Quick answer: Sea Freight Cases lose their seal to three physical points inside a 40-foot box: night condensation, 18-layer stack load and 30 days of salt fog.

Condensation: the 45 °C to 20 °C Gap
Desiccant Dose: 20 g/m³ of Volume
Stack Load: 18 Layers, 400 kg
Pallets and Salt Fog
The 48 Hours Before Packing
Vacuum Bags and USD 1.10
FAQ

1. Condensation: the 45 °C to 20 °C Gap

A 40-foot high cube runs 12.03 m long and 2.39 m high inside. On an equatorial run the steel roof hits 45 °C at noon and falls to 20 °C after dark, so relative humidity climbs from 60% to 95% and the case skin collects the difference.

Air at 45 °C and 60% RH holds 39 g of vapour per cubic metre. At 20 °C saturation allows 17.3 g, leaving 21.7 g to condense, which is 0.6 L to 1.2 L a night across 110 m² of wall. Vapour enters at the O-ring face and valve membrane, not through 5 mm of PP at under 0.02 g a day. Thirty days at sea is thirty cycles, and net silica uptake falls to 40% of rated, so Sea Freight Cases are judged on swing and dwell time rather than average humidity.

Time	Air temp	RH	Dew point	Case skin
06:00	20 °C	95%	19 °C	Wet all over
12:00	45 °C	60%	35 °C	Dry
00:00	24 °C	88%	22 °C	Running water

2. Desiccant Dose: 20 g/m³ of Volume

Silica gel holds 22% of its weight at 25 °C and 80% RH, but only 12% at 40 °C. With 45 °C by day, a charge works at half its room-temperature efficiency.

Dose on interior volume, never on the whole container volume. A sealed case takes 20 g/m³. Paper cushioning or EVA foam means ×1.5, since both sit at 8% to 10% moisture; no vacuum bag means ×3.

Interior volume (m³)	20 g/m³ (g)	Paper ×1.5 (g)	No vacuum ×3 (g)
0.04	0.8	1.2	2.4
0.06	1.2	1.8	3.6
0.12	2.4	3.6	7.2

A 2 g sachet is the smallest pack, so 0.8 g rounds up to 2 g. For Sea Freight Cases, add 1 kg bars, four per 40-foot box and 4.2 g equivalent a case.

Sea Freight Cases stacked: black shell closed, two red catches, flat parting line

3. Stack Load: 18 Layers, 400 kg

Interior height is 2.39 m and a 130 mm flat case measures 132 mm cartoned, which allows 18 layers. Four cases a layer on a 1.2×0.8 m pallet gives 72 cases at 400 kg, all on four bottom cartons.

A carton with 5.2 kN/m edge crush resists 3.4 kN. Moisture from 8% to 14% cuts that 40% to 2.0 kN, dropping the safety factor from 4 to 2.4, and thirty days above 80% RH guarantees the climb. Compression of 12 mm then takes lid overlap from 8 mm to 5 mm and gasket squeeze from 30% to 18%, which fails the 1 m, 30 min immersion test.

Three fixes for Sea Freight Cases: a 5 mm honeycomb sheet every 6 layers, a 1.6 m cap at 12 layers, and a three-runner base, cutting bottom load from 400 kg to 260 kg.

4. Pallets and Salt Fog

Wood packaging leaves under ISPM 15, core at 56 °C for 30 min plus an IPPC stamp. An untreated pallet is held whole at destination, against USD 35 a pallet and from USD 120 a day in storage.

Keep pallet moisture under 20%. A 22 kg pine pallet drying from 22% to 12% releases 2.2 kg of water, a humidifier running 20 days inside the box. Hours above 80% reach roughly 200 on a 30-day voyage: an 8 μm zinc latch shows white rust at 96 h, 12 μm reaches 240 h, 304 stainless runs 500 h. Zinc and aluminium sit 0.9 V apart, so corrosion at a rivet hole runs 3 times faster within 0.5 mm — hence 304 latches and nylon washers on Sea Freight Cases builds.

Sea Freight Cases conditioning: orange case open, grey foam cut for two tools

5. The 48 Hours Before Packing

Hold the case at 23 °C and 50% RH for 48 hours. PP absorbs under 0.01%, so the liner is the issue: EVA takes 1.5% to 3%, and a 1.2 kg liner carries 30 g of water, enough to push interior humidity to 70%.

Seal within 20 min of leaving the conditioning room; past 40 min and 3 °C of skin offset, the trapped air already carries risk. Stretch wrap is not waterproofing, it breaks the capillary path up the wall: 0.02 mm PE, three turns at 50% overlap, 40×40×3 mm guards, five-wall carton, 50 mm tape over hand holes, about 90 s a case. Guards also cut local pressure from 1.8 MPa to 0.6 MPa and corner cracking by 70%, which matters on an 18-layer Sea Freight Cases order.

6. Vacuum Bags and USD 1.10

The set is a vacuum bag, a desiccant charge and a humidity card. Use 0.1 mm PA/PE pulled to -0.08 MPa, residual air under 8%, and a three-spot card at 5%, 10% and 60% inside the lid.

Item	Specification	USD a case	Function
Wrap and guards	0.02 mm, 3 turns	0.12	Breaks capillary path
Foil bag	0.08 mm	0.35	Reflects radiant heat
Vacuum bag and 2 g silica	0.1 mm PA/PE	0.48	Holds interior under 40%
Card and conditioning	5%/10%/60%	0.15	Read at arrival

Sea Freight Cases above 35 days and 60 L take the full set at USD 1.10, 6% of an USD 18 case; under 20 days and 30 L, wrap, guards and a sachet cost USD 0.20. The foil bag earns its USD 0.35 on an equatorial run, cutting the swing inside the case from 25 °C to 9 °C and condensation by over 60%.

Conclusion

Sea Freight Cases fail on three numbers: a 25 °C daily swing, 400 kg on the bottom tier and 200 hours above 80% RH. Fit 20 g/m³ of interior volume plus four 1 kg bars, cap the stack at 12 layers with honeycomb sheets, verify pallet moisture under 20% and move latches to 304 stainless. At USD 1.10 a case against USD 18, the set buys a gasket that still seals on arrival.