How long a shipping container lasts, and how to get more out of it

What kills a container on land

Containers do not wear out from use the way machinery does. They corrode, and corrosion needs three things: moisture, oxygen and time. Remove the moisture and the clock effectively stops.

There is a hierarchy of failure and it is worth knowing because it tells you where to spend your attention.

1. Bottom rails and cross members. The number one killer. Water sits under a container that is set too low, grass grows against the steel and holds it there, and the corrosion happens on the underside where nobody looks until a foot goes through the floor.
2. Floor. Marine ply is durable but it is still timber. Once water gets to it, from a roof pinhole above or a rotted cross member below, it delaminates and goes spongy.
3. Roof. Thin corrugated steel with dents that pond water. Ponded water plus a chipped coating equals a pinhole in a few years.
4. Door hardware and gaskets. Gaskets harden and set, hinges seize, cams stop engaging. Rarely fatal, always annoying, cheap to fix if caught.
5. Side panels. Last to go. Dents and surface rust look dramatic and matter least.

Notice that the things that kill a container are all at the bottom, and the things people worry about are all at eye level.

Realistic lifespans

Nobody can put a warranty on this, and anyone giving you a precise figure is guessing. What can be said honestly is how the variables stack up.

A sound used unit, set on pads with air underneath, on a dry inland site, painted once in its life, is still perfectly serviceable twenty-five or thirty years after it left the wharf. A new one-trip unit in the same conditions has longer again, because it starts with intact factory coating everywhere including the underside.

Cut those numbers hard for these conditions:

• Salt air. Within a kilometre or two of the beach the coating is under constant attack. Coastal sites want more frequent inspection and a repaint sooner.
• The tropical wet. High humidity and long wet seasons through the north keep everything damp for months at a time.
• Direct ground contact. A unit sitting on soil with grass against the rails can be perforated in under a decade.
• Shade and vegetation. A container under trees never dries out, collects leaf litter that holds water on the roof, and gets dripped on constantly.
• Industrial atmosphere. Anywhere with corrosive fallout in the air.

The units that fail early nearly all share the same photograph: sitting flat on dirt, grass to the rails, under a tree, doors facing the weather.

The three things that add the most years

1. Get it off the ground and keep air moving under it

This is worth more than everything else combined. Pads under the four corner castings that raise the box 100 to 200 mm let air circulate underneath, let the steel dry after rain, and stop capillary moisture wicking up into the cross members. It also lifts the floor away from ground damp, which helps with condensation inside.

Do it at delivery, because doing it afterwards means jacking a standing container. Hardwood sleepers, besser blocks bedded on firm ground, stacked pavers or poured concrete pads all work.

2. Control where water goes

Do not site a container in the low point of a yard or across the path water takes after real rain. Put gravel or weed mat under it before it lands. Keep the grass down around and under it — a whipper snipper twice a year is the cheapest maintenance in this entire guide.

On the roof, clear leaves and debris out of the corners and off the top rails. Anything that holds moisture against the steel is a future hole.

3. Look at it once a year

Fifteen minutes, once a year, ideally at the end of winter or after the wet. Kneel down and look along both bottom rails at eye level with the ground. Look at all four corners. Get up and look across the roof at a low angle for ponding and patches. Shut yourself inside for thirty seconds and look for daylight. Work the locking bars.

Everything on that list is free, and every one of them catches something years before it becomes a repair.

Rust: what to do about it and when

Surface rust is not an emergency. It is the paint failing, not the steel. Left alone in a dry climate a container will carry patches of it for years without consequence. Left alone near the coast it will not.

The treatment is the same as any steel: get the loose material off, kill what is left, and put a coating back on. Wire brush, grinder with a flap disc, or a needle scaler for the serious stuff. Then a rust-converting primer or a zinc-rich primer, then a topcoat. Any decent exterior enamel or an industrial direct-to-metal coating works; the trick is preparation, not product.

Priorities, in order: bottom rails first, roof second, door frames and hardware third, walls last. That is the reverse of the order people actually paint in, because walls are where the paint shows.

Perforation — a hole rather than a stain — is a different job. Small holes can be cleaned back and welded, ground and coated. A rail that has gone soft over a long run needs a section replaced, and that is fabrication work. Neither is a job for silicone or tape, and a unit patched that way should be treated as one that will let water in.

Repainting a container properly

People repaint for appearance, and get a durability benefit as a bonus. Both are legitimate.

Clean it first. Pressure wash, degrease anything oily, and let it dry properly. Sand or wire brush every failed area back to sound material. Spot prime the bare steel. Then two coats of topcoat, brushed, rolled or sprayed. A light colour reflects heat and will measurably reduce how hot the inside gets on a summer afternoon, which also cuts the condensation load.

Do not skip the underside of the door bottoms and the inside faces of the rails. Those are where the water actually sits and they are the areas everyone misses because they cannot be seen from standing height.

A container painted a plain colour also draws far less attention from neighbours and from councils than one still wearing a shipping line's livery and a decade of rust streaks.

Gaskets, hinges and the door end

The door end is the only moving part and it is where most of the annoyance lives.

Grease the hinge pins and the locking bar cams once a year — any general purpose grease is fine. If a bar is stiff, deal with it now: a seized bar gets forced, a forced bar gets bent, and a bent bar is a new bar.

Check the gaskets by hand. They should feel supple. When they harden and take a set, they stop sealing along the bottom of the doors, which is exactly where you will not notice water getting in until something on the floor is wet. Replacement gasket is inexpensive and it is a job a competent person can do in an afternoon.

And if a bar has suddenly become stiff when it was fine last year, do not start with the hardware. Go and check the pads. Nine times out of ten a corner has settled and the frame has twisted slightly, and re-levelling fixes the doors immediately. Leave it long enough and the steel takes a set it will not come back from, so the door end stays twisted after the pads are fixed.

Buying with lifespan in mind

If you want thirty years out of a container, two decisions at purchase matter more than everything you do afterwards.

The first is grade. New and cargo-worthy units are checked wind and watertight before leaving the yard, and they still have the bones for decades. Units sold as-is are not sold watertight, and while they are entirely appropriate for a scrap store or a shell, they are not the unit to buy if you want it standing and dry in 2050. The grades page lays this out.

The second is what is under it on day one. Prepare the pads before the truck comes. It is an afternoon of work and it is worth more to the container's life than any amount of paint.

If you want an honest read on how much life is left in a particular unit, ask — we will tell you what we see on the bottom rails and the floor, and we send photographs of the actual container on request and before delivery. Ring 1300 467 776, or read what we check on the inspection page.