A used shipping container is one of the better value purchases available in steel — provided the one you buy is structurally sound and actually keeps water out. Most of what separates a good used box from a bad one can be assessed in twenty minutes with a flashlight, a screwdriver and a tape measure.
This is the inspection we run before a unit ships, laid out so you can run it yourself. Work through it in order; the early checks are the ones that would make you walk away, and there is no point examining door gaskets on a container with a rotted bottom rail.
Before You Start: What You Need
- A bright flashlight — the single most useful tool here.
- A screwdriver or awl for probing suspect corrosion and floor timber.
- A tape measure.
- A camera. Photograph everything; you will want the record later.
- Something to stand on, or a way to see the roof. Roof defects are the most commonly missed.
1. Structural Rust — Where It Matters
Every used container has rust. The question is never whether, but where and how deep. Containers are built from weathering steel — the alloy family covered by ASTM A588, A242 and A606, of which COR-TEN is the best-known trade name. Weathering steel is designed to form a tight surface oxide that slows further corrosion instead of flaking away, which is why cosmetic rust on a container is genuinely cosmetic.
What is not cosmetic:
| Location | Acceptable | Walk away if |
|---|---|---|
| Bottom rails | Surface bloom, light scale | Flaking layers, perforation, a screwdriver goes through |
| Corner posts and castings | Surface rust, paint loss | Deformation, cracked welds, scale at the casting |
| Cross-members (underside) | Uniform surface rust | Sagging, holes, sections eaten away |
| Side panels | Rust patches, dents | Pinholes you can see daylight through |
| Roof panels | Dents, pooling stains | Perforation, deep dents that hold standing water |
| Door frames | Surface rust | Distortion that stops the doors sealing |
Bottom rails first, always. That is where water sits, where soil contact happens, and where the structural corrosion that ends a container's life begins. If the bottom rails are sound, most other problems are repairable.
2. Floor Condition
Container floors are typically 1⅓-inch marine-grade plywood on steel cross-members, and they are engineered to serious loads — published carrier data puts the design case at a forklift axle load in the order of 5,460 kg (about 12,000 lb) with a minimum contact area per wheel, and a distributed loading of roughly 4.8 tonnes per running metre in a 20ft and 3 tonnes per running metre in a 40ft.
Check for:
- Soft spots. Walk the full length, heel down. Any flex means delamination or rot underneath.
- Delamination. Plywood splitting into its layers, usually at panel edges and around fixings.
- Gouges and forklift damage. Cosmetic unless deep enough to breach the panel.
- Staining and odour. Container floors are treated against insects and decay as a condition of international movement, and spilled cargo can leave residue. Relevant if you are storing anything food-related or sensitive to smell.
- Gaps at the edges. Where the plywood meets the side rail, gaps let in water and pests.
3. Doors, Gaskets and Gear
Doors are the most-used moving assembly on the container and the most common source of complaint after purchase.
- Open both doors fully. They should swing without lifting or forcing. Binding usually means the container is racked — either from damage or from sitting unlevel — and racking is expensive to fix.
- Work the cam-and-rod gear. Handles should rotate through their full travel and the cams should seat into the keepers. Seized gear can be freed; bent rods are a repair.
- Inspect the gaskets. Run a finger along them. They should be pliable and continuous. Flattened, cracked or missing sections let water in — cheap to replace, but budget for it.
- Check the hinges. Rust at the hinge pins is normal; elongated hinge holes or cracked welds are not.
- Close the doors and check the seal line. Even, consistent compression all round.
4. The Daylight Test
The fastest and most conclusive watertightness check there is. Step inside, close both doors, and stand still for a full minute until your eyes adjust. Then look systematically: roof, then each wall from top to bottom, then the door seal line, then the floor edges.
Any pinprick of daylight is a hole, and a hole in the roof is worse than a hole in a wall because water pools rather than runs. Photograph the position of anything you find from the inside, then locate and mark it from the outside.
Follow it with a look along the roof from above, ideally at a low angle so dents show as shadows. Dents that pond water are the leading cause of roof perforation over time, and they are invisible from ground level.
5. The CSC Plate
The CSC plate is the only part of a container that carries verifiable, dated information. Under the International Convention for Safe Containers, the plate must be permanent, non-corrosive and fireproof, at least 200 mm by 100 mm, and must show the month and year of manufacture, the maximum gross weight in both kilograms and pounds, and the stacking and racking test load values.
Containers in the periodic examination scheme show a next examination date. The scheme requires the first examination before the fifth anniversary of manufacture and subsequent examinations at intervals not exceeding 30 months, so the dates on the plate tell you both how old the unit is and whether anyone has been inspecting it recently.
If you plan to ship or stack the container, a current plate is a hard requirement. If it will sit on a gravel pad forever, the plate is still worth reading for the manufacture date alone.
6. Squareness and Racking
A container that has been dropped, badly lifted or left sitting unlevel goes out of square. The symptoms are doors that will not latch and a floor that is not flat. Check the diagonals: measure corner to corner across the door end, and compare. Sight along the top rails and the side panels for a wave or a twist.
Racking is the defect most often missed at purchase and least often economically repairable. If the doors do not close cleanly on level ground, find out why before you buy.
7. Ventilation, Vents and Modifications
Look at what somebody else has already done to the box. Factory vents are small louvred openings near the top of the side walls and should be clear. Aftermarket penetrations — cut vents, cable entries, patched holes — are worth examining closely: a badly sealed penetration is a permanent leak and a rust origin.
Quick Inspection Scorecard
| Check | Pass | Negotiate | Walk away |
|---|---|---|---|
| Bottom rails | Surface rust only | Isolated scale | Perforation or soft steel |
| Floor | Firm throughout | Localized damage | Widespread flex or rot |
| Doors | Swing and latch freely | Perished gaskets | Will not close on level ground |
| Daylight test | No light visible | One or two wall pinholes | Roof perforation |
| Roof | Flat, no ponding | Shallow dents | Deep dents holding water |
| Squareness | Diagonals match | — | Visible twist or racking |
| CSC plate | Present and legible | Missing but unit sound | Missing and needed for shipping |
Buying Without Seeing It
Most online container purchases are made from photographs, which makes the seller's honesty about grade the thing you are really buying. Ask for photographs of the interior with the doors closed, of the bottom rails, of the roof, and of the CSC plate. Ask for the grade in writing. Ask what has been repaired.
Every unit in our used inventory is inspected before dispatch and listed with the grade it actually holds — and there is a 30-day return window if it arrives other than described, with return haulage paid by the buyer and a 15% restocking fee. If you want the grade terminology explained first, the grades guide defines each one, and the buyer's guide covers the wider purchase decision.
For pure storage duty, a 40ft storage-class standard or a 45ft high cube wind-and-watertight unit covers most requirements; the standard dry containers category lets you compare grades at the same size. If you want a used 20ft box, a used 20ft storage container is the usual starting point.
Frequently Asked Questions
How much rust is too much on a used container?
Surface rust anywhere is normal and expected on weathering steel. What ends a container is scale you can push a screwdriver through, particularly on the bottom rails, corner posts and underside cross-members. Perforated roof panels and rust that has eaten through a side panel are also disqualifying for anything that needs to stay dry.
What is the fastest way to tell if a container is watertight?
Step inside, close both doors, wait a full minute for your eyes to adjust, then scan the roof, walls, door seal line and floor edges for daylight. Any visible pinprick is a hole. Follow it with a look along the roof from above for dents deep enough to hold standing water.
Do I need a CSC plate?
Only if the container will carry cargo internationally or be stacked in a certified operation. For static storage the plate is still worth reading, because it records the month and year of manufacture along with the maximum gross weight and the stacking and racking test values — the only dated, verifiable data on the unit.
Are container floors safe for food storage?
Container plywood is treated against insects and decay as a condition of international movement, and used floors may also carry residue from previous cargo. For anything food-related, sensitive to odour, or destined for a habitable conversion, plan on sealing, overlaying or replacing the original floor.
What if the doors are hard to open?
Test them on level ground first — a container sitting unevenly twists slightly, and twisted doors bind. If they still bind when the unit is level, the container is racked from damage or poor handling. That is the defect most often missed at purchase and the one least likely to be economical to repair.