Reading a container's markings — owner codes, numbers and the CSC plate

The identification number

Look at the doors, the sides and the roof of any container built to the international standard and you will find the same string: four letters, then seven digits. It appears in several places on purpose, so it can be read from a crane, from a ship's deck and from ground level.

The string breaks into four parts:

• Owner code — three letters. Registered to the company that owns the box, usually a shipping line or a leasing company. Codes are registered internationally and are not reused casually.
• Equipment category identifier — one letter. On virtually everything you will ever buy this is a U, meaning a freight container. J is detachable equipment and Z is trailers and chassis, so if you are looking at a U you are looking at the right sort of object.
• Serial number — six digits. Assigned by the owner. It means nothing on its own.
• Check digit — one digit, usually in a box on its own. Calculated from the other ten characters.

That last digit is the useful one. It is arithmetic, not decoration: each letter is given a numeric value, each of the eleven positions is weighted, and the total resolves to a single digit that must match. Terminals and depots validate it automatically. For you it is a sanity check — if a number has been restencilled by hand and the check digit no longer works, somebody has painted a number on a box rather than the box's own number.

The practical test is simpler than the arithmetic. Walk the unit and confirm the same number appears, identically, on both doors, both sides and the roof. Numbers that disagree, or a patch of fresh paint where a number used to be, deserve a question. It is not automatically sinister — repaired and repainted units get restencilled all the time — but you want the answer to come from the seller rather than from you a year later.

The ISO size and type code

Beside or below the identification number sits a four-character code that tells you exactly what shape the box is. It is worth knowing because it does not lie and marketing words sometimes do.

The first character is length. The second is height and width. The last two are the type. A few you will see constantly in Australia:

Code	What it is
22G1	20ft standard height general purpose
22P1	20ft flat rack or platform
25G1	20ft high cube general purpose
42G1	40ft standard height general purpose
45G1	40ft high cube general purpose
45R1	40ft high cube refrigerated
20G1 / 2EG1	10ft general purpose, depending on the standard's era

The characters that matter most day to day are the first two. A 4 at the front means forty feet. A 5 in second position means high cube — 300 mm more internal height than a 2 in that position. If somebody tells you a unit is a high cube and the plate says 22G1, believe the plate. Our dimensions page has the measured figures for each of these.

The weight markings

Painted on the doors of every unit, usually in a block under the identification number, are three weights. They are given in kilograms and in pounds.

• MAX GROSS. The heaviest the container is certified to be, including its own weight. On most 20ft and 40ft general purpose units this is 30,480 kg, and a newer 40ft is sometimes plated at 32,500 kg.
• TARE. The weight of the empty container. Roughly 2,200 kg for a 20ft, roughly 3,800 kg for a 40ft, though a repaired or repainted unit can vary by a hundred kilograms or so.
• NET or PAYLOAD. Max gross minus tare. What you may legally put in it at sea.

For storage on the ground, none of these will ever be your limiting number — road mass limits stop you long before the container's rating does. Where they do matter is lifting. If a unit is being craned with anything in it, the crew needs a real weight, and tare off the door is the starting point for that sum.

The CSC plate

Riveted to the left-hand door, usually at eye height and often under a few coats of paint, is a metal plate carrying the Safety Approval issued under the International Convention for Safe Containers. It is the container's registration paper and it is the single most informative thing on the unit.

What is on it:

• The approval reference and country of approval. Who certified the design and where.
• Date of manufacture. Month and year. This is the container's age and it is not written anywhere else.
• Manufacturer's serial number. Independent of the owner's painted number, which is handy when the painted one has been changed.
• Maximum operating gross mass. Same figure as the door.
• Allowable stacking weight. How much load the unit may carry through its corner posts when stacked — typically expressed for a 1.8g acceleration, because a ship at sea is not a still environment.
• Racking test load value. The transverse force the frame was tested against.
• Next examination date, or an ACEP marking. The one that decides whether it can still be shipped.

Age, and what it tells you

The manufacture date is the figure buyers should look at first. Boxes generally come out of sea service at roughly ten to fifteen years of age, which is why the used market is full of units of about that age and why that age is not, by itself, a problem. A container is a very slow-ageing object when it is standing still on dry pads.

Where the date is useful is as a cross-check. A unit presented as a lightly used box with a plate showing twenty-five years is telling you something the paint is not. A unit with a very recent date and heavy damage has had a hard life somewhere. Neither is automatically a reason to walk, but both are reasons to look harder at the floor, the rails and the door seals.

Examination dates and whether you should care

Under the convention, a container in international service has to be examined periodically. Two schemes exist. The older one stamps a next examination date on the plate. The more common one now is an Approved Continuous Examination Programme, marked with an ACEP decal and a registration reference, under which the operator examines units on a defined cycle rather than to a date.

Here is the part that matters to a buyer: if the container is going to stand on your block as storage, an expired examination date changes nothing at all. It is not a safety statement about the box sitting still. It simply means the unit is no longer certified to carry cargo across an ocean.

If, on the other hand, you intend to ship in it — a genuine export, a relocation overseas, a project cargo — then certification is the whole question and you need a unit that carries it. That is a different unit, a different price, and a conversation to have before you order rather than after. Say so up front.

Other markings worth knowing

• Timber treatment decal. Australian biosecurity requires container flooring to be treated, and the decal records what with. Worth a look if the floor has been replaced at some point.
• Consolidated data plate. Many modern units combine the CSC approval, the customs approval and the timber declaration onto one plate.
• Height warning. High cubes carry a black and yellow marking on the doors and sometimes a strip along the top rail, because a 2.89 m box under a 2.6 m awning is a bad afternoon.
• Repair stencils and patch stamps. Some yards mark repairs with a date. A welded, ground and painted patch is a legitimate repair; tape and silicone are not a repair at all.

How to use all this in a yard

Ninety seconds, in this order. Read the ISO code and confirm the size and height are what you were told. Read the tare and max gross. Find the CSC plate and read the manufacture date. Check the painted number matches on both doors and both sides. Then stop reading and start inspecting — the plate tells you what the container was built to be, and the floor, the roof and the door seals tell you what it is now. Our inspection page covers what we check before a unit goes out, and the grades page explains where each condition sits.

If you want to look for yourself, the yard at 51-55 Bromley Street, Cornubia is open Monday to Friday 7:30am to 5pm and Saturday morning, and the units are on hardstand where you can walk around them. Ring 1300 467 776 first so the unit you are after is pulled out where you can walk around it. If you are buying from one of the other depots — Gympie, Rockhampton, Mackay, Townsville, Cairns, Grafton, Darwin or Fremantle — ask for photographs of the specific unit, including the plate. We send them on request and before delivery.