Container Seals: Bolt Seals, ISO 17712 and Why the Seal Number on Your B/L Matters

When a full container is packed and closed in China, a hardened steel bolt with a stamped number is driven through the locking handle. That seal, and the number on it, is recorded on the packing declaration, the bill of lading and the export documents. From that moment the seal is the evidence that no one opened the doors between the shipper premises and lawful inspection. If it arrives intact with the right number, the chain of custody held. If it is missing, cut, or a different number, customs treats the box as compromised. This guide covers the seal standard, how the number travels through your documents, and what a seal discrepancy does to a Bangladesh clearance. It complements VGM, the bill of lading types guide, and NII container scanning.

What ISO 17712 requires

ISO 17712 is the international standard for mechanical seals on freight containers. It sets three things. First, a strength classification: seals are graded as indicative, security, or high security, based on how much force they resist in tension, shear, bending and impact tests. The bolt seal used on the vast majority of ocean containers is the high security H class. Second, tamper evidence: the seal must show clear physical proof if someone tries to defeat it and reattach it. Third, a manufacturing and audit regime for the companies that make the seals, so a seal number can be traced to its maker. Customs administrations and security programmes such as authorised economic operator schemes expect loaded export containers to carry an ISO 17712 high security seal, not a plastic strip or a padlock.

A bolt seal has two parts, a bolt and a locking barrel, both steel. Once pushed together it can only be removed by cutting the bolt with a cable cutter or bolt cutter, which is deliberately destructive and visible. Each seal is laser marked with a unique alphanumeric number and usually the maker mark.

How the seal number travels through your documents

The number is written down at least four times, and all four must agree:

• Container Load Plan or stuffing report — recorded by the shipper or the loading warehouse when the doors are closed.
• Bill of lading — the carrier prints the container number and the seal number together. This is the reference customs and your bank rely on.
• Export customs declaration in China — the seal number is part of the export record.
• Arrival and gate records at the discharge port — the terminal notes the seal condition and number when the box comes off the vessel and again at the gate.

For a shipper-loaded full container, the shipper applies the seal and its number goes on the bill of lading as shipper seal. For an LCL consolidation the freight forwarder seals the consolidated box after stuffing multiple consignments, and the seal number appears on the master bill of lading, not on your house bill. Knowing which applies to your shipment tells you whose seal number you are checking.

What a broken or wrong seal triggers at Chattogram

If the container arrives with the seal intact and matching, the seal is a non-event; it quietly supports a smooth clearance. If it does not match, the consequences are real:

• Automatic diversion to physical examination. A discrepant seal moves the consignment out of any facilitated channel and into a 100 percent examination. The doors are opened under customs supervision and the contents checked against the packing list piece by piece.
• Shortage and pilferage claims. If cargo is missing, a broken seal is the pivot of the insurance claim. Underwriters will ask for the seal condition report, the carrier remarks, and photographs. A clean seal at origin and a broken seal on arrival supports the claim; a seal that never matched the bill of lading weakens it.
• Carrier liability questions. Where and when the seal failed determines whether the carrier, the terminal, or a party in between is answerable.
• Delay and cost. Examination scheduling, extra handling, and the demurrage and detention that accrues while it is resolved all land on the importer first, to be recovered later if fault is established elsewhere.

What the importer should actually do

• Get the seal number in writing before the vessel sails and check it against the bill of lading yourself. A transposed digit is easy to fix at origin and painful to fix after arrival.
• For a full container, ask the loading party for a photo of the sealed doors showing the container number and the seal number in one frame, plus photos of the packed cargo before the doors close.
• On arrival, have your C and F agent record the seal condition at the terminal before the box moves, and photograph it. If it is broken or wrong, get that noted on the equipment interchange receipt and the delivery order immediately.
• If there is any seal irregularity, do not let the box be unstuffed without customs present and, if goods may be missing, without a surveyor. Opening it first destroys your claim.
• Keep the seal itself after devanning until any claim is closed.

Seals are not theft-proof, only tamper-evident

A determined thief can cut a bolt seal in seconds; the point of the seal is not to stop entry but to make entry impossible to hide. That is why the number and the condition report matter more than the hardware. A common fraud is to cut the real seal, remove cargo, and fit a counterfeit seal with the same number. This is why ISO 17712 traceability exists and why photographs of the original seal, close enough to read the maker mark and any micro-features, are worth taking. If your goods are high value, ask the loader to also fit a secondary numbered cable seal or a barrier seal, and record both numbers.

How we manage seal integrity on your shipments

On full-container shipments DE International records the seal number at stuffing, requires door and cargo photographs from the loading warehouse, and reconciles the number to the bill of lading before departure. On arrival our C and F team checks and photographs the seal at the terminal before the container moves, and if anything is off, we stop the unstuffing and bring in a surveyor before the doors open. Tell us about your next FCL booking and we will build the seal checks into the plan.

Seal types you may see and what they signal

Not every seal on a container is equal, and the type tells you something about how the box was handled:

• Bolt seal (ISO 17712 high security). The steel bolt-and-barrel unit on most shipper-loaded ocean containers. Requires a cutter to remove. This is what a full-container export should carry.
• Cable seal. A steel cable through the handles locked into a barrel, also available in a high-security grade. Often used as a secondary seal on high-value cargo alongside a bolt seal.
• Plastic indicative seal. A cheap strip that only shows tampering and offers almost no physical resistance. Fine for a domestic trailer, not acceptable as the sole seal on an export container.
• Electronic or smart seal. A bolt or cable seal with a chip that logs opening events and sometimes location. Used on sensitive shipments and in some customs security programmes.

If your FCL arrives with only a plastic seal where the bill of lading says a bolt seal was applied, that is a discrepancy in itself, even if the number matches, and it should be recorded before the box moves. Ask your loading party which seal type they use as standard and confirm it is the high-security bolt seal.

DE International sources, inspects and ships from China to Bangladesh, and handles the customs and warehousing side once the goods land. If you want help applying any of this to a live shipment or a facility you are planning, tell us the product, the volume and the location, and we will build a plan and a quote around it. Start at our services page, see how our China sourcing and buying agent service works, browse the shop, or contact us directly.