Container Quality Control: The SCS Global Factory QA/QC Process

The principle is simple: catch a defect at the stage that created it, when it is cheap to fix, rather than at the gate when the box is built. That is why container QA QC here is a sequence of stage gates, not a single final inspection. The sections below expand the stages that decide build quality, and link to the manufacturing and certification detail. The full build sequence sits in how our containers are made.

Quality control starts before fabrication, on the incoming steel. Grade, thickness, chemical composition and tensile strength are checked on the weathering-steel coil, and material traceability is recorded so every panel can be traced back to its certificate.

Material that fails intake never reaches the line, which removes a whole class of defects downstream. Recording traceability matters because it is one of the things the classification societies audit, and because a buyer in a regulated sector may need to demonstrate provenance. The grade, gauge and coating specification we inspect against is set out in the steel and materials we inspect. Getting the steel right at intake is the cheapest quality decision in the whole process, because every later stage assumes the base metal is to specification.

Container weld inspection covers every weld, visually inspected, measured and approved before assembly continues. Acceptance is to ISO 5817 quality levels under an ISO 3834 welding quality-management system, with non-destructive testing applied where the specification calls for it.

Welds are where a container fails under load, so this is the stage that earns the most attention. The container welding process runs to controlled parameters, and each weld is signed off before the next sub-assembly is added, rather than batch-checked later. Welding shipping containers to a consistent standard depends on qualified procedures and qualified welders, which is what the ISO 3834 system governs.

Weld acceptance standards:

• ISO 3834: quality requirements for fusion welding, covering welder qualification and procedure control.
• ISO 5817: weld imperfection quality levels (B, C and D) that set the acceptance criteria.
• ISO 17635: non-destructive testing of welds and method selection.

These are the same weld standards that matter on dangerous goods storage compliance builds, where weld integrity is safety-critical.

Panel and frame tolerances are checked continuously through assembly, so structural accuracy is held as the box is built, not measured once at the end. Non-destructive testing is applied to welds where the specification requires it.

Dimensional drift is what stops containers stacking, interlocking and sealing, so the checks track corner-fitting positions, diagonals and panel fit against the ISO 1496-1 type-test geometry. Continuous in-process measurement catches a frame going out of square early, when a single weld can be corrected, rather than after boxing when the whole structure has to be reworked. The combination of dimensional control and weld NDT is what keeps a finished unit interchangeable with standard freight equipment worldwide.

A high-pressure water-jet shower test confirms each unit is watertight before it ships. Jets simulate driving rain across the roof, seams and door seals, and any light visible from inside or any ingress sends the unit back for rework.

Watertightness is the test that protects whatever the buyer ships inside, so it is run on the assembled, sealed box with the doors closed and latched. Nozzle pressure, distance and coverage are controlled so the test is repeatable rather than a quick hose-down. Weatherproofing is part of the ISO 1496-1 type-test battery, and a leak found here costs a rework; a leak found in the field costs a cargo.

A container pre shipment inspection, often written pre-shipment, takes place at about 80% production complete, checking paint, weld integrity, finish and dimensional accuracy. Sampling follows an AQL standard, with critical, major and minor defect classes deciding accept or reject.

The shipping container inspection that matters most to a buyer is this one, because it is the last gate before dispatch. Sampling to ISO 2859-1, the AQL standard for inspection by attributes, sets how many units are checked and how many defects trigger a reject. Running it at around 80% complete, the point established as best practice by inspection authorities such as QIMA, means problems are caught while the line can still correct them. Sampled units also take a structural and functional type-test, at a minimum of one per hundred, against ISO 1496-1.

Third party container inspection is the external check on the whole process. SCS's factory is independently audited by ABS, DNV, Lloyd's Register and Bureau Veritas, covering welding procedures, material traceability, lifting systems, structural integrity, coatings and final inspection.

This is the strongest trust signal a manufacturer can offer, because it is not self-certified. An authorised classification society inspects where a contract or standard requires it, and the same societies audit the facility itself. ABS, DNV, Lloyd's Register and Bureau Veritas are the bodies behind that audit. The same societies complete the CSC sign-off at the factory, and the wider compliance picture is set out in our certification explained guide. Offshore units carry the heaviest QA load of all, which is why DNV 2.7-1 offshore containers add further inspection on top.

Every order ships with a documentation pack: a full photographic QC report stage by stage, plus Factory Acceptance Testing on engineered units. The buyer sees the build, rather than taking it on trust.

The pack is the difference between claiming quality and proving it. Stage-by-stage photographs record the welds, coatings and tests as they happened, and the FAT results document that an engineered unit performed to specification before it left the factory. For procurement, that pack is auditable evidence that the eleven stages above actually ran on the unit being bought, not on a representative sample from another order. It is also what lets a buyer in a regulated sector close out their own supplier-qualification paperwork without a site visit.

For engineered and custom units, SCS builds and tests a prototype under real conditions before committing to series production. The testing and certification data is then reviewed to refine the design, so faults are designed out before the full run begins.

This is the quality gate that matters most on a custom order, because it moves risk from the field back to the factory. A prototype is built, tested against the performance and compliance targets, and the results reviewed at a design-and-product review before series production is scheduled. The model behind it, the ten-stage enquiry-to-delivery process with its prototype gate, sits in our production line and factory capability. For a buyer commissioning a non-standard unit, a prototype-first regime is the strongest assurance that the design works before they take delivery of a batch.