Steel Building Factory Acceptance Test (FAT): Witness & Docs

Inside the fabrication shop: H-columns and beams staged for FAT, an inspector with a theodolite on column verticality, trial assembly jig on the floor, tagged crane beams alongside.

A steel building that passes on the shop floor can still fail on site—if the beam cambers were never verified, the bolt holes never trial-assembled, or the mill certs never checked. That is why a factory acceptance test is a contractual hold point: no shipment leaves the plant until the buyer's witness signs off. A steel building factory acceptance test is not a spot check. It is a staged, witnessed protocol: dimensional verification, trial assembly of critical connections, NDT sampling, and a document review—all before crating. Our third party inspection steel building article covers pre-shipment checks at the port or yard—counting crates, verifying marks, checking packaging. FAT happens weeks earlier, inside the fabricator's shop, where defects can still be corrected cheaply.

What Is FAT vs. Third-Party Inspection?

FAT stands for Factory Acceptance Test, and it happens inside the fabricator's shop, before any steel leaves the floor. It is a contractual hold point: the buyer's representative (or a delegated third party) witnesses specific stages, and no shipment is released until those stages are signed off. FAT is typically triggered by crane buildings, multi-story frames, export projects, or owner specifications that demand witness at key milestones.

It is not the same as third-party inspection at the port. The third party inspection steel building stage happens later, at the dock or yard, and focuses on crate count, marking, packaging, and outward appearance. FAT happens on the shop floor, where a mis-drilled bolt hole can be corrected in hours rather than on site in weeks. The two are complementary, not interchangeable: FAT is the manufacturing quality gate, while port inspection is the shipping and logistics gate. More on the broader inspection logic is in steel quality inspection and steel building inspection checklist.

Typical FAT attendees are the buyer's representative, a third-party inspector (often SGS, Bureau Veritas, or Intertek), the fabricator's quality manager, and—on critical projects—the design engineer. Remote video witnessing is increasingly common for overseas buyers who cannot travel.

FAT Scope — Dimensional & Trial Assembly

Dimensional checks are measured directly on the shop floor, not assumed from shop drawings. Column verticality must not exceed H/1000 and 12 mm (1/2 in) absolute. Beam sweep and camber are within L/1000 and 10 mm (3/8 in). Splice-end elevation is held to ±3 mm (1/8 in), and bolt-hole group positions to ±1.5 mm (1/16 in). Overall building length and width are checked to ±L/2000 and ±10 mm (3/8 in).

Trial assembly is the highest-value FAT activity. Critical moment connections and crane beam splices are trial-assembled on the shop bed. High-strength bolt pass-through rate must be at least 85% without reaming; if it is lower, the holes are corrected before shipment. End-plate milling flatness is checked to 0.3 mm per meter. This is where the fabricator earns the right to ship—because a 2 mm hole mismatch discovered on site is a multi-day delay.

Hold points are scheduled in advance. HP1 is material incoming (heat number verification and witness sampling). HP2 is critical connection trial assembly. HP3 is weld NDT sampling. HP4 is coating dry-film-thickness verification. HP5 is the final release signature. Site-side acceptance of what arrives is covered in steel building site acceptance inspection; first-off verification logic is in steel sample prototype first article inspection and steel building sample confirmation. FAT is the quality gate at the end of the production line; for the upstream fabrication steps that precede it—CNC oxy-fuel and plasma cutting, H-beam assembly, SAW web-to-flange welding, drilling, shot-blasting, and painting—see our steel structure fabrication process walkthrough.

FAT Hold Point Schedule	Hold Point	Stage	What Is Witnessed	Acceptance Criterion	If Failed
HP1	Material incoming	Heat number match, mill cert	Cert matches material tag	Reject lot, re-certify
HP2	Critical connection	Trial assembly, bolt pass-through	≥85% pass without reaming	Ream / repair, re-witness
HP3	Weld NDT	UT / MT sampling per class	Per contract NDT plan	Repair weld, re-test
HP4	Coating	DFT, adhesion	DFT avg compliant, min ≥80%	Touch up / re-coat
HP5	Final release	Dimensional + docs review	All prior HPs closed	No shipment until closed

Typical hold-point schedule; exact HP list per project FAT protocol.

Weld NDT & Coating Verification

NDT sampling is not a random guess—it is tied to weld class. Class 1 (full-penetration, primary frame) welds receive 100% UT or 100% MT. Class 2 (secondary, partial-penetration) welds are sampled at 20%. Crane beam flange butt welds get 100% UT plus 10% MT surface check. The witness selects weld numbers from the drawing at random; the seller's NDT technician executes, and the result is recorded in the FAT report. NDT laboratories should operate under ISO 17025 Testing and Calibration Laboratories accreditation.

Coating verification measures dry film thickness (DFT) at five points per member: the average must meet spec, and the lowest point must be at least 80% of the specified value. Pull-off adhesion must reach at least 3 MPa (435 psi). Appearance is checked for holidays, runs, and pinholes. Hot-dip-galvanized members are checked for a minimum 85 µm zinc thickness. Fasteners are not forgotten: high-strength bolt assemblies are checked for torque coefficient per lot, and slip-critical faying surfaces are slip-tested.

Welding procedure background is in steel welding process; coating measurement detail is in steel coating inspection testing; the underlying contractual requirements are in steel structure technical specification.

| NDT & Coating Acceptance Criteria | Item | Method | Sampling Rate | Acceptance Threshold (Metric / Imperial) | Standard | |---|---|---|---|---| | Class 1 weld | UT / MT | 100% | No indications per code | AWS D1.1 | | Class 2 weld | UT / MT | 20% sample | No rejectable indications | AWS D1.1 | | Crane flange butt | UT + MT | 100% UT / 10% MT | Per bridge spec | AASHTO / AWS | | Coating DFT | Magnetic gauge | 5 pts / member | Avg spec, min ≥80% | ISO 12944-6 | | Adhesion | Pull-off tester | 1 per batch | ≥3 MPa / 435 psi | ISO 4624 | | Galvanizing | Magnetic gauge | 5 pts / member | ≥85 µm / 3.3 mil | ISO 1461 |

Typical acceptance thresholds; project spec governs where tighter.

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We run FAT as a staged hold point: dimensional verification, trial-assembled connections, witnessed NDT, and a complete document package—all signed off before crating. You fly in or we video-witness.

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What Buyers Often Miss in FAT

The most common FAT failures are not technical—they are omissions. Buyers who only check dimensions skip the document review and discover after shipment that the mill cert heat numbers do not match the member tags. Buyers who only inspect appearance skip trial assembly and find mismatched bolt holes on site. Buyers who skip coating checks discover on site that DFT is 60% of spec. And buyers who do not issue a Non-Conformance Report (NCR) have no paper trail when a defect surfaces later.

NCRs are graded. Critical defects—undersized welds, wrong material grade, failed NDT—must be repaired and re-witnessed before release. Major defects (minor dimensional drift, cosmetic coating) require written buyer approval before release. Minor items are logged and tracked to closure. Every NCR and its disposition becomes an appendix to the FAT report.

Disputes that survive FAT are handled in steel building quality claim; the documents that support handover are assembled in steel building project handover documentation.

| Common FAT Non-Conformities & Disposition | Defect Type | Example | Severity | Disposition | Re-Witness Required? | |---|---|---|---|---| | Wrong material grade | S275 used where S355 specified | Critical | Replace / redesign | Yes | | Undersized weld | Fillet 5 mm vs 8 mm required | Critical | Reweld + NDT | Yes | | Bolt hole mismatch | Holes do not pass in trial | Major | Ream / bush, approve | Yes (re-assembly) | | DFT below spec | Avg 60% of required | Major | Additional coat | Yes (re-measure) | | Surface rust on cleaned steel | Light flash rust before paint | Minor | Blast / touch up | No | | Marking / tag missing | Member ID absent | Minor | Re-stamp, log | No |

Typical NCR disposition; severity grading per project quality plan.

FAT Documentation Package & Release

The FAT release is not just a signature—it is a document package. It includes mill test certificates to EN 10204 Metallic Products — Inspection Documents 3.1B, welding procedure specifications (WPS), procedure qualification records (PQR), and welder qualifications. It includes NDT reports (UT/MT/PT), dimensional measurement records, coating DFT and adhesion records, and fastener lot test results. It includes every NCR and its closure evidence.

When the buyer's witness signs the FAT release, that signature is effectively the shipping permission note. No booking, crating, or container loading should proceed until it is issued. The FAT report travels with the steel (or is delivered electronically in advance) and becomes part of the project handover file. Packaging and lashing logic is described in steel building shipping packaging and steel ocean shipping lashing securing.

For overseas buyers who cannot travel to the shop, remote video FAT has become standard practice. A fixed camera on the trial-assembly bed, a handheld unit for dimensional checks, and a live feed to the buyer's office let the witness inspect in real time. The same video is archived with the FAT report, so any later dispute has both the signed data and the visual record. This does not remove the need for a written hold-point plan—it just makes the witness cheaper and faster to execute. Whether in person or on video, a steel building factory acceptance test that is run as a true hold point converts a risky shipping decision into a documented release.

Frequently Asked Questions

Q1: What is the difference between FAT and third-party inspection?

A factory acceptance test (FAT) happens inside the fabricator's shop, before shipment—witnessing dimensional checks, trial assembly, NDT, and documents. Third-party inspection typically happens later at the port or yard, checking crate counts, marks, and packaging. FAT catches structural defects while they are still cheap to fix.

Q2: Who should attend the FAT?

At minimum, the buyer's representative (or a delegated third-party inspector like SGS/BV), the fabricator's quality manager, and—for critical projects—the design engineer. Witnesses sign off at each hold point. Remote video witnessing is common for overseas buyers.

Q3: What dimensional tolerances are checked during FAT?

Typical checks include column verticality ≤ H/1000, beam camber tolerance ±L/1000, bolt-hole group position ±1.5 mm (1/16 in), and splice-end milled flatness ≤ 0.3 mm/m. These are measured directly on the shop floor, not assumed from shop drawings.

Q4: What happens if FAT finds a defect?

A Non-Conformance Report (NCR) is issued. Critical defects (e.g., under-sized weld, wrong material grade) must be repaired and re-witnessed. Major defects need buyer written approval before release. Minor defects are logged and tracked. No shipment leaves until all critical NCRs are closed.

Q5: Is FAT worth the cost for a small building?

For a simple single-span warehouse, a lightweight document review may suffice. But for crane buildings, multi-story frames, or export projects, the cost of one shop-floor repair is far lower than correcting a bolt-hole mismatch on site. FAT pays for itself the first time it catches a fit-up error.

Case Example

A pre-engineered crane building for an overseas industrial buyer illustrates why a staged FAT pays off. The project was a roughly 4,800 m² (52,000 sq ft) single-bay workshop spanning 24 m (80 ft), fitted with a 10 t (11 USt) overhead crane, in an anonymized midwestern U.S. industrial park. Because the buyer could not travel to the shop, the riskiest moment was the crane-beam splice fit-up. We ran remote video hold points: heat-number verification, trial assembly of six critical moment connections, and NDT sampling. Trial assembly exposed a 1.8 mm (1/16 in) bolt-hole mismatch on two splices, corrected in two shop days rather than weeks on site. Final on-site high-strength bolt pass-through reached 96%, and no critical non-conformance report traveled with the shipment. The pre-port companion check is third party inspection steel building, and the on-site mirror step is steel building site acceptance inspection.

Conclusion

A steel building factory acceptance test is a staged, witnessed quality gate on the shop floor—dimensional verification, trial assembly, NDT sampling, coating checks, and a complete document package—all signed off before crating. It is not the same as port-side third-party inspection; FAT catches structural defects while they are cheap to fix. If you treat FAT as a number-counting exercise, you lose its value. If you run it as a contractual hold point with clear NCR rules, you sign the release once and ship with confidence. If you need a FAT protocol tailored to your project, our engineers can scope the hold points, witness plan, and document package before production starts.

FAT That Catches Defects in the Shop — Not on Site.

We run factory acceptance tests as staged hold points: dimensional verification, trial-assembled connections, witnessed NDT, and a complete document package. You sign off before crating.

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Reference Links

• EN 10204 Metallic Products — Inspection Documents — defines 2.1, 2.2, 3.1 and 3.2 mill certificate levels required in the FAT document package.
• ISO 17025 Testing and Calibration Laboratories — accreditation standard for the NDT laboratories that perform FAT weld inspection.

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About the Author

Senior Structural Engineer

With over 20 years of hands-on experience in steel structure design and prefabricated building engineering, our in-house senior structural engineer has personally contributed to more than 500 steel building projects—including warehouses, industrial factories, aircraft hangars, agricultural buildings, and commercial structures. The focus is on translating design codes such as AISC 360, ASCE 7, and Eurocode 3 into buildable, cost-effective steel solutions that balance structural performance, fabrication efficiency, and total project cost.

Learn more about our engineering team