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Factory Acceptance Testing & Commissioning

Factory Acceptance Testing & Commissioning

Independent verification before the final payment goes out and the handover is signed

The moment you sign off Factory Acceptance Testing is the moment your negotiating leverage disappears. Before that signature, a supplier will fix a defect quickly to get paid. After it, the same defect is a warranty claim, a dispute, or a cost you absorb yourself. FAT and commissioning are where a capital project's paper specification either gets proven true on the plant floor, or doesn't — and the difference is worth every day spent checking properly.

This page sets out what a thorough, independent FAT and commissioning programme actually covers, the difference between cold and hot commissioning, and why independence from the equipment supplier matters at exactly this stage of a project.

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What FAT Actually Verifies

Factory Acceptance Testing confirms that what was specified, quoted and contracted is what has actually been built and installed — before the client's final payment and before commissioning begins in earnest. A thorough FAT covers six distinct areas, not just "does it switch on":

AreaWhat is actually checked
P&ID conformityAs-built pipework, valves and instrumentation match the approved P&ID, not a supplier's simplified version of it. Document revision numbers are recorded before testing starts — a disproportionate share of post-FAT disputes trace back to one party testing against a superseded drawing.
Mechanical completionEquipment installed, aligned, supported and connected per the mechanical specification; no temporary fixes left in place
Electrical & instrumentationControl philosophy matches the functional design spec; interlocks, alarms and safety instrumented functions actually do what the document says they do — tested, not assumed
SCADA/HMI vs P&IDTags, equipment representation and interlock logic on every mimic screen checked against the P&ID for accuracy — but the visual layout doesn't need to mirror the P&ID's own drawing orientation; screens are commonly reorganised for operator clarity. What matters is that the mimic correctly reflects the actual physical plant layout and flow direction, so an operator isn't disoriented comparing the screen to the real plant in front of them.
Hygienic designDrainability, dead-leg elimination and material finishes are verified primarily by visual inspection against the agreed standard and drawings — that is the main method, not an instrument readout. Surface roughness is measured by profilometer (Ra ≤0.8µm per EHEDG/3-A) as the one genuinely quantitative check. For vessels and tanks with manway access, CIP spray coverage is separately verified once commissioned (see below). Pipe runs are verified differently — weld-by-weld, during fabrication, before the run is closed up, since there is usually no manway to inspect through afterward.
Safety systemsExplosion venting/suppression, isolation, and inerting systems (where applicable) verified against the design basis — not just present, but correctly specified for the actual product and process conditions

The Full Sequence: Protocol, Software, Cold, CIP, Hot

Five stages, strictly in order. Compressing or reordering any of them is where most avoidable commissioning cost comes from.

  • Protocol review and approval — before any testing happens, the FAT/commissioning test protocols themselves — every test case, method and pass/fail criterion, including the software test script — are reviewed and formally approved by the client's engineer. This is standard practice precisely because it removes ambiguity about what "pass" means before anyone is stood in front of the equipment arguing about it.
  • Software/control logic FAT — before any field device is connected, the PLC/HMI/SCADA logic is tested using simulated I/O signals (bench simulators, or a digital-twin simulation platform) to verify sequences, interlocks and safety-instrumented functions behave as specified. No product, no real motors or valves are involved — this can be done at the panel builder's works, sometimes before the panel has even shipped.
  • Cold commissioning — the plant, its utilities and the CIP system are now run for real, without product. This proves mechanical and electrical operation, and confirms the control logic already validated in simulation behaves correctly against real field devices.
  • Cleanability verification (vessels and tanks) — only possible once the CIP system is proven to run (it needs real flow, temperature and chemical dosing, which is why it cannot happen before cold commissioning), and only practical on equipment with manway access to inspect afterward. A synthetic tracer — riboflavin — is deliberately applied to product-contact surfaces, the actual CIP cycle is run, and the surfaces are then inspected under UV light through the manway: any residual fluorescence marks a spray shadow or dead spot the cycle didn't reach. This is a visual pass/fail call, done with a synthetic tracer rather than real product, so cleanability is proven before any product is put at risk. Long pipe runs are not tested this way — there is no manway to inspect through once installed, so pipework integrity is checked weld-by-weld during fabrication instead (see Safety Systems, below, on dye penetrant inspection for crack detection — a distinct test from riboflavin, using a different dye for a different purpose).
  • Hot commissioning — product (or an approved simulant) is introduced, and the process is verified against the guaranteed performance parameters in the contract: throughput, temperatures, yields, energy consumption, and product quality. This is where a supplier's performance guarantee is actually tested, not assumed.

The cost of finding a fault rises sharply at each stage you defer it to: caught in the protocol review, it's a redline on a document; caught in software simulation, it's an edit and a re-test; caught cold, it's an afternoon on site; caught at the cleanability stage, it's a design fix before anything is at risk; caught hot, it can cost a batch of product, a day of downtime, or damage to equipment.

Why Independence Matters at This Stage

An equipment supplier has an inherent commercial interest in their own equipment passing acceptance testing — final payment is usually tied to sign-off. That is not a criticism of any particular supplier; it is simply the structure of the relationship, and it is exactly why an independent party reviewing against the client's own specification, not the supplier's account of it, changes the outcome. The same independence principle that applies to due diligence on an acquisition applies here: whoever signs off the test should have no stake in the result.

The punch list is the whole point. A FAT that produces no punch list has either found a genuinely perfect installation, or has not looked hard enough. A properly run FAT identifies deviations, categorises them by severity (safety-critical, performance-affecting, cosmetic), and tracks each one to closure with a named owner and a date — not a verbal assurance that "it'll be sorted."

Safety Systems: A Specific Risk Area

For any dry-processing dairy plant — spray dryers, milk powder handling, big-bag filling — combustible dust explosion protection is a FAT area that cannot be verified by walking past the equipment. The relevant frameworks:

  • UK/EU — DSEAR (Dangerous Substances and Explosive Atmospheres Regulations) governs the risk assessment obligation; ATEX governs the equipment used in the hazardous area itself.
  • International/US reference standards — NFPA 652 (fundamentals of combustible dust, requiring a formal Dust Hazard Analysis), NFPA 61 (agricultural and food processing specifically), NFPA 68 (deflagration venting) and NFPA 69 (explosion prevention systems) are widely referenced even outside the US on international projects.
  • VDI 2263-7 — a European guideline specific to spray dryers, often producing a more proportionate venting specification than a blanket application of NFPA 68, which was not written with spray dryer geometry specifically in mind.

Verifying explosion venting or suppression at FAT means confirming the installed system matches the Dust Hazard Analysis for the actual product being dried — dust characteristics vary significantly between products — not that a vent panel of some size is fitted somewhere on the chamber.

Weld and chamber integrity: dye penetrant inspection

A spray dryer chamber goes through repeated thermal cycling in service, which makes weld fatigue a real risk — a genuinely different concern from cleanability, and checked with a genuinely different test. Dye penetrant inspection (DPI) uses a fluorescent (or visible red) penetrant dye applied to the weld or surface, drawn into any surface-breaking crack by capillary action; excess is removed, a developer draws the dye back out of the crack, and the surface is inspected under UV light (fluorescent) or white light (visible). In food and dairy applications, a water-washable, food-safe penetrant is used specifically so no residue is left behind on product-contact surfaces. This is not the same substance or the same logic as the riboflavin test above — riboflavin checks that cleaning removed something; dye penetrant checks whether a crack retains dye a cleaning cycle wouldn't remove. See our dedicated page on spray dryer crack testing for the full detail.

Microbiological Verification: The Definitive Test for UHT and Aseptic Lines

Every check so far — mechanical, hygienic, safety — is necessary groundwork. For a UHT or aseptic line specifically, none of it is the actual proof the plant works. That proof is microbiological, comes in two distinct stages, and both matter.

Post-CIP microbiological verification

Riboflavin proves spray coverage — that cleaning solution physically reached a surface. It says nothing about whether anything living was actually killed. Confirming that requires swabbing cleaned surfaces and testing for total viable count, with ATP bioluminescence now the industry-standard rapid method for this. The ATP measurement itself — swab, reagent, luminometer reading — takes minutes, not days.

Product incubation testing: proving commercial sterility

Commercial sterility is defined by Codex Alimentarius (CAC/RCP 40-1993) as the absence of microorganisms capable of growing in the product under normal non-refrigerated storage. The standard verification method, referenced in both EU and US practice: filled samples are incubated in their final packaging at 30°C (mesophilic spoilage risk) and, in parallel, at 55°C where thermophilic spoilage is a concern — directly relevant for product exported to hot-climate markets. Typical incubation periods run 7–15 days (the Tetra Pak Dairy Processing Handbook cites 15 days at 30°C or 7 days at 55°C as sufficient). Samples are checked for physical spoilage signs (coagulation, gas, off-odours, pack swelling) and pH drop. For low-acid products specifically, mesophilic and thermophilic anaerobic spore testing is added, given the specific risk of Clostridium botulinum in an under-processed low-acid product.

This is exactly why commissioning matters as a distinct exercise, not just routine QC: it is standard industry practice to run this microbiological verification specifically during commissioning of new equipment, to generate the data proving the process and its controls actually work before relying on routine testing alone. Two figures matter here, and they are not the same thing: industry reporting describes ATP-based rapid methods cutting the traditional 7–14 day product hold to 48 hours or fewer as the release-decision timeline; at least one commercial ATP system is reported to deliver its actual result within 30 minutes once primary incubation is complete — the incubation step itself still happens, but the detection read-out that used to take days now takes minutes.

Documentation & Sign-Off

A defensible FAT and commissioning programme produces a paper trail that still means something a year later, when a warranty question arises: the approved FAT protocol itself, the punch list with closure evidence for each item, commissioning logs for both cold and hot phases, microbiological verification records, and a formal handover certificate that states clearly what was accepted, by whom, and against which specification revision.

Frequently Asked Questions

What is Factory Acceptance Testing in dairy plant projects?
Factory Acceptance Testing (FAT) is the formal verification that plant, equipment or a complete process line meets the agreed specification before or immediately after installation, and before full commissioning begins. It covers mechanical completion, P&ID conformity, electrical and instrumentation checks, hygienic design compliance and safety systems, and produces a documented punch list of any deviations that must be closed out before proceeding to commissioning.
What is the difference between cold and hot commissioning?
Before any physical testing, the test protocol itself is reviewed and approved by the client. Software FAT then tests the PLC/HMI/SCADA logic using simulated I/O signals, with no field devices connected. Cold commissioning runs the plant, its utilities and the CIP system for real, without product. For vessels and tanks with manway access, cleanability is then verified using a synthetic tracer such as riboflavin, checked visually under UV light. Hot commissioning introduces product (or an approved simulant) and verifies the process actually performs as designed — temperatures, flows, yields and quality — against the guaranteed performance parameters in the contract.
Why use an independent consultant for FAT rather than relying on the equipment supplier?
An equipment supplier has an inherent interest in their own equipment passing acceptance testing. An independent consultant has no such interest, reviews the documentation and physical installation against the client's own specification rather than the supplier's, and reports any deviation without commercial pressure to sign it off. This protects the capital investment before final payment and handover, when the client's negotiating position is strongest.
What is the real proof that a UHT or aseptic line works?
Mechanical and hygienic checks are necessary but not sufficient. The definitive proof is microbiological: post-CIP swabbing (ATP bioluminescence, with the assay itself taking minutes) confirms cleaning actually killed microorganisms, and product incubation testing after hot commissioning — samples held at 30°C and, where relevant, 55°C for 7–15 days and checked for spoilage — confirms commercial sterility as defined by Codex Alimentarius. Rapid ATP methods cut the traditional 7–14 day release hold to 48 hours or fewer; the detection step itself, once incubation is complete, can take as little as 30 minutes.
Disclaimer: This information is provided for general guidance only. While every care has been taken to ensure accuracy, Watson Dairy Consulting (JWC Services Limited, SC246124) accepts no liability for any loss or damage arising from its use. Explosion safety, hygienic design and commissioning requirements are project- and jurisdiction-specific; always verify against the current applicable regulations, the equipment manufacturer's documentation and suitably qualified engineering advice before relying on this material for a live commissioning programme.

References:

  • Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) 2002 (UK); ATEX Directive 2014/34/EU.
  • NFPA 652 — Standard on the Fundamentals of Combustible Dust; NFPA 61 — Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities.
  • NFPA 68 — Standard on Explosion Protection by Deflagration Venting; NFPA 69 — Standard on Explosion Prevention Systems.
  • VDI 2263-7 — Dust fires and dust explosions, hazards, assessment, protective measures: spray dryers.
  • EHEDG — riboflavin fluorescence (cleanability) test methodology; EHEDG/3-A surface roughness guidance (Ra ≤0.8µm).
  • Control system FAT practice — simulated I/O testing of PLC/HMI/SCADA logic prior to field connection, per established automation commissioning practice.
  • FAT protocol review and approval as a precondition of testing — standard practice per ISPE, Pharmaguideline and multiple industry FAT/SAT guides.
  • Riboflavin (synthetic tracer) cleanability testing — Dairy Foods; 3-A Sanitary Standards definition of CIP; SCADA/HMI graphics verification against P&ID — SCADA FAT procedure guides.
  • Dye penetrant inspection (DPI/DPT) — ASNT, Wikipedia; food-safe fluorescent penetrant for dairy/food equipment — Accutest International.
  • Codex Alimentarius CAC/RCP 40-1993 — definition of commercial sterility; Tetra Pak Dairy Processing Handbook — UHT/aseptic incubation testing parameters.
  • ATP bioluminescence for rapid commercial sterility screening — Hygiena; Food Safety Magazine on aseptic product testing practice.

Further reading: John Watson publishes articles on dairy industry topics on LinkedIn. Browse all articles by John Watson on LinkedIn →

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