Expert Takeaways
- FAT proves the supplied system against an approved design in a controlled environment; SAT proves the installed system and real interfaces on site.
- Acceptance criteria, responsibilities and test prerequisites must be approved before testing begins.
- Commissioning documentation is evidence of readiness and configuration—not paperwork to assemble after start-up.
Many projects “pass FAT” and still lose days during site commissioning. The usual cause is not the test team's effort; it is an unclear boundary. Simulated signals were mistaken for proven field loops, third-party interfaces were excluded without being recorded, or punch items travelled to site without owners and closure dates.
Factory acceptance testing (FAT), site acceptance testing (SAT) and commissioning form a connected assurance process. Each stage should retire a different set of risks and produce records that let operations understand exactly what was tested, what changed and what remains open.
FAT vs SAT: The Practical Difference
| Question | FAT | SAT |
|---|---|---|
| Where? | Supplier or integrator facility | Final installed location |
| What does it prove? | Build, configuration and simulated function | Installation, field wiring and live interfaces |
| Main benefit | Find defects before shipping | Prove readiness in the operating environment |
Build the Test Plan Before the Equipment
The test procedure should trace back to the user requirement, approved drawings, data sheets, functional specification, cause-and-effect and interface documents. Give every test a unique number, prerequisite, method, expected result, evidence field and pass/fail status.
Traceable test records connect approved requirements to observed results, comments and sign-off.
FAT Prerequisites
- Approved design inputs and frozen test software version.
- Completed internal quality checks and calibrated test equipment.
- Representative panels, devices, networks and simulation tools available.
- Approved procedure, witness points and attendee responsibilities.
- Backup and restoration method demonstrated before functional tests.
SAT Prerequisites
- Mechanical completion and installation inspection signed off.
- Power, earthing, networks, utilities and field devices available.
- FAT punch items closed or formally accepted for site completion.
- Approved energisation, isolation and permit arrangements.
- Current drawings, software backups and vendor support on site.
What a Strong FAT Should Test
Verify physical construction against drawings; power supplies and redundancy; I/O allocation; network health; controller logic; sequences; interlocks; alarms; HMI navigation; trends; reports; users and permissions; failure modes; time synchronisation; and backups. Safety-related tests should challenge relevant states and resets under controlled conditions.
Record simulator limitations. A simulated analogue input can prove scaling and logic but not the installed transmitter, impulse line or process response. The report must distinguish what was proven from what remains for SAT.
What SAT and Commissioning Must Add
SAT confirms equipment identity, damage-free installation, terminations, end-to-end loops, communications, alarms and field actions. Commissioning then establishes the configured system under operating conditions: tuning, calibration, sequence trials, performance tests, operator training and controlled transition to operations.
Manage Punch Lists by Risk
Classify punch items using agreed categories. A safety, compliance or operability defect should block energisation or start-up. A minor labelling correction may be accepted with an owner and due date. Every item needs a description, location, responsible party, target date, closure evidence and independent verification where required.
Commissioning Documentation Checklist
- Approved requirements, design basis, specifications and interface register.
- Issued-for-construction and final as-built drawings.
- Equipment data sheets, certificates, calibration records and serial numbers.
- FAT, SAT, loop-check, functional and performance test records.
- Cause-and-effect results, alarm settings and trip setpoints.
- Software source, compiled files, licences, versions and verified backups.
- Punch list status, deviations, concessions and management-of-change records.
- Operating, maintenance and proof-test procedures plus training records.
- Spares, warranties, vendor contacts and recommended lifecycle plan.
The Handover Gate
Do not define handover as “the plant is running.” Define objective readiness criteria: required tests passed, blocking punches closed, residual risks accepted by authorised roles, backups verified, operators trained and the document index complete. That turns handover into a controlled governance decision.
About the Reader Persona: Handover-Focused Priya
Priya leads commissioning across multiple vendors. She needs test boundaries that prevent repetition, punch lists that reveal risk and a turnover dossier operations can actually use after the project team leaves.
Make Acceptance Evidence Part of the Design
Mbonyasambe builds structured FAT, SAT, commissioning and handover requirements into EPCM delivery so scope, testing and lifecycle accountability stay connected.
Strengthen Your Test and Handover Plan