Factory Acceptance Testing (FAT) vs. Site Acceptance Testing (SAT): What's the Difference?
Factory Acceptance Testing (FAT) and Site Acceptance Testing (SAT) are important verification stages used to confirm that equipment, systems, and automation solutions meet defined project requirements. Although both involve testing and acceptance, they are performed at different locations and focus on different aspects of system readiness.
FAT is generally performed at the manufacturer’s, supplier’s, or system integrator’s facility before the equipment or system is shipped to the project site. It gives the customer an opportunity to verify the system against agreed requirements before installation.
SAT is performed after the equipment or system has been installed at the actual site. It focuses on confirming that the system works correctly in its installed environment and interfaces properly with site infrastructure and other systems.
In simple terms: FAT verifies the system before shipment, while SAT verifies the installed system at the site. The exact scope of each test depends on the contract, approved test procedures, system design, and project requirements.
What Is Factory Acceptance Testing (FAT)?
Factory Acceptance Testing (FAT) is a structured test conducted at the supplier, manufacturer, or system integrator’s facility before equipment or a system is delivered to the customer’s site.
The objective is to demonstrate that the supplied system meets the agreed functional and technical requirements before shipment. FAT is particularly useful for complex automation and control systems because problems can be identified and corrected before the equipment reaches the project site.
Depending on the system, FAT may involve hardware checks, software and configuration verification, input/output testing, control logic testing, alarm testing, operator interface checks, communication testing, and documentation review.
When Is FAT Performed?
FAT is normally performed after the equipment or system has been manufactured, assembled, configured, and made sufficiently ready for testing, but before it is shipped to the project site. The timing should be defined in the project schedule and agreed upon by the supplier and customer.
What Does FAT Verify?
- Equipment or system configuration
- Hardware installation and identification
- Software configuration and control logic
- Input and output functionality
- Operator interfaces and graphics
- Alarms and applicable shutdown functions
- Communication interfaces
- Functional requirements
- Applicable documentation
- Compliance with approved specifications and test procedures
What Is Site Acceptance Testing (SAT)?
Site Acceptance Testing (SAT) is performed after equipment or a system has been installed at the customer’s or end user’s site.
Its purpose is to verify that the installed system operates correctly in its actual environment and is properly connected to the required site infrastructure, field devices, utilities, and other systems.
Successful FAT does not automatically prove that a system will work correctly after transportation, installation, wiring, configuration changes, utility connections, and integration with site equipment.
The scope of SAT depends on how much was already demonstrated during FAT. In some projects, SAT may repeat selected FAT functions using the installed system and actual field connections. In others, it may place greater emphasis on site-specific interfaces and integration.
When Is SAT Performed?
SAT is normally performed after the equipment or system has been delivered, installed, connected, and made ready for site testing. The test is conducted before the system is formally accepted for its intended operational use, subject to the project’s acceptance and commissioning procedures.
What Does SAT Verify?
- Correct installation at the project site
- Field wiring and connections
- Communication with field devices
- Interface with site utilities and infrastructure
- Input/output signals from actual field equipment
- Control system functionality
- Alarms and applicable interlocks
- Communication between connected systems
- Site-specific operating functions
- Resolution of installation-related discrepancies
FAT vs. SAT: Key Differences
| Factor | FAT | SAT |
|---|---|---|
| Full form | Factory Acceptance Testing | Site Acceptance Testing |
| Location | Supplier, manufacturer, or system integrator facility | Customer or project site |
| Typical timing | Before shipment | After installation at site |
| Main purpose | Verify the system before delivery | Verify the installed system at its operating location |
| Environment | Controlled factory or integration environment | Actual project environment |
| Field devices | Often simulated or represented through test arrangements | Can be tested through actual site connections where applicable |
| Primary focus | Design, configuration, functionality, and factory readiness | Installation, site interfaces, integration, and site functionality |
| Typical result | Approval or release for shipment, subject to project requirements | Acceptance of the installed system, subject to project requirements |
FAT and SAT Example
Consider a new PLC-based control system being supplied for an industrial processing facility.
During FAT
At the system integrator’s facility, the customer and supplier may test the PLC hardware, software configuration, I/O mapping, control logic, operator graphics, alarms, communication functions, and other agreed requirements.
Where actual process equipment is not available, suitable simulation or test arrangements may be used.
If a control logic error is identified during FAT, the supplier can correct the configuration before the system is shipped to the site. This is one of the practical advantages of performing FAT thoroughly.
During SAT
After the control system reaches the project site, it is installed and connected to the actual field infrastructure.
SAT can then verify items such as field wiring, communication paths, actual I/O signals, interfaces with field devices, site-specific alarms, and interaction with connected equipment.
SAT therefore provides a second level of confidence: the system that passed testing in the factory has also been correctly installed and integrated at the actual site.
What Are the Main Benefits of FAT?
Conducting FAT before shipment allows project teams to identify problems while the equipment and technical specialists are still at the supplier’s facility. Correcting issues at this stage can be easier than troubleshooting the same problems after installation at the project site.
- Identify configuration and functional issues early.
- Reduce the risk of costly site rework.
- Verify compliance with approved requirements before shipment.
- Provide an opportunity for customer representatives to witness testing.
- Improve readiness for site installation.
- Reduce potential commissioning delays.
- Create documented evidence of factory testing.
What Are the Main Benefits of SAT?
SAT confirms that the equipment or system continues to meet the required functionality after transportation and installation. It also provides an opportunity to test site-specific interfaces that cannot always be fully verified in a factory environment.
- Verify correct site installation.
- Confirm field wiring and connections.
- Test communication with actual site systems.
- Identify installation or integration issues.
- Verify site-specific functionality.
- Confirm readiness for the next project stage.
- Document site acceptance results and outstanding issues.
Who Participates in FAT and SAT?
The participants depend on the project contract and testing requirements. FAT commonly involves the supplier or system integrator and customer representatives, while SAT generally involves the site team in addition to relevant supplier, contractor, engineering, and commissioning personnel.
Typical participants may include:
- Client or owner representatives
- Equipment manufacturer
- System integrator
- Automation and control engineers
- Electrical and instrumentation engineers
- Commissioning engineers
- Construction or installation teams
- Operations representatives
- Quality assurance and quality control personnel
What Should Be Included in a FAT Procedure?
A FAT should be based on an agreed test plan or procedure. The document should clearly define what will be tested, how it will be tested, the expected result, responsibilities, acceptance criteria, and how deviations will be recorded.
Depending on the system, a FAT procedure may cover:
- Scope and objectives of the test
- Applicable specifications and reference documents
- System configuration
- Hardware verification
- Software and logic testing
- I/O verification
- Alarm and event testing
- Operator interface testing
- Communication testing
- Functional testing
- Test records and acceptance criteria
- Deviation and punch-list management
- Final FAT report and approvals
What Should Be Included in a SAT Procedure?
The SAT procedure should address the installed system and the site-specific conditions that need to be verified. The scope should be coordinated with the FAT so that testing is neither unnecessarily duplicated nor omitted.
- Verification of installed equipment
- Site wiring and termination checks
- Power and utility availability checks
- Field device interface testing
- I/O signal verification
- Communication and network testing
- Alarm and interlock verification
- Control functionality testing
- Interface testing with other site systems
- Site-specific functional testing
- Documentation of deviations
- Final SAT report and acceptance
FAT vs. SAT: Is SAT Just a Repeat of FAT?
No, SAT should not automatically be treated as a complete repeat of FAT. The amount of repeated testing depends on the project’s requirements, the extent of FAT, the system architecture, and the risks associated with site installation and integration.
Some FAT functions may be repeated during SAT when they are necessary to demonstrate that the installed system continues to meet requirements. However, SAT should also address site-specific conditions and interfaces that could not be fully tested at the factory.
A well-designed test strategy therefore uses FAT to identify and correct issues early and SAT to verify the installed system and its site integration.
FAT, SAT, and Commissioning: What’s the Difference?
FAT and SAT are sometimes confused with commissioning, but they are not necessarily the same activity. Acceptance testing is intended to demonstrate compliance with defined requirements, while commissioning generally involves preparing, testing, starting, integrating, and verifying systems as they transition into operation.
| Stage | Primary Purpose | Typical Location |
|---|---|---|
| FAT | Verify the supplied system against agreed requirements before shipment | Factory or supplier facility |
| SAT | Verify the installed system and site-specific interfaces | Project or customer site |
| Commissioning | Prepare, test, start, integrate, and verify systems for operation | Project site |
Common FAT and SAT Challenges
Incomplete Test Documentation
Testing can become inefficient when test procedures, specifications, drawings, or acceptance criteria are incomplete or not aligned with the current system configuration.
Unresolved FAT Findings
FAT findings should be documented and tracked to closure or formally accepted according to the project’s deviation and punch-list process. Carrying unresolved issues into site installation can increase the risk of delays.
Changes After FAT
Hardware, software, configuration, or documentation changes made after FAT may require additional testing. The project should identify and control such changes before SAT.
Site Integration Problems
A system can perform correctly in a factory environment but encounter problems when connected to actual field devices, networks, utilities, or other site systems. SAT provides an opportunity to identify these site-specific issues.
Poor Coordination
FAT and SAT involve multiple stakeholders. Clearly defined responsibilities, test schedules, acceptance criteria, and documentation requirements help prevent misunderstandings during testing.
Best Practices for Successful FAT and SAT
- Define FAT and SAT requirements early in the project.
- Agree on test procedures and acceptance criteria before testing starts.
- Use the latest approved drawings, specifications, and system configuration.
- Invite the required customer and project representatives to witness applicable tests.
- Record test results and deviations systematically.
- Track FAT findings through an agreed punch-list or deviation process.
- Control all changes made after FAT.
- Use SAT to focus on actual site installation and integration.
- Ensure required site utilities, field devices, networks, and interfaces are available before SAT.
- Maintain signed test records and final acceptance documentation.
Typical FAT to SAT Sequence
Although the exact project sequence varies, a typical acceptance testing workflow can be represented as:
Design & Configuration
The system is designed, configured, and prepared according to approved project requirements.
FAT Planning
The test procedure, scope, participants, acceptance criteria, and required test arrangements are agreed.
Factory Acceptance Testing
The system is tested at the supplier or integrator facility before shipment.
Issue Resolution
Identified deviations and findings are addressed or formally tracked according to project requirements.
Site Installation
The equipment is delivered, installed, connected, and prepared for site testing.
Site Acceptance Testing
The installed system is tested against site-specific requirements and interfaces before progressing to the next stage.
This sequence is not universal for every project. Some projects may overlap activities or modify the order depending on the equipment, schedule, contractual requirements, and commissioning strategy.
Why Choose Tensor for Testing and Commissioning Support?
Tensor supports industrial and oil & gas projects with testing, inspection, pre-commissioning, commissioning, system verification, and documentation requirements based on the project scope and applicable procedures.
Our approach focuses on structured testing, proper documentation, system readiness, coordination, and practical project requirements from factory testing through site installation and commissioning.
Need FAT or SAT Support?
Discuss your project requirements with Tensor and explore the testing and commissioning support applicable to your equipment or facility.
Discuss Your ProjectFinal Takeaway
Factory Acceptance Testing (FAT) and Site Acceptance Testing (SAT) provide two complementary opportunities to verify industrial systems. FAT focuses on demonstrating that the system meets agreed requirements before shipment, while SAT verifies that the installed system works correctly in its actual site environment.
A strong FAT can identify configuration and functional issues before they become expensive site problems. SAT then confirms that installation, field connections, interfaces, and site-specific functionality are working as required.
The most effective approach is to plan FAT and SAT together, with clearly defined scopes, acceptance criteria, responsibilities, documentation, and procedures for managing deviations and changes.
FAQs
FAT, or Factory Acceptance Testing, is performed at the supplier or manufacturer’s facility before equipment or a system is shipped. SAT, or Site Acceptance Testing, is performed after installation at the project site to verify that the system works correctly in its actual environment and interfaces with site equipment and infrastructure.
FAT generally comes before SAT. The system is tested at the supplier’s facility before shipment, and after installation at the project site, the required site acceptance testing is performed.
The main purpose of FAT is to verify that the equipment or system meets agreed functional and technical requirements before it is shipped to the customer or project site.
Not necessarily. Some FAT tests may be repeated during SAT where required, but SAT should also address site-specific installation, field connections, interfaces, and integration that cannot be fully verified at the factory.
FAT commonly involves the equipment manufacturer or system integrator and representatives from the customer or owner. Depending on the project, automation, engineering, quality, commissioning, and operations personnel may also participate.
SAT typically involves the site team, customer or owner representatives, supplier or system integrator personnel, commissioning engineers, contractors, and other technical specialists required by the project.
Failed FAT items are normally documented as test deviations or punch-list items. The responsible party investigates and corrects the issue, after which the affected test may be repeated or otherwise resolved according to the approved project procedure before shipment or acceptance.
In many automation projects, process equipment that is not yet available at the factory can be represented using suitable simulation or test arrangements. The exact approach depends on the FAT procedure and project requirements.
Not necessarily. Whether FAT is required, and how extensive it should be, depends on the project specifications, contract, equipment type, system complexity, risk, and customer requirements.
SAT and commissioning are related but should not automatically be treated as the same activity. SAT is an acceptance test focused on demonstrating compliance and site functionality, while commissioning generally covers the broader process of preparing, testing, starting, integrating, and verifying systems for operation.
FAT and SAT help identify problems before they affect full-scale operation. FAT can catch design, configuration, and functional issues before shipment, while SAT verifies installation and site-specific integration after delivery.
