Industrial equipment can be expensive, technically complex and difficult to replace once installed at a project site.
So how can a project team verify that equipment works correctly before it becomes part of a larger industrial system?
Two important testing stages are commonly used:
FAT — Factory Acceptance Testing
SAT — Site Acceptance Testing
Both tests are designed to verify that equipment or systems meet agreed requirements, but they happen at different stages and serve different purposes.
The simplest way to understand them is:
FAT checks the equipment before it leaves the factory. SAT checks the equipment after it has been installed at the project site.
Both can be important components of industrial project execution, particularly for projects involving complex equipment, automation systems, multiple OEMs and integration with existing plant infrastructure.
What Does FAT Stand For?
FAT stands for Factory Acceptance Test.
A FAT is a structured test performed at the manufacturer’s or supplier’s facility before equipment is delivered to the client or project site.
The purpose is to verify that the equipment or system meets the agreed technical and functional requirements before it leaves the factory.
Depending on the equipment, a FAT can involve testing:
- Equipment functionality
- Control logic
- Instrumentation
- Alarms
- Interlocks
- Communication
- Performance
- Safety functions
- Documentation
- Operating sequences
The exact test procedure depends on the equipment and project specifications.
What Does SAT Stand For?
SAT stands for Site Acceptance Test.
SAT is performed after equipment has been delivered, installed and connected at the project site.
The purpose is to confirm that the equipment works correctly within the actual site environment.
This is important because equipment that performs correctly in a manufacturer’s factory may encounter different conditions after installation.
At the site, the equipment may need to communicate with:
- Existing PLCs
- SCADA systems
- Plant instrumentation
- Electrical systems
- Other equipment
- Process systems
- Communication networks
SAT provides an opportunity to verify these site-specific interfaces.
FAT vs SAT: What’s the Difference?
The main difference is where and when the testing takes place.
| FAT | SAT | |
| Meaning | Factory Acceptance Test | Site Acceptance Test |
| Location | Manufacturer’s/supplier’s facility | Client/project site |
| Timing | Before delivery | After installation |
| Main purpose | Verify equipment before shipment | Verify equipment in its actual operating environment |
| Focus | Equipment and system functionality | Site installation and system integration |
| Participants | Client, OEM, engineers, project team | Client, contractors, engineers, OEM/integrator |
| Main benefit | Identify issues before shipment | Confirm correct operation at site |
FAT and SAT are therefore complementary rather than interchangeable.
Why Is FAT Important?
A factory test provides an opportunity to identify problems before equipment leaves the manufacturer’s facility.
This can be valuable because correcting a problem at the factory is generally easier than correcting it after equipment has been transported, installed and connected at a project site.
Imagine an industrial control panel is delivered to a remote facility and only then discovered to have incorrect control logic.
The project team may need to:
- Troubleshoot the system
- Modify the software
- Re-test the equipment
- Coordinate with the OEM
- Delay commissioning
- Potentially arrange additional site support
A well-planned FAT can identify some of these problems earlier.
What Is Tested During a FAT?
The exact FAT procedure depends on the equipment.
For an automated industrial system, testing may include:
Functional Testing
Does the equipment perform the functions specified in the project requirements?
Control Logic
Does the PLC execute the expected control sequences?
Alarm Testing
Are alarms triggered when abnormal operating conditions occur?
Interlock Testing
Does the equipment respond correctly when predefined conditions are met?
Instrumentation
Do sensors and instruments provide the expected signals?
HMI Testing
Are the required information, controls and alarms correctly displayed?
Communication Testing
Can the equipment communicate with other required systems?
Documentation Review
Are drawings, manuals, test records and other technical documents complete?
What Is Tested During SAT?
SAT focuses on the equipment after it has reached the project site.
Testing may include:
- Equipment operation
- Installation verification
- Electrical connections
- Instrumentation
- PLC communication
- SCADA communication
- Alarms
- Interlocks
- Control functions
- Communication with existing equipment
- Process interfaces
The objective is to verify that the complete installed system operates as intended.
Why Can Equipment Pass FAT but Fail SAT?
This is one of the most important things to understand about FAT and SAT.
Passing FAT does not necessarily mean that there will be no problems during SAT.
The factory and project site are different environments.
During FAT, the equipment may be tested under controlled conditions.
At the site, it may need to interact with:
- Existing equipment
- Existing control systems
- Site electrical infrastructure
- Actual process conditions
- Site communication networks
- Installed instrumentation
- Other contractors’ systems
For example, a new PLC may communicate perfectly with the manufacturer’s test equipment during FAT.
After installation, however, the PLC may have difficulty communicating with the client’s existing SCADA system.
That is a site integration issue, not necessarily an equipment manufacturing problem.
This is why industrial systems integration needs to be considered alongside FAT and SAT.
FAT and SAT for Multi-OEM Projects
Complex industrial projects may involve equipment from several manufacturers.
For example:
- Compressor OEM
- Pump OEM
- Process equipment OEM
- PLC supplier
- SCADA supplier
- Electrical contractor
- Instrumentation contractor
Each system may work independently.
But the real question is:
Can all the systems work together?
This is where multi-OEM integration becomes important.
FAT can verify the functionality of individual equipment packages and, where practical, test interfaces between systems.
SAT can then verify that the integrated systems work correctly within the actual project environment.
FAT and PLC Integration
PLC integration can form an important part of FAT.
The project team may need to verify:
- Input signals
- Output signals
- Control logic
- Equipment status
- Start/stop commands
- Alarms
- Interlocks
- Communication
- Operating sequences
Testing these functions before equipment reaches the site can help reduce commissioning problems.
However, the final PLC integration still needs to be verified after installation because the actual site environment may introduce additional interfaces.
FAT and SCADA Integration
SCADA systems provide operators with monitoring and control capabilities.
During FAT, the project team may test whether:
- Equipment status is displayed correctly
- Process values appear correctly
- Alarms are generated
- Commands are transmitted
- Trends work as expected
- Communication is functioning
The exact scope depends on the project architecture.
At SAT, the SCADA system can then be tested against the actual equipment and plant infrastructure.
How Is a FAT Performed?
A typical FAT process may follow these steps:
1. Define the Test Requirements
The project team establishes what needs to be tested.
2. Develop the FAT Procedure
The test procedure defines the individual tests, expected results and acceptance criteria.
3. Review the Procedure
The client, engineering team and supplier may review the procedure before testing begins.
4. Conduct the FAT
The equipment is tested against the agreed requirements.
5. Record Results
Test results, observations and failures are documented.
6. Resolve Issues
Problems identified during testing are corrected.
7. Re-Test
Failed or modified functions are tested again.
8. Approve the Equipment
Once the agreed acceptance criteria have been satisfied, the equipment can be approved for shipment.
How Is a SAT Performed?
SAT generally follows a similar structured process.
1. Confirm Installation
Equipment must be installed and connected correctly.
2. Verify Connections
Electrical, mechanical, instrumentation and communication connections are checked.
3. Conduct Functional Tests
The equipment is operated to verify functionality.
4. Test Interfaces
Communication with other equipment and systems is verified.
5. Test Alarms and Interlocks
Safety and control functions are checked.
6. Document Results
Test results and outstanding issues are recorded.
7. Resolve Problems
Issues are corrected and re-tested.
8. Confirm Acceptance
The client and project team confirm whether the system satisfies the agreed acceptance criteria.
What Is a FAT/SAT Test Procedure?
A FAT or SAT should not simply involve switching equipment on and seeing whether it works.
A structured test procedure defines what needs to be verified and what constitutes an acceptable result.
A test procedure may include:
- Test number
- Description
- Test method
- Expected result
- Actual result
- Acceptance criteria
- Pass/fail status
- Comments
- Responsible personnel
This provides a documented basis for determining whether the equipment has passed the test.
Who Participates in FAT and SAT?
The participants depend on the project.
A FAT may involve:
- Client representatives
- OEM/manufacturer
- Systems integrator
- Engineering team
- Project manager
- Quality personnel
- Instrumentation/control engineers
SAT may additionally involve:
- Site contractors
- Installation teams
- Electrical engineers
- Commissioning engineers
- Operations personnel
- Maintenance personnel
The key stakeholders should understand the test requirements before testing begins.
FAT, SAT and Commissioning
FAT and SAT are closely connected to commissioning but they are not the same thing.
FAT verifies equipment before delivery.
SAT verifies equipment after installation.
Commissioning involves preparing the installed systems for actual operation and verifying that the complete facility or system performs as required.
A simplified sequence could be:
Engineering → Procurement → FAT → Delivery → Installation → SAT → Commissioning → Start-Up
The exact sequence can vary depending on the project.
Effective engineering and project execution should account for testing and commissioning requirements from the beginning.
What Happens If Equipment Fails FAT?
A failed FAT does not necessarily mean the project has failed.
It means that one or more acceptance criteria have not been satisfied.
The issue should be documented and investigated.
Depending on the problem, the supplier may need to:
- Modify equipment
- Correct software
- Replace components
- Update documentation
- Adjust control logic
- Reconfigure communication
- Repeat specific tests
The equipment can then be re-tested.
The important point is to identify and resolve problems before they create larger issues later in the project.
What Happens If Equipment Fails SAT?
A SAT failure can indicate problems with:
- Installation
- Wiring
- Instrumentation
- Communication
- Configuration
- PLC programming
- SCADA integration
- Equipment interfaces
- Site conditions
The project team needs to determine the cause before corrective action is taken.
Once the problem is resolved, the affected test should be repeated.
Outstanding SAT issues may also need to be tracked through a commissioning or punch-list process.
How FAT and SAT Reduce Project Risk
FAT and SAT provide structured checkpoints throughout the project.
Instead of waiting until final commissioning to discover problems, project teams can identify issues earlier.
FAT can help identify:
Manufacturing → Configuration → Control → Documentation → Equipment
issues.
SAT can help identify:
Installation → Communication → Integration → Site → Operational
issues.
Together, they provide greater visibility into whether the project is progressing toward successful operation.
Frequently Asked Questions About FAT and SAT
What does FAT stand for?
FAT stands for Factory Acceptance Test. It is performed at the manufacturer’s or supplier’s facility to verify that equipment meets agreed technical and functional requirements before shipment.
What does SAT stand for?
SAT stands for Site Acceptance Test. It is performed after equipment has been installed at the project site to verify its functionality and integration within the actual site environment.
What is the difference between FAT and SAT?
FAT takes place before equipment leaves the factory, while SAT takes place after equipment has been installed at the project site. FAT focuses primarily on equipment functionality, while SAT also considers site installation and system integration.
Is FAT mandatory?
Not for every project. Whether FAT is required depends on the equipment, contract, project specifications, risk level and client requirements.
Is SAT mandatory?
The requirement depends on the project specifications and acceptance process. Complex industrial projects frequently use SAT to verify equipment after installation.
Can equipment pass FAT but fail SAT?
Yes. FAT and SAT occur in different environments. Equipment can perform correctly at the factory but encounter installation, communication or integration problems at the project site.
What is tested during FAT?
FAT can test equipment functionality, control logic, instrumentation, alarms, interlocks, communication, HMI functions, documentation and other requirements specified in the test procedure.
What is tested during SAT?
SAT can verify equipment operation, installation, electrical connections, instrumentation, communication, PLC and SCADA interfaces, alarms, interlocks and interaction with existing plant systems.
Who conducts FAT and SAT?
Testing is generally carried out by the equipment supplier, client representatives and relevant engineering or project personnel. Site contractors, commissioning engineers and operations teams may also participate in SAT.
What happens after FAT?
Once the agreed acceptance criteria are met and outstanding issues are resolved or formally accepted, the equipment can proceed toward shipment and site installation.
What happens after SAT?
After successful SAT, the equipment can proceed toward commissioning, performance verification and eventual operational start-up, depending on the project requirements.
FAT and SAT Are Part of a Larger Project Execution Strategy
Testing should not be treated as an isolated activity at the end of an industrial project.
FAT and SAT requirements should be considered during engineering, procurement and project planning.
The equipment needs to be specified correctly.
The control system needs to be designed appropriately.
Interfaces need to be identified.
Installation needs to be coordinated.
And the acceptance criteria need to be understood before testing begins.
SOC Energy Services supports industrial clients through engineering and project execution, including technical coordination, equipment integration, testing and commissioning support.
For projects involving multiple systems and OEMs, FAT and SAT can provide important checkpoints for verifying that equipment performs as expected and that the complete system is ready to move toward reliable operation.
Proper testing does not simply answer the question “Does the equipment work?”
It helps answer the more important question:
“Does the equipment work as part of the system it was designed to support?”
