Digital Twin as Contractual Guarantee in Fat: Reducing Disputes and On-Site Changes

ByMarco Bellini (B&B)

The Factory Acceptance Test (FAT) is an extremely critical contractual milestone in automation projects.

The adoption of a Digital Twin transforms FAT from a partial check to a comprehensive verification, enabling simulations and validations prior to physical construction.

This approach reduces disputes, on-site changes, and contractual risks, ensuring traceability and compliance with IEC/ISA standards.

1. REGULATORY CONTEXT: FAT AS A CONTRACTUAL MILESTONE

IEC 62381 and ISA-105 standards define roles, checklists, and FAT documentation, highlighting its value as a shared verification and a trigger for contractual payments.

2. WHY TRADITIONAL FAT IS PARTIAL AND GENERATES DISPUTES

For years, FAT has been performed on electrical panels with manual simulations of PLC/HMI/SCADA control software.

This method only reproduces conditions similar to reality, often resulting in on-site commissioning requiring changes and adjustments for aspects not verified during FAT or to resolve functional errors previously undetected.

The above leads to sometimes significant cost variations and possible delivery delays, always negatively impacting client relationships.

The Digital Twin fills this gap by enabling simulation of the entire plant (including safety functions) and creating a shared environment where all client-required checks can be performed, resulting in approval not only of automation panels but also of all management software (tested under different operating conditions).

3. DIGITAL TWIN: DEFINITIONS AND REFERENCE STANDARDS

The Digital Twin is defined by ISO/IEC 30173 as a digital representation with data synchronization. IEC 62832 provides the framework for the Digital Factory.

4. FROM PHYSICAL FAT TO VIRTUAL FAT: ADMINISTRATIVE EFFECTS

Virtual FAT enables complete validation, traceability, and dispute reduction. It generates digitally signed reports and logs, useful for audits and claim management.

5. CONTRACTUAL CLAUSES TO ENHANCE THE DIGITAL TWIN

It is possible to include specific documentation in contractual clauses to enhance:

  • Digital Twin deliverable compliant with IEC 62832
  • IEC 62381 checklist
  • Measurable acceptance criteria and change management based on Digital Twin evidence.

6. ADMINISTRATIVE AND LEGAL BENEFITS

The administrative benefits of a FAT approach using Digital Twin are numerous and highly impactful:

  • Reduction of ambiguity
  • Proof of due diligence
  • Accelerated payments
  • Reduced rework costs and regulatory compliance

All of this eliminates conflicts arising from design mismatches, improving the work environment and ultimately client relationships—essential conditions for a successful business relationship.

7. OPERATIONAL GUIDELINES

The operational guidelines include:

  • Include the Digital Twin in the RFP (Request For Proposal)
  • Plan FAT with technicians capable of understanding and approving the functionalities to be verified
  • Document using IEC checklists

It is also possible to go further by planning operator training in advance.

8. CONCLUSIONS

The Digital Twin transforms FAT into a contractual guarantee:

  • Test before building
  • Document before shipping
  • Accept before installation.

References

IEC 62381: FAT/SAT/SIT; IEC 62832: Digital Factory; ISO/IEC 30173: Digital Twin; ISA-105 Guidelines; Siemens Virtual FAT White Paper

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