Upgrading critical ESD control, with minimal downtime and improved reliability.

An offshore operator required a full modernisation of its ageing Emergency Shutdown (ESD) system. The existing system used legacy Triconex Version 8 hardware and DOS based development tools, which presented both obsolescence and maintainability issues. The objective was to migrate to Triconex Version 11.5 hardware and a modern Windows based Tristation 1131 development environment, while retaining all existing functionality and maintaining continuous production wherever possible.

Challenges

• Ageing hardware with several I/O module types no longer supported
• Legacy DOS based PLC code requiring full migration and structural improvement
• Safety critical functionality with no tolerance for operational disruption
• Need for SIL3 compliance, including enhanced diagnostics and structured software lifecycle
• Serial communications changes requiring redesigned connectors and cable adaptations
• Replacement of 48 VAC output modules with new 24 VDC supervised modules requiring interposing SIL3 relays

Solution

• The integrator delivered a complete hardware and software upgrade including:
• Replacement of processors, communication modules, and selected I/O modules
• Hot swap replacement of backward compatible I/O modules while the plant remained live
• Shutdown based replacement of non compatible modules and processor hardware
• Introduction of SIL3 rated solid state safety relays to handle legacy 48 VAC field circuits
• Software migration from DOS logic to structured IEC 61131 3 routines within Tristation 1131
• Retention of all tag names, execution order, communications mapping, and Modbus aliases
• Integration of SIL3 diagnostic alarms and gated write access functions
• Updates to HMI alarms, status indications, and diagnostics visibility
• Comprehensive testing including Autotest verification, FAT and SAT witness testing

Outcome

The upgraded system achieved:

• SIL3 capable hardware and software
• Improved maintainability through structured PLC programs and modern toolsets
• Stronger diagnostic coverage and operator visibility
• Zero loss of production during Phase 1 (hot swap) works
• Controlled and fully tested shutdown during Phase 2
• A verified, compliant system with full documentation, revised drawings, and updated wiring databases

This upgrade extended the operational life of the ESD system and aligned it with modern safety and reliability standards.