From obsolescence to opportunity: modernizing control systems for sustainable operations

Understanding control system aging

In reliability engineering, the gradual loss of dependability over time is well represented by the bathtub curve. As described by O’Connor and Kleyner in Practical Reliability Engineering (Wiley, 5^th Edition, 2012), electronic systems typically follow a bathtub-shaped failure rate curve that includes:

• Early life: higher failure rates
• Long phase: stable operation
• Final wear-out: increasing failures

This same principle applies to industrial control systems. After years of service, controllers, I/O modules and communication hardware may still function, but they’re often in the wear-out stage of the curve where reliability declines.

At this stage, outdated firmware, legacy protocols and limited spare parts create significant operational risks, even if the system still runs normally. A single hardware failure can halt operations for hours or days while replacement parts are sourced online. Older PLCs running on Ethernet with outdated firmware may also fail to comply with modern cybersecurity standards, creating additional vulnerabilities within the network. Recognizing when a system has entered this wear-out phase allows clients to plan modernization before unplanned downtime, rather than react to it.

Figure 1 – The Bathtub Curve of Failure Rate over Time Adapted from Practical Reliability Engineering by Patrick O’Connor and Andre Kleyner (Wiley, 5th Edition, 2012). The model illustrates early-life failures, a stable useful-life phase, and a final wear-out region.

Recognizing when a system has entered this wear-out phase allows clients to plan modernization before unplanned downtime, rather than react to it.

Modernization as an opportunity for improvement

Replacing legacy platforms is more than just a hardware upgrade; it’s a chance to rethink the entire control system infrastructure. A modernization project provides an opportunity to:

1. Validate and improve engineering design: Review I/Os, safety interlocks, control schematics, PLC programming, HMI graphics and network architecture to align with current standards.
2. Simplify maintenance: Standardized components and programming tools make troubleshooting and component replacement faster and more efficient.
3. Integrate IT and OT securely: Apply the Purdue Model and IEC 62443 standards to segment networks and control access, improving cybersecurity resilience.
4. Increase reliability and visibility: Modern PLCs and DCS platforms provide better diagnostics, event recording and integrated alarm management, improving situational awareness and maintainability.
5. Extend operational life with confidence: Proactive migration prevents unplanned downtime and positions the facility on a renewed life cycle where equipment, firmware and security updates can be managed predictably and sustainably.

Conclusion

At BBA, we approach modernization as both a technical and strategic process, helping clients transition from legacy platforms to modern architectures that align with today’s standards and prepare their operations for the future.

System modernization is no longer a luxury; it’s a necessary step to maintain safe, reliable and sustainable operations. As control systems reach the wear-out phase of their life cycle, the risks of downtime, cybersecurity exposure and loss of support increase.