The distributed control system (DCS) has been in use since the mid 1970s while the programmable logic controller (PLC) has been around slightly longer. Some early installations still are operating today using microprocessors that predate the original personal computers. The ARC Advisory Group, Dedham, Mass., estimates that over $65 billion worth of DCS installations are approaching and, in many cases, exceeding 20 years in service — and this doesn’t include other control platforms such as PLCs or supervisory control and data acquisition (SCADA) systems. So, industry faces an enormous need to replace these computer-based systems. Doing so poses a substantial challenge in justifying the investment, managing the risk, and executing the project with minimal impact to cash flow.
As with most investments, project justification for control system replacement or migration should consider two key factors: risk reduction and lost opportunity.
The risk elements associated with control systems are similar to those of many computer-based systems. An unscheduled production outage because the normally reliable control system fails can prompt an incident that poses high risks to people, production and facilities and also might lead to potential environmental violations and damage to reputation — all the typical risk matrix impact or consequence dimensions.
The main reason the control system itself fails or can’t properly be maintained is obsolescence of parts and equipment.
A related culprit is lack of people (due to retirements, cutbacks, etc.) skilled in maintaining the hardware and, perhaps more importantly, the software/applications that run the plant. Unfortunately, these legacy control systems don’t support the programming tools used today. Understanding the legacy code to ensure proper porting to the new platform can pose a real problem.
Fortunately, suitable risk management and planning can avoid this potential worst-case scenario. A relatively recent report from the International Association of Oil & Gas Producers  provides guidance on how to maintain integrity, high availability and low lifecycle costs in return for a small investment in planning.
The other facet of justification, opportunity lost, usually is difficult to quantify and is site specific. The opportunities generally fall into several broad categories:
• Additional capacity or production through increased asset utilization, which often is tracked as return on net assets. A control project may allow a plant to operate with reduced process deviations and, thus, closer to operating and physical process constraints without incident or upset. Modern systems use many of the same technologies found in the office environment — this significantly improves integration between the systems and, hence, visibility of plant floor data upward into the enterprise for accurate and timely decision-making.
• Improved asset utilization and lower maintenance costs. Effectively using the inherent diagnostics contained in intelligent devices able to communicate over digital networks enables better planning and also makes the maintenance exercise easier, faster and less prone to errors. These improved practices and procedures decrease maintenance costs, which may represent as much as 50–70% of the control system budget, by 25%.
• Enhanced operator effectiveness. This leads to better decision-making and fewer operational errors. Features in newer control systems aid access to information and recommended actions, including semi- or fully automated procedures or workflows that can offload many standard actions required of operators.
• Built-in cyber security measures. Newer control systems have been designed to consider and incorporate cyber-security capabilities; older systems may lack such capabilities or, as a minimum, require bolted-on security at extra cost and effort.
Justifying a project on the above factors often is challenging; it’s somewhat akin to purchasing insurance. That’s why many facilities continue to put off their migration project. Because the impact isn’t immediate, it’s an easy budget cut when money becomes scarce.
One way to prevent the perpetual delay of migration projects is to incorporate strategic planning into the annual automation system budgeting process using the information in Ref. 1 as a clear roadmap and way to document the level of risk associated with poor planning.
Once the migration activity is approved, a plant should form a project team with the objective of providing a new control system at minimal investment. Minimal investment doesn’t mean minimum cost. Because the capital investment in a control system represents at most 25% of its total lifecycle cost, the team should focus on minimum total installed cost. Moreover, with migration such a rare event, cutting corners can lead to missing some of the opportunity benefits cited above, generating a lower return on your effort. With the lifecycle of only five years for some control system components, such as servers, if a project is too spread out, the entire migration will become a continuous part of the annual budget and work plan.