Converting a legacy platform to a modern DCS may look complex, but using these best practices provides opportunities for significant process improvements.
By Chris King, PlantPAx migration business development manager, Rockwell Automation
Here’s the good news. If you think your distributed control system (DCS) has run its course, you’re not alone. The global DCS installed base nearing end of life totals about US$65 billion. And many of these systems are more than 25 years old and in dire need of updating.
Why is there such a backlog of outdated systems? The simple truth is many still are keeping a plant running, albeit not running as well as it could. Often, organizations would rather live with the significant pain an obsolete system inflicts than be subjected to the perceived risks and costs of migrating to a modern system.
Another truth is for many plants and organizations: Insufficient in-house staff and expertise exist to manage large capital projects internally, particularly for specialized tasks performed infrequently, such as a DCS conversion.
Let’s face the facts: Automation projects can be difficult to manage and difficult to justify financially. Every day, we work with companies who have made the case for modernization successfully based on both existing system shortcomings and the significant improvements of a new, state-of-the-art modern DCS.
Reasons to replace a DCS can include:
- An increased failure rate.
- Higher incidence of off-spec product.
- Accelerating maintenance costs.
- Lack of legacy DCS expertise.
- Capacity limitations.
- Inability to interface with contemporary systems.
On the flip side, many industrial firms also come to recognize that a DCS modernization is a rare opportunity for significant process improvements and innovation.
What’s the Plan?
Converting a legacy control platform to a modern DCS may be complex, and it’s not a one size fits all endeavor. To help mitigate risk — and spread costs over time — many companies choose a phased approach to migration. On the other hand, a “rip-and-replace” conversion strategy is appropriate for others.
Simply put, each modernization project is unique. And the most successful projects require proper planning.
Define the Strategy
In most cases, it’s essential to perform the conversion with very little downtime and minimal risk, and these requirements determine much of the upgrade strategy.
You must decide on three main strategic choices before conversions take place.
1. First, determine if the upgrade will be vertical or horizontal. In a vertical upgrade, just one process area is upgraded at a time. In a horizontal upgrade, multiple similar process units are upgraded simultaneously, generally across process areas. For example, if a site has eight boilers, all would be upgraded at once in a horizontal upgrade, as opposed to upgrading only the boiler(s) in the vertical process unit.
2. Determine if the upgrade will be done by replacing all automation system components simultaneously (rip-and-replace) or with a phased migration approach. With a phased approach, replacing the automation system takes longer, but will require less downtime and entail less risk.
Breaking the planned downtime into multiple short phases is often a great advantage for maintaining production, and it spreads out migration costs over a longer period.
3. The final strategic decision made is “hot versus cold” cutover. With hot cutover, the old DCS and the new automation system operate simultaneously, with one control loop at a time migrated from the old DCS to the new automation system at the I/O level. With cold cutover, the old DCS is replaced by the new automation system, with the entire process being restarted at once (see table).
The hot cutover option is more expensive in terms of upgrade costs, but with an overall lower cost in most cases when downtime is considered. Risk is also lower with hot cutover because only one loop is converted at a time, with the old DCS still available in case of any unforeseen difficulties with the new automation system.
Benefits of hot vs. cold cutover include:
- Less downtime.
- Reduced risk.
- Easier to troubleshoot potential issues.
- Simpler to implement on-the-job training on the new automation system.
Drawbacks of hot vs. cold include (see table):
- More expensive.
- Takes up more space.
- Requires simultaneous operation of old and new automation systems.
- Takes longer.
Five Best Practices
So what is the best way to develop your conversion and implementation strategy?
Based on experiences working with hundreds of companies, we’ve identified five best practices that lead to modernization success.
1. Early Planning. A successful modernization begins long before any detailed engineering — with an upfront, comprehensive evaluation of the legacy system. Initial objectives at the front end include aligning automation outcomes with business goals, determining the preferred options, obtaining capital funding, and finalizing the scope, cost and schedule.
Through these activities, you establish justification for the project, define it — and align all stakeholders. Keep in mind, the most cost-effective time to define the scope is at the beginning. Costs escalate considerably if basic decisions such as which areas of the plant to include or what interface to apply are revisited later.
2. Engage Experts. Chances are, you already know who to call when faced with a perplexing application challenge. It could be a system integrator or automation supplier. This same network of support can also provide critical assistance throughout your conversion process. In the end, calling on experts when needed saves both time and money.
3. Establish Standards. Establishing — and following — standards is as critical as early planning. If appropriate company standards don’t exist, they will need to be developed using internal expertise — or by calling on a system integrator or automation supplier for help.
The more thoroughly you specify and document network protocol, security requirements, I/O and HMI criteria, interface requirements and controller configuration, the easier it will be to maintain and improve your system. Take our word for it. Your company’s future employees will thank you.
4. Execution Discipline. A DCS conversion is complex. And like any extensive undertaking, it requires sound project management. Without execution discipline, any large project runs the risk of spiraling out of control.
To keep your conversion on time and on budget, be sure to follow a consistent execution strategy based on accepted industry best practices. If you don’t have resources on staff, consider engaging a certified project management professional (PMP) to help guide your project.
5. Expect Innovation. Don’t be content with merely duplicating the content in your old control system. Remember, 25-year-old legacy systems are unlikely to deliver the same advantages that a state-of-the-art modern DCS can. Your migration project is an extraordinary opportunity to leverage new technologies to control your process optimally. Don’t replicate. Innovate.
With innovative thinking, each upgrade area is examined for opportunities to enhance how the system performs. Return on investment (ROI) due to these improvements over legacy systems is often very quick; improved operations, better quality, more throughput, few safety-related incidents, augmented cyber-security and less unplanned downtime are the primary benefits of converting to a modern DCS in their new Connected Enterprise.
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