Most legacy control systems run critical manufacturing processes that typically cannot be shut down or taken offline for very long without noticeably affecting a plant’s output of saleable product. Consequently, many replacement projects for legacy control systems include extremely aggressive (very short time duration) cutover windows to replace the old gear with the new. This extreme time restriction poses a significant challenge to the integrator/supplier responsible for making the cutover without adversely affecting plant operations.
Casual planning can lead to a cutover disaster and cost the plant significant money in lost opportunities for production. Diligent and comprehensive planning can greatly increase the probability of getting through the cutover to the new control system with the least amount of surprises and difficulties. Let’s examine some of the many touch points to consider when planning a short-duration legacy system cutover.
Start with existing system documentation. Operate based on the likelihood that the drawings are not accurate and are not current. Plan to meticulously field-verify the hardware and wiring against the drawings. Expect to find devices mounted in panels that don’t show up on the drawings. Conversely, expect to find devices and wiring on drawings that are nowhere to be found in panels or on the plant floor. Don’t panic when either or both arise; simply document and move on.
Field-verifying the legacy system will most likely reveal inconsistency in device naming and labeling along with wire labeling. For example, a shutoff valve might be labeled CV301 on the piping and instrumentation diagrams (P&IDs), labeled V301 on the schematics, and labeled 301 on the metal asset tag on the valve body itself. The corresponding wiring from the controller to the valve’s actuator solenoid might be labeled Y234 at the output module, wire 2 at the marshalling panel or junction box, and have no label at the valve actuator itself. It’s much better to find these inconsistencies prior to the critical cutover window to save precious time during the cutover. Additionally, upgrading legacy control systems is an excellent opportunity to correct these common labeling and naming inconsistencies.
Critical to a successful short-duration cutover is a comprehensive understanding of the operational functionality of the existing system. Here again, system documentation will most likely not be current. Changes, edits or additions to the control code might have been made over the years to improve production, but not adequately documented. Worse yet is when no document of the control functionality can be found; only the legacy system exists. It is unrealistic to expect the integrator to somehow glean all the intricate functionality and nuances of the controls for the new system simply because the integrator is in possession of the control code and human-machine interface (HMI) application. The stakeholders need to commit to allowing the plant’s operators, maintenance and supervisors to share their tribal knowledge of the system with the integrator. Plan for extensive design reviews with the plant’s active participation—the more reviews the better. Have in-depth factory acceptance tests (FATs) where the operators run the new system under full simulation with mass balance, energy balance, alarms, upset conditions, manual control and system recovery. And create a living document during all of this that captures the operational functionality of the new system when it goes live on the plant floor.
Coordinating and meticulously planning the activities and responsibilities of all the participants—including plant personnel, integrator, contractors and even suppliers—prior to the short-duration cutover is paramount to achieving results. Successful short-duration legacy system cutovers require carefully orchestrated execution of everyone’s roles and responsibilities. What pre-work will be performed and by whom, such as device or wire tagging, panel mounting, or conduit installation and wire pulls? Who will configure and pre-test controllers, I/O, networks, servers and panels, and how extensively? Will the existing instrumentation be recalibrated before or during the cutover? Who will perform the calibration and how long will they be given to do it? Who will mount and wire any control or network enclosures? Will any pneumatic tubing rework be needed? If so, who will perform the work, when, and how much time will it take? Are other projects planned at the plant at the same time as the legacy cutover during the short-duration time window that could impact or interfere with the cutover, such as repairing/resealing floors in areas where checkout and water trials need to happen? If a device or critical system component fails, who should be contacted at the supplier to expedite equipment replacement? Lastly, what is the plan, how much time should be allocated and who (specifically) will be involved in running dry and wet tests of the new control system with the existing process and utility systems to ensure production starts up on time with minimum impact on efficiency and output? Success is better guaranteed when everyone knows what’s going on, precisely who’s doing what, and exactly when during each step of the cutover.
Cutovers of legacy control systems are stressful enough and carry an increased level of risk. The stress and risk factors become elevated when directed to execute the cutover in a short amount of time. Project managers, plant operators, the integrator and contractors can greatly reduce the risk and significantly increase the probability of success with extensive planning, copious amounts of communications and coordination with all involved, and sticking with the plan. Follow the checklist for success. Surprises will undoubtedly surface during the short-duration cutover. The key is to encounter only a small number of these surprises by taking the steps ahead of time—plan the work, then work the plan.
Steve Malyszko, P.E., is president and CEO of Malisko Engineering Inc., a certified member of Control System Integrators Association (CSIA). See Malisko Engineering’s profile on the Industrial Automation Exchange.
