Hot cutover boosts control system migration

Keeping critical unit running provides significant economic and implementation benefits

By Eric Schnipke, Ineos Nitriles

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The transition package seamlessly transferred the original DCS’ analog and discrete points plus loops into the interim workstations, as well as node operating status, configuration information and online tuning. No reconfiguration of old equipment was required. When connected in parallel, operating and tuning changes made from the transition package were automatically updated into the original system and vice versa. Very helpfully, the transition package added state-of-the-art event reporting, history collection, and enhanced alarming and diagnostics to the original controls.

At operator request, the original graphics, including alarms, were replicated as closely as possible in the transition package. Graphics followed guidelines of the Engineering Equipment & Materials Users’ Association (EEMUA) Publication 201 with regard to alarm management, colors, contrast, etc.

Conversion from old consoles to new workstations took less than one week per control house.

Phase 1 also included paralleling and then switching serial links from the old equipment directly to the project’s first new controller. This avoided two-step conversion (old to interim to new control) of 1,400 serially communicated points.

All Phase 1 work was accomplished hot with the plant running. No process trips occurred.
Phase 2 replaced all the old controllers and I/O equipment, as well as the deep-well-injection/surge-tank Modicon PLC, with new controllers, I/O, workstations and networks. The interim workstations were slowly converted to pure DeltaVs.

Cutover
The cutover of the deep-well/surge PLC and the acetonitrile unit was next on the list. We performed a cold cutover because this work could be scheduled so it didn’t impede critical acrylonitrile production.

The PLC had 148 points in the pump building’s main rack for injection logic and another 60 points for surge control in a coax-connected remote I/O rack in a distant control cabinet. The conversion of both could take no more than three days — the time it would take for the surge tanks to become full. Because space was available in the injection building, a new controller cabinet was installed near the PLC cabinet. Cutover required removing the PLC and then both retraining existing wiring and adding wiring from the old cabinet to the new. The old cabinet remains as a marshalling enclosure. The two-stage PLC conversion task was completed in three 14-hour days.

Cold cutover of the acetonitrile unit was scheduled during a five-day outage that also included non-control work. The switch involved straightforward tearing out old cabinets, installing new cabinets, wiring up and checking out 292 I/O points, about 75% analog. Cutover took four days, plus a fifth day for tuning and tweaking.

It was important that a few parameter indications, such as cyanide drum levels, be relayed to the control room during cutover. This was achieved by temporarily powering the new acetonitrile cabinets with an extension cord to limit the interruption of vital indications to a matter of minutes.

The acrylonitrile unit was cut over last and hot. The cutover of its 1,023 I/O points was spread over a two-month period ending in late November 2006. A team of two experienced contract electricians, a very knowledgeable and helpful operator, and me worked full-time on the project. The operator was essential for knowing how the control strategy and loops work — or should work — and for performing all of the necessary bypassing and hand-jacking of control valves. Although I know the process quite well, I’m a controls engineer, not a process engineer.

On average, we converted and tuned three to five active control loops a day. Indication points usually were converted and rung out while waiting for loop tuning and process bumps to settle. The original tuning methods and parameters generally translated well. We made rough calculations of the tuning sets in the old controllers and then plugged these parameters into the new system. Many of the loops were also then tweaked using DeltaV supplied software. Our tuning upsets made operators nervous at times but never affected product, equipment or output.

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