DeltaV SIS Saves Space, Integrates Data on Offshore Rig

Oct. 1, 2008
Benefits of an Integrated Safety Approach

Murphy Oil had experience with Emerson Process Management’s DeltaV as the basic process control system (BPCS) for several of the company’s offshore platforms in the Gulf of Mexico. So when it came time to select the automation and safety architecture for the new Thunderhawk platform, DeltaV again got the nod for the controls—as well as for the safety.

“My co-presenter, Butch Taggart from Murphy Oil could not be here, because he’s cleaning up the damage caused by Hurricane Ike—to his plant and his own house,” explained Emerson’s Sean McCormack of the Emerson Hydrocarbon and Energy Industry Center, in Calgary, Alberta, “so I’m going to do the presentation for both of us.”

“Using DeltaV and DeltaV SIS allowed the engineering team to use the same easy-to-use engineering tools and operator interface for both the safety and process control system.” Emerson’s Sean McCormack related the benefits of an integrated safety approach on Murphy Oil’s Thunderhawk platform.

The Thunderhawk Field is located in Mississippi Canyon Block 734 in the Gulf of Mexico. The Thunderhawk platform is a stand-alone, semi-submersible floating production unit with an estimated capacity of 45,000 barrels a day, expandable to 60,000 barrels a day.

Typically, on previous Murphy Oil platforms, DeltaV has only been the basic process control system, with other vendors providing the safety-instrumented system, or SIS, and the ESS, or emergency support system (the fire-and-gas safety system).

However, on some of the other platforms, Murphy had noted problems with the integration of the safety system with the BPCS, including unexplained and dangerous OPC failures. Murphy Oil also had severe equipment footprint constraints on the Thunderhawk, because it is a semi-submersible platform.

So the decision was made to award Emerson all three systems: the BPCS (DeltaV), the process safety system (DeltaV SIS) and the ESS.

Currently, the Thunderhawk Project is the largest DeltaV offshore installation and the first DeltaV SIS installation in the Gulf of Mexico. “There are 1,400 I/O points and 103 logic solvers in the SIS system,” McCormack said, “and integration with the BPCS information is seamless. There’s no need to map data or use an OPC server to read/write between the BPCS and the SIS. This, of course, provides easier integration between the BPCS and SIS and removes a potential point of failure that Murphy engineers were already concerned about.”

McCormack continued, “Using DeltaV and DeltaV SIS also allowed the engineering team to use the same easy-to-use engineering tools and operator interface for both the safety and process control systems. And there was a significant cost saving associated with reduced footprint: fewer cabinets.”

“We were able to accommodate 448 installed and future I/O points with marshalling in one system cabinet,” McCormack said. “Cross-wiring between cabinets is eliminated. We were able to integrate marshalling and I/O in a single cabinet.”

Due to increased I/O and undefined vendor packages, the EPC increased the I/O by 24% on the ESS system. With no available room in the motor control center I/O room, a remote panel was added to the production deck of the platform.

“The ability to install a remote panel with minimal impact proved an adaptive solution to this problem, resulting in reduced project capital,” McCormack noted.

There were also significant I/O type changes. Where other systems require a change in card and a rewiring of the I/O, the DeltaV allows “I/O type” to be changed in the software. On the Thunderhawk Project 32 tags changed I/O type in the ESS system. This flexibility saved significantly in project costs.

Hot Stuff

“The addition of the remote ESS cabinet on the production deck meant that the cabinet was not in a climate-controlled atmosphere,” McCormack said. “The ambient temperature in the Gulf of Mexico can reach 40°C, 104°F. That’s hot.”

While this isn’t near the high-end specification for temperature for the DeltaV SIS, prolonged operation at elevated temperatures has been shown to reduce the lifetime of electronic components, McCormack said.

“After examining the remote cabinet space constraints and evaluating the temperature class of equipment installed on the deck, a vortex cooler was added to the remote cabinet with an appropriate purge panel. The capability of integrating a vortex cooler with a purge panel resulted in the ability to cool the equipment adequately within the cabinet at a reduced cost compared to typical refrigerant-based air conditioners,” he said.

“In planning the I/O, the key to success was assignment of I/O based on individual safety-instrumented functions and logic groupings,” McCormack said.

“Properly assigning the I/O to the logic solvers is an integral part of future expansion and not being limited by the system capacities,” he said. “The architecture of Delta V SIS allows the user to concentrate on individual safety-instrumented functions (SIFs) and each logic solver becomes a home for the SIFs assigned to it. This is very different from the traditional safety system, which involves placing hundreds of SIFs in a central logic solver.

“When the SIFs are assigned to the logic solvers and the I/O assignment is completed based on the SIF allocation, the end user will not be limited by the system capacities,” McCormack said. “A complex fire-and-gas safety system can be achieved without nearing the system capacities as long as the front-end planning is performed.”