"Put all your eggs in one basket, and—WATCH THAT BASKET!" This advice from Mark Twain is well understood by engineers and staff at Texas Gas Transmission, who monitor and supervise its 6,200-mile natural gas pipeline system across seven states from Louisiana to Indiana. Texas Gas is part of Williams Companies Inc. (Tulsa, Okla.). Around-the-clock operations previously required continuous, in-person monitoring and supervision at the pipeline's 26 compressor stations.

To reduce operating and labor costs, Texas Gas recently upgraded the pipeline's monitoring and control capabilities with a Citect 5.21 supervisory control and data acquisition/human-machine interface (SCADA/HMI) system from Ci Technologies (Charlotte, N.C.). Managers and engineers can now check real-time conditions at each of the 26 stations from Texas Gas' central offices, field locations, or remotely via the Internet. This helped Williams consolidate monitoring and control functions, and implement condition-based maintenance.

The new Citect HMI/SCADA system operates over a 384-kbps wide area network (WAN) to monitor data from the pipeline's 68,480 control and 129,827 data points, which communicate with Texas Gas' central operations center. The pipeline continues to operate 24 hours per day, but the HMI/SCADA system allowed staffing to be reduced to one maintenance shift at most compressor stations, and eliminated full-time staffing at smaller stations. Texas Gas saved tens of thousands of man-hours and more than $5 million per year.

Managers also save by remotely viewing pipeline data and taking corrective action from any location via Texas Gas' network or the Internet. Issues are often resolved now without requiring support personnel to visit a station or make unscheduled maintenance calls.

To move from its old scheduled maintenance procedures to its new condition-based maintenance program, Texas Gas required more data from the pipeline and related facilities via its HMI-SCADA system. For example, its Citect-based system now monitors and logs fuel consumption per cubic foot pumped. If consumption changes from the norm, then the compressor is scheduled for a checkup.

Citect's built-in redundancy also allows the system to withstand any single point of failure in hardware or communications. During it first 18 months of operation, the pipeline's new HMI/SCADA system hasn't experienced any significant downtime due to its Citect equipment.

This reliability is aided by each station's Citect Server, which handles all communications, alarming, and historical data for the site. At the central operations center, a Citect Proxy Server contains project configuration for the entire pipeline. Finally, Citect Internet Display Clients allow users to view pipeline-related data supplied by the proxy server, which is more efficient than each user interacting with each field server.

On-screen refresh rates are 1 sec for operators and 2 sec on Williams' business network because Citect's data optimization only transfers tag data for graphics while that data is being used, which saves more bandwidth. Data viewed by Williams' operators include 5^th degree polynomial equations for each compressor, which model efficiency based on horsepower and suction pressure. By overlapping efficiency curves with real-time operating data, users can ensure that the compressors are running at optimum efficiency for any given load.

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