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Enbridge relies on state-of-the-art controls to operate pipeline system. (Longest Crude Oil Pipeline).

Crude oil and its derivatives can be transported by many different means--by tanker across the ocean, by rail car across the country, and by track across town. In North America, oil is also transported by pipeline. sometimes halfway across the continent.

Although not without its own set of challenges, oil transport by pipeline is a very efficient means of moving large amounts of oil over a long distance on land: it also addresses environmental and safety issues that would be prevalent if the same quantity of oil were being transported over long distances by tracks on crowded roadways. In addition, the integration of sophisticated electrical control components into the pipeline facilitates control of the entire system and its contents from one centralized location--a feat that would be impossible by any other means.

Enbridge Pipelines Inc. operates the world's longest crude oil and liquid hydrocarbon pipeline system. With a right-of-way stretching for 7,190 km and the ability to transport more than 2 million barrels of liquid petroleum products per day, the system ships more than 75 different types of light, medium and heavy crude oils; synthetic crude oils; natural gas liquids; and refined petroleum products from producer refineries and tank farms located across Canada to markets in Eastern Canada and the Midwestern United States via 16 pipelines. Enbridge also operates the OCENSA pipeline in Colombia that runs from oilfields in Cusiana and other outlying areas to the port of Cove-as.

The Enbridge North American pipeline system has more than 15,000 km of piping, thousands of motorized valves, 14 lank farms, and 181 pumping stations along its length. Schneider Electric equipment, including Modicon 984, Quantum and Compact programmable logic controllers (PLCs); Square D M6 low voltage and Isoflex 5 kV medium voltage motor control centers (MCCs); Federal Pioneer 5kv metalclad switchgear; and Square D power transformers facilitate powering and controlling operations along the pipeline system and are key to maintaining the smooth flow of product from one site to the next.

Open, Reliable Control System Vital

Enbridge's Canadian pipeline network operates with more than 170 Quantum PLCs controlling a total of 100,000 I/O points. At each pumping station, located about every 100 km along the pipeline system, up to 24 1,000 to 5,000 horsepower (HP) motors are connected to Square D low and medium voltage MCCs, Federal Pioneer 5kv metal clad switchgear and automation systems (which communicate to the Control Center via dedicated telephone lines) that control staffing, stopping, and monitoring functions.

"We specified Schneider Electric MCCs and switchgear because they are high quality, reliable equipment whose delivery met our tight deadlines," said Roger Belanger, Senior Engineer, Enbridge. "The switchgear is also adaptable and easy to maintain," added Iqbal Singh Kaler, Senior Electrical Engineer, SNC Lavalin.

Wanting to replace pumping station relay panels with PLCs to reduce equipment maintenance and installation costs, Enbridge selected Schneider Electric Quantum PLCs because of its technology and connectivity to the standard Modbus protocol.

"The Quantum PLCs are reliable and easily upgradeable at minimal cost," said Arnold Rivera, Engineering Specialist, Enbridge. When a new pumping station's PLC is upgraded, the existing PLC program of old stations can be transferred to the newly upgraded PLC system with minimal modification.

Because each pumping station was originally built with a unique I/O configuration, upgrading the entire pumping station network with a Ladder Logic language would have required extensive reprogramming and rewiring of each I/O system. This problem was avoided by upgrading to Modicon Concept software, which, because of its ability to adapt to each station's existing I/O configuration, allowed Enbridge to standardize programming for all of its pumping stations, thereby saving large rewiring and programming costs.

"Because Concept has the same logic with variable tags, which allows us to assign internal variables to external I/O points, no rewiring or reprogramming of the pump stations was necessary," explained Brace Miller, Project Manager, Enbridge. This capability is especially important lot applications such as sectionalizing valves, where there are common inputs and outputs used at each station. which Concept can map to the standard variable names regardless of the I/O points' physical location.

"Also, because Concept conforms to the IEC-1131-3 standard, we can encapsulate object-oriented custom Enbridge code into a separate function block, and can easily reuse it in other stations and applications," continued Miller. "We also like Concept's user-friendly format and ability to perform complex mathematical calculations using structured text," added Rivera.

"Because Concept can encapsulate and standardize complex routines, and the Quantum PLC can do floating point math, we were able to simplify and streamline the program structure and minimize programming error and debugging," he said.

"Concept programming software provides powerful solutions to complex process control problems," said Les Crowley, Electrical/Instrumentation Discipline Manager, SNC Lavalin, Edmonton. SNC Lavalin Group is one of the world's leading engineering and construction companies in the petrochemical industry.

Because Concept is linkable to any I/O configuration, it is also used as a troubleshooting tool for detecting field device wiring problems at the pumping stations.

Enbridge also had Cybertech Automation Inc. of Edmonton, Alberta (Cybertech) develop a generic PLC application that could be installed in every pumping station, regardless of station configuration. Cybertech allowed for new devices to be easily added to the system without incurring additional programming.

"Cybertech's genetic PLC, application, combined with Concept's flexibility', allowed us to quickly and cost-effectively install the pump control system in every location," observed Rivera. "We were able to reduce commissioning costs and time from two weeks to two days, and reduce maintenance costs."

Tank Farm Control System Easily Upgradeable

Because tank farms (where crude oil is stored) have no surge capacity and are located at various points along the pipeline system, a failure in the tank farm control system can potentially impact the mainline pipeline operations. This might cause a shutdown of the main pipeline system, which in turn might cost Enbridge thousands of dollars in throughput revenue.

Federal Pioneer 5kV metalclad switchgear provides reliable distribution to the tank farms. Square D low- and medium-voltage MCCs ensure reliable operation of pumps and valves. "The Electric MCCs and switchgear are key to maximizing tank farm reliability," said Belanger.

To maximize system reliability, Modicon 984B PLC systems in a hot standby configuration were installed to control site valves, motorized pumps and oil sampling systems.

"The 984B systems have performed extremely reliably over the past 10 to 12 years," said Darren Day, president of Edmonton, Alberta-based DCD Engineering Ltd.(DCD). "These large platform PLC controllers have also been able to easily accommodate the tremendous growth in control requirements as the tank farms have expanded over this time frame."

New Quantum systems have also been added to support new I/O drops located in remote areas of the tank farm sites. Another Quantum hot standby PLC, running on Concept software, was added to one of the tank farm control systems specified by consulting engineers SNC Lavalin to relieve the communication errors caused by the fact that the PLC remote I/O network had exceeded the maximum length specified.

"We were able to quickly and easily migrate some of the existing I/O from the 984B PLC to the new Quantum PLC because it supported the existing 800 series I/O," Crowley said. Communication between the 984B and Quantum PLCs was done via Modbus Plus over fiber optic media. PLC and remote I/O communication was also done via fiber optic media.

Ensures Accurate Custody Transfer Metering

Transferring oil from the Enbridge pipeline system to the shipper (custody transfer) requires accurate measurements of the amount of liquid hydrocarbons or crude oil to track incoming supplier batch shipments and outgoing deliveries to the customer through the pipeline system. This information is used to determine how much material has been transferred from one site to another, and to generate production reports. Through the use of Modicon Compact PLCs and specialized software, Enbridge is able to implement a cost-effective method of custody transfer.

"Industry standard Modbus communication between Enbridge and its customers is becoming extremely important, as these customers require vital crude oil batch data for accountability and leak detection systems," observed Day. "Concept software provides a systems platform which has allowed DCD Engineering Ltd. to develop very extensive and highly structured Modbus communications routines to interface with an almost unlimited number of slave devices. Concept's data array structures and math capabilities facilitated the development of Modbus Plus routines that would have been very difficult to implement on a large scale in 984 Ladder Logic programming."

SCADA Aids Centralized Customer Batch Tracking

To ensure individual batch integrity, each batch of crude oil or liquid hydrocarbon is separated from the other batches by "buffers"--a synthetic crude oil of sufficient density that it does not mix with the customer "batch" crude--which are injected between each batch.

To time injections and maintain batch integrity, Enbridge must be able to locate each batch in the pipeline system. This is accomplished by placing a densitometer, a device that measures batch density, upstream from inch tank farm and pumping station facility. The densitometers relay batch density information real-time via Modicon 984 and Quantum PLCs to the SCADA system, thereby allowing operators to track each batch (which has a different density) and detect leakage as the crude moves along the pipeline.

"We used Concept's derived function Mock capability to develop a standard analog scaling block to ensure repeatability of densitometer signals for every site," said Rob Van Soest, president of Cybertech Automation Inc.

Minimizing Valve Leakage And Pumping Energy Costs

In addition to motor and valve control, the PLCs, operating as remote terminal units (RTUs), relay operational status information and diagnostics via Modbus over a modern to a main control center. From this central location, the complete operational status of the pipeline can be monitored and controlled in real time.

All pipeline control systems communicate to the central SCADA system via Modbus protocol. Each station has its own Modbus Plus network.

"Modbus' wide industry acceptance makes Modicon PLCs ideally suited to pipeline applications," said Kevin Matwichuk, president of Cybertech Automation Inc.

Facilitating Pipeline System Expansion

Enbridge recently constructed a 600-km pipeline to transport crude oil and liquid hydrocarbon from Suncor's Fort McMurray, Alberta production facility to the Enbridge tank farm located in Hardisty, Alberta. SNC Lavelin were secured by Enbridge to manage the design and construction of the civil, process, mechanical, piping, electrical and instrumentation engineering, including the I/O layout, PLC drawings and electrical diagrams.

"In addition to specifying the communication media for remote I/O and Modbus Plus, and providing the third-party interfaces for the flow computers, we specified Modicon Quantum PLCs running on Concept software," said Crowley. Square D low voltage M6 and medium voltage Isoflex 4 MCCs control the valves and pumps.

The capacity of the pipeline system from Kerrobert, Saskatchewan to Chicago was also recently expanded. This expansion, "known as the Terrace Phase 1 Project, included standardizing the sites to operate using Quantum PLCs running on Cybertech's generic Concept application. Square D M6 and Isoflex 4 MCCs control the valves and pumps. Enbridge is upgrading pump station control systems to Quantum 434 controllers and Quantum I/O running on Cybertech's generic Concept application.

Tank farm systems are being upgraded to replace the existing 984B systems with new Quantum 534 controllers in a distributed tinged architecture connected with fiber optics.

"The Transparent Factory Ethernet-based PLCs, switches and hubs maximize data throughput and permit easy connectivity to Enbridge's Wide Area Network (WAN) for communications to the company's remote centralized control room in Edmonton, Alberta," Day said.

"Reliable, real-time centralized control of the entire pipeline system including the tank farm sites is now possible and the conversion to Ethernet-based Modicon PLC systems will play a large role in the overall success of this conversion as the system migrates to Ethernet," he said.

Added Crowley, "Modbus TCP/IP is a dependable, fast and efficient communications protocol that allows the user to effectively employ conventional products in process control communications."

New tank farm software standards are also being developed by DCD Engineering Ltd. in Concept's Function Block and Structured Text programming languages to facilitate the standardization and repeatability of all Enbridge tank farm systems.

"All major components in all tank farm systems will utilize the same software routines. This ensures system repeatability, minimizes system errors and cuts commissioning time substantially," Day said.

"Maintaining the software and performing future plant additions now becomes extremely easy and effective as the standards are already developed in a highly structured format," he said.

Currently under way is the Terrace Phase 2 Project, which will increase pipeline throughput from Hardisty, Alberta, to Sarnia, Ontario. Additional pumping stations will be controlled using Quantum PLCs running on Cybertech generic Concept applications. New tank farm equipment will be integrated with the existing control system by DCD Engineering Ltd. using Quantum PLCs. This new system is being integrated in parallel with the Quantum 534 controller upgrade of existing tank farms.

Through the use of the Transparent Factory Ethernet-based PLCs and related components, Enbridge can continue to expand its pipelines with the knowledge that technology facilitates this expansion, while bringing control of the system ever closer to home.

Author's Note: Louise Jones is a communication specialist at Schneider Electric's Waterman, Ontario, office. Andrew J. Holt is a freelance writer with Integritas Communications.
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Article Details
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Author:Jones, Louise; Holt, Andrew J.
Publication:Pipeline & Gas Journal
Geographic Code:1CANA
Date:Oct 1, 2002
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