Every day, nearly 750,000 barrels of crude oil and refined products flow through 16 U.S. pipelines owned by Conoco Oil., spanning over 8,200 kilometers (5,000 miles). In 1994 Conoco Oil Company took a good look at their legacy system and didn’t like what they saw. The centralized control system, which had been installed in 1978, used multi-drop, leased telephone lines. Four operators at consoles in Houston, Texas, controlled the pipelines for 12 hours a day. This left large stretches of its pipeline unmanned, with no support. The system was already operating at maximum capacity and had many technical risks. They were concerned about the availability of replacement parts for the old RTU, loop controllers and alarm annunciators. They needed to know the exact contents of a pipeline, wherever it was, instead of the meter-in/meter-out leak detection they had. Their data entry system was cumbersome, in some cases requiring that data be entered two or three times.
“The company reviewed its control system strategy and concluded that it had a unique and hard-to-maintain system. It consisted of dedicated, custom built and programmed RTUs along with a lot of odds and ends,” said Richard Parker, lead project engineer for Conoco Oil Company.
In short, they needed to improve their pipeline reporting system by adopting a platform that would let it automate the manual activities to improve efficiency in their 5,000 miles of small-diameter, high-pressure pipelines running throughout the United States.
Over the last 5 years Conoco has upgraded this system. First, abandoning their old leased telephone lines and going to a VSAT satellite system. The VSAT Ku Band Network system supports 170 sites where Conoco has 200 PLCs and RTU addresses handling about 20,000 I/O points.
In addition to the VSAT, Conoco has recently installed a dial backup using analog lines and communicating via the Modbus protocol to 140 critical sites.
“To make a long story short,” said Ken Hopwood, Development Engineer for ProSoft Technology. “When Conoco installed the new equipment, the old equipment couldn’t communicate with it. So, they used the ProSoft 3150-MCM module as an interface.”
ProSoft then went into development for Conoco to create a new module especially for them: the 3150-CMS module.
“When Conoco approached us, they needed to eliminate the need for continuous polling that was necessary on their old system,” said Hopwood. “It created communication delays when using the satellite which were expensive. The 3150-CMS is basically a Modbus Slave but with a few modifications. One, it has Report by Exception, giving it the ability to send timed, unsolicited data reports to the Master Station in Houston. This eliminated the need for continuous polling. The CMS module also contains some specialized data that is unique to Conoco.”
“Development like this is one of the things we at ProSoft Technology are most proud of,” said Sharratt. “The team of professionals we have at ProSoft love to find a solution to a customer’s specialized needs. We’ve geared ourselves to move quickly when the market demands it.”
“In the past many communication systems were closed,” said Michael Rush, Central North American Regional Sales Manager. “Since the Modbus protocol is open it has become a defacto industry standard for many industrial devices today, especially in the oil and gas industry. The popularity of our Modbus module doesn’t really surprise me. I see instances like Conoco on a weekly basis. Using the Modbus module to communicate from old equipment to new equipment is simply the most cost-effective way (and in some cases, the only way) to accomplish their goals.”