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Improving Fault Diagnostics At Remote Production Sites
By Donald P. Galman
Information obtained from a gas monitoring system can be used to help maximize uptime, efficiency, safety, and profits.
The scene is an offshore oil drilling platform. The sun goes down, and the search for oil goes on. The crew, however, is never in the dark about what's happening. Smart field devices monitor every variable that affects production: temperature; humidity; flow; pressure; positioning; vibration levels; gas leaks.
Fugitive gas leaks can occur at valves, seams, body castings—almost anywhere in the mix of gas extraction, gas purifying and gas delivery equipment. Safety is a paramount concern, but time and money are also critical business drivers (one hour of downtime can cost an oil producer up to $250,000 in profits, according to one industry source). As a result, producers are taking a closer look at field bus instrumentation such as gas monitors, to determine how the components of a safety instrumented system (SIS) can be used to aid productivity, efficiency, and profitability—as well as preventing catastrophic events.
Today, most distributed control systems support the implementation of field buses on their system where fire and gas monitoring systems reside with process automation systems. The systems share the same control network and are able to use common visualization, engineering and asset management tools, while the logic executes separately for each system. The integration of these systems also satisfies some of the requirements of a SIL2/SIL3 system design (see Figure 1).
Connecting a gas detection system to a field bus has significant advantages:
- Additional information can be obtained for preventive maintenance and troubleshooting, reducing maintenance costs.
- Remote locations can interrogate instrumentation through wired, wired-to-wireless or wired-to-less wire communication protocols.
- Operators can interrogate the transmitter directly by using a magnetic wand on the display or, if the device is mounted in hard-to-reach areas, by using handheld instrumentation. These options provide operators with added mobility and time to focus on more productive tasks.
- Safety engineers, chemists, operators and others working as a team can more accurately predict instrument failures, and respond faster and more efficiently to maintain uptime.
According to one safety engineer, "Sharing a common platform can reduce costs related to installation or custom integration as well as provide a unified view of control and asset management that encompasses the SIS and the basic process control system. In this way, managers can make faster, more informed decisions about protecting people, equipment and environment, as well as a company's bottom line."
For a large offshore operation or a remote industrial plant, the cost savings could be millions of dollars.
Adopting a Universal Communications and Sensing Platform
Not so long ago, monitoring different gas families (toxic and flammable) meant using different gas transmitters — each with its own gas sensing technology, configuration challenges and maintenance problems. Today manufacturers are moving away from the stand-alone transmitter to the universal transmitter. Today's most advanced universal gas transmitter offers a common platform that supports all major industrial communications protocols including HART, Modbus and Foundation Fieldbus (see Figure 2). Caption. Universal communications platform In addition, the universal gas detection/ transmitter platform can be built to support all major gas sensing technologies— including catalytic bead, electrochemical, point and open-path infrared.
The XNX Universal Transmitter by Honeywell Analytics is one example of a universal transmitter. It accepts any combination of milliamp or millivolt signal inputs, converts the inputs to a standard HART digital communications protocol, and transmits the data from anywhere on the production area to the control room via an economical HART digital data link over a twisted wire pair. One twisted wire pair replaces expensive dedicated wires. Modbus or Foundation H1 Fieldbus are optional protocols, and provide additional communications capabilities.
With standard HART, operators can access programming and status information for each channel from the control room, or from any termination point using the universal transmitter's interface or by using a standard HART hand-held communicator for interrogation of the unit. All process, status and diagnostic information can be accessed by the HART-based control system. The transmitter can be powered by tapping into a junction box for rapid deployment in the field. For complex systems, the transmitter can be connected to an explosion proof, intrinsically safe controller that operates on multiple channels (examples: 10-channel Honeywell Analytics HA71 model or 4-channel Honeywell Analytics HA40 model).
The transmitter can also support a smaller, dedicated gas detection system where special mobility may be desired, as is found in a lightweight solar-powered wireless gas detector. The universal transmitter supports all sensing technologies through a modular choice of inputs accepting catalytic bead, electrochemical, point and open-path infrared sensing devices for both flammable and toxic gas detection. Together, these form the basis of a universal gas sensing platform (see Figure 3).
With these multiple sensing options, and Foundation FieldBus and Modbus providing multidrop network support, the universal gas transmitter effectively reduces wiring and accessories. For example, one can install ten gas detectors together on a bus system while reducing wiring requirements from 30 wires to merely four.
Finding Success in the Field: A Summary
With improved diagnostics, the safety manager on the offshore oil platform mentioned earlier now has a higher degree of confidence in his ability to make informed decisions. He knows exactly how much sensor life exists in each gas detector on the system because the database provides him with a calendar countdown and timely alerts. Armed with this knowledge, he can schedule appropriate maintenance accordingly. Or if an alarm should sound, he can calmly examine data to pinpoint the location and probable cause of failure or whether the alarm was in fact triggered by an actual safety incident. In these cases, he can hold off calling for an unnecessary emergency helicopter evacuation.
System designers can benefit from additional information too. Let's say that the system designer wants to replace a valve component with a more reliable, high-performance unit. Typically she will give consideration to material, pressures, temperatures, inspection frequency and other factors. Accordingly, she may also want to analyze the history of fugitive gas leaks at valves throughout the site, the direct and indirect costs associated with maintenance, the frequency and severity of safety non-compliance fines, calibration cycles and other cost elements occurring over the life of the gas monitoring equipment.
"As we all know, companies are continually looking to reduce costs," said one engineer. "Operators, contractors and safety managers all must increase collaboration to better predict failures, and to respond quickly and effectively before they happen. It is also important to meet tougher compliance requirements as well, such as the Safety Integrity Level (SIL) requirements which determine the SIL rating in light of all safety instrumented systems."
Oil and gas operators currently use real-time operations centers to increase production and accelerate well delivery. Today additional diagnostic information can be provided on fault and alarm histories, gas trend analysis, calibration cycles, sensor life expectancy and other dynamics of the gas detection system—delivered through flexible communications and multi-sensing platforms.
By adopting the universal platform approach, the facility manager can expect better monitoring control, faster mitigation, and reduced installation, operation and maintenance costs—all leading to lower cost-per-point gas detection. Also, by improving fault diagnostics, one can only enhance safety, which maximizes uptime, increases production, and drives profits.
Donald P. Galman is a technical writer and editor for Honeywell Analytics, Honeywell's gas monitoring instrumentation business. He can be reached at firstname.lastname@example.org
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