FINANCIAL pressures, combined with increasing safety and environmental requirements, have resulted in a significant increase in the need for valve-position monitoring in industrial plants. However, the potential cost involved in putting a monitoring system in place means that larger numbers of valves remain unmonitored.
Keeping a large population of unmonitored valves has several implications. For example, a manual valve may be incorrectly left open, closed or partially open. Since most manual valves are not monitored, those events can go undetected for a significant time, causing considerable operational losses, along with environmental and safety risks.
A major restriction when installing automation systems is the need to use wires to connect sensors and actuators. Wiring an automation system in a modern plant is time-consuming and costly [for example, due to the cost of cables, cable trays, cabinets, and associated input/output (I/O) points and installation], leaves a considerable footprint and adds significantly to weight.
Due to wiring cost, only one third of the automated valves have limit switches (only the solenoid is wired), leaving two thirds of these automated valves without any position feedback.
The valve industry has reacted to this need by developing wireless technological solutions to help plants increase the number of monitored valves, avoiding the financial burden. According to recent research, wireless technology can triple monitoring instrumentation in a typical plant.
This technology can be applied to both manual and automated rotary or linear valves, and it provides real-time information about a valve’s status directly into the control system, increasing safety and yield. In addition, it can provide the valve’s operational signature, enabling cost-effective predictive maintenance. Finally, in new construction, it can reduce material costs, simplify engineering and installation, reduce commissioning and startup costs and help in space-constrained situations.
NEED TO MONITOR VALVES
The need to remotely monitor valves in a wide range of plant applications is driven by several key factors: facilities must operate efficiently, and they must adhere to industry and regulatory standards for safety and the environment.
There is mounting evidence of the cost of incidents and accidents. Of all major incidents and accidents in the refining and petrochemical industry, about 30 per cent result in injury or loss of life, and over 60 per cent result in regulatory fines and production downtime. In addition, while the occupational safety incidents in these two industries declined by 90 per cent between 1993 and 2005, the level is still considerable because, on average, plants in these industries will have one incident for every 500,000 work hours. The material cost of each incident in the same period has risen by 50 per cent. The average cost of each incident is about $12/1,000 barrels (bbl) of refining production.
Plant management is increasingly seeking a higher awareness of plant conditions to improve efficiency and safety. In addition, plants must adhere to a growing body of safety and regulatory requirements that often increase the need for monitoring.
Lack of valve monitoring alone is not the reason for all of the safety, efficiency and environmental issues mentioned above; those incidents happen for a number of reasons other than lack of valve monitoring. However, the understanding of valve status needed to support these objectives can only be achieved through real-time monitoring.
MONITORED VS UNMONITORED
Despite the ability of monitoring systems to address many of these valves’ efficiency, safety and regulatory issues, installation of valve monitoring technology is limited. Industry research indicates that as many as 70 per cent – 85 per cent of valves in plants are not monitored. The range of automation of valves varies largely from one plant to another. Manual valves can make up between 10 per cent and 55 per cent of the valve population of a plant, and practically all of them will have no monitoring. Among automated valves, typically two thirds will also have no monitoring. In total, that leaves as many as 70 per cent – 85 per cent of valves without monitoring capabilities.
IMPLICATIONS OF UNMONITORED
One of the main implications of having a large number of unmonitored valves has to do with safety. Less monitoring means less information about valve positions in both manual and automated systems, which increases uncertainty and risk. Without remote monitoring, many plants must physically inspect valves to ascertain their statuses. This sends personnel into potentially dangerous environments or limits inspection.
Lack of monitoring also affects efficiency and performance in plants. The adage, “You cannot improve what you cannot measure,” applies almost perfectly to this situation. Valves precisely control the flow of media in process plants. Lack of information from a large percentage of these valves can lead to a bad batch and significantly limit plant engineers in their efforts to control and improve efficiency.
There are also environmental implications. If an outflow valve that should be closed is accidentally left open, media can leak to the environment without notice or until another part of the control system discovers the error.
A major study in the offshore oil and gas industry showed that almost 50 per cent of valve incidents resulting in leakage to the environment were attributed to “operational issues” (not to valve defects or malfunctioning), and almost 30 per cent of these operational issues were the direct result of a valve simply being left open or wrongly opened without notice.
RESTRICTIONS FOR MONITORING
In valve-intense applications, monitoring has historically been achieved with wired systems. These systems facilitate monitoring but present many challenges that restrict the extent to which they can be deployed. The challenges are inherent to wired systems and include such fundamentals as the cost of installation and constraints on design and expansion.
Design limitations are presented by many factors, including weight, the number of installed devices and the complexity of the system. Costs are driven by installation of an infrastructure of wires, cable trays, cabinets and I/Os. For a typical industrial installation, this may total $2,000 to $5,000 per valve.
A wired system can increase maintenance requirements in industrial or severe service applications. Wires can wear and break, and connections can shake loose. These systems require knowledgeable personnel to ensure reliability and performance, which can involve training and/or certifications.
MANUFACTURER RESPONSE
Wireless technology is the industry’s response to the increased need for remote valve monitoring in manual and automated applications. In contrast to wired systems, wireless valve monitoring uses radio signals and a networked system of field monitoring devices. The technology is integrated with DCS, PLC and Scada systems to provide real-time information on valve status, along with flow, temperature and density conditions with wireless transmitters.
Wireless technology varies among manufacturers; however, a typical manual valve system consists of a wireless device at the valve, a wireless router, and a gateway connected to the plant network’s maintenance and operations functions. Automation adds a return leg, with DCS/PLC controllers and solenoid wiring back to the valve. Integration with the plant network is facilitated with open protocols such as object linking and embedding for process control (OPC), Modbus remote terminal unit/transmission control protocol (RTU/TCP), and Profibus.
Battery-powered monitoring devices used in the field are typically configured with a mesh network topology, which ensures full redundancy and avoids any single point of failure. Within a network, data is routed using the most expedient path.
Wireless remote-monitoring systems address many of the challenges inherent in wired systems. Chief among these is a significant reduction in cost, which provides a more affordable valve-monitoring system that can be applied to a larger population of valves and a greater percentage of plant operations.
Wireless valve monitoring can reduce the cost per valve versus that of a wired system by 25 per cent to 60 per cent, depending on factors such as the application, area, classification and distances. The cables and routing (cost of attachment) that can sometimes account for 50 per cent of the installation budget for a wired system are eliminated with wireless monitoring. The difference can account for thousands of dollars in installation costs over conventional wired systems. Lower installation costs mean that monitoring can be economically extended to a larger, more complete valve population, providing the information needed to improve efficiency and reduce risk. Health and safety risks are reduced because fewer personnel are required in the field to determine valve status, thereby limiting exposure to hazardous situations.
Reliability and security standards are key advantages of wireless monitoring technology. Wireless systems have an inherent reliability based on multiple paths of communication. If a device fails or a path is blocked, another route is used to ensure that valve data reaches the control system. Devices based on industry standards have greater than 99 per cent data-transfer reliability.Wireless security advantages include encryption to prevent reading of intercepted data. Each message must also be authenticated, which requires that the origination and receiving devices recognise each other — a function that is built into the devices.
LIMITATIONS OF WIRELESS VALVE
Wireless systems have limits that should be considered when examining any application. Most of these boundaries are related to the distances and topologies, which may vary depending on the protocol used. Care should be taken in choosing the most appropriate wireless technology to address these considerations.
These real-world constraints include the free space in a plant’s layout and in obstructions that can block communications. Weather can also be a limiting factor. Rain, ice and snow all affect transmission error rates.
Area classification can also limit the use of wireless technology. These restricted areas may include hazardous and corrosive environments, as well as remote, unmanned platforms. Some limitations may be due to incorrect perceptions. For example, even though batteries can last up to eight years, there is a persistent concern about unexpected failure.
NEXT WAVE OF VALVE MONITORING
Complete understanding of what is happening within the facility is a key point of the future industrial facility. Incremental sensors are the foundation for collaborative applications and advanced process management.
Companies will increase the use of risk analysis to determine how much monitoring is required. Risk is defined as a function of the likelihood that an event will happen and the consequence or cost if it happens. This will drive an increase in monitoring and, therefore, the use of wireless technology.
An increase is also expected in wireless valve monitoring driven by companies trying to automate their processes and reduce labor. Some companies that currently operate remote plants (such as Shell’s Ormen Lange gas plant in Norway) are setting goals of operating and maintaining the plants with as few people as possible. To accomplish this, online condition-monitoring systems are employed to monitor virtually everything that moves in the plant, including pumps, compressors and valves (especially emergency shutdown valves).
