Detection and correction of faults in an industrial plant increases plant availability and improves plant efficiency, thus economising plant operations. And this is imperative in todays competitive world. Traditional fault detection techniques involve correlating the data and deducing faults. This is time-consuming, and delays in fault detection and corrective action add to the cost of plant operation. The asset management solution (AMS) software enhances the benefits of using field devices by reducing installation and commissioning costs as well as operating costs of the process plant. Conventional field devices depend on mathematical models to detect process abnormalities in the plant. Smart devices have the advantage of providing necessary information directly to the plant operator. Thus, advance corrective action can be taken to prevent unnecessary shutdown before the problem becomes serious. Increase in economic efficiency of the plant operations is the most challenging task for plant engineers and managers. Figure 1 displays the traditional control scheme where signal validation methods are applied. It is easy to determine the inefficiency of this scheme when one considers signal linearisation, damping and communication delays that mask true readings. Plant engineers get increased process efficiency by implementing optimum process control schemes and providing monitoring devices for analysis of the process conditions. However, in this case, increase in the efficiency is limited to advanced control schemes. Increase in plant availability has larger impact on the efficiency of plant operations. This is achieved by detecting abnormalities and providing condition-based maintenance. These approaches are complementary because having the best control scheme is limited in the event of a catastrophic critical component failure.
The need for asset management
As discussed in the earlier section, increased availability of field devices is the key to economic efficiency of plant operations. Industry data shows that rotating types were the least reliable instruments, while transmitters were the most reliable. However, nearly 20 per cent of the maintenance budget is spent on inspecting transmitters, which are the least likely candidates for inspection in case of an abnormality. Maintenance log reports of large chemical industries show that nearly 65 per cent of the time these transmitters were reported healthy, leading to waste of resources that increase the operating costs of the plant.
Smart transmitters are capable of advanced diagnostics that increase the quality and quantity of information from the field devices. Besides communicating variables, the function blocks provide significant value-added information such as extensive diagnostics and quality status indicator. The field instruments become data servers and can provide extensive diagnostics that allow preventive and predictive maintenance. This helps streamline operations calibration and diagnostics. It also reduces maintenance costs while keeping the plant up and running. The detailed process and device diagnostics help pinpoint potential problems, and minimise the impact of a process that is upset due to device failure or calibration drift. This allows the operator to do a much better job troubleshooting process problems and to make better decisions on how to handle a process upset. Maintenance log reports of a large chemical company as shown in Figure 3, indicate that 35 per cent of the trips were routine check issues and 28 per cent of the trips were reactions to a problem but were not found in the transmitter. A total of 63 per cent of the trips were unnecessary and could be eliminated only if the health of the transmitter was known. With advancements in communications and software technology, the transmitter is able to provide diagnostic information on the health of the sensor, the health of the process and even the health of other equipment connected to the process, for example, the valve, the compressor and others. This reduces the operating costs of a process plant by 8 to 9 per cent.
User benefits of AMS
Asset management solution (AMS) is a software programme that accesses status and diagnostic data from smart devices and monitors their performance. The architecture of AMS is shown in Figure 4. One can increase product quality and minimise unplanned downtime and thus, improve productivity and profitability.
The user benefits of implementing AMS are :
- Enhance productivity: The AMS software enables the plant operator to quickly and easily change device configurations from the workstation and download them onto the devices. The configuration changes made in the field can also be uploaded on the workstation to maintain integrity of Fieldbus device database. For example, the configuration database of a failed instrument can be uploaded on the workstation and the same configured parameters can be downloaded on the replacement device.
- Increase maintenance effectiveness: The AMS software provides online access to device status and diagnostic information enabling the plant operator to identify the problem quickly and accurately. This reduces the number of field inspections.
- Improve process availability: The AMS software provides online diagnostic on-field devices that help identify potential problems before they occur. This helps one proactively schedule the maintenance on the failing device, order spare parts and allocate resources to perform the maintenance at the best time, thus reducing downtime and increasing process availability.
- Reduce commissioning time: The AMS software enables users to set the configuration parameters from the control room. It also minimises the time in validating a loop problem. For example, one can determine the actual stem position of the control valve and compare it with the requested position without spending time in travelling to the field.
A few case studies to appreciate the real-time benefits of AMS implementation…
Shell Production and Exploration reduced operating costs and improved control reliability on the Brent Alpha North Sea Platform by implementing Fieldbus architecture and AMS software. A key criterion for the redevelopment project was to reduce the time for commissioning field devices and also reduce the future operating costs. The goal was to determine whether it was possible to save time and justify additional cost of installing the software. The traditional method was to send technicians to locate field devices and configure devices using handheld calibrators. The AMS solution allowed the equipment status and diagnostic information to be communicated directly to a centrally located PC. The software monitored field devices for signs that maintenance or service was needed. Thus, significant reduction in commissioning time was obtained.
The test was conducted on commissioning identical sets of field devices by traditional method as well as by using AMS software. With AMS software, commissioning engineers installed the devices using less labour and the devices were commissioned faster than expected. The software group loaded, configured and calibrated 34 transmitters in just five hours. In comparison, the traditional group was able to commission only 29 transmitters in 12.75 hours; the remaining four devices could not be calibrated due to installation problems identified by technicians due to lack of diagnostic information.
Eastman Chemical Company, a 3,00,000 metric tonne per year polymer plant in Pahag Malaysia, is realising substantial savings in its device documentation and calibration due to AMS. AMS saves at least 20 minutes per device calibration because technicians no longer waste time hunting for information required. Accurate up-to-date specifications on 750 field devices in the AMS database make it possible to save 250 man-hours per year on calibration of the devices
Aurora Energy L L C in Fairbanks, Alaska wanted to bring the coal-fired steam generating plant in operation in a few months before the millennium. The selection of Fieldbus architecture with AMS drastically reduced the commissioning time because of online diagnostics and configuration of field devices. The AMS software also provided diagnostic information on the process needed to increase the efficiency of the heat transfer and distribution. The project was completed on time and within budgeted costs. The AMS software, with its vast capacity to organise data from the field, was able to pinpoint operational irregularities.