- Published on Monday, 22 April 2013 11:29
- Written by Mark Buzzell
The ability to prevent unexpected shutdowns and maintain control valve performance is directly linked to profitability. The ARC Advisory Group estimates that the average cost of plant downtime is $12,500 per hour with some plants. For some, of course, that rate is significantly higher, running upwards of $1 million per day of downtime.
When a so-called preventive or schedule-based maintenance strategy is followed, many valves are often needlessly maintained during shutdowns. One study by the Gartner Group found that, in process plants, 50% of maintenance work was not necessary and 10% was actually harmful. You simply cannot afford to spend 50% of your time working on the wrong things. Maintenance personnel have to do a better job of assessing problems and taking appropriate corrective action.
That, however, may be asking a lot. In the manufacturing and process industries, large numbers of experienced workers are retiring and they are being replaced by a leaner and less experienced workforce. At the same time, plants are trying to increase their production by extending shutdown intervals and decreasing shutdown periods. This means that end users need access to a new generation of tools that allow them to interpret data and devise appropriate corrective strategies while avoiding the pitfalls outlined above. They should be able to do this with confidence even though they may not have years of experience under their belts.
The latest development in the field of diagnostics—referred to as the “third generation of diagnostics”--is now playing an important role by facilitating this transition from traditional corrective and schedule-based maintenance to predictive maintenance. It could not have happened at a better time. Before considering third-generation diagnostics, let's take a brief look at the preceding generations.
First and Second Generations
Control valve diagnostics have been in use for more than two decades to help maintenance managers and engineers with planning shutdown activities. The first diagnostics tools were developed during the 1980s, and since then the technology has taken giant leaps, further providing a wide range of new possibilities. The stand-alone diagnostics tools from the 1980s, the first digital positioners from the 1990s, and the intelligent valve controllers that have been available since the early 2000s differ greatly when compared with each other from the perspective of the diagnostics information they provide.
The first diagnostics tools [Figure 2] were based on stand-alone devices that needed to be separately connected to the control valves to be able to collect the diagnostics. Typically, with these devices, separate tests needed to be conducted on the valve to collect the diagnostics. The tests could only be performed when the process was offline, meaning the valves were not in their normal operating environment during the tests and the users did not have any online diagnostics information available while the process was running.
The digital positioners of the 1990s included embedded sensors and micro-controllers, enabling them to perform this same task, without the need for separate stand-alone diagnostics tools. At the turn of the century, the first intelligent valve controllers made it possible to collect diagnostics on the control valve performance while the process was running [Figure 3].
Trending of this performance data is helpful for determining how possible problems have developed and how they may develop into the future.
Besides collecting trend information, these devices are also capable of analyzing the data and providing online alarms and warnings of possible valve performance degradation. These kinds of devices are often described as providing “second-generation diagnostics” because of the possibility to conduct the basic analysis on the data collected offline and online.
Third-Generation Graphic Intelligence
It has been roughly 10 years since the launch of the first intelligent valve controllers, and the technology has been further developed and refined. With the first- and second-generation diagnostics, a valve specialist is required to analyze the available data and make conclusions based on it. With the third-generation diagnostics this is no longer the case.
In order to make all of the data we are capable of collecting useful, there needs to be a good method for accessing and displaying it. With the widespread adoption of international standards such as FDT/DTM (IEC 62453) and EDDL (IEC 61804-3), accessing device configuration and diagnostic data is no longer a challenge.
Today’s state-of-the-art devices are capable of processing the collected diagnostics and presenting information about the valve's condition in a visual format that can be understood instantaneously. This makes the available information much more accessible to individuals without technical training and easier to use.
Third-generation diagnostics rely on greatly improved valve management software that interacts with intelligent valve controllers to process the existing data and represent it in an intuitive GUI (Graphical User Interface), incorporating indices relating to various problem areas, including:
- control performance
- valve condition
- actuator condition
- positioner condition
- environmental conditions.
Figure 4 shows an example using valve management software. The display also provides information from several built-in sensors that measure various internal parameters. Because these indices are generated using experience-based mathematical algorithms, users without extensive training can confidently make decisions about the condition of the control valve and decide on the best corrective measures. Reporting capabilities further simplify analysis by providing text descriptions of any problems that are found along with recommended actions.
Visualizing Optimal Results
So what is the end-user benefit to having third-generation diagnostics?
- With simple graphical diagnostics information, maintenance managers, engineers and process operators are capable of making prompt, educated decisions concerning control valve maintenance without having to use additional software tools to process data.
- Unexpected shutdowns can be avoided, and the control valve performance can be maintained at an optimal level.
- During a shutdown the available maintenance resources can also be more efficiently allocated therefore shortening downtime.
Whereas third-generation diagnostics are already available for control valves, the same level of information cannot yet be received from on-off—or from emergency shutdown (ESD)—valve performance. It should only be a matter of time before device manufacturers start to make these features available for the on-off and ESD valves as well.
Currently, the industry standard for on-off valves is the use of solenoid valves to control the on-off movement. However, solenoids cannot provide any diagnostics data on valve performance. To resolve this problem with critical ESD valves in new green field projects, smart partial stroke testing (PST) devices are being implemented. The state-of-the-art PST devices can be used to conduct different tests on the ESD valves, both online and offline, providing diagnostics information on the ESD valve condition. The next step is to have the smart PST devices analyze the data further and provide graphical indices like the ones presently being used in third-generation diagnostics for control valves.
For applications other than ESD, several device manufacturers now offer integrated solenoid and limit switch combinations. An on-off valve controller can also provide basic diagnostics by giving fault alerts that identify potential automated valve malfunctions. Should problems occur during process operation, maintenance personnel will be aided by rapidly locating failure causes, consequently speeding up valve repair and operation renewal.
Some end users have already identified the need for the addition of predictive maintenance capabilities to their process-critical on-off valves. In response, several intelligent valve controllers for on-off valves are now available.
These include diagnostic features that are especially designed for on-off applications [Figure 5]. The future will tell how well this new technology will be accepted and adopted among process industry end users.
Control valve diagnostic tools have taken a giant leap since the first devices were introduced in the 1980s. The third-generation diagnostics are taking predictive control valve maintenance to a new level, making it possible to enhance maintenance efficiency, improve process performance and achieve significant maintenance cost savings.
In the years to come, new measurement advancements will improve the range and accuracy of the predictive analysis of valve conditions using data that is automatically captured and analyzed and presented in highly actionable graphic formats. These new possibilities should help improve the value of predictive maintenance practices, leading them to be widely adopted and become the industry standard.