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Valves: Why Browser-Based Predictive Maintenance?

Half of this problem was solved by giving digital positioners the intelligence to automatically collect trends that would enable operators to predict how long they could leave a valve on-line for the …

Half of this problem was solved by giving digital positioners the intelligence to automatically collect trends that would enable operators to predict how long they could leave a valve on-line for the lowest possible life cycle cost without experiencing unacceptable performance degradation or unplanned maintenance resulting in the costly shutdown of the process loop. However, this data is of little value unless it is captured, tabulated and analyzed. In many mills, there isn’t anyone available to do this time-consuming work.

However, once the decision has been made to put digital positioners on-line, web-based browsing technology holds a solution to this problem and at very low incremental costs. Field browsing technology automatically monitors valves, collects performance trends, tabulates data, and posts it to a web page that can be analyzed as needed to evaluate emerging problems and to plan for cost-effective maintenance.

How it works

Some browser-based predictive maintenance systems can monitor any field device, capture data for computer-automated diagnostics and send alarms via Internet, intranet and digital phone.

Field device browsing systems can be used with mixed networks, including any manufacturer’s digital valves, pressure, temperature and flow transmitters and any other field device. Browsing systems will:

Continuously monitor all field devices on a network.

Capture any diagnostic or performance information generated by the device.

Send alarms when user-selected limits are exceeded.

Post all data captured to a comprehensive database, which can be used by a variety of computer automated diagnostic packages.

Generate a web page with colored indicators showing the condition of every field device on the network.

Allow authorized users to view all the information collected by the system using any web browser.

How it is used

There are many installations of field device browsing technology worldwide in the pulp and paper as well as the chemical, petrochemical and refining processing industries.

The user’s intent is two-fold: First, to monitor field devices and distribute alarms indicative of emerging problems that, if unattended, could lead to a process disturbance; and, secondly, to automatically collect performance data from field devices and post it to a file server in a universally accessible database format. This data is then readily available for emergency trouble-shooting or for methodically analysis prior to shutdown for developing the most cost-effective maintenance plan.

Since major mill shutdowns typically occur once every one to four years, it will take some time to collect actual savings realized by implementing browser-based maintenance programs. However, initial users are finding that the payback can be almost immediate.

Metsa-Botnia linerboard mill

As one example, the Metsa-Botnia linerboard mill in Kemi, Finland, has invested in Metso Automation’s Neles FieldBrowser system as the primary tool for maintaining performance and predictive maintenance of control valves and intelligent process measuring devices. The system was installed on its 340,000 ton per year “Polar Queen” machine, which produces coated and uncoated white-top linerboard.

Erkki Kahkola, maintenance manager, said that the system helps his staff understand the behavior of this process in detail, which, in turn, helps increase the competence of his staff. As a result, he said, “Our core competence in maintenance prediction, planning and implementation is in our own hands.”

Automation Service Supervisor, Erkki Rantavuoti, also reiterated the need for the online predictive maintenance systems, “We are now putting our emphasis on predictive maintenance and reducing time-based preventive maintenance. We must, therefore, fully use the capability of the online systems to be sure that our work plan is well prepared before the next plant shutdown.”

It automatically scans the condition of 70 valves and several consistency transmitters on the board machine. These smart devices communicate with a remote terminal via a HART protocol network. Through a colour-coded video display, service technicians can see at a glance the valves that are performing well, those showing signs of poor performance or exceeding alarm limits. Warnings or alarms also can be transmitted remotely, across a network, or by email and pager messages.

The system collects diagnostic information from ND800 digital positioners at the point of control and posts it to a database that is accessible from the company’s intranet. Weeks prior to shutdown, the information is reviewed to determine which valves are contributing to excessive process variability or are showing signs of wear that would indicate a need for maintenance. For example, deterioration in the valve’s precision in following control signals very often indicates excessive friction in the valve or positioner. Actuator load factor is another critical variable that indicates changes in torque required to reach the required valve position.

The system at the Kemi linerboard mill has alerted the mill’s maintenance staff to several control valve problems, leading to corrective actions during planned shutdowns. In one case, Neles FieldBrowser warned that a dryer section steam control valve exceeded the 2% travel deviation alert level. During the next shutdown, both hysteresis and step response tests showed acceptable results. However, during a process run, the online travel deviation trend on the same day showed very poor behavior.

Based on the alarms from online monitoring, the valve was taken off the line, disassembled and analyzed. They found that the coating of the ball and seat was destroyed, causing high friction and sticky operation. Longer use would have led to a complete jamming of the valve and an unplanned shutdown of the board machine. Rantavuoti believes this example illustrates the value of online valve performance testing under real process conditions.

Metsa-Botnia is learning to use these types of tools in conjunction with its on-line diagnostics software to avoid the unnecessary expense of taking valves off-line for maintenance prematurely and the catastrophe of leaving valves in service so long that emergency repairs result in unplanned shutdowns.

Implications of the technology

Field device browsing technology is low in cost, easy to implement and capable of transforming the potential cost reductions of preventive maintenance into realized profitability. Important attributes of the technology include:

Low incremental cost of adding field devices to a field-browsing network.

Broad-based distribution of field device condition status signals and alarms.

Trend monitoring to identify when field devices are approaching unacceptable performance.

Elimination of manpower costs required for preventive maintenance data collection.

Monitoring and collecting data from any field device.

Viewing data with any browser.

Transferring data to any database.

Analyzing data with any diagnostic software.

Upward compatibility with Foundation Fieldbus and Profibus PA networks.

This open systems approach allows any mill to implement a field device browsing system without sacrificing its investment to date in specific field devices or analytical software. It is also readily adaptable to any company’s maintenance philosophy. In the hands of the right organizations, field-browsing technology will help make realizing the benefits of predictive maintenance a reality.

Eric Fillion is the marketing manager for Metso Automation.