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Brent Baker, Fisher Instrumentation Product Manager, and Jordan Mandernach, Fisher Instrumentation Software Product Manager, recently published an article in the June 2021 issue of Plant Engineering. The article describes how smart valve positioners can be coupled with diagnostic software to significantly reduce maintenance costs and shorten plant shutdowns. The article is titled Advanced Valve Diagnostics Drive Savings and is summarized below.

Prediction is Challenging

Predictive maintenance has been the goal of plant personnel all over the world. In theory it is a fantastic idea. If the plant can predict when equipment is beginning to fail, it can react proactively to plan and resolve developing issues before they blossom into equipment failure and unexpected shutdowns.

 While simple in concept, predictive maintenance can be devilishly difficult in practice, since prediction is not so easy. How can one determine when a critical control valve is starting to fail? This can be especially difficult since the control loop often masks deteriorating valve performance until it fails completely, creating significant process upsets.

 To avoid unexpected failures, many plants simply pull and inspect every control valve on a routine basis. This method usually detects developing problems and reduces unplanned failures, but it comes at a price. The resulting maintenance costs can very high and the work often extends plant outages.

 A Better Way

Fortunately there is an alternative method to address these issues, as the authors explain: 

There is another option, made possible by advances in smart positioner diagnostics (Figure 1). Armed with an array of sensors, a digital position controller is uniquely placed to monitor the control valve and detect abnormal conditions as they develop.

Figure 1: Smart positioners, like this Fisher FIELDVUE DVC6200, employ an array of sensors to detect air, actuator, packing, and valve problems well in advance of total valve failure. 

Smart positioners can detect developing issues and communicate this information to an asset management system, where it can be highlighted and addressed. Any base level smart positioner offers self-calibration features to ease valve setup, but some positioners have capabilities well beyond that and can be used to create a valve signature for a new valve (Figure 2). This signature captures myriad performance details that can be compared to future valve signature test results. Such a comparison quickly identifies developing issues.

Figure 2: Valve signature information can be captured when a control valve is commissioned and compared against future stroke performance to highlight developing problems and troubleshoot failing components. 

More advanced positioners can monitor valve performance while the valve is online, noting when a valve fails to reach commanded states or exhibits abnormal behavior. Other positioners can be programmed to detect specific events and capture historical data associated with them. This data can be invaluable to help technicians troubleshoot and resolve valve problems. Top-tier positioners enable partial stroke testing even when a valve is online. 

Developing a Diagnostic Program

Taking advantage of positioner diagnostics starts by evaluating the current state of the plant positioners. Much of the equipment required may already exist. If possible, digital signatures of each valve stroke should be captured to create a baseline of data. 

The next step is to identify mission critical valves and update those positioners as necessary to obtain the diagnostics needed. Some positioners can be upgraded to incorporate higher levels of diagnostics without replacing the whole unit. 

The final step is install the necessary software, and establish communication networks to capture valve data and alert relevant personnel to developing problems (Figure 3). Data has minimal value if it is not transferred to the right person in a timely manner.

Figure 3: Diagnostic data is only useful if alerts are transferred to the correct personnel and acted upon quickly. 

Diagnostic data is particularly useful when planning shutdown work because it indicates which control valves need repair and which do not. 

Real World Savings

The authors describe three cases where plants realized significant savings by taking advantage of smart positioner diagnostics. 

A herbicide plant in Iowa reduced annual maintenance costs by $230,000 by using advanced control valve diagnostics to transition their plant from reactive to predictive maintenance. In one case alone, the plant saved nearly $100,000/hour by detecting and addressing a developing control valve issue before it shut down the unit. 

A paper mill in Louisiana was suffering routine boilers trips due to damper positioning problems. Upgraded smart positioners with advanced diagnostics eliminated these trips, avoiding losses of $18,000 an hour due to unscheduled outages. 

A combined cycle power plant was reworking all critical valves during every outage in an effort to maximize uptime when the plant returned to service. After installing a number of upgraded digital valve positioners and implementing diagnostic alert software, the plant was able to focus their outage repair efforts more efficiently. The plant saved $68,000 in one outage alone, and it has experienced year-to-year cost reductions of $33,500. 

Prediction is no easy task, but the advanced diagnostics available in smart, digital positioners can go a long way towards helping maintenance staff do exactly that. 

All Figures are courtesy of Emerson. 

About the Authors

Brent Baker is a Product Manager for Fisher Instrumentation at Emerson with 14 years of experience. He spent 12 years as an instructor and content developer for Emerson Educational Services, focused on training customers and Emerson personnel on the installation, operation, maintenance, and troubleshooting of Fisher control valves and instrumentation. His current role responsibilities include support for current Fisher Instrumentation and new product development.

Jordan Mandernach is a Software Product Manager for Fisher Instrumentation. He has 8 years of experience in the process control instrumentation and software industry. His background is in new product development and software marketing.