Smarter valves portend maintenance savings

Predictive/preventive maintenance programs featuring microprocessordriven diagnostics systems could save users substantial dollars in repairs and product losses.

Eyeing potentially significant savings in maintenance costs, plant and corporate managers are demanding improved process equipment with built-in or add-on diagnostic capabilities. Valve equipment suppliers are responding with "smart" (intelligent) valve positioners and valve systems, which have the potential to deliver major benefits in the area of preventive/predictive maintenance, dramatically reducing maintenance costs and product losses which may otherwise result from malfunctioning equipment.

According to statistics compiled by FisherRosemount, plant maintenance worldwide costs $69 billion a year, which is 4% to 8% of the annual replacement value. In addition, research firm Deloitte and Touche says that "49% of U.S. plants surveyed are looking at significant maintenance budget and process changes."

InTech contacted several major refiners and chemical producers. Most indicated they were aware of potential major benefits of valve systems with diagnostic capabilities and acknowledged predictive maintenance is a high-priority effort. However, because field-based systems are only beginning to emerge and smart valve technology is also relatively new, most indicated testing was still ongoing and sufficient data has not been collected to report conclusive results. Chevron, for example, was typical. A spokesman for the firm acknowledged that "Chevron is very interested in predictive/preventive maintenance. We have been working with vendors on this and have recently installed many digital positioners at some of our refineries. We are still in the data collection and learning mode, however."

One company willing to provide some details on its programs and experiences was Eastman Chemicals, Kingsport, Tenn. The chemicals maker has begun what Charles Bailey, Eastman vice president, manufacturing, calls "reliabilitybased maintenance" to increase equipment uptime and lower costs.

"We have four separate strategies," Bailey told In Tech in an interview. They are:

Preventive maintenance, an older technique, used since the 1960s, which typically requires completely shutting down a chemical process after a year or so to check out equipment.

Predictive maintenance, which is currently preferred; it involves some 40 different technologies Eastman has developed in recent years, with the goal of predicting failures before they occur and replacing faulty devices without having to completely shut down a process.

Proactive maintenance, which puts the human element into the equation, looks for "root-cause failure analysis," for example. Reactive maintenance, or responding to emergencies. This category currently represents about 20% of Eastman's maintenance efforts; Bailey wants it to decline to only 5% by the year 2000. "Hopefully, we're going out of the 'reactive' business," he said. Bailey estimated Eastman Chemical's current annual maintenance budget at about $200 million. By the year 2000, the goal is to reduce that amount by 25% and to "always predict failures before they occur." The company achieved a 5% budget reduction in 1996 and has sufficient data to be confident another 5% can be cut in 1997, the manufacturing executive said.

While smart valves can be a major contributor to maintenance savings, not every valve needs to be smart. "In a retrofit situation, a process loop that might have 15 to 20 valves, there are only 3 or 4 key valves that need a smart positioner," Bailey said. On new capital projects and expansions, typically 20% to 25% are smart valves, and "maybe as low as 10%," depending on the application. (For additional details on Eastman's predictive maintenance efforts, see related story, page 46.)

Handles digital or analog signals

Microprocessor-based valve positioners, like smart transmitters, accept either analog or digital control signals. Typically two-wire products, they have onboard microprocessors for functions such as valve characterization, diagnostics, alarm definition, and similar tasks. Unlike smart valves, smart positioners do not include sensors and, therefore, do not offer multivariable process measurement capabilities.

According to a just-completed study by Automation Research Corp., a Dedham, Mass.based market research firm specializing in industrial automation, the use of smart positioners offers many benefits over conventional positioners, including remote access, predictive maintenance, diagnostics, and overall feedback of valve condition.

Smart positioners improve operations by making it possible to access positioners remotely, as well as to diagnose problems and discover degradations that could cause future failure. Smart positioners can also be used to detect changes in actuator, positioner, and I/P (current-to-pressure) transducer performance. This allows users to see performance changes in a fouled pump, or the pressure drop from fouling in piping.

As international fieldbus standards are established, control valves with smart positioners will be able to communicate even more information. With fieldbus, smart positioners will be able to integrate control input information, valve position status, and auxiliary sensor inputs such as air supply pressure and packing gland pressure. Onboard intelligence, combined with these input variables, will enable smart positioners to provide information to the control system to change a process or anticipate and schedule necessary maintenance and repair.

AMR researcher David Clayton predicts tough environmental regulations will further stimulate smart positioner sales. Using smart positioners with built-in documentation capabilities will help users deal with the mountains of paperwork and logistics involved in meeting regulatory requirements.

Smart positioners also are beneficial in adapting to new regulatory environments because they not only can store information regarding their own performance, but also can document specific aspects of the processes they control, AMR said.

Sales of smart positioners only represent roughly 4% of the total 1995 North American positioner revenues, notes the ARC report, entitled Control Valve Outlook for North America. However, Clayton predicts that situation will shift towards the end of this decade as control valves become an integral part of open control systems and more suppliers release smart positioner products.

Clayton puts the current total North American control valve market at $1.066 billion. He expects that figure will exceed $1.2 billion by 2000. With an average annual growth rate exceeding 50%, smart positioners will experience the most dramatic growth in this segment, he said (see Figure 1).

There are a number of suppliers who have recently released a smart positioner product or have a model in the development stage. AMR says Fisher Controls dominates the smart positioner market in North America with its FieldVue product. Smar has a commercially available Fieldbus Foundation-compliant positioner, called the FY302, which incorporates function blocks such as PID, communication master capability, and continuous self-diagnostics. Sensycon also released a smart positioner in 1995 known as the TZID intelligent positioner. Other companies with smart positioner products on the market or on the way include Brandt and Masoneilan.

In Tech contacted several valve system manufacturers to see what type of technical approaches they were taking in the area of valve diagnostics.

Valtek International, Springville, Utah, has built its valve control systems around signatures.

A signature is a reproducible test that is run on a control valve. Valtek's system can run two types of signatures, step and ramp, while the valve is opening or closing.

Step, ramp signatures explained

A step signature is generally run to diagnose problems on an on/off valve, while a ramp signature is used for throttling valves. In either case, the user defines the starting and ending valve positions for the signature and how long data should be gathered for later analysis.

Signature data differs from historical data. In the case of signature data, the valve movement is defined by how the signature was set up to be run. Historical data, on the other hand, is gathered while the process controller is setting the valve position. "This distinction is important, because the user must recognize that the process will be upset while a signature acquisition is being run," a Valtek spokesman said. Users, therefore, must watch the process so the upset doesn't harm equipment, personnel, or material being processed.

In a step signature, starting and ending valve positions are defined, as is how long the data is to be recorded. Valtek's StarPac system, for example, gathers data at approximately 20millisecond intervals during the specified period of time. Data gathered at each sample point includes time after the step command; top and bottom cylinder pressures; I/P conversion; command signal; stem position; upstream and downstream process pressures; process temperature; and values of the inputs from the discrete input and auxiliary analog channels.

A ramp signature gathers the same data as the step signature except the step command sent to the I/P converter changes at the rate defined in the signatures dialog box. Data is gathered at 50-millisecond intervals and also includes the gas or liquid flow rate through the valve. Valtek sells a Microsoft Windows-based program to view signatures.

Alerts prior to process problem

Fisher-Rosemount (F-R) claims its FieldVue/ ValveLink system is the first implementation of the Fieldbus Foundation's data-link layer (DLL), Layer 2, which controls message transmission to the fieldbus through Layer 1.

With FieldVue, up to 42 data points can come out of the valve, explained F-R representative Mark Boland. The ValveLink software can pull a valve off-line, taking it out of service, then diagnostics can be run such as a hysteresis test, where the valve's "factory signature" is overlaid with the actual one to determine a "best fit" line.

FieldVue controllers provide continuous valve and instrument diagnostics and alert technicians to problems before they affect the process.

The FieldVue DVC5000 digital valve controller and the control valve can be operated and monitored from a field junction box, marshaling panel, or control room. The ValveLink software is Microsoft Windows 3.1 PC-based and presents information via an easy-to-interpret Windows display. Online help messages explain available options and show users how to complete tasks. F-R says it can be used for configuring, calibrating and diagnosing operating characteristics of FieldVue instruments over an existing 4-20 mA signal wiring using the HART communication standard. Using HART, the software can work with Bailey, Honeywell, Foxboro, ABB, and other DCS systems. FieldVue can be attached to some non-Fisher valves, as well. The software can print a report that contains all the configuration data for an instrument, including the instrument tag, type, serial number, and date.

Foundation fieldbus-compatible

Honeywell has launched a Foundation fieldbus-compatible smart valve interface line called the SVI 3000, which consists of a positioner/ controller and a transducer/controller and a number of control function blocks which, the company claims, allows flexibility in control operations without need for an external controller.

Designed to be integrated with the Honeywell TDC 3000, the interface features diagnostics technology, including an integral pressure sensor, designed to prevent valve, loop, and process failures (see Table 1).

Honeywell says baseline performance signatures are used to compare actual control valve performance to determine the condition of valve and actuator components such as trim, stem seals, bearings, pneumatic tubing, and diaphragms.

HART is also key to diagnostics reporting for Siemens's Sipart PS intelligent electropneumatic positioner for linear and rotary actuators.

Boris Tolkien, Siemens's technical specialist and product manager for positioners and transmitters for the U.S. and Canada, said valve diagnostics monitored using the HART version include total changes of direction; total length of travel; total alarms; change of mechanical top and lower position; spring failure; and leakage of actuator, seat, and packing via external pressure switch. Other diagnostics include-in both directions-change of travel times, impulse length, dead band, and pulsing code.

Sipart PS, which also is available in a nonHART version, controls electropneumatic valves using fast-acting piezo valves. The system is designed to provide significant savings in compressed air costs, requiring only about 2% of the amount of air normally required by nozzle and baffle plate positioners, Tolkien said. While only HART-compatible at present, future versions of Sipart PS are expected to support both Profibus and Foundation fieldbus networking protocols.

System flashes alert

StoneL Valve Communication and Control's Quartz series includes a feature called SST Alert Valve Diagnostics, which connects directly to the logic interface connectors of two solid-state sensors and auxiliary devices. The feature, which monitors both the sensors and solenoid valve, can detect faulty valve operations, the company says. Two auxiliary input connections are available for monitoring other related valve conditions.

When a valve malfunctions, the alert system flashes two LEDs, and both open and closed switch circuits energize simultaneously to alert the control computer of a problem. The system is designed to also detect fugitive emissions and air supply pressure problems, without additional wiring, and receive inputs from temperature, flow, or level switches. It can speed installation by alerting personnel of improper valve setup, reduce troubleshooting time, and identify sluggish valve operation or torque requirements, said Gregory Schaeppi, marketing manager for Fergus Falls, Minn.-based StoneL.

Automatic Switch Co. (ASCO Valve), Florham Park, N.J., arms several of its solenoid valves with a proximity (noncontact) switch to provide accurate position sensing. The valves, installed with an integral GO switch, also help controllers pinpoint a malfunction, such as a loss in air pressure, mechanical malfunction of the actuator, or failure of the valve to shift. IT

Copyright Instrument Society of America Jan 1997
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