Valve Technology How Control Valve Developments Are Improving Quality,

Productivity, and Profitability in the Process Industries

George Ritz, Contributing Editor

C ontrol valves play a vital role in flow, pressure, temperature, and level control. They account for more than 90% of all indus- trial process contro13oops.

Often neglected as the “pig iron” of process control, control valves have not received the attention as compared to other components in the control loop. However, times are changing and so is the technology.

In general, control valve technology has evolved slowly, with the

areas, control valve enhancements have made dynamic contributions to the process industries, helping to improve quality, productivity, and profitability, and to meet government regulations.

Computerized control yalveq In 1990, the control valve’s 45-year evo- lutionary era ended-abruptly with the introduction of the industry’s first “smart” control valve, the Sth’F’ac from Valtek Inc., Springville, Utah. The Starhc unit packaged the whole control loop- flowmeter, temperature and pressure

sensors, valve positioner, controller, &d a computer-right on the valve assembly. While other valve manufacturers are exploring the advantages of micro- processorequipped control valves, the lack of a digital fieldbus communication standard likely has slowed these devel- opment efforts. (See story, page 18.)

Valtek’s StarPac module offers the flexibility of being operated as a stand- alone unit or controlled from the con- trol room as part of a distributed con- trol system. Despite its relatively high price, users report the expense can be

justified in areas of severe ser- advent of some new body vice, such as slurry flows types such a~ ball, plug, but- where standard flowmeters terfly, and diaphragm valves may plug, or where credit can in a broad variety of new be taken for those loop sens- materials. The pneumatic ing devices that are eliminat- diaphragm actuator has held ed. The StarPac system makes its dominant place as the loop sensing devices redun- valve actuator of choice dant, users report. despite the advent of electric Charles Ruddell, senior motorized and piston types instrumentation planner for during the past 20 years. Cape Industries, installed a 2-

Indeed, convol valves have in. StarPx unit in a by-prod- hardly participated in the dig- uct stream with a consistency ita1 control revolution ush- similar to hot molasses at the xed in with the microchip company’s dimethyl tereph- u1 1980. And control valves thalate (a polyester precursor) are the last remaining air- plant in Wilmington, N.C. Dperated relic of the pneu- “ I t was a real problem matic control era. With the keeping this viscous materi- addition of onboard micro- a1 flowing until we installed ~~ocessors, control valves are the Starl’ac about a year ago,” xperiencing their first quan- Ruddell says. “In estimating m leap in technology since the conventional loop cost be birth of modern process against the $ I 1,000 StarPac :ontrol in 1940. cost, we came within $43.

Other more evolutionary So, we decided it was worth tdvances in valve technolo- a try. We even found that the N have been in stem sealing, unit gave us batch counting, tctuators, and in-plant valve valve diag,iostics, and other gagnostic and maintenace Figure 1. Globe control valve equipped with Fisher Controls’ iervices. In each of these new FieldVue digital valve controllel:

capabilities which were well worth the extra $43:’ he says.

Cape Industries plans to add several more StarPacs in similar hard-to-han- dle services in the near future, Rud- dell adds.

The control valve arm of Marshall- town, Iowa-based Fisher Controls Inter- national recently announced its Field- Vue digital controller and transducers (Figure 1). A “black box” mounted on the control valve actuator permits twc- way digital communication with the control room. The new package allows operators and process engineers to analyze the valve’s dynamics for early warning signals and to fine-tune valve performance locally or from the con- trol room. Savings to offset the cost of the system result from less field wiring and terminations, fewer input/output (I/O) cards, and elimination of external travel stops, limit switches, and posi- tion transmitters, claims the company. The unit is ruggedly built with encap- sulated wiring boards and a field wiring termination box designed to handle hostile environments. The unit also will integrate with the Fisher*Rosemount Systems Div.’s new RTM/l integrated real-time process control architecture.

Other valve companies also have ongoing research and development programs in the smart valve arena, so users can expect developments in the coming months. Meanwhile, Valtek already is developing the second gen- eration of the StarPac line for launch later this year.

“Smart valves are a good idea because they lead toward more dis- tributed control,” says Bruce Hover- male, Fluor Daniel’s electrical and instrumentation head in the compa- ny’s Greenville. S.C., office.

Brown Engineers. “That prevents unauthorized tinkering with control settings in the plant,” he says!

low-emission valve seals The Clean Air Act Amendments (CAAA) of 1990 and the U.S. Environmental Protection Agency’s (EPA) implemen- tation of the act call for drastic reduc- tion of fugitive emissions from process equipment such as pumps and control valves. Because there often are at least five times as many control valves as pumps in an average process plant, sealing the valves is a major target of EPA’s regulations.

The act requires that 187 hazardous air pollutants (HAPS) meet the regula- tions through a leak detection and repair (LDAR) program for control valves. The annual cost for compliance with the LDAR program in a large organic chemical plant could cost more than $1 million. That’s a cost that will more than capture upper manage- ment’s costcontainment attention.

Fortunately, LDAR has been around in certain non-attainment areas for some time, but only for benzene and vinyl chloride.

In response to the EPA requirements and to a huge potential market for improved valve seals, many valve man- ufacturers have developed new fami- lies of innovative rising and rotary valve stem seals.

The most effective (essentially zero leakage) seal is the bellows seal (Fig- ure 2). Bellows seals are more costly than packed seals so they typically are used only in severe operating condi- tions or in especially toxic or lethal ser- vice. Examples of lethal service are

“There is probably some natur- Table 1. a1 marketresistance to accept- ing any new technology, but What to Look For in a smart valves seem to fill a need Low-Emission Control Valve where initial cost is not a prob- lem,” he says.

Guaranteed maximum leakage rate Good valve stem guidance

However; not everyone favors the smart-valve approach of putting individual control units out in the plant. “I favor restrict- ing access to plant operations by operating from the main con- trol console,” says Wayne Ryen, process controls manager in the Stamford, Conn., office of John

Live loading to compensate for consolidation Minimum of RMS-4 surface finish on valve stem Fire-safe packing if required Thermal cycling effects

*Temperature rating for materials Long stroke life Type of plant environment a t valve Leakage sniffing port

ed leaf con- struction. This ap- proach, however, was prone to weld- stress failures and was quickly replaced by longer-life formed bel- lows. Bellows seals for new valves and retrofits are now available in stainless steels, Monel, Inconel 625, or several Hastelloy alloys from most leading bel- lows manufacturers.

At DuPont’s freon plant in Louisville, Ky., instrument specialist Tom Boyle experienced some failure of the plant’s original welded bellows in anhydrous HF and BF3 service. “The original weld- ed bellows in Inconel material failed fairly quickly. When we replaced them with hydroformed-style bellows in Hastelloy, we eliminated the leakage problem:’ he says. A thin tubular shield protects the bellows during shipping and installation.

If retrofitting an existing valve, a new and longer cast metal valve bonnet often will be needed to fit the longer bellows seal. The new top assembly will be from 3-in. to Gin. taller than the standard packing it replaces, so space

problems may be encountered if the valve already is located in a tight place.

Don Jordan of Champion Paper’s integrated newsprint mill in Houston reports, “We have installed bellows seals on all chlo- rine handling valves in our bleach plant.” As an example of bellows seals use for nontoxic but haz- ardous service, Champion also has installed bellows seals on critical valves in hot black liquor service. This is to protect personnel from caustic and thermal burns.

(Continued on p35)

CONTROL MARc.H 1993 33 I

(Continued from p33) Rubicon Chemical Co., Geismar, La.,

handles a number of HAPS, including phosgene and chlorine gases, in its iso- cyanates production facility. “We have a program to install bellows seals in all lethal and hazardous services,” reports Gary Tanner, maintenance supervisor. “So far we have changed to bellows seals on 50 control valves and they are working well so far,” he says.

For services not requiring zero leak- age on rising and rotary valve stem seals, a new family of improved packed seals is available. Most of the new seals claim to reduce fugitive emissions to a maximum leakage rate of less than 100-ppm, which is well below EPA‘s 1994 upper limit of 500-ppm. ;

The heart of most highdciency stem packings is the V-shaped sealing rings, which generally are made of plastics such as Teflon, Kalrez, or carbon impreg- nated materials. These materials tend to “cold flow’’ so they must be retained top and bottom by close-fitting washers. And because the materials may consolidate

over tinie, the seal assembly must be live- loaded with springs or Belleville washers to apply a constant pressure knd keep the seal tight over time.

Carbon impregnated (e.g. Grafoil) rings are used for high temperature ser- vice and fire safety sealing. Typically, the packing rings are arranged in two sets of packing on each side of the metal bushings, which are required to keep the valve stein movement in line.

If the stem cycles in an offcenter con- dition, premature wear and seal failure may occur. Some manufacturers claim a strokecycle life of 1 million strokes or better. Because seal life is strokedepen- dent, eliminating needless valve “hunt- ing action” through proper control loop tuning is vital for long seal life.

Fortunately, simply piling on addi- tional sealing rings does not improve a valve seal’s effectiveness or life. Hence, most retrofit seals,will readi- ly fit into existing valve packing boxes. Care is required to train maintenance people in working with these new units. Too much gland pressure will

prematurely I

consolidate live-loaded packings and destroy the seal.

Because they only move a quarter turn, rotary valves are easier to seal than rising stem units, but the seal designs are similar. The stem must be kept concentric and a live load must be applied to the packing (Figure 3). The inherently good sealing charac- teristics of quarter-turn plug valves fit- ted with low-emission stem seals also offer good potential for meeting EPA’s demanding LDAR regulations.

(Continued on p36)

Eliminating the Control Valve For hard-to-handle viscous materials, traditional control valves Dow Corning selected Viking’s magnetic drive model and orifice flowmeters can cause nothing but headaches. because of pump sealing problems with the difficult material. But now there’s a new alternative from Viking Pump, Cedar The company also liked the improved measuring accuracy Rapids, Iowa, that eliminates the control valve as well as the and reduced pumping head compared to the old system, Miller other components of a traditional flow control loop. says. “The units have been in for over a year now and are

The Flow Manager System is a self-contained, variable giving us excellent service in a once high maintenance area,“ speed pump that also provides a complete f low control loop. A standard gear, vane, or lobe pump i s f i t ted w i th a variable speed drive motor controlled by a micro- pro c e sso r.

The system eliminates flowmeters, con- trol valves, PID controllers, isolation valves, and associated piping. In addition to saving on hardware costs, operating costs are reduced by lowering the pump head.

Robert Miller, senior instrument tech- nician at Dow Corning’s silicones manu- facturing plant in Elizabethtown, Ky., was among the f i rst to t ry out Viking’s new approach and currentlv is usinq three svs-

he says. Key to the system‘s operation is a knowl-

edge of the specific pump‘s characteris- tics in relation to the physical properties of the fluid being handled. First, the pump‘s operating profile is recorded and fed into the unit‘s computer memory. Profiles of the material’s temperature-to-viscosity and temperature-to-specific gravity relation- ships also are programmed. Four sensors for inlet and outlet pressure, motor speed, and temperature are used to calculate and control the pump‘s output.

Viking claims volumetric accuracy of 0.5%. which is comaarable to the exoected . .

tems for continuous feeding i f high i s - ~kjng’sFlow Managersystem uses cumulative accuracy obtainable i rom a COSity polymers to an extruder. ”These upstwam anddownstreampressure flowmeter, Controller, and Control valve were the first Flow Manager units placed sensors, a temperature sensol; and combination. The system originally was in service, so w e looked a t them very knowledge 0 , thepump’scharacter- developed for high viscosityfluid applica- Carefully. We sent a 55-gal. drum of poly- istics and theflujd’sphysicalproper- tions, but the positive displacement gear mer for bench testing of the units,“ Miller Q &&onsh@s to controlflow to pumps can handle liquids of virtually any says. within 0.5%. viscosity.

(Continued fmmp35) Fisher Controls’ family of Enviro-Seal

packings was developed through a research effort that involved Texas East- man’s petrochemical comqlex in Longview, Texas. “The progyiim was initiated as part of Texas Eastman’s proactive corporate approach to pol- lution abatement and compliance with the impending EPA regulations,” says Jim Cemto, Texas Eastman’s field test coordinator. “We in the plant also are

interested in an environmentally sound work place as well as a healthy locale to raise our families,” he adds.

Texas Eastman is now in the process of upgrading its control valves with Enviro-Seal units to be ready for Phase I1 of EPA’s rules, which are due to take effect in 1994. The plant should be able to minimize the effects of EPA’s impending LDAR program.

One potential problem with high effi- ciency seals is that the valve stem’s high- ly polished finish must be maintained. This can be difficult in plant environ- ments, says Rubicon Chemical’s Tan- ner. “We found that airborne dirt and grit was settling around the exposed valve stems and working its way into the packing. Normal valve stroking caused wear on the packing and valve stem, creating leaks,” be says.

Actuator options 1 -

Despite its power limitations, the pneu- matic spring diaphragm valve actuator

remains the process industries’ work- horse and retains the lion’s share of the valve actuator market. However, pis- ton pneumatic, hydraulic, and electri- cally-powered valve operators have been nibbling away at market share in recent years.

Electric actuators offer the advantage of eiiminating entirely the need for an instrument air supply and current-to- pressure O/P) converters. An electron- .. ic control system with electrically, dri- ven smart valve actuators and posi- tioners offers some appeal in our mod- ern computercontrolled world. On the downside, however, electric actuators are not as reliable and are subject to corrosion and the resulting high main- tenance costs.

Corrosion is a longstanding problem in process industry applications, says Wayne Ulanski, vice president of The Rotary Actuator Co. (RAC), Hackensack, N.J. His f m plans to offer customers in the U.S. a new line of corrosion resis-

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tant quarter-turn pneumatic actuators that have proven themselves in Europe.

The line of actuators (Figure 4 ) fea- tures epoxy-filled fiberglass composite components where they are exposed to hostile environments. All other exposed metal parts are 316 stainless. RAC is also developing microchip-oper- ated control modules to add commu- nications and control functions to the actuator-valve package, Ulanski says.

Valve manufacturers also are enhanc- ing the performance of traditional pneumatic spring actuators. For exam- ple, NelesJamesbury, Worcester, Mass., recently introduced a Quadra-Power I1 pneumatic spring actuator to replace its Quadra-Power I line. The new actu- ator has a fully-supported rolling type diaphragm with spring pressures of 20- psi to 80-psi to deliver torques from 10-ft.lbs. to 533-ft.lbs. The new actuator can be combined with the company’s new Finetrol rotary plug control valve (Figure 5) for a broad range of control valve applications.

In-plant contractor services The specialty service of in-plant valve maintenance is not new. This service has shown a 10% per year growth for the past decade, but is now expecting a greater surge of business brought on by the CAAA. It is anticipated that the LDAR program alone will overload the maintenance crews in most large chem- ical process plants and force them to use outside services.

Monitoring and documenting the new LDAR programs and changing to the new low-emission seals to maintain compliance with EPA regulations will be personnel-intensive. Some firms, such as Texas Eastman, already are in the process of using a contractor to change out their valve seals in HAP ser- vices, as well as training their own in- house LDAR monitoring team [CON- TROL-Jan. ’93, ~ 3 9 1 .

Those field service contractors not already doing LDAR programs report that they are developing documenta- tion protocols for client use in com- plying with EPA rules. Because many plants will not be able to respond with sufficient in-house staff, contractor ser- vices offer a viable option.

The volume of leak testing, data log- ging, and support documentation

required by EPA is anticipated to be onerous and will result in significant operating expense. And becahse non- compliance in this area can cause sus- pension of a plant’s operating permit, there will be intense pressure on plant management to meet EPA’s LDAR rule requirements. Plant maintenance departments should be developing their LDAR protocols now to meet the minimum requirements that will become effective in 1994.

Rubicon Chemical’s Geismar plant already uses a contract service for mon- itoring and reporting valve emissions. “Presently, [the contractor] monitors all hazardous service valves on a month- ly basis and reports results quarterly,” says Monty McNutt, manager of the plant’s inspection department. “We will see how that stacks up to EPA regula- tions when they kick in,” he says.

Another in-house service experienc- ing growth is control system diagnostic and auditing programs. Some firms will audit an entire plant and provide advice on tuning and diagnosing problems with the plant’s control loops. Champion Paper’s Jordan lauded the results of a recent survey by EnTech Control Engi- neering, Toronto, of Champion’s Hous- ton paper mill, an operation covering several thousand loops. “About 60% of the control valves showed need for var- ious kinds of maintenance to bring them up to par;” Jordan says. “Prior to the audit, our maintenance people estimat- ed that maybe 10% of the valves might need reworking,” he adds.

Champion opted for follow-up train- ing programs and now are doing their own diagnostics, using EnTech only for consulting and interpretation of results. f ie beneflts of this service are improved process control leading to higher effi- ciency, improved product quality, more satisfied customers, and improved prof- itabitity. In addition to the process con- trol diagnostics and audit report, they offer training courses for plant personnel, enabling owners to keep control sys- tems in tune themselves.

DuPont’s ethylene plant in Orange, Texas, was among the first to use Fish- x Controls’ FlowScan diagnostic soft- ware program to analyze control valve performance. Jim Rodda, a DuPont technical associate, was coordinator 3n the project. “Process line downtime

and maintenance are expensive nightmares: Rodda says. “But by using FlowScan to test our valves before an outage, we save a ton of money. Testing prior to the outage lets the maintenance team repair only those valves or items on each valve that need work.” A fringe benefit of FlowScan is an ongoing pre- dictive preventive maintenance pro- gram built on the accumulated data- base from previous audits, he says.

Engineers with engineering and con- struction firms echo their clients’ desires to meet or better EPA’s control valve emissions regulations. “We often speci- fy the tapped-hole option for leak detec- tion on control valves: says Bob Burris, a design engineer with Perigon Engi- neering, Charlotte, N.C. “We add pres sure switches and alarms to indicate pos sible failure of the primary packing set.”

Most control system design engineers lean toward the concept of more dis- tributed control fostered by the smart valve concept. “In my opinion, smart valves can fill a need where they are cost effective. They also suit the cur- rent trend of decentralizing the con- trol function,” says Chuck Savageau, control systems engineer in Fluor Daniel’s Cincinnati office.

Over is the dormant state of control valve technology. Given the vital role these valves play in process control, advances will continue in new design concepts, hardware development, soft- ware systems, and services. The process industries will need to apply this new technology to survive in today’s worldwide, highly-competitive marketplace and environmental regu- latory climate. 0

CONTROL MARCH 1993 37