Control Valve Control Valve Trim Flu Fluid id Exi Exitt Kinetic Kinet ic Energy and Velocit elocity y History and Basis
By Her Herbert bert L. L . Miller, P. E. August 2007
22591 Avenida Empresa Rancho Santa Margarita, Margarita, CA 92688 949.858.1877 Fax 949.858.1878 ccivalve.com
Index #
Questions
Page
1
What are the kinetic energy design criteria?
2
2
What is the basis o the criterion o 4.8 Bar (70 psi) or the valve trim exit kinetic energy.
3
3
What is the basis or the velocity criteria used in the trim exit kinetic energy?
4
4
Can the kinetic energy criteria be made non-dimensional?
5
5
Why are other major manuacturers not using a kinetic energy approach as a criterion or assuring a good control valve application?
6
6
How are other valve manuactures responding to the kinetic energy design criterion?
6
7
Why is the trim outlet kinetic energy considered instead o the valve outlet velocity?
7
8
Why does ISA not endorse the kinetic energy criteria?
7
9
Why are the kinetic energy criteria not in an ISA/IEC Standard?
8
10
When will the ISA Guideline on Control Valves be revised or a new edition issued?
8
11
What is the “Retroft Experience”?
8
12
What i the kinetic energy criteria are ignored?
8
Conclusion
9
Reerences
9
selection and body design to assu re the appropriate pressure
Background: In the ISA publication “Practical Guides or Measurement and Control – Control Valves,” Reerence 1, there is a discussion regarding the use o the valve trim uid kinetic energy as design criteria. When presented to many users in the control valve industry a number o questions arise. The answer to many o t hese questions along with a historical background is presented below. I have tried to answer eac h question so that they are independent and thus could be lited se parately and provided to a customer. 1. Question: What are the kinetic energy design cr iteria?
boundary codes are also met. Then as a nal verication that the selected design will result in a good process control element with low operating cost, the uid kinetic energy exiting the valve trim is calculated and compared to the cr iteria in Table 12.3 o the ISA Practical Guide on Control Valves. This table is shown below. Low operating costs are reali zed through low wear and e rosion o the trim parts, inrequent maintenance and a low vibration and quiet installation. The energy criteria account or the impact o the uid density and its velocity withi n the same parameter. The use o the kinetic energ y density e xpression in uid ow
Fluid Kinetic Energy = ρ V /2g where ρ is the density and V is
can be traced back more than 100 years. A couple o signifcant
the velocity o the uid. This expression is also reerred to as
reerences relative to uid ow through pipes, valves and other
the dynamic pressure, kinetic energy density and as velocity
restrictions in the 1930s are presented in Dimensional Analysis
head in dierent uid ow applications.
by Bridgeman, Reerence 2, and a Crane Company publication
2
,
Response: It is a criterion associated with t he valve design and the
valve’s application. The design process it to frst select a valve style and size to assure it will allow all o the application’s pressure drop and ow requirements. This initial step a lso includes material
in 1935 titled “Flow o Fluids and Heat Transmission, Reerence 3. The Crane publication was the precursor to the well known Technical Publication 410, Reerence 4.
Table 12.3 of the ISA Guidelines – Reference 1
Service Conditions
Kinetic Energy Criteria
Equivalent Water Velocity
Psi
KPa
ft/sec
m/s
Continuous Service, Single Phase Fluids
70
480
100
30
Cavitating and Multi-phase Fluid Outlet
40
275
75
23
Vibration Sensitive System
11
75
40
12
2. Question: What is the basis o the criterion o 4.8 Bar (70 psi)
or the valve trim exit kinetic energy?
B. Industry
A signifcance reerence to the use o the kinetic energy expression is
Response: A. Similitude
made in the 1973 ISA paper, “Smoothness Aects Noise Generation
The trim Exit Kinetic Energy criterion was selected as a means
in Valve Maniolds – Fact or Folklore?” by J. G. Seebold, Reerence
o expanding the criteria, used or liquids to other uids and to
6. The principle was also presented in a Hydrocarbon Processing ,
account or the lower density in gas applications 1. The velocity
article titled “Reduce Noise in Process Piping,” by J. G. Seebold, in
criterion had been used or many years in defning successul
1982, Reerence 7. James Seebold has been a uids ow expert or
control valves in critical and severe service applications. The 4.8
many years at Chevron Corporation in Richmond, Caliornia and
Bar (70 psi) criterion is based on water traveling at 30 m/s (100
was actively involved as an ofcer in the Institute o Noise Control
t/s), which was the criterion or trim exit used in many valves and
Engineering. A quote rom his publications is:
or many years by CCI. Thus; ρ V 2 /2g, is nearly equal to 4.8 Bar (70
As ar as ow itsel is concer ned, noise generation is related
psi) when the velocity is 30 m/s and the density (water) is 1000 kg/
to the dynamic pressure. This determines the t urbulence
m3 (62.4 lb/t 3).
intensity and hence the uctuation pressure levels in the
The ormula, ρ V 2 /2g, is requently reerred to as the velocity head, it
turbulent boundary layer. A thumb rule is that as long as
is also the dynamic pressure o the uid traveling at velocity, V, and it is the volumetric kinetic energy o the uid (kinetic energy density). Thus the kinetic energy is a strong representative expression o the orce driven by the pressure dierence causing the expansion o the uid through the valve. It incorporates the inuence o density and
the velocity (in eet per second) does not exceed about 100 times the square root o the specifc volume (in cubic eet per pound) or gases and two-phase ow, and 30 eet per second or liquids, no noise problems should result. St andard piping practice rarely exceeds these velocities.
amplies the destructive infuence o the fuid velocity . This dynamic
The rule noted by Mr. Seebold works out to a kinet ic energy o
relationship allows extrapolation to other applications with the
0.076 bar (1.1 psi). For 10 m/s (30 t/s) liquid velocities, velocity
use o sound engineering principles. The dynamic similarity has
head is about 0.43 bar (6.3 psi). This is much more conservative
been proven successully with over 20 years o experience in using
than 2.75 to 4.8 bar suggested by the ISA Guide. However, it is
this relationship. The specifc measurement results noted in the
applied to the piping, not a ruggedly designed valve. It supports
1997 ASME Paper “Fluid Kinetic Energy as a Selection Criteria or
the use o a density and velocity relationship to evaluate a uid
Control Valves,” Reerence 5, provides urther support o the dynamic
system or acceptability.
similarity as a means o assuring a successul valve applications. A valve application that can provide excellent process control and a long valve lie with minimum operation costs. An airplane cruising at di er ent alt itu des shows a comm on
The American Petroleum Institute Recommended Practice 14E, Oshore Production Platorm Piping Systems, Reerence 8, uses the kinetic energy density as a design criterion. The orm o the equation is:
engineering example o the similitude in the use o the kinetic energy expression. A plane’s velocity increases as the density decreases with altitude while maintaining essentially the same dynamic pressure orces, lit, on the wings. As the density decreases with height more velocity is needed to provide the equivalent lit on the wing surace and to hold the plane at a constant height. 1
For very high pressure gases the density can e xceed 320 kgs/m3 (20 lb/t 3) more than 1/3 that o many liquids.
Ve =
c √ pm
where: V e = uid erosion velocity, t/s C = empirical constant pm = gas/liquid mixture density at owing pressure and temperature.
Table 2, Kinetic Energy Density, API RP 14E comparisons c
ρV2/2g
Solids Free Continuous Service
100
0.075 bar (1.1 psi)
Solids Free, Corrosion Controlled, Intermittent Service
250
0.046 bar (6.7 psi)
CCI valve criterion and equivalent value o ‘c’
805
4.8 bar (70 psi)
Application
In this expression c2 is equal to the density times the velocity
The valve indust ry ha s in some cases defned velocity t hrough
squared. Values o ‘c’ presented in the recommended practice and
the trim as a design guideline. These are presented in Ho
the equivalent value o kinetic energy density are shown in Table 2.
(1995), Kowalski, et al. (1996), Laing, et al. (1995), Miller
As noted rom Table 2, the API Re commended Practice va lues o kinetic energy density are quite conservative when compared to the valve criterion. This again reects the more rugged construction associated with the valve versus t he piping systems. 3. Question: What is the basis or the velocity cr iteria used in
the trim exit kinetic energy?
(1993, 1996), Stratton and Minooar (1995) and are used as a basis or the presentation o the cr iteria discussed in t his paper. Schabush (1993) argues or emphasis on the driving orce, pressure drop, instead o the results o the driving orce (velocity and kinetic energy) as the selection criteria. Just looking at the pressure drop or uid velocity at the trim exit ignores the density o the uid, which is an important
Response: Many valve companies have had internal limits on
parameter in accessing potential problems. A guideline
uid velocity that they have used or design purposes, however
based on the kinetic energy ex iting the valve trim involves
they were treated as t rade secrets or internal design limits and
the driving orce, pressure drop, the resultant velocity and
were not published. The velocities us ed were at var ying locations
the uid density. Many years o experience in applying this
in the valves. Some companies did publish the limits in their
criterion have indicated it is a reliable indicator that is not
valve literature, spec ifcally literature in the past by ABB Introl
overly conservative and is applicable to all valve designs.
and Neles have shown velocity limits or the valve inlet and/or
There have been a number o publications o guideli nes regarding
outlet. These internal industry velocity limits and design criteria
pipeline velocities or liquids and gases. Generally these are in
were never organized and published. A summar y o what is
handbooks in the uid transport and power industry. These
available is included in the ASME Paper “Fluid Kinetic Energy as
velocities a re much lower than would be allowed in a valve t rim
a Selection Criteria or Control Valves,” Reerence 5. A couple o
because the valve is much more rugged than a pipe suspended
paragraphs rom the ASME paper are repeated here:
between widely spaced supports.
Driskell2 (1983) in his chapter titled ‘Velocity, Vibration,
There have also been three valve industry st andards that limit
and Noise‘ discusses the reasons why velocity should be
the applicability o the standard to velocities that do not exceed a
controlled. Excessive velocity causes all o the destructive
stated value. These are:
eects that result in a poor valve application. He notes that velocity induced vibration and noise are ‘...a blessing in disguise in t hat they are a warning o impending ailure.‘ Driskell does not discuss where in the valve t he velocity needs to be controlled. Unortunately, when velocity guidelines have been translated to control valve selection they have been interpreted as the velocity exiting the valve body. By the time the uid is ready to exit the valve body, the inuence o ‘high
AWWA C 504, which is or r ubber lined butter y valves and provides a limit o applicability o 5 m/s (16 t/s) The other two are earlier versions o the ISA SP 75.01.01 and IEC 605348-3 noise prediction standards that limit their applicability to Mach numbers less than 0.3 and 0.2 or conventional designs and tortuous trim designs, respectively. Mach number is a dimensionless uid velocity.
energ y‘ has already been imprinted into the uid stream. For
From interviews w ith a number o experienced experts in the
example, the uid velocity ex iting the trim may have created
uid control industry an anecdotal input results regarding the
high velocity, erosive jets, and areas o low pressure with
use o uid trim velocity as a design criteria other than t hat
resulting ashing and cavitation damage and noisy shock
published in the valve literature noted. An interesting input rom
waves. Velocities should be controlled at the trim outle t, not
this interviewing process was that the 23 m/s (75 t/s) velocity
the valve outlet.
as a cavitation limit originated with the invention o the steam powered ship in the 1800s. At that time it was observed that the
2
The book by L es Dr iskel l noted abov e is tit led; Control-Valve Selection and Sizing, Reerence 9.
tip speed o the propellers on these new inventions had to be
maintained below 23 m/s or the props would be consumed by
Another actor or making a non-di mensional actor may be to
cavitation. (Note that 23 m/s in water correspond to 2.75 bar
select specifc uid properties. For example, the uid density
(40-psi) kinetic energy, the cavitation limit presented in the ISA
at a owing condition or at a standard condition and the sonic
Practical Guide.)
velocity or the uid could be used. Thus the act or would be:
The requirements or not ex ceeding 75 eet per second were used
(ρV2 /2g)/(ρsc2 /2g)
or many years in US government specifcations and eventually the government or valves. Richard Sel, the ounder o CCI and
Where: “ρ “ is a density at a specifc set o conditions and “c” is s the sonic velocity or the uid conditions.
the inventor o the DRAG ® valve (1967) worked or many years
The disadvantage o such a orm is t hat it frst discount s the
in the aerospace program and brought that velocity control
inuence o density in considerations o whether a trim exit
experience to the control valve industry. Although Dick Sel
energy level could create a problem. For liquids the density ratio
published a number o papers on the DRAG ® concept he never
is essentially one so only the velocity is considered. This may
revealed the design criteria that were used because he considered
not be too bad because the densities or most liquids tend to all
it a trade secret. The velocity control concept has been refned
within a narrow range and velocity is t he most dominant variable
over the years to include the density o the uid via the kinetic
in destructive inuences.
got passed down to the aerospace industry in specifcations rom
energy limit approach and to allow higher energy levels or noncavitating uid situations.
For gases, there is a large change in density as the uid moves through the valve when large pressure drops occur and
Another common example o velocity is the common water aucet.
experience indicates that the pressure level is as signifcant as the
The velocities seen through the vena contracta in common aucets
pressure letdown. So the density to be used in a dimensionless
or a municipal water supply at 4.14 bar (60 psi) are approximately
ratio has some uncertainty as to whether it would be meaningul.
30 m/s (100 t/s). While the aucet can be heard to audibly cavitate, most aucets will last or many years. This is due to the low energy, entrained gas and the small size o the uid stream.
I the sonic velocity is used to make the velocity nondimensional then the actor basically includes the Mach number (squared). The Mach number has not been a very defnitive guide
4. Question: Can the kinetic energ y criteria be made non-
dimensional?
in the past because it imposes too conservative a criterion. For example, many specifcations and manuacturers use a criterion
Response: Maybe, however this is not readily apparent. I the
o not allowing the valve outlet Mach number to exceed 0.3.
pressure drop across the valve is used as a non-dimensional
This generally results in large r valves t han necessary and breaks
actor then the ratio o the velocity head to the pressure drop is
down completely when a very low outlet pressure exists. I the
basically a loss coefcient or the geometry. That is;
outlet pressure is a vacuum or example the outlet rom the valve will almost always be sonic or near sonic a nd it is impossible
(ρV2 /2g)/ ∆P
to achieve a 0.3 Mach number value. The presence o a sonic velocity at t hese partial vac uum pressures is not a problem or
The loss coefcient is not a good measure o whethe r a valve
concern in most applications because o the low uid density.
design is right or the application being considered. A variety o trims with dierent loss coefcients could be used in the valve
The use o the Mach number is a very good indicator o the noise
but as experience has indicated some are very destr uctive and
being generated by a valve trim. However, or other damaging
others may only do part o the pressure letdown with borderline
inuences such as vibration, erosion and cavitation it is almost
acceptability.
a non-issue. The desire is to come up with a actor that will ft a
Some valve designers have suggested that the ∆ P should be used
wide range o issues t hat when met there is a high probability o success in the valve application.
as the dominant indicator o whether a valve design is best suited or the application. The question is which pressure drop? The
Experience was gained in reviewing the data obtained rom
most indicative is the pressure drop across the valve orifce or
the 500 valves that have been retroft with trim t hat resolves
last stage in the case o multi-stage trim designs. I t he orifce
problems with the original installations, Reerence 10. This
pressure drop instead o the valve pressure drop is used then
review did not show any consistency that would suggest a means
any debate tends to become quite academic as to whether the
or non-dimensionalizing the criterion. In addition, since the
velocity is important or the pres sure drop, since it is the pressure
criterion is essentially a constant or all applications it would not
drop that creates the velocity. However, using the velocity in
be a candidate or non-dimensionalizing as it is not a variable, a
its squared relation assigns the emphasis to this variable that is
necessary requirement or a non-dimensional approach.
indicative o its potentially destructive in uence.
5. Question: Why are other major manuacturers not using a
• Justignoreand/ornotacknowledgeanybenetforthecriteria.
kinetic energy approach as a c riterion or assuring a good
• Thecriteriaarenotincludedinanyindustrystandards.
control valve application?
• Wecancontrolthelocationofthecav itationwhereitdoesnot
Response: The frst input is that the kinetic energy criterion has
only been published or a short time, although it is approaching 10 years. Also the inertia to change the current application approach is very large. This inertia is increased due to competitive situations
cause damage. • Wecancontroltheintensit yofthecavit ationwhereitdoesnot cause damage. • Wecancontrolpressurestopreventcavitationdamage.
between the control valve manuacturer as well as some o our
In spite o all o t hese promises, feld problems occur requently.
human nature to not trust input that is not ully u nderstood or
The user is then in a position o working around the problem,
that was not developed through our own eorts.
continuing with inerior perormance or completely replacing the
A second input is that many o the ot her manuact urers do meet the criteria in t heir valve selections. They just are not aware that they do because the calculation is not being made and it certainly has not been used as a criterion in design. Most pre-designed valves a re selected out o a cata log with minimum considerat ion
valve. Without a specifc trim exit jet design criteria there is no confdence that the suppliers’ promises can be kept. The valve users do not get to make the trade-o decisions that consider all o their economic and perormance requirements. These decisions are made by the suppliers, which have dierent priorities.
o the application needs. They tend to be selected only on the
Another approach is to discount the energy criteria by providing
basis o meeting the capacity requirements and a trade-o made
a lot o technical nonsense. This may take the orm o detailed
to provide a competitive oering.
fnite element analysis that are pretty and look impressive but say
I a manuacturer knows o a particularly severe or traditional
nothing about the ability o the criteria to provide a good control
tough service they will oer a special product. This special
valve installation. In some cases, these fnite element models are
product almost always has design eatures in t he trim t hat meet
manipulated to make t he supplier look good. These fnite element
the kinetic energy c riteria published in the ASME/ISA papers
models may be used to show dierences between the uid jet peak
reerenced. In some cases it may be higher than t he criteria and
and average velocities, thus implying a problem with the kinetic
the particular application is considered OK because that valve
energy criteria, which uses average velocities. Using average velocity
application always has to be serviced requently, or it has always
keeps the criteria simple and avoids the complexity o determining
been difcult to control with that valve. Routine checks a nd
the peak velocity. I peak velocity were used it would simply mean
adherence o the k inetic energy parameter or all valves can head
a lower criteria value to compensate or the dierent between peak
o later problems in the feld application.
and average velocit y, about (7/8)2 or a normal turbulent ow feld.3
A manuacturer may not have a multi-stage trim in their portolio that will support a low energy design cr iterion and thereore would not be supportive o a change in the application approach. Many manuacturers have a max imum pressure drop permitted or the dierent designs, a constraint established many decades ago. Since the pressure drop does not account or pressure level a number o problems such as cavitation, erosion and vibration can occur. The technical paper “Comparison o Pressure Control versus Discha rge Energy Control in Cavitation Service,” Reerence 11 discusses a typical example in which pressure control has ailed to provide a good installation. 6. Question: How are other valve manuactures responding to
the kinetic energy design cr iterion? Response: The most injurious comments t he valve user hea rs
is a statement that in esse nce means the user should trust t he supplier. This takes the orm o: We have done this application many time s.
•
• Weunderstandyourneeds. • ThecriteriaareonlyapplicabletoCCIanditsproducts. • Thecriteriaaretooconservative(andthuscostly).
For valve trims the peak velocity could be as high as 1.5 to 2 times the average velocity. The ratio o the pea k velocity to the average velocity is mainly an academic issue. For use in comparing valve trims the average velocity is most signifca nt. Typical comparis ons o average velocity show that many tr ims that are not using a kinetic energy design cr iteria have average velocities much higher than even the peak velocity or the DRAG® design. An analogy that is sometimes used by others is that CCI is driving through a crowded town at 150 kilometers/hour in reerring to a high peak velocity. Because the ow path through drilled holes is claimed to be smoother, aster velocities are allowed like on a reeway. However what is not said is that the drilled holes discharge onto seating suraces and the plug. In other words, the other suppliers are speeding at an average o 550 kilometers/hr down a reeway including the exit ramp. Occasionally the other suppliers will select a convenient defnition or provide an assumption that they claim CCI is ollowing and then show that the errant result demonstrates that 3
The adjus tment i s calc ulate d or a ty pical t urbule nt model o : v = vmax 1- r R where v i s veloc ity a nd r is rad ius.
1 7
the criteria are not good. None o the presumed assumptions we
the trim outlet and that inuence carries downstream, in some
have heard about rom the users bears any resemblance to what
cases or a very large number o pipe diameters. For example, or
CCI has said in its publications or that we ollow in our practice.
acoustic noise there is only about 1 decibel o noise attenuation
The best thing or the user to do is to ask CC I i the assumptions
or every 100 meters o downstream pipe length. (For large
provided are indeed our practice.
ducting, such as the exhaust to a condenser, the noise may
The user must unders tand that the supplier has a di erent set o priorities and making sure the valve provides a low cost, low maintenance, and good control is not always at the top o the manuacturer’s list. On the other hand, CCI has been very open. Our publications show the criteria, how they are to be interpreted, and numerous successul installations solving feld problems, The use o the criteria by the user will provide a means to compare and evaluate a supplier’s oering. Reerence 12 shows how the calculations can be made by the user. (In spite o all o CCI’s publications, some vendors do not know their products well enough to make an accurate calculation o the trim e xit kinetic energy. In most cases this is likely because the sales person does not get to their knowledgeable engineer.) 7. Question: Why is the t rim outlet kinetic energy considered
instead o the valve outlet velocity? Response: The uid jet exiting the valve body cannot be ignored,
but it is secondary to the higher energy in the jets exiting the trim.
attenuate about 1 dBA or every 10 meters.) The trim exit jet will create an entire spectrum o requency output at dierent power levels that are capable o exciting the piping system, as well as the stier va lve trim components. An example that illustrates t he olly o ignoring the t rim ex it jet energy is that i one ocuses on the valve exit it would indicate that a buttery valve would be as eective as a multi-stage globe valve. I both valves have the same outlet, then they would be judged to be equivalent in terms o t heir impact on the application. This o course makes no sense and indeed the various va lve suppliers do make di erent valve design decisions, which in e ect say t hat the tr im select ion is very important. I n selecting dierent trim confgurations the vendor is implicitly controlling the trim exit uid jet energy. 8. Question: Why does ISA not endorse the kinetic energy criteria? Response : ISA has a orm letter that they issue when asked
stating that the ISA publication Practical Guides or Measurement and Control – Control Valves, Reerence 1, “provides applications-
oriented coverage o fnal control elements by documenting
In general, the va lve outlet velocity is equivalent to the uid
the unique experiences and methods o individual industry
velocity in the outlet piping. Fluid velocit y in pipe ow design
expert s… and reects practical guidance based on his [the
has been a historically strong criterion going back or more than
author’s] experience.” As such ISA, and other standards writing
70 years. Pipeline velocities are quite low when compared to the
organizations, avoid any commercial endorsement that may
uid velocities that can be handled in the more rugged valve
compromise their independence and integrity. CCI supports the
body enclosure. So looking at a uid velocity exiting the valve
ISA and IEC e orts in w riting standards or control valves and
that is equal or near the pipeline uid velocity is misleading, and
has no argument with t heir position.
will not provide the war nings needed at t he valve selec tion stage to assure a successul application.
The ISA response also indicates t hat the mater ial in Reerence 1 was reviewed by industry exper ts. Indeed, the material o
It is important to look at the valve exit velocities relative to the
Chapter 12 that includes the kinetic energy c riteria was reviewed
pipeline velocity. This is because when an expander is used
by at least three industry ex perts, all users. To our knowledge
between the valve and the pipe there could be a jet exiting
there were no reviewers rom a valve manuacturer. Since the
the valve. Depending upon the amount o expansion and the
reviewers were confdential, CCI does not know their names.
dierences in the jet and pipe velocity, there may be a signifcant audible noise source and/or a pressure recovery wave that would act as a mechanical vibration source or the piping system.
Recent history has shown that utilizing valve users as reviewers was a good decision by the editor, Guy Bordon. All t hat has resulted rom the valve manuacturers is a ver y deensive, closed
By ocusing on the valve outlet trim kinetic energy, one is
mined response. These responses have used many trivial and
looking at the source o the highest energy jets and the root cause
meaningless arguments against the trim e xit energy control. Not
o most problems encountered in poor valve applications. “Fluid
one manuacturer has taken the challenge o testing the concept
Kinetic Energy Based Limits in t he Design o Control Valves and
in their own business to measure the signifcance o the cr iteria
Valve-Related systems,” Reerence 13, provides a disc ussion o the
applied to their products. The inertia to change seems to be
link o the energy to common valve problems. These problems
restricting this evaluation.
range rom unstable orces on the closure member, vibration, noise, cavitation and erosion. I the ocus is on the valve outlet, the damaging inuence has already been created upstream at
When CCI initially published the kinet ic energy criteria in 1997, Reerence 5, our intent was to challenge the industry to
try the concept on all control valves so as to aid the users in making sure they end up with a valve that meets t heir cost and control expect ations. CCI is open to modiy t he criteria i such experience would dictate a change. Unortunately the industry response has not taken this direct ion. As a result, CCI has evaluated the concept by scr utinizing all o t he valves retroftted4 with energy controlled t rim on problem valves in the feld. T his study is published in Reerences 10, 14-16. The titles and location o the publication are listed below. This study reinorced the
10. Question: When will the ISA Guideline on Control Valves be
revised or a new edition issued? Response: The editor, Guy Bordon, asked ISA in February 2007,
o their plans or a revision. He was advised that there were no plans or a revision or a new edition. A review by ISA as a result o his request indicated that ISA had a our year supply o the current edition, which implied that there would be no consideration or a number o years.
beneft and integrity o the criteria in assuring a good control
Some valve suppliers’ sales personnel have said that there is a
valve inst allation.
letter rom ISA indicating that a revision was planned. Obviously
• “TheCaseforaKineticEnergyCriterioninControlValves–
this is a alse statement.
Part 1,” paper ISA05-P133, presented at the ISA EXPO 2005,
11. Question: What is the “Retroft Experience?”
Chicago, October 25-27, 2005.
Response: Reerences 10, 14-16 present the results o a review
• “TheCaseforaKineticEnergyCriterioninControlValves–
o all o the retrotted valves that CCI has supplied . A retroft is a
Part 3,” paper presented at the Ninth NRC/ASME Symposium
modifcation o a valve that involves only a change out o the
on Valves, Pumps, and Inservice Testing, Washington D.C.,
internal trim, t he part taking t he pressure drop in the valve.
July 17-19, 2006.
The new trim controls the trim uid exit energy level to a speci fed
• “FluidJetEnergyCriterionEliminatesControlValve Problems,” Valve Magazine, vol. 18, no. 2, April 2006. • “Whenallelsefails–Akineticenergycriterionforcontrol valves v ia trim retroft is the fnal solution,” InTech, vol. 53, issue 4, April 2006. 9. Question: Why are the kinetic energy criteria not in an ISA/
IEC Standard? Response: In light o the negative response by the control valve
criterion. The body o the original valve insta llation was used unchanged and new parts provided to interace the new multistage, multi-path tortuous path trim. The replacement trim met the criteria o kinetic energy density defned in ISA Practical Guidelines or Measurement and Control – Control Valves , Reerence
1. The guideline calls or the trim exit kinetic energy density to be held to a value o 4.8 bar (70 psi) as a design criterion to be implemented ater all the conventional steps in good control valve design have been ollowed.
suppliers, CCI has not yet proposed the kinetic energy criteria be
The retrofts took place becaus e the valves were not perormi ng
included in an ISA or IEC standard even though we have been
their intended control unction and/or were continually being
encouraged to do so by a number o major users and engineering
maintained. The database shows that a ter retroft and using trim
frms. At this time there is not enough support on the standards
that limits the kinetic energy, a valve application resulted that met
committees. The committees are dominated by valve vendors that
or exceeded the user’s expectation. The population o retroftted
have not examined their own products to even know what they
valves cover s a wide range o sizes, pressure classes, design types,
are supplying to the users. There needs to be more users involved
applications, and original suppliers.
in these committees to counteract the proprietary interest o the valve manuacturers. We thereore wait a s the user s gain more knowledge and experience in the implementation o the criteria.
The study reviewed the many causes or a user to take the difcult step o retroftting a control valve in t he feld. The step to retroft is only taken ater many trials to fx a problem valve. The retrofts o
The dominance o the suppliers on the standards committees
almost 500 valves have shown the power o assuring that t he design
also leads to statements such as, “IEC clarifes that valve trim exit
meets a minimum trim exit uid kinetic energy density criterion.
velocity need not be less than 70 psi.” CCI would not expect such a statement rom the committee but would expect this to be stated by individuals on the committee reecting their company’s position. A committee response would likely take the orm o simply stating that the criteria are not included in their current standards.
One o the most signifcant observations was the very high kinetic energy levels ex isting in the original valve designs. This energy was available to enorce and ampliy any damaging impact o the trim ex it jets and to eed the turbulence that negatively impacts the piping system. These high jet energy designs ailed repeatedly. The ailures were made into successul applications, or a wide range conditions that encompass the entire control valve
4
A retr oft is a mod ifcat ion o a val ve that i nvolves onl y a chan ge out o the internal tr im o the valve. The valve body is not altered so that the only impact o the retroft is to provide a change to an ener gy control trim.
spectrum. The only change in the retroftted valve was to reduce the uid energy level e xiting the va lve trim to acceptable levels.
12. Question: What i the kinetic energy c riteria are ignored? Response: I the criteria a re ignored, the user will risk buying
a valve that may not meet the requirements or good control and reliable perormance. It will allow the supplier to avoid any measure o risk associated with the insta llation. It will allow the supplier to provide a low cost valve that meets capacity
CCI requently benefts rom installations that have not paid attention to the valve trim exit jet energ y. We get a chance to replace or retroft (when possible) valves that are not perorming to expectations.
Conclusion: 2
but may not meet your expectations or good control and low
The use o kinet ic energy, ρ V /2g, as a means o e xtrapolating
maintenance costs. Providing the lowest cost approach that
good control valve experience to new applications is sound
meets capacity usually means the valve will have the highest
engineering practice.
trim jet kinetic energies allowed by the supplier (even though
Experience gained in the uid ow industries has helped to
the supplier may not know the level or value o the resulting jet
establish values or the kinetic energy level t hat result in good
kinetic energy).
control valve applications.
References:
10. Miller, H. L., Stratton, L. R., and Hollerbach, M. A. “Fluid
1.
Borden, G., Jr., editor. “Control Valve Applications.” In Control Valves – Practical Guides or Measurement and Control .
Research Triangle Park, N. C.: Instrument Society o America, 1998. 411-477. 2.
Bridgeman, P. W. Dimensional Analysis. New Haven: Yale University Press, 1931.
3.
Flow o Fluids and Heat Transmission, Chicago: Crane
Company, 1935. 4.
presented at the Valve World 2006 Conerence and Expo, KCI Publishing BV, Zutphen, The Netherlands, October 2006. 12. Liu, G., Miller, H. L., and Stratton, L. R. “Establishing Control Valve Trim Flow Velocity.” Paper ISA04-P211, 2004. 13. Sherikar, S. V., Nagpal, V. “Fluid Kinetic Energy Based
Miller, H. L., and Stratton, L. R. “Fluid Kinetic Energy as a
Limits in the Design o Control Valves and Valve-Related
Selection Criteria or Control Valves.” Paper FEDSM97-3464,
Systems.” Paper presented at the Fith ASME/JSME Joint
presented at the ASME Fluids Engineering Division Summer
Fluids Engineering Conerence, San Diego, Cali., July
Meeting, Vancouver, British Columbia, Canada, June 22-26,
30-August 2, 2007. 14. Miller, H. L., Stratton, L. R., Hollerbach, M. A. “The Case or a Kinetic Energy Criterion in Control Valves – Part
Valve Maniolds – Fact or Folklore? ” Paper FCE 736457,
1.” Paper ISA05-P133, presented at the ISA EXPO 2005,
Instrumentation Society o A merica, 1973. 49-54.
Chicago, October 25-27, 2005.
Seebold, J. G. “Reduce Noise in Process Piping.” Hydrocarbon Processing , October 1982. 5-79. Recommended Practice or Design and Installation o Oshore Production Platorm Piping Systems . RP 14E. Washington D. C.:
American Petroleum Institute. 9.
Discharge Energy Control in Cavitation Ser vice.” Paper
Company, 1941. Precursor to Technical Publication 410 o
6. Seebold, J. G. “Smoothness Aect s Noise Generation in
8.
11. Steinke, J., Liu, G. “Comparison o Pressure Control versus
presented at the ISA EXPO 2004, Houston, October 5-7,
1997.
7.
Valve Magazine. Vol. 18, no. 2, April 2006.
Flow o Fluids through Valves, Fittings, and Pipe . Chicago: Crane
the same title that is in its 25th edition. 5.
Jet Energy Criterion Eliminates Control Valve Problems.”
Driskell, L. “Control-Valve Select ion and Sizing.” Research Triangle Park, N. C. : Internat ional Societ y or Measurement and Control, 1983.
15. Miller, H. L., Stratton, L. R., and Hollerbach, M. A. “The Case or a Kinetic E nergy Criterion in Control Valves – Part 3.” Paper presented at the Ninth NRC/ASME Symposium on Valves, Pumps, and Inservice Testing, Washington D.C., July 17-19, 2006. 16. Miller, H. L., Stratton, L. R., Hollerbach, M. A. “When all else ails – A kinetic energ y criterion or control valves via trim retroft is the fnal solution.” InTech. Vol. 53, issue 4, April 2006.
