valve trim retrofits
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7/29/2019 Valve Trim Retrofits
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Flow direction
TorusMeasurement direction
Measurement point
Torus
Spring Can
36A Valve
T
vibrationeliminate damaging
Multi-stage valve trim retrofits
tion of pre- and post-retrofit vibration measpiping systems was experienced during these
Figure 1 shows the locations and orienExcessive vibration of these valves and
tion severity.
velocities will still represent the same vibra
change as a result of the retrofit, equivalent
Thus, even if the vibration frequencies
pre- and post-retrofit vibration amplitudes.
velocity a useful parameter for comparing
frequency range. This characteristic makes
constant vibration severity over a wide
Ibecause a given velocity represents relatively
commonly used measurement parameter
tion frequency. Vibration velocity is a
this simulation.
to achieve the fluid conditions needed for
Control valves (36A and 36B) were installed
fluid conditions required for this simulation.
control valve was needed to achieve the
tested under a dynamic simulation. A
so that the safety-related pumps could be
pump bypass loop. This loop was necessary,
of auseRHR pump testing required the
The industry change to perform periodic
velocities to eliminate cavitation.
ment times the vibra
tional to the displac
and is also propor-
vibration frequency
ation divided by the
tional to the acceler
Velocity is propor-
displacement.
both acceleration an
that is related tovibration parameter
Velocity is a
RHR system.
and elsewhere in the
nearby Spring Can
as well as on a
bonnets and actuato
RHR system with vibration measurement location.Figure 1.
the RHR valve
terms of velocity on
Vibration measurements were taken in
cavitation’ in the literature.phenomenon has been described as super-potential fatigue failures in the
stream from the valves themselves. This
cavitation extended several diameters down
primarily to a high level of cavitation. This
associated piping vibrated excessively due
During test operation, the RHR valves and
RHR valve operation
flow had to be reduced.
RHR system tests, and, in practice, rated
required, i.e. the minimization of fluid
consideration in the design process is
Quad Cities dictates that an additional
excessive vibration caused by this design at
originally installed. As discussed later, the
design a single-stage trim similar to the one
most control valve manufacturers would
these low differential pressure conditions,
specified with two pumps running. Under
Talbe 1 shows the operating conditions
designed for throttling operation.
similar component configurations), also
and 36B which are of(designated 36A
seat, globe valves of flow-to-open design
Units 1 and 2 were conventional, single
The original RHR valves at Quad Cities
Original RHR valves
lems then ceased.
retrofitting. The damaging vibration prob-
existing valve bodies, this process is called
trim assemblies were installed into the
multi-stage, tortuous path trim. These newRHR valve trim was replaced with
Ultimately the original single-stage
tried with little improvement.were
o relieve this problem, several ‘fixes’
E. Katz (Control Components Inc., USA)
Company, USA), Herbert L. Miller and Robert
By John R. Arnold (Commonwealth Edison
RHR system piping.this high vibration raised fears of
the system was in required periodic test operation. In addition,
components have suffered severe vibration and damage whenever
valves and related system piping and otherheat removal (RHR)
reactors at the Quad Cities Nuclear Power Plant, the 14” residual
since the 1973 commissioning of its two 828MW boiling water
Illinois, is the largest nuclear utility in the United States. Ever
Commonwealth Edison Company, headquartered in Chicago,
7/29/2019 Valve Trim Retrofits
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tion is a term used to reflect more than one
disk stack was ‘characterized ’. Characteriza
cage in this modified trim, the multi-stage
In addition to the incorporation of the
achieved.
circumstances design flow rate would be
requirement that under all
by the safety-related
This design was necessitate
incorporating large holes.
occurs through a cage
remaining 20% of stroke
stroke; flow at the
achieved at only 80% of f
isv,C100% capacity,
fitted valves. Note that
characteristic of these retr
vs per cent strokevcent C
Figure 5 shows the per
These disk stacks are designed to freelyneutralized.
noise and piping vibration were completely
damaging cavitation was eliminated, and the
(14m/s). By limiting fluid velocity,
while retrofit trim is as low as 45ft/s
velocity was approximately 90ft/s (28m/s)
with two pumps operating, trim exit
further reduced the total exposure, in
controlled areas, the simplified work scope
heavy parts. Additionally, in radiologically
new weld x-raying, and rigging to move
process obviated much cutting and welding,
replacement. Among other things, this
significant time savings over total valve
considerable cost reduction and permitted
actuator produced
existing valve body and
process using the
This retrofittingvalves at Quad Cities.
to retrofit the RHR
the decision was made
out of the piping. Thus,
need to cut the valves
body modification or the
plished without valve
This could be accom-
valve bodies (figure 2).
equal to about 50% of additional rated flow
further, permitting flow through the cage
flow be impaired, the valves will open
should 100% rated4 and 5. Now,in figures
with the cage above the disk stack as shown
unlikely event, the valve trim was modified
tion. Because of a possible repetition of this
flow during initial RHR system trial opera-
left in the system severely reduced valve
was installed, a plastic Rad bag inadvertently
retrofit trim incorporating only disk stacks
But after the originalcapacity degradation.
withoutpass normal system particulates
In the original designthe design criteria.
reduction trim arrangement uses velocity as
pressure reduction. This multi-stage pressure
built-in, right angle turns create multi-stage
3, whosetortuous-path disks similar to figure
rating. This trim incorporates a stack of
controlling all flows up to 100% of its
multi-stage trim is capable of precisely
The pressure reducing portion of the new,
valve retrofit trimRHR
pressure-reducing trim into the existing
feasibility of installing new, multi-stage,
Edison power plants demonstrated the
Experience at other Commonwealth
directives.Achievable’ (ALARA)
‘As Low As Reasonablykeeping with site
recorded.wereas high as 2.550"/s(65mm/s)
Spring Can previously mentioned, vibrations
1 with both pumps in operation. On the
figuremeasured at the locations indicated in
provides pre-retrofit vibration velocities as2
Tableited the highest system vibration level.
ator and the nearby Spring Can which exhib-
its actu-urements taken on RHR valve 36A,
Figure 3. Typical tortuous Drag® disk pattern.Figure 2. RHR valve elevation.
OutletInlet
sectorFlow
ring (cavety)equalizingPressure
Limitorque
C 38 38 38 16
Table 1. RHR valve operating conditions.
O
F 100 100 100 60
Temperature,
O
/sec 0.567 0.574 0.574 0.675
Pressure in/out, psig 140/20 130/5 160/5 130/30
Pressure in/out, MPa 0.97/0.14 0.90/0.03 1.10/0.03 0.90/0.03
Flowing Delta P, psi 120 125 155 100
Flowing Delta P, MPa 0.83 0.87 1.07 0.69
Temperature,
3
1 2 3 4
Flow rate, gpm 9000 9100 9100 10,700
Flow rate, m
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varying the number of right angle turns in
the disks to provide higher resistance/lower
flow disks for the lower part of the stack
and provide lower resistance/higher flow
disks above. This helped reduce valve stroke
requirements while still meeting velocity
requirements. Since the pressure reduction
through these RHR valves is relatively low,
the number of right angle turns is corre-
spondingly low as well. In many applications
right angle turns of up to 30 turns and more
can be built into these disks.
Each disk in the stack incorporates a
pressure equalizing ring (PER) on its inside
diameter to assure that equal pressures act
radially around the circumference of the
plug at any stroke position. This design
keeps the plug centered at all loads and
prevents plug vibration. All of these trim
(4.5mm/s), or a 93%
reduction.
Figure 6 demonstrates
the dramatic reduction in
valve vibration velocity
and frequency when the
original single-stage trim
was replaced with multi-
stage, fluid velocity
controlling trim.
The pre-retrofit
section shows that the
single-stage trim had a
peak frequency of 230
Hz. Since piping system
frequencies are much less
than 40 Hz, the vibration
source creating the peak
was clearly the cavitating
fluid. The
post-retrofit
section shows
the dramatic
Figure 4. Characterized disk
stack with cage.
design features hold noise
levels below 85 dBA at three
feet (lm).
Results
Table 3details post retrofitvibration levels and per cent
reduction from pre-retrofit-
ting values at the same
valve/actuator/Spring Can
locations and orientations as shown in figure as peaks at 2460 Hz and 1530 Hz. However,
1. At the most severe point of valve vibra- the peak velocity of 0.010"/s (0.25mm/s) at
tion, location 3, the vibration velocity of 2460 Hz is an even more significant vibration
1.220"/s(31mm/s) has been reduced to component reduction; less than one per cent
0.105"/s(3mm/s), a 91% reduction. Also, is attributable to the presence of the valve.
at the previously mentioned Spring Can, Thus, the valve contribution to the piping
location 6, vibration velocity has dropped vibration was inconsequential after the retrofit
from 2.550"/s (65 mm/s) to 0.175"/s trim had been installed.
Figure 5. 14" valve capacity vs stroke.
reduction in peak velocity and
frequency after the tortuous path
trim retrofit.
The peak velocity has been
reduced by 91% as noted in tables
2 and 3. However, the peak
vibration now is due to the fluid
turbulence acting on the piping
system as demonstrated by the
peak frequency of about 20 Hz.
The vibration attributed to the
flow control valve now shows up
Tests were also run at 50% flow with
one pump operating. The reduction in cav
tation and associated vibration levels was as
dramatic as the results for two pumps
running. Runs made on the 36B system at
both flow rates also showed the consistent
and large reductions in vibration levels
through the use of velocity control trim.
Lessons learnedDue to space limitations above the torus,
these valves were mounted with stems othe
than vertical (i.e. stems
pointing off in the 4:00
o’clock position). The y
design was critical to
prevent sagging due to the
overhung load from the
SMB-3 operators. A roll
type of anti-rotation devic
was designed to precludeproblems previously expe
enced with sliding key/slo
type anti-rotation devices
utilized on the original
valves. In addition, the mounting configura-
tion presented several additional challenges
installation of the new retrofit components
Several difficulties were experienced in
holding the trim and disk in place while
installing the bonnet bolting due to
mounting position and lack of available ove
head rigging points. Tight tolerances
Location Vibration Velocity
"/s mm/s
1-36A valve, perpendicular to centre line 0.432 10.9
2-36A valve, in line with pipe centre line 0.412 10.5
3-36A valve, vertical* 1.220 31.0
4-36A actuator, in line with pipe centre 0.440 11.2
5-36A actuator, perpendicular to pipe centre line 0.443 11.3
6-Spring Can, perpendicular to pipe centre line 2.550 64.8
Table 2. Pre-retrofit measured vibration.
*Rotational around pipe centre line
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Figure 6. Valve vibration velocity vs frequency (perpendicular to piping centre line).
normally designed between stem and
packing follower disappeared when the
bonnet did not get installed square to the
body due to mounting position and the
effect of gravity. The stem and packing
follower on one valve (36B) was damaged
when the valve was first stroked for testing
and had to be removed and repaired.
Tolerances had to be opened up between
the stem and packing follower to prevent
future problems. A tight tolerance graphite
bushing was utilized to keep the stem
centered in the
packing gland. The
Flexatalic graphite
gasket had to be held
in place with ‘super
glue’ in the counter-
bore to prevent gasket
shifting as the other
parts were assembled.
A yellow plastic
Rad bag was sucked
into the suction side
of the RHR pump as a
result of improper FME (foreign material
exclusion) practices during this outage and a
failure mechanism not anticipated in the 10
CFR 50.59 evaluation was experienced. The
bag extruded into the tortuous-path trim and
severely reduced the pump’s flow capacity.
The space above the trim (normally solid)was modified as a result (of this problem) to
allow 50% over-capacity flow through large-
diameter holes by allowing the disk to open
past full open and pass fluid through the
large ports (of the emergency capacity cage).
This feature has become a standard part of
Quad City’s specificat ion on the purchase of
new control valves. It eliminates a possible
failure mechanism and in the case of small
metallic objects preventing full valve closure,
thus even allowing for some self cleaning.
Should the trim start to plug in the
future due to FME (such as a plastic bag,
Conclusions
Through the RHR valve trim retrofit at
Quad Cities with multi-stage, tortuous-path,
pressure reducing disks and an emergency
capacity cage, the damaging vibration pre-
viously experience during system test opera
tion has been eliminated. Further, an unlike
repetition of the previously experienced val
blockage by a Rad bag or any other medium
has been precluded by the 50% over-capaci
cage in the last 20% of valve stroke. Also,
previous concerns regarding possible piping
fatigue failures within th
RHR system as a result
past severe vibration pro
lems have been eliminate
Acknowledgement
This article has been
presented at Power-Gen
International 96 and is
zebra mussels etc.), the valve can be opened
further to allow full rated flow and
continued operation, even though vibration
reduction capability would be diminished
short-term. Thus, adequately planned main-
tenance (possibly running to the next
outage) would be possible, rather than aninoperative system and a plant shutdown.
reprinted with permission.
About the authors
John R. Arnold is Valve Group Lead Engineer a
Quad Cities Nuclear Power Station, Common
wealth Edison Company. Herbert L. Miller (Vi
President) and Robert E. Katz (Manager of
Retrofits) work at Control Components Inc.
Location Vibration Velocity Percent
"/s mm/s Reduction
1-36A valve, perpendicular to centre line 0.199 5.1 54
2-36A valve, in line with pipe centre line 0.155 3.9 72
3-36A valve, vertical* 0.105 2.7 91
4-36A actuator, in line with pipe centre 0.226 5.7 49
5-36A actuator, perpendicular to pipe centre line 0.184 4.47 58
6-Spring Can, perpendicular to pipe centre line 0.175 4.5 93
Table 3. Post retrofit measured vibration and percent reduction
*Rotational around pipe centre line
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