valve trim retrofits

7/29/2019 Valve Trim Retrofits

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1

6

5

4

3

12

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,


http://slidepdf.com/reader/full/valve-trim-retrofits 3/5cation, characterization was accomplished bydesign of velocity control disk. In this appli

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



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



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

valve trim retrofits

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