Download - Control Valves Course Basic 2010 Handouts
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CONTROL VALVES
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ISA – Lima – PeruOctober – 2010Jorge Souza
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AGENDA• Valve Types• Basic Components• Piping Connections• Pressure Ratings• Materials• Operation Concept• Fire Safe Construction• Control Technical Issues• Flow Characteristic Curves• Instrumented Air Quality• Noise, Cavitation and Flashing• Control Valve Sizing• Cv• Severe Service Applications
Valve Types - by application
• Manual
- type of operator - lever, gearbox or other.
• Automated on-off
- type of actuator - pneumatic SA or DA, electric or other.
• Control
- type of actuator - pneumatic SA or DA, electric or other.
- type of positioner - smart, electronic or pneumatic.
• Other
- safety relief - self operated (regulator) - check (non return) - multi port - steam trap - sample valve - etc.
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2
4
Valve Types - by construction
Butterfly – 2 and
3 excentricSegment
Excentric
Plug
Top Entry
Balls
Globe
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•• BODYBODY•• SEAT, PORT, CONNECTION, STEMSEAT, PORT, CONNECTION, STEM
•• ACTUATORACTUATOR•• PNEUMATIC, ELECTRIC, SPECIALSPNEUMATIC, ELECTRIC, SPECIALS
•• DOUBLE ACTION DOUBLE ACTION X X SINGLE ACTIONSINGLE ACTION
•• POSITIONERPOSITIONER•• PNEUMATIC, ELECTROPNEUMATIC, ELECTRO--PNEUMATIC, DIGITALPNEUMATIC, DIGITAL
BASIC COMPONENTS
TRIM
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PIPING CONNECTIONS
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Connections
• Screwed
• Wafer (clamp between flanges)
• Wafer Lugged (single flanged)
• Flanged
Flat and raised face, surface finish, ring type joints.
• Weld
Socket weld, butt weld, extended butt weld.
• Other
Special clamping systems.7
8
Wafer Type
Lugged
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4
10
Flanged
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Welded
Clamp ring connection
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PRESSURE RATING
Pressure Rating
• Describes the ability of the valve (or piping system) to withstand the forces imposed by the temperature and pressure of the internal fluid.
• It depends on the thickness of the pressure retaining parts and the strength of the materials they are made from.
• The limits are expressed in tables or graphs of pressure / temperature for particular material.
• Ratings are expressed as:
- ANSI Class 150, 300, 600, 900, 1500, 2500, 4500.
- DIN PN 10, PN 16, PN 25 , PN 40, PN 64, PN 100 .
- JIS PN 10K, PN 16K, PN 20K, PN 30K, PN 40K, PN 63K
Rating – Pressure x Temperature curves
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6
Rating - Pressure / temperature tables
Body Material Ratings
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
50 150
250
350
450
550
650
750
Carbon Steel
Chrome Moly
Stainless Steel
Strength
Based on
ANSI 300#
Temperature Celsius Degrees
Pressure Class PN (barg)
Pressure Class ANSI (barg/psig)
10 16 20 25 40 50 64 100 150 250 150 300 600 900 1500 2500
15 24 30 38 60 75 96 150 225 375 Aço Carbono 30/435 78/1125 156/2250 233/3375 388/5625 647/9375 Aço Inox 30/435 75/1080 150/2160 225/3240 375/5400 625/9000
ANSI X DIN
JIS
Pressure Class JIS (barg)
10K 16K 20K 30K 40K 63K 21 41 51 78 102 161
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MATERIALS
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Coating Properties
Coating DescriptionHardness
HRC/HVThickness mm
Hard Chromium Electrolytic Coating 70 / 1000 < 0,1
NiBo Ni-Base Alloy (S&F) 55 / 600 0,5 - 1,0
Stellite SF 6 Co-Base Alloy (S&F) 45 / 450 0,5 - 1,0
Tungsten Carbide WC-Co Tungsten Carbide (HVOF) 70 / 1000 0,1 - 0,2
Tungsten Chromium Carbide (W/Cr)C Tungsten Chromium Carbide (HVOF) 70 / 1000 0,1 - 0,2
CrC Chromium Carbide (HVOF) 65 / 800 0,1 - 0,2
Thermal Spray Processes:
S&F Spray and Fuse
HVOF High Velocity Oxyfuel
Plasma Plasma Spraying
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Trim Valve Sliding PairsBall Seat Medium Service
Hard Chromium Celsit Liquid / Gas Moderate pressure and
temperature. Corrosion
resistance equal to 316
Stellite SF 6 Celsit Liquid Moderate pressure and
temperature. Corrosion
resistance equal to 316
NiBo Stellite 12 Gas up to 550 C High pressure and high
temperature. Poor
corrosion resistance
Tungsten Carbide WC-Co Tungsten Carbide WC-Co Gas up to 400 C
High pressure and
moderate temperature.
Poor corrosion
resistance
Tungsten Chromium Carbide (W/Cr)C Tungsten Chromium Carbide (W/Cr)C Liquid Moderate pressure and
temperature. Good
corrosion resistance
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Relative Resistance to Cavitation Damage
Material Hours Tested Index*
Stellite 6 over 316 120 20
17-4 PH 45 HRC 12 2
AISI 316 6 1
Carbon Steel 2,25 0,38
Brass 0,5 0,08
Aluminium 0,033 0,006
* 316 SS is the
reference. The
others were tested
until they showed
approximately the
same amount of
damage as did the
316 SS sample
after 6 hours of
testing
Seat Technology
• Severe service• Solids handling
• Slurries
• Solids suspended in gas
• Control service
• High temperature designs to 1100°F
• Application & industry specific• Polymer Proof – Chemical
• Severe Shock – Pulp & Paper
• Erosion – Mining
• Delayed Coking – Refining
• Surge Control - LNG
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Coatings & Surface Treatments
• Hard Chrome
• Chrome Carbide
• Nickel Boron
• Stellite
• Nitride
• Tungsten Carbide
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Trim Coatings• Hard Chrome (HCr)
- Plugs
- Coating process – Electroplated
- Hardness – 64-69 HRC
- Corrosion resistance similar to 316 SS
- Do not use with acids
- Max. temp – 842 F
• Cobalt based hard facing (Stellite)
- Trims
- Coating process – PTA (Plasma transferred arc welding)
- Hardness – 36-43 HRC
- Resistant to adhesive wear, erosion, cavitation, and corrosion
- Max. temp – 1112 F
• Nickel Boron (NiBo)
- Plugs
- Coating process – thermal spray and fuse
- Hardness – 55-60 HRC
- Not suitable for corrosive liquids
- Used in high temp and abrasive applications
- Max. temp – 1112 F
• Chrome Carbide (CrC)
- Trims
- Coating process – HVOF
- Hardness – 60-65 HRC
- Excellent wear and and corrosion resistance
- Max. temp – 1472 F
• Tungsten Carbide (WC-Co)
- Trims
- Coating process – HVOF
- Hardness – 65-70 HRC
- Excellent wear and and corrosion resistance,
especially in high cycle applications
- Max. temp – 842 F
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OPERATIONCONCEPT
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• Operates on a pneumatic signalfrom a controller
• Operation is based on force-balance principle
• Double and single actingfor rotary and globe valves
• They accurately position the control valve assembly in response toa change in input signal
• The dynamic behavior can be changed by choosing differentsize pilot valves
• The direction of operation can be changed simply by reversing the built-in change over piece and the cam. External piping not be modified.
Operation – Pneumatic Concept
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Operation – Electro Pneumatic Concept
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Operation - Digital Concept
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FIRE SAFE CONSTRUCTION
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Fire Safety - Fire TestedRemember:Most valves do not need to be “Fire Safe”
Fire Safety is the term used to describe a valves ability to withstand the effects of a fire actingon its outside surfaces. The basic idea being that in the event of a fire a “Fire Tested” valvewill not add to the intensity of the fire or its dangers by leaking its flammable or dangerouscontents.
There are a number of very different tests applied to valves to qualify them to be described as firetested/safe:
Some only require that the test valve is burned for a short time while it is full of water and that itdoesn’t leak more than a certain amount to atmosphere. There are rubber lined butterfly valves thatpass this test (Lloyds register). Others require that the test valve is burnt for long enough to ensurethat any soft materials are completely destroyed, that it remains operable and retain some ability toshut off flow, with higher than usual seat leakage but little or no external leakage. This was the mostcommon fire safe test based on the old BS5146. (based on the old OCMA Oil Companies MaterialsAssociation, FSV1 test)
The current most recognised tests:BS6755 part 2 (Europe(France – ELF)) and API 607 edition 4 (USA) which require that the valve isburned in the closed position full of water for a considerable time. The water turning to superheatedsteam and at high pressure in any cavities. Any external leakage is very restricted during the burning.After cooling the valve is operated a number of times and then tested for seat leakage.
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CONTROL TECHNICAL ISSUES
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PROCESS MODEL
q
p1 p2
p1
p2
q = Flow
p = Pressure
h = % opening
I = Signal
∆p0∆p ∆pm ∆pf
Qm Qf
i
DPp
p
DPp
p
m
m
f
f
=
=
∆
∆
∆
∆
0
0
q
p p p
f
=
= −∆1 2
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Recommended Velocity Limits for Liquid Service
• Erosion
• Corrosion
• Stability (butterfly)
Ball, Segment, Globe
33 fps (continuous)
39 fps (infrequent <10%)
Butterfly
23 fps (continuous)
27 fps (infrequent <10%)
Dead time (td)
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Dead time is the the interval of time between input change and the start of
output change.
In valves it is caused by friction load and the compressibility of air
Time
Input signal
td
Valve travel
Dead band
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Dead band is the range through which the setpoint signal can be varied without
response from the valve (actuator). It is caused by backlash and friction.
Dead band is measured by changing the setpoint slowly until the valve moves, and
then changing the setpoint slowly to the other direction until the valve moves again.
The dead band is the setpoint change needed to get the valve moving after the
direction change.
Time
Setpoint
Valve position
Setpoint change needed to get the
valve moving after a change in the
direction
Dead band
Dead Band = Stiction + Backlash
StictionResistance to the start of
motion, to overcome static
friction during signal reversal
BacklashA relative movement between
interacting mechanical parts,
resulting from looseness, when
motion is reversed
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Hysteresis plus dead band
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Time
Valve
travel
Hysteresis plus dead band is the maximum deviation between the
valve positon with an increasing signal and the valve position with a
decreasing signal. The measurement is made when the valve position
has stabilized.
h+db
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Hysteresis plus dead band
Ou
tpu
t
Ou
tpu
t
Ou
tpu
t
Input Input Input
Dead band Histeresis + Dead band Histeresis
• Measure of the input
• Results from stiction
and backlash
• Cannot be measured
without the effects of
dead band
• Measure of the output
• Results from the
inelastic quality of the
package
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Linearity
Upscale curve
Downscale curve
Specified curve
Input
Outp
ut
The maximum deviationrelation to the reference line
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40
Entech Specification for Control Valves
• Backlash + Stiction (= Deadband) Less than 1%• Speed of Response by following table (step 2%)
Size Td T63 T98
(in) (s) (s) (s)
0 - 2 0,1 0,3 0,7
> 2 - 6 0,2 0,6 1,4
> 6 - 12 0,4 1,2 2,8
> 12 - 20 0,6 1,8 4,2
> 20 + 0,8 2,4 5,6
Entech v. 2. 1 Stroke Times
STEP RESPONSE
Load Factor
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PA
PB
PA
Lp p
pDOUBLE
A B
s
=−
*100%
Lp p
p pp pSINGLE AIR
A J
S J
A J_ *=−
−≥100% when
JA
j
jA
SPRINGSINGLE ppp
ppL <
−= when %100*_
PJ
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Process variability
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Process variability is the variation of process variable.
Time
[ ] [ ] [ ]Variability x x% % %max min= −
[ ]
mean value=X
deviation standard=
1002
%
σ
σ
where
XyVariabilit ⋅=
error absolute integral
error absolute timeintegral
=
=
IAE
ITAE
SOME CALCULATION METHODS:
�
�
�
�
Globe
Rotary
1 2 43 5 6 7 8 9 10Operations (thousands)
0
Stem Seal Life
Ste
m s
ea
l le
aka
ge
GlobeRotary
40 times
Cost
$0
$5.000
$10.000
$15.000
$20.000
2 3 4 6 8 10Size (inch)
HPBF Seg. Ball Ecc. Plug Globe
Size (inch)
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WEIGHT - Flow Capacity and Compactness
Ball, segment ball, BF: flow capacity ≈ 2 x Globe
To high capacity applications - Ball, Segment,
Butterfly
To medium capacity applications - Ball, Segment,
Butterfly, Globe,
Eccentric Plug
To low capacity application - Segment, Globe
Weight
0
500
1000
1500
2000
2 3 4 6 8 10Size (inch)
HPBF Seg. Ball Ecc. Plug Globe
Size (inch)
po
un
ds
NEMA Ratings (General Purpose Areas)
Most Significant Ratings
• NEMA 4 - Waterproof
• NEMA 4X - Waterproof & Corrosion Proof
• NEMA 6 - Temporary Submersibility
• NEMA 7 – Class I (Obsolete)
• NEMA 9 – Class II (Obsolete)
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Hazardous Area Ratings
Hazardous Area Approvals (North America)• Manufacturers May Use Ratings on Labels Even Though Non Third
Party Approved
• Third Party Approval Agencies; Equipment must be Tested by Third
Party to NEC Standard to have Logo on Label:
- FM (Factory Mutual, US Market)
- UL (Underwriters Labs, US Market)
- ULc (UL for Canada & US Markets)
- CSA (Canadian Standards Association)
Process Environment
• Enclosure Standards & Protection Concepts
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Process Environment
• Enclosures
Process Environment
• Hazardous Area Descriptions
Process Environment
• IEC & EU Standards
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Process Environment
• Guide to Hazardous Locations
Process Environment
•Chemical Compatibility
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FLOW CHARACTERISTIC CURVES
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THEORICAL CHARACTERISTIC CURVES
0
0,2
0,4
0,6
0,8
1
0 0,2 0,4 0,6 0,8 1
Rela
tive flo
w c
oeff
icie
nt
Relative valve travel
Equal percentage
Quick opening
Linear
Real and Typical Flow Characteristic Curves
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0
50
100
150
200
250
300
350
400
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Cv
Relative valve travel (opening)
80 Ball valve
80 Segment valve
80 Butterfly valve
80 Globe valve
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INSTRUMENTED AIR QUALITY
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Air Quality
Air quality according to ISA S7.3 and ISO 8755 Standards:
• Dew point 10 Celsius degrees less than the minimum temperature registered on the region of the installation. But not too low dew point because too dry air cause wearing of pneumatic instruments, like positioners;
• Particle size less than 3 micra;
•Less than 1 ppm oil content ;
• No chemical contaminants
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NOISECAVITATIONFLASHING
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REASONS FOR NOISE
• Noise is energy;
• Energy is coming from the moving liquid;
• Everything in the pipeline causes noise;
• In the valve there is differential pressure in
a short distance - lot of energy is turned in to
noise;
• Noise is generated mainly by the region
just after the vena contracta point;
• The nature of the dB values is such as a
small increase in dB number means big
changes in human ear and in sound energy:
• 3 dB increase is just noticeable;
• 5 dB increase is clearly noticeable;
• 10 dB increase is twice as loud;
• 20 dB is much louder.
• Human ear - 20 to 20.000 Hz;
• Need to consider pipe wall attenuation
dBA Example
130 Rock Band
125 Threshold of pain
95 Power mower (1 m)
70 Vacuum cleaner (3 m)
65 Cocktail party (second drink)
20 Electric clock (at 3 a.m)
0 Threshold of hearing
Valve Size Noise
(in) Limit
up to 3 80 dBA
4 to 6 85 dBA
8 to 14 90 dBA
16 or larger 95 dBA
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64
Nature of Aerodynamic Noise
• When compared to the hydrodynamic noise the aerodynamic noise is not so dangerous
• When noise levels raise high enough the vibrations can cause some disturbance to the action of the positioner or can cause mechanical damages in the pipeline;
• 100 dB causes heavy vibration on the pipeline;
• 110 dB means very heavy vibrations, mechanical damage.
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Pressure
Velocity
Sudden expansion and compression
Aerodynamic Noise Generation
• Sudden expansion and compression at vena contracta→Severe turbulence
• Supersonic velocity downstream of vena contracta → Shock waves and very severe turbulence
• Turbulence generates sound waves
• Sound waves propagate down the pipe and through pipe wall
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Valve Noise Generation
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67
NOISE RADIATIONPoint Source:• 6 dB reduction per doupling of distance away from source• ex.: voice, atmospheric venting
Line Source:• 3 dB per doupling• ex.: long pipe, busy highway
1 m
1 m
Point to
calculate
the noise
Douplings
1 1 m
2 2 m3 4 m
4 16 m
5 32 m6 64 m
7 128 m
8 256 m
The dB values has a
logarithmic scale.
Potential valve problems in gas flow
• High trim and outlet velocity may cause :
- erosion
- noise
- vibration
- V max < 0.5 Mach (continuous duty)
- V max < 0.7 Mach (infrequent duty)
• Noise is energy !
- downstream noise is what counts
- gas noise can be carried significant
distances in downstream piping
- 110 dBA may cause vibration
- at high noise levels the instrument may
not perfom optimally
- 85 dBA is common limit to avoid hearing
defect
- Never quote the valve exceeding noise
level 120 dBA !68
•Source Control
-Quiet valve
-Static restrictor
•Path Control
-Distance
-Heavy Wall Pipe
-Thermal or Acoustic Insulation
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Valve Noise Reduction Strategies
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Noise and Anti-cavitation Trim
P1
P2WithoutQ - Trim
WithQ - Trim
PRESSURE DROP STAGING FLOW DIVISION
Q - TrimPlate
Diffuser
71
Single- or Double-stage.Capacity not limited.Suitable when Dp/p1 ratio is very highCustom-made for each case.
15 to 20 dBA attenuation
Attenuator plate (A-plate)
• Easy to mount, Cost-effective.
• Suitable when Dp is app. constant and Dp/p1 rather high
• Capacity is limited, since max. hole area is about 40% of total area.
• When more capacity is needed, plate must be bigger.
• Plate sizes and Cv-values have been standardized.
• A-plate together with Q-trim can achieve up to 25 dBA attenuation.
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25
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In Line Silencer
Up to 50 dBA attenuation
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Vent Silencer or Diffuser
15-20 dBA attenuationUp to 50 dBA attenuation
Relative pipe wall attenuation (db)
75
Nominal SCH SCH SCHPipe Size 40 80 160
2 0 -4 -10
4 0 -4 -10
8 0 -4 -11
12 0 -5 -12
16 0 -6 -13
Pipe Wall Effect
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No
ise R
ed
ucti
on
(d
BA
)
0000
5555
10101010
15151515
20202020
25252525
Thickness in Inches
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.20 0.4 0.8 1.2 1.6 2 2.4 2.8 3.20 0.4 0.8 1.2 1.6 2 2.4 2.8 3.20 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
Practical limit due to acoustic “short circuits.”
Thermal
Acoustic
Τηιχκνεσσ ιν µµΤηιχκνεσσ ιν µµΤηιχκνεσσ ιν µµΤηιχκνεσσ ιν µµ
0 10 20 30 40 50 60 70 800 10 20 30 40 50 60 70 800 10 20 30 40 50 60 70 800 10 20 30 40 50 60 70 80
Insulation
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Cavitation
vapour pressure
P2
P1
Pv
P
Vena contracta
Cavitation
When differential pressure has reached the choked flow limit (a.k.a. Terminal Pressure Drop or Allowable Pressure Drop) at vena contracta, and when downstream pressure recovers above liquid vapour pressure, cavitation is produced.
Liquid Noise Generation - CavitationCavitation occurs in two stages:
• Liquid boiling point depends on pressure. Pressure at vena contracta drops below liquid’s boiling point, bubble formation -boiling - will start without any change in temperature..
• Pressure after vena contracta increases, boiling stops and vapour bubbles implode.
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79
Cavitation damages
• Damaged surface is spongy and rough.
• Damages can be inflicted in fairly short time.
• Cavitation is countered mainly by staging the pressure drop.
Cavitation damage
80
∆P about 580 psi. Hot water 140°F
Cavitation Damage Prediction
Maximum Calculated SPL
UP TO 3” VALVE SIZE 80 dBA
4” TO 6” 85 dBA
8” TO 14” 90 dBA
16” AND LARGER 95 dBA
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82
Q-trim valve
One-plate
Anti-cavitation design-rotary valves
P1
P2
Q-Trim
No Q-Trim
QLM-ball
83
Fixed resistors for liquid
Baffle-plate Orifice-plate
Used to share total pressure drop between valve and plate. Works well, but only at flow rate plate is designed for.
84
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pressure
p1
p2pvc
velocitypv
Flashing
cavitation
flashing
Vena contracta
29
85
Flashing
vapour pressure P2
P1
Pv
P
Vena contracta
Flashing
When differential pressure has reached the choked flow limit (a.k.a. Terminal Pressure Drop or Allowable Pressure Drop) at vena contracta, and when downstream pressure remains below liquid vapour pressure, flow is flashing.
86
Flashing damages
• Typically, damage potential of flashing is smaller than in cavitation.
• Damages are those or erosion type wear, smooth grooves and cavities.
• Flashing is tamed by material selection and by reducing downstream velocity.
87
Coping with flashing
Hardened trim
Rotary valves (flow direction, No Q-trim)
Equipment
Lower temperature
Use enlarged downstream piping
Locate flashing valve near receiving vessel
Pipe/process design
Coping with flashing
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88
CONTROL VALVESIZING
Valve Size
• Manual and automated on-off valves are mostly the same size as the pipe.
• Control valves need to be “sized” using the actual working conditions to do the best job. Only rarely are they the same size as the pipe, never bigger and mostly one size smaller.
• Recommended not less than middle of the inletpiping diameter.
89
Liquid flow
90
Flow rate (q) through a valve depends primarily on
• Pressure differential (Dp), and
• Capacity (Cv).
q Cv
∆p=
31
91
pressure
p1
p2
velocity
Liquid flow through an orifice (valve)
Vena contracta
Gas, vapour, steam flow
92
Flow rate (q) through a valve depends on
• Pressure differential (Dp), and
• Capacity (Cv).
q Cv
∆p=
But interrelation between pressure and flow rate is not as clear as in liquid sizing! Similarities exist at small Mach Nos. where compressibility plays a very small role.
93
Gas flow through a valve
pressure
p1
p2velocity
32
94
CvFlow Coeficient
95
Sizing parameters measurement - Cv
Done in manufacturer’s laboratory• Cv values - inherent characteristic curve,
• Noise values,
• pressure recovery factor (FL),
• Incipient cavitation pressure drop ratio (z), and
• Choked flow pressure drop ratio (xT).
Cv is dimensionless figure. Definition:
Number of US gallons of 60°F water flowing
through a valve in one minute, at one psi
constant differential pressure.
96
SEVERE SERVICEAPPLICATIONS
33
Typical valve for anti-surge application
• Trunnion mounted top entry ball valve
• Triple excentric butterfly valves
• Segment valves
97
Metso valves for dirty service
• Requirements
- non-clogging design
- low leakage to atmosphere
- rugged trim
- reliability
98
99
Refinery Fuel Gas Applications
•Heaters
•Furnaces
•Exchangers
•Steam Generation
•Power Generation
34
100
Fuel Gas Products
•FM Supervisory Cock Valves
•FM Gas and Oil Shutoff Valves
•FM Emergency Shutoff and Firesafe Valves
•CSA Gas Shut off and Vent Valves
Dampers - Furnaces
• Dampers
- Variability reduction
- Reduction of residual O2;
- Economy of fuel gas;
- Smooth operation;
- Feedback position to control room
∆ατε Αυτηορ Τιτλε101
CONTROL VALVES
102
ISA – Lima – PeruOctober – 2010Jorge Souza