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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

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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

Qq

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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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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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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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

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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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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)

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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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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

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∆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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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

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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.

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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.

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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.

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Liquid flow

90

Flow rate (q) through a valve depends primarily on

• Pressure differential (Dp), and

• Capacity (Cv).

q Cv

∆p=

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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

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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.

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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

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99

Refinery Fuel Gas Applications

•Heaters

•Furnaces

•Exchangers

•Steam Generation

•Power Generation

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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