control valve functional testing - swetha
TRANSCRIPT
Control Valve Function Testing
BySwetha Sundaram, P.Eng
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Control Valve Function Testing
Why it is required?What are some of the things that are checked?Types of testing:Common Testing
1)Test procedure to verify valve travel.2) Setting limit switches on valves.2) Hydrostatic Testing.3) Valve Seat Leakage Test
Special Testing1) Capacity Test.2) Fugitive Emissions.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
FUNCTIONAL TESTING
Functional Testing is done on finished products to verify a range of performance
parameters.
The control valve is completely assembled and fitted with all accessories
such as positioner, solenoid valve etc.
All accessories are tested to see if they work the way they are supposed to.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
CONTROL VALVE – FUNCTIONAL TESTING
• Why is Functional Testing important for control valves?
• The control valve behavior has a major impact on the performance of the Control Loop.
• Functional testing is done to verify the proper performance of the control valve.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Valve AccessoriesSome of the valve accessories are:
• Actuator – a device used to move something. Used to open or close a valve.
• Taps in our homes are examples of valves.Anyvalve can be made into a control valve by
adding an actuator.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Valve Accessories contd
• Positioner – receives signal from controller & sends signal to actuator to move the valve.
• Limit Switches – provides confirmation signal to PLC or DCS.
Actuator
DVC Positioner
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• Hand Wheel – used to manually open/close the valve.
• Solenoids – allows air into actuator when energized.
• Volume Boosters – supplies air to actuator when high stroking speed is required.
Valve Accessories contd
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
What are some of the things that are checked?
• The gauges on the positioner are checked to see if they are working properly.
• The calibration of the valve positioner is verified and adjusted as needed.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Functional test Procedure
• The valve, I/P positioner, current source generator, and instrument air supply are set up .
• Instrument air supply P is checked. It is set according to the I/P positioner requirements.
• 4 mA current signal is applied to the I/P positioner. The valve stem shall be in 0% travel. 20 mA current signal is applied to the I/P positioner; the valve stem shall be in 100% travel.
• If the valve stem travel indication didn’t show correctly 0% or 100% travel, then travel is calibrated using the HART communicator
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• The five point stem travel is checked for hysteresis and linearity check on 0%, 25%, 50%, 75%, 100% and then 100%, 75%, 50%, 25% and 0% stem travel.
• The three point stem travel is checked for deadband check on 5%, 50%, and 95% stem travel.
•
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Diagram showing typical test set-up. http://www.youtube.com/watch?v=m-b1Llp6ik0&feature=related
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
What are some of the things that are checked? contd
• All required stroking times are checked & valve rated travel is verified.
• http://www.youtube.com/watch?v=jzffBXYrsxo&feature=results_video&playnext=1&list=PL4572CC2C362FEE57
• http://www.youtube.com/watch?v=NDYR53Tdwdo
• It is checked to see if the valve fully opens & closes.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
What are some of the things that are checked? contd
• If the control valve is equipped with a hand wheel, the valve is fully closed and opened using the hand wheel.
• Limit switches on control valves are checked to see if it is set properly for the open & close position.
• http://www.youtube.com/watch?v=SUI1U5I9bbc&feature=related
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Hydrostatic Testing
• Hydro tests can be done on just the valve body or with the actuator assembled.
• This is a safety test to verify the mechanical integrity of the valve body.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• The valve is filled with a suitable liquid and is pressurized in accordance with the table shown below.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• The minimum duration of test pressure before the start of inspection is as per the following table.
Once the test is complete, the valve is inspected for any visible leaks or deformities.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Seat Leakage Test
Seat Leakage Test is performed to check
If valve will shut-off properly when it is
required to do so throughout the service life
when installed in field.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
If proper shut-off is not met
- there is loss of fluid downstream of
the valve.
- Leakage results in trim damage to
both seating surfaces on the plug
and seat ring.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• ANSI specifies 6 classes for seat leakage.
Class I: Not required to shut-off at all.
Class II to IV: the allowable leakage
decreases from Class II to Class IV.
Class V: For metal seated valves to
meet class V sophisticated changes
to seating profile is reqd.
Class VI: Is for soft seats.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
• Class V is tested @ actual service pressure. Other classes are tested at a lower pressure.
• Valve may pass the seat leakage test but may notmeet the real requirements in the field. This is true for all classes except Class V.
• The testing medium is either air or water.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
If valve failed the seat leakage test it could be because
a) We don’t have good contact between seating
surface & plug. Mating surfaces have not been
machined properly.
b) Actuator & valve stem are not properly connected
and aligned.
c) Sufficient seat load required to bring the
plug & the seat surface together and to
hold them tightly under service condition has not
been met.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Capacity Testing
• Applies to custom designed valves only or for some special design cases.
• Flow Coefficient Cv of a valve is a relative measure of it’s efficiency at allowing fluid to flow.
• The valve flow coefficient takes into account all factors that affect flow including dimensions and flow direction changes.
• the flow coefficient Cv is the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
The Test Valve is isolated between two throttling valves in the above set-up so that the DP across the test valve can be carefully controlled.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
The upstream & downstream throttling
valves are adjusted so that the DP is 1 PSI.
The flow is measured in USGPM.
The measured flow in USGPM is the Cv of
the valve.
Example: If @ 60 F & a DP of 1 PSI across
the valve, the flow rate is measured as 60
USGPM then the Cv is 60.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Fugitive Emission
• Tests for fugitive emissions are not part of the regular functional testing for valves.
• They are performed by the packing manufacturer so as to certify the packing meets the requirements.
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Test to check fugitive emission
• Fugitive emission is the unanticipated emission of process fluid to the environment.
• This can cause significant damage to the environment.
• affect the health & safety of people.
• And lastly, can result in economic losses as well.
• http://www.youtube.com/watch?v=XLaz29jGwGc&feature=results_video&playnext=1&list=PL4572CC2C362FEE57
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer
Assignment
• Capacity testing is done on a 3” Fisher valve. The valve model is ED and the trim characteristic is equal %.
• The test conditions are listed below. The valve is wide open.
• Inlet T 60 F
• DP 1 PSI across the valve.
• Flow rate Q 136 USGPM
• What is the rated CV of the valve?
BY: SWETHA SUNDARAM P.Eng, Instrumentation & Controls Engineer