SIS “Final Element” Diagnostics Including The SOV, Using A Digital Valve Controller
1. SIS “Final Element” Diagnostics
Including The SOV, Using A
Digital Valve Controller
C B Chakradhaar– Instrument & Control Specialist
Riyaz Ali – Director Instruments
2. Presenters
C B Chakradhaar - I & C Specialist
Riyaz Ali – CFSP
3. Introduction
SIS “Final Control Element” Diagnostics by Digital
Valve Controller
Basic Concepts and Need
Traditional Test Methods
Present Field Issues & Pains
Digital Valve Controller to the Rescue
SOV Health Monitoring
Critical Evaluation of Solution
Ras Gas (End User) Field Experience
Evaluation of Solution
Lesson Learned
4. Dike Passive protection layer
Emergency response layer
Plant and
Emergency
Response
Process
Value
Normal behaviour
Basic
Process
Control
System
Process control layer
Basic Concepts and Need
Operator
Intervention
Process control layer
Process alarm
Process
Shutdown
Trip level alarm
Safety
Instrumented
System
Safety layer
Emergency
Shut Down
Prevent
Mitigate
x x
Relief valve,
Rupture disk Active protection layer
Safety Through Layers of Protection
5. Basic Concepts and Need
50% failures are in
Final Control Element
Safety Instrumented System
Basic Process Control
System
Why Focus on the Final Element ?
6. Typically operate in one position - only move
upon an emergency
Without mechanical movement, unreliability
inherently increases
Frequent testing ensures valve availability upon
Demand
Historically, inexpensive mechanical jammer or
expensive labor intensive pneumatic testing
methods are used
Basic Concepts and Need
Why does the SIS Final Element account for 50% of failures?
7. Traditional Test Methods
Objective:
Reduce the Probability of Failure on Demand (PFD)
OFF LINE
Total Stroke
Process Down
ON LINE
Total Stroke
By-Pass In Service
Component Test
Partial Stroke
Solenoid (SOV)
Traditional test methods (pneumatic local panels, pin retainers, by-passing, etc.)
are difficult to operate and maintain with risks and high operational costs
Test Methodology
8. Present Field Issues & Pains
By-pass Valve
Pneumatic panels Mechanical retainers
Existing Test Methods Have High Costs
Logic Solver with Limit Switch
9. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
10. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
IMPROVE PFD
Reduce labor costs
Improve flexibility
Valve exercised to an
extent
11. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke is done on-line.
FIELDVUE Partial
Stroke capable of
being trimmed to suit
the process.
12. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke Test avoid to
casually close the
valve
13. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke Test checks
valve movement and
collects travel and
pressure data.
14. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke could be start
using a simple push
button
15. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke test Speed can
be varied to Suit
Process.
16. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke Test takes
valve to its original
position. If stuck, will
provide an alert.
Travel, pressure and
device condtion
monitored regularly.
17. Digital Valve Controller to the Rescue
Simple Operation
Safety Audit
Ensures Valve Returns to Normal Position
Stroke Test Speed
Final Element Variation
Avoiding Accidental Closure Testing
Maintaining the Process
The Test objectives
FIELDVUE Partial
Stroke Test result
stored in the
instrument.
ValveLink Audit Trail &
Documentation
18. Digital Valve Controller to the
Rescue
Increase SIL Level
– Implementation of Partial Stroking on Final Control Element
improves PFD to achieve better SIL level
Validation of SIS
– Partial Stroking Validates the proper operation of the FCE
– Final Control Elements are commonly untested and are inherently
unreliable
Maintains SIL Level
– Safely extend turnaround times
1/PFD(t)
Time
Test Interval
Without testing the PFD increases
PFDavg
The Influence of Partial Stroke testing
19. Digital Valve Controller to the Rescue
Partial Stroke “Valve Stuck” ALERT
– If the valve does not move or sticks the Digital
Valve Controller STOPS the test
– Valve returns to normal operation position and
alert is generated
– The valve will not slam shut, causing a plant
“Spurious Trip”
Trigger ALERT
– Captures valve movement or pressure changes
– Automatically stores travel, pressure and
deviation data in the digital valve controller
Supply Pressure ALERT
– Low supply pressure causes an alert
Unique Alert Features
20. Digital Valve Controller to the Rescue
Any safety DEMAND overrides Partial Stroke Test
Mode
Remote push button test returns to normal
operation if:
– partial stroke fails
– push button is held outside 3-5 seconds
timeframe
– Safety DEMAND occurs
Write Protection or ‘tamper-proof’ lock
– Deters local unauthorized access to
calibration or configuration parameters
Specific Safeguards
21. Digital Valve Controller to the Rescue
Diagnose VALVE failures before
they happen
– Moves the SIS valve into
predictive maintenance
regimes
– Additional diagnostics
• Friction buildup
• Valve shaft shear
• Air supply pressure
deviations
– Option to collect data during
a demand
Diagnostics
23. Digital Valve Controller to the Rescue
Companion Software Alert Log
Companion Software Audit Log
Companion Software Test DataBase
Intrument Alert Log
Last Partial Stroke Test Stored in the
Intrument
Audit Documentation
24. Port B
Port A
Supply Pressure
0-20 mA Point To Point
Or 0-24 Volts Multidrop
From Logic Solver
0 mA or 0 Volt ESDV Closed
20 mA or 24 Volts ESDV Open
24 Volts DC From Logic Solver
Solenoid Valve Health Monitoring
25. Port B
Port A
Supply Pressure
0-20 mA Point To Point
Or 0-24 Volts Multidrop
From Logic Solver
0 mA or 0 Volt ESDV Closed
20 mA or 24 Volts ESDV Open
24 Volts DC from Logic Solver
Pressure Measurement Downstream
SOV
Solenoid Valve Health Monitoring
26. Port B
Port A
Supply Pressure
0-20 mA Point To Point
Or 0-24 Volts Multidrop
From Logic Solver
0 mA or 0 Volt ESDV Closed
20 mA or 24 Volts ESDV Open
24 Volts DC From Logic Solver
PULSE
Solenoid Valve Health Monitoring
27. Solenoid Valve Health Monitoring
The solenoid valve can be pulsed for a split second
– Long enough so that the solenoid vents
(verification that the solenoid valve is functional)
– Short enough so that the actuator doesn’t bleed
enough pressure to make the SIS valve move.
28. Critical Evaluation for Solution
PST Scripted avoiding Human Error
Chances of Spurious Trip Reduced during PST
Demand Overrides PST
“Valve Stuck” Conditions Alerted
Health Detection of “Final Element”
SOV Health Monitoring
Trigger Capability to Capture Safety Demand
Event
Compare and Overlay Previous Results to Predict
Valve state
Audit Documentation by Date and Time Stamp
41. Real Life Examples from Ras Gas - Qatar
Benefits realized
FST and PST signatures taken during loop check
FST signature compared with Factory signature
to study valve wear and tear
PST performed with 10% valve movement
PST – SOV test signature saved
Diagnostic errors assist in identifying issues and
enable taking necessary corrective actions
42. Lesson Learned
PST Recommendations / Learning
– Use the valve signature to refine the partial stroke test
parameters, such as minimum pressure and upper operating
pressure.
– When a valve fails to move, adjust the speed, minimum
pressure or pause time.
– Map the HART bit of FIELDVUE Instruments to HOST for
getting SOV Health
– Check travel deviation or pressure deviation alert point to
ensure correct configuration, this can be the cause of failure.
– Enable pressure mode to reduce stroke time of valve.
– Test more often than required to exercise valves if necessary.
– Baseline data from initial valve signature is PRICELESS!!!
43. Business Results Achieved
Testing valve On Line Improves Reliability and
Plant Availability
Trigger Data Available in case of “Safety
Demand”
Continuous Health Monitoring of Final Element
SOV Integrity Check
Predictive Maintenance
Improved PST Flexibility
Reduced Labor Cost
Compliance to Regulatory Requirements
Integration to Logic Solver Possible
44. Summary
Possible Issues on Final Element Testing
Customer Needs and Requirements
Field Issue and Concerns
Possible Remedy – Digital solution
Critical Evaluation of Solution
Field Experience from Ras Gas
45. Where To Get More Information
IEC61508 – Functional Safety of Electrical / Electronic /
Programmable Electronic Safety Related Systems
IEC61511 – Functional Safety – Safety Instrumented
Systems for Process Industry Sector
ISA-TR84.00.02-2002 – Part 1 to 5
Control System Safety Evaluation & Reliability – W M Goble
Safety Integrity Level Selection – Ed Marszal and Eric
Scharpf