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Standards
Certification
Education & Training
Publishing
Conferences & Exhibits
PARTIAL STROKE TESTING
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Top Customer Issues Regarding Safety
Production Uptime Tests are known to cause outages Some types of tests require outages
Regulatory compliance HSE and OSHA and others are turning up the heat New customer guidelines on the horizon include 29CFR part 1910
Easy and safe integration of PAS and SIS
Control, alarms, configuration Elimination of SIS tests as they are manpower intensive potentially dangerous
An incident with two fatalities due to the by-pass valve being left open after aSIS test
Increase the confidence that the SIS will perform on demand Easy Maintenance with increasingly fewer staff
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PFD Calculation : Simple Math
= (1) (d) (1/2) = 0.5 (d)
PFD avg = [(DC)(d) (TI/2 ]p + [(1-DC)(d) (TI/2)]F
Assumptions: DC is 70% for partial stroke and 100% for full stroke
TI is 4x/yr for partial and 1x/3 yrs for full
Adding Partial Stroke Testing
= [(0.7)(d) (0.25/2)] + [(1-0.7) (d) (3/2)]= 0.09 (d) + 0.45 (d) = 0.54 (d)
Conclusion: Partial Stroke Testing enables extending the full-stroke
testing interval to 3 years and sti ll maintaining the same PFD!
Full Stroke Testing Only
PFD avg = [(DC)(d) (TI/2)]
Assumptions: DC is 100% and TI is 1x / yr
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Analysis of safety loop failures
(Source: OREDA)
42%
50%
8%
Safety Systems
Sensors
Final Elements
Does the Final Control Element lead potential SIS loop failures?
Is there Empirical Evidence or Field Experience that suggests the Final
Control Element must be tested?
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Why does the SIS valve
account for over 50% of failures
Valves in SIS Applications typically operate in one staticposition all the time and only move upon an emergency
situation. The problem: the valve being in a static position without
mechanical movement for long periods of time, inherently
increases unreliability. To ensure availability on demand, SIS valves must have
regular testing
Until recently, SIS valves could only be tested through
expensive, labor intensive pneumatic testing methods
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Test Methods
The primary objective of testing is to reduce the Probability ofFailure on Demand (PFD)
OFF LINE
Total StrokeProcess Down
ON LINE
Total StrokeByPass In Service
Component Test
Partial Stroke
Solenoid (SOV)
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The power of partial stroke testing Increase SIL Level
Implementation of Partial Stroking on Final Control Element can increase orachieve desired 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
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Current Test Methods
Manual Interlock Pneumatic Panel
Solenoid PanelBypass Valve
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ISA S84.01-1996: A Safety Instrumented System is a distinct,
reliable system used to safeguard a process to prevent a
catastrophic release of toxic, flammable, or explosive chemicals
What is a Safety Instrumented System?
How can we
Prevent the
Catastrophe?
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SIS Tests Options
Low Risk
Process Availability
Manual Interlockor J ammer
Device
Solenoids withLimit Switches
Reduces Chance forHuman Error
Low Complexity
Low OPEX
Known Valve
Performance
Automated
Low CAPEX
IntelligentPositioner
By-PassValves
SolenoidPulsing
Panels
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(Hardware and Software)
Logic solver
Sensor Logic Solver Control
Element
What is a Safety Instrumented System?
SIS Loop Sub-components
IEC61511: Safety Instrumented System (SIS)
Instrumented system used to implement one or more safetyinstrumented functions. A SIS is composed of any combination ofsensor (s), logic solver (s), and final elements(s)
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Separation of BPCS from SIS is Recommended. If you share any
loop elements, all SIS Requirements flow to BPCS
- Do you see any common
elements between BPCS and SIS?
Basic Process Control System (BPCS) vs.
Safety Instrumented System (SIS)Control Safety
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IEC 61511 - End-user/Integrator Standard
Applies to the Entire Loop
Effects of:Weather
Corrosion
IEC 61511
Wiring
ImpulseLines
Piping
Power
Loop Components
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IEC 61508 - Applies to Component
Manufacturers Not the Entire Loop
IEC 61508
Sensors
Final ControlElements
Logic
Solver
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Overview of SIS Industry Standards
Manufacturers &
Suppliers of Devices
IEC61508
Sections 2&3
Manufacturers &
Suppliers of Devices
IEC61508
Sections 2&3
Safety Instrumented
Systems Designers,
Integrators & Users
IEC61511
Safety Instrumented
Systems Designers,
Integrators & Users
IEC61511
Process Sector
Safety Instrumented Systems
Process Sector
Safety Instrumented Systems
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Process Hazards and Risk Review
(IEC 61511 Section 8) Purpose
Identify the possible hazards including fault conditions andreasonable foreseeable misuse
Assessment
Human Injury/loss of life
Loss of Assets
Environmental Impact Typical process/tool
HAZOPS Analysis
Output of HAZOPs will determine required risk reduction - Safety
Integrated Level
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SIL applies only to the entire LOOP / SIF
PFDFCE
PFDPLC
PFDSensor
Loop SIL equals:PFDFCE + PFDSensor +PFDPLC
Individual PFD =Risk that the:
transmitter reads a
false safe flow?
control system
wont shut down
if flow is unsafe?
Valve (FCE) stays
open?
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SIS Design and Engineering
(IEC 61511 Section 11)
Separation of BPCS and SIS
Human Interface System Design
Shut Down and Start-up design
Requirements of Components and Subsystems
Fault Tolerance
Sensor Speed
Proof Testing Intervals
Wiring Practices
System Interface Maintenance
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Other Considerations for Optimizing Safety Consider real-world common causefailures:
Performance (even with redundancy)
Practices (selection, installation, maintenance)
Hardware/sensor/interface failures
Select devices with best performance
Installed performance under real-world conditions
Dynamic response to match application
Experience minimizes common causefailures Has the vendor field-proven this device?
Has the user site-proven this device?
Is the user familiar with this device?
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What is the Future Direction ?
Certified
PIU
Certified
PIU
Today 2007
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Limitations to traditional testing methods
Panels:
Expensive, up to 10-15K per panel (not including labor cost/hr.)
Test procedures are complex Labor-intensive testing
Solenoid Pulsing
Doesnt Validate or Test Valve Movement; Only tests the solenoiditself
Coil burnout due to increased cycling
increased risk to process disruption
By-Pass valves
Testing is expensive and time consuming; Testing becomes
infrequent
Cost of by-pass deters economic feasibility for valves in larger sizes
Piping and space
100% diagnostic coverage and can not be replaced by partial stroke
technology
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Limitations to traditional testing methods
Solenoids w/ Limit Switches
No validation testing on Limit Switches (test is only as reliable as
the limit switches) Can take you to spurious trip if coil does not energize in
time(burnout)?
No ability to collect friction data or valve stickage(no
diagnostics) Calibration/Set up for this solution is expensive and time
consuming
Manual Interlock or J ammer device
Has the jammer been removed? Is the FCE available? No data or validation
manual and labor-intensive testing
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Summary of Savings
Elimination of By-Pass Valve, Piping, Wiring
4Cooper-Cameron Full-Bore API rated / Bettis / Solenoid / Limit Switch
Assembly Cost: $5000 Estimated Piping & Wiring Savings: $750
Estimated Total CAPEX savings: $5750
Elimination of Full Stroke Testing & By-Pass Valve Procedures over3 year run-time
Field Technician Hours saved: 10 hrs X $60/hr = $600
Administrative/Procedural safety engineering: 10 hrs X $90/hr = $900
check-in/check-out, operations validation, etc
Estimated Total Test savings: $1500
Total Savings due to Implementation of Partial Stroke Testing andelimination of By-Pass Valve/Procedures
$7400 Savings
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INSTALLATION
***Solenoid valve and FIELDVUE digi tal valve contro ller are powered separately
S
LOGIC SOLVER
SOLENOID VALVE
DVC6000 SERIES DIGITAL
VALVE CONTROLLER
ESD VALVE AND ACTUATOR
EXHAUST
4-20 MA DC
24 VDC
SUPPLY PRESSURETRAVEL FEEDBACK
SEPARATE POWER
SOURCES FOR DIGITAL
VALVE CONTROLLER
AND SOLENOID VALVE
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S
SUPPLY PRESSURE
DVC6000 SERIES DIGITAL
VALVE CONTROLLER
LINE
CONDITIONER
24 VDC
LOW POWER
SOLENOID VALVE
ESD VALVE AND ACTUATOR
EXHAUST
TRAVEL FEEDBACK
SINGLE POWER SOURCE
FOR BOTH THE DIGITAL
VALVE CONTROLLER AND
SOLENOID VALVE
LOGIC SOLVER
INSTALLATIONINSTALLATION
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SUPPLY PRESSURE
DVC6000 SERIES DIGITAL
VALVE CONTROLLER
LINE
CONDITIONER
24 VDC
ESD VALVE AND ACTUATOR
TRAVEL FEEDBACK
24 VOLT DC POWER
SOURCE
LOGIC SOLVER
INSTALLATIONINSTALLATION
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Push
Button
Push
Button
RS485
MAINTENANCE
ValveLink WorkStation
DCS
Operator WorkStation
MODBUS
INSTALLATIONINSTALLATION
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Trip Protection
Partial Stroke Travel
Min Pressure
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Future
Simple, Flexible, Local or Remote On Line Test -Improved PFD
Improved Diagnostics - Predictive Maintenance-Increased system Availability
Safety Defaults
System Audit Documentation - Storage and Comparison Reduced Cost Of Ownership