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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:

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

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