10 Safety Valves
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Transcript of 10 Safety Valves
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Western Regional Boiler
Association Annual Meeting
March 17, 2010
Steve Teeter- Bay Valve Service
Safety Valves
Operation, Handling and CodeCompliance
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Mechanical Device designed toprotect against an over pressure
condition. Last Line of Defense
What is a SAFETY VALVE?
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Protects Life and Property bymaintaining control of safe working
pressures of related piping andequipment.
What does a Pressure Relief
Valve do?
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Set Pressure: Gauge pressure at the valve inlet
for which the safety valve has been set to relieve atTolerance:Section 1: 15-70 psi + or 2 psi
71-300 psi + or 3 % of Set
301-1000 psi + or 10 psi1001 and up + or 1% of SetSection 8: 15-70 psi + or 2 psi
71 psi and up + or 3 % of Set
Operating Pressure: Gauge pressure to which theprocess or system normally operates in service,Not to exceed 90% of valves set pressure for aspring operated valve.
Definitions:
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Issues affecting Capacity Superimposed Back pressure:
Constant and Variable
Constant: Fixed Value and existscontinuously prior to and duringvalve opening
Variable: Varies over a range andexists prior to and during valveopening
Definitions:
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Blow down: Difference between set pressure and
reseating pressure of a pressure relief valveexpressed as a percentage of the set pressure
Section 1: 15-67 psi 4% of Set Pressure
68 to 250 psi 6% of Set Pressure
251 to 375 psi 15 psi 376 and above 4 % of Set Pressure
Section 8: To Manufacturers Specs (5-10% of Set
Pressure approximate) Maximum Allowable Working Pressure (MAWP)
Maximum gauge pressure permissible in a vesselat a designated temperature
Definitions:
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Overpressure: Pressure increase overthe set pressure of the primaryrelieving device. Highest Pressure atwhich the primary safety relief valve isset to open.
Definitions:
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LIFT
The disc rise in a Safety Relief
Valve
Typically 1/4 of the bore diameterat full capacity
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A spring exerts a closing force on avalve disc.
The spring force has to be largeenough to hold the valve disc closedat normal operating pressure and
sized correctly to open when thepressure exceeds the set pressure ofthe safety Valve.
How does a Safety Valve work?
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The set pressure is made byadjusting a compression screwabove the spring.
The blowdown of the safety valvemust be adjusted as well.
This is accomplished by using an
upper adjusting and lower adjustingcompression ring to achieve desiredblowdown specifications.
How does a Safety Valve work?
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Lift Lever Assembly
Adjusting Screw
Spring Assembly
Spindle
Guide
Disc Holder
Disc
Adjusting Rings
Nozzle
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SAFETY VALVES
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WHY PRESSURE RELIEFDEVICES?
WHAT BACKS UP A SAFETY
VALVE ??
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TENNIS SHOES ?!!?
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What is
Good Operating Condition??
What must be done to maintain a
Safety Valve in good workingorder?
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Hey we have a steam leak!
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ASME/National Board CodeStamped Valves
Code Valves must be identified by amanufacturers metal tag with applicable NationalBoard ASME symbol stamps on the tag attachedto each valve.
Without the manufacturers tag the valve should
not be in service.
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ASME CODE
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ASME CODESYNOPSIS
ASME Section I - Power Boilers
Set Pressure Tolerances
Blowdown Requirements
System Overpressure Allowances No Block Valves
Safety Valves Only
Valves Calibrated (set) on Steam Lifting Lever Required
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NBIC A07 2.5.8
Recommended Inspection and TestFrequencies for Pressure Relief
Devices a) Power Boilers
1) Pressure less than 400 psig: ManualCheck every 6 months; Pressure test
annually to verify nameplate setpressure or as determined by operatingexperience as verified by testing history.
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NBIC A07 2.5.8
2) Pressure greater than 400 psig:
Pressure test to verify nameplate setpressure every 3 years or as
determined by operating experience as
verified by testing history
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NBIC A07 2.5.8
3) Pressure tests should be performed
prior to bringing the boiler down forplanned internal inspection so neededrepairs or adjustments can be made
while boiler is down.
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NBIC A07 2.5.8
Note: When any boiler experiences
an overpressure condition such that
the safety or safety relief valvesactuate, the valves should be
inspected for seat leakage and
other damage as soon as possibleand any deficiencies corrected.
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NBIC A07 2.5.8
3) Service Records with test
results should be maintained for
all overpressure protectiondevices.
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For a Safety Valve to be Safe it
must:
Relieve at the proper setpressure
Relieve the required capacity
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Means to Determine a SafetyValve will relieve at the Proper
Set Pressure1. Lift the Valve Lever (High Risk)
2. Individual Safeties and Over-pressuringthe Boiler (Live Set) (High Risk)
3. Lift Assist Device (EVT) (Low Risk)
4. Removing Safety Valve and having ittested at a Certified Shop (No Risk)
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Means to Actuate a Safety Valve
1. Lift the Valve Lever
Must be done at a minimum of 75% ofoperating pressure
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Means to Actuate a Safety Valve
2. Live Set on the Boiler
Exercising the Valves by overpressuringthe relief valves above Set Pressure
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Consolidated EVT II
Portable Diagnostic Tool
In-Line Pressure ReliefValve Testing
ASME Code Approved
Records ValvePerformance Signatures
Data Retention &Reports
Detect PerformanceIssues
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Means of Determining a Safety
Valve can Relieve Remove Valve and bring to Valve Repair
Shop for Verification
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National Board VR Certification
Provides the industry the means toidentify organizations that havedemonstrated an adequate quality
system for the repair of Safety Valves The goal is to improve the caliber of
repairs for ASME capacity certifiedsafety and safety relief valves tocontinue to protect boilers and systemsfrom catastrophic overpressures
VR Repair A thori ation
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Repaired Valves Meet ApplicableASME Standards for New Valves
Stringent Quality Control Program
Technician Training and EvaluationProcess
Documentation & Record Keeping
Steam, Air, Water Testing
Annual Audits
VR Repair AuthorizationProgram
NATIONAL BOARD VR CERTIFICATE
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NATIONAL BOARD VR CERTIFICATE
H dli f S f t R li f V l
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Handling of Safety Relief Valves
1. Field Hydrostatic Testing of your Boiler
Importance of gagging safety relief valves toprevent damage
Should be gagged by a certified technician
If Safety Valves are not gagged they should beremoved
2. Storage: Flanged Safety Valves should bebolted to a pallet in vertical orientation tomaintain spindle and disc alignment
Handling of Safet Relief Val es
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Handling of Safety Relief Valves
3. Wiring of Lift Levers
Valves have lift levers wired to the body toprevent exercising the valve by picking it upby the handle or rigging it by the handle
Valves will function correctly with lift lever wiredto the body of the valve, but should beremoved after installation.
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Boiler Non Return Valve
Stop Check Valve versus Boiler NonReturn Valve
Purpose Function
Issues to be aware of
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Questions?
Thank you!