Colin Deddis
Transcript of Colin Deddis
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Relief and Blowdown Systems
Are you sure you can rely on them?
Colin Deddis, June 2013
This document is created for general illustration only and is not intended as a substitute for specialist advice in relation to
any particular situation. All liability is expressly disclaimed.
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Relief and Blowdown Systems
• Relief and blowdown systems as layers ofprotection.
• Relief and blowdown systems’ functionality.
• What can go wrong?
– Overview
– Relief valve provision and set pressure
– Inadequate design capacity
– Liquid accumulation
– Vibration
• Design verification.
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Relief and Blowdown Systems
Process
Design
Critical
Alarms &
Human
Intervention
Emergency
Shutdown &Safety
Instrumented
Functions
Physical
Protection
e.g. Pressure
Relief
Post Release
PhysicalProtection
e.g. Blowdown
EmergencyResponse
HA
Z
A
R
D
C
O
N
S
E
Q U
E
N
C
E
Basic
Process
Control
TOP EVENT
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Relief and Blowdown Systems- Functionality
HP Flare Drum
Process systems
Relief
valves
Blowdown
valves
Manual
valves
Rupture
disks
Control
valves
High pressure “wet” flare system
High pressure “cold” flare system
LP Flare Drum
Low pressure flare system
Liquids to process system
Liquids to process systemor LP Flare Drum
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Relief and Blowdown Systems - Functionality
Emergency SourcesRelief devices
Depressurisation
Operational SourcesStart-up/shutdown
Process upsets
Maintenance vents
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Relief System Incidents (70 examples)The Institute of Petroleum Guidelines for the Safe and Optimum Design of Hydrocarbon Pressure Relief and Blowdown Systems. 1999
Pressure build-up/
chokes
Vibration
Slugging/hydraulic
hammer
Reverse flow
Incompatible fluids
HP/LP interfaces
Materials of
construction
Capacity of flareVent ignitionPurge ratesJet reaction forces
Liquid hold-up/
flare drum sizing
Design specification
Installation/
maintenance
Operation
Control and
instrumentation
Layout and drainage
Relief valve provision,
sizing and set pressure
Management of change
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Pressure Relief Devices PerformanceInspecting the inspection data, TCE , December 2011/January 2012, Flower & Jones
% Set Pressure Number of Valves % Valves
130% 253 3.6
Test data for ~7,000 operational relief valves period 2000 - 2008
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Relief System Sizing Basis
• Flare sized for full flow relief from single train
• Export route can be common for both trains
• Simultaneous blocked outlet of both trains discounted on basis of:
• segregated air supplies to SDV-001 and SDV-002 &
• air accumulators on each valve with single check valves in the supply line
SDV-001
SDV-002
To export
To export
Train 1
Train 2
To flare
To flare
Full flow reliefBlocked outlet
Full flow relief
Blocked outlet
FC
FC
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Actual air supply to SDVs
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Liquid Accumulation/Slugging
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Vibration
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Complex Failures
PAH
gas
SWS
SWR
Heat Exch.LAH ESD
ESDV
Closeddrain
HP Flare
Drum
LP flare
drum
Over-board
ESDV
disc failure
no alarm
tell-tail blocked?water
enters
drum
does not
trip
seawater
pumps
not tightshut-off fills fills
overfills
no level
>LAH
press =
4 barg(no alarm)
closed
What happened?
liquid @+40m
Source: HSE Safety Alert 01/2008
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STHE Overpressure Protection – the “problem”
Two major hazards associated with bursting disk failures:
• Impairment of relief system – liquid inflow & overfill.
• Incident escalation - reverse rupture leads to uncontrolledhydrocarbon release from systems connected to the relief system.
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STHE Overpressure Protection – the “problem”
• Increased use of bursting disks to protect STHEs over past 10 to 15years
• Estimated frequency of guillotine tube rupture
– 0.0009 per unit per year (~1 per 1,100 years)[1]
• Frequency of bursting disk failures protecting STHEs
– 7 incidents in 13 years (~50 exchangers)
– 0.011 per unit per year (~1 per 90 years)[2]
• Future growth in numbers of high pressure STHEs requiring
overpressure protection
• Has the balance of risk shifted?
1. IP Guidelines for the Design and Safe Operation of Shell & Tube Heat Exchangers to Withstand the Impact of Tube Failure, Aug 2000
2. Estimate based on incident details collated by Energy Institute JIP
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Relief Systems Design Verification Process
Agree Scope of Work
Data Gathering
Design Verification
Competency Assessment
Presentation of Findings and Recommendations
Agreement of Actions and Closeout Priorities
Disposal SystemDesign
Flare Capacity
Liquids Handling
Design
Specification
HP/LP Interfaces
Management of
Change
Relief Device
Selection
Relief Load
Relief Device Inlet
Piping
Design &
Construction
SIL & LOPA AnalysisFlare Stack / Vents /
Headers & Tail Pipes
Emergency Shutdown
Purge Rates Materials Selection
Control &
Instrumentation
Overpressure
Protection
Flare Radiation
Emergency
depressurisation
Operation
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Relief System Design Verification
Categorisation of Findings
Pressure build-
up/ chokes8%
Vibration3%
Slugging/hydraulichammer
2%Reverse flow
3%
Incompatible fluids4%
HP/LP interfaces2%
Materials ofconstruction
6%
Capacity of flare3%
Vent ignition1%
Purge rates3%
Jet reaction forces0%
Liquid hold-up/flare drumsizing 5%
Design specification19%
Installation/maintenance2%
Operation1%
Control andinstrumentation
6%
Layout and drainage1%
Relief valve provision,sizing and set pressure
22%
Management ofchanges, modifications
and upgrades10%
15 Reviews, 551 Findings
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Relief Device – Design Verification
70.3%
29.4%
0.3%
313 Relief Devices - Findings
Relief Valves Adequately Sized
Governing Relief Case Incorrect
No Relief Provision
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64%
36%
Inlet Line Loss Checks
Inlet line Losses Acceptable
Inlet losses unacceptable(>3% of set pressure)
Relief Device – Design Verification
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Summary
• Relief and blowdown systems are complex pressure systems
• Design constraints can be violated; impairing the relief and blowdownsystems.
• Design verification can be successfully deployed to determine
system robustness prior to operation.
• Design verification findings indicate some systemic design flaws.
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Thank-you
Any questions?
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References
1. The Institute of Petroleum Guidelines for the Safe and Optimum Design of
Hydrocarbon Pressure Relief and Blowdown Systems, 1999
2. IP Guidelines for the Design and Safe Operation of Shell & Tube Heat
Exchangers to Withstand the Impact of Tube Failure, Aug 2000
3. Inspecting the inspection data, TCE , December 2011/January 2012, Flower
& Jones
4. HSE Safety Alert 01/2008 Flare system impaired by cooling water loss
through bursting disc failure on an intercooler heat exchanger.