Optimizing PFP through Risk Based Structural AnalysisJames Loudoun
Onder Akinci, Mike Stahl
25 October 2017 1
Agenda
• What is PFP?
• Approaches to Identifying PFP Application
• Utilizing Existing Safety Studies to identify Time Dependent Thermal Loading
• Optimizing PFP using Structural Analysis
25 October 2017 2
What is PFP and When Do We Apply It?
25 October 2017 3
Passive Fire Protection
25 October 2017 4
Passive Fire Protection has three main aims:
• To prevent load-bearing structure reaching elevated temperatures, where the steel structure may become impaired.
• To protect process vessels and piping (no disproportionate escalation).
• To prevent heat transfer through walls into habitable spaces by limiting the inner wall temperatures.
PFP Criteria Definition
• Protected element: barrier or load-bearing
• Type of fire and associated heat flux
• Required duration of protection effectiveness
• Resistance to environment
– Installation: transport, erection
– Operating: vibration, mechanical, chemical, ageing, weather, abrasion, erosion, hosing, impact (non-accidental), temperature (high: flare, low: frost)
– Accidental: thermal shock, blast, projectiles / missiles
25 October 2017 5
Determination of PFP Requirements
Prescriptive Method
• Code/Standard based
• Systematic Method (not optimized, and sometimes conservative)
• May not be conservative (e.g. top flange exposed etc.)
25 October 2017 6
Determination of PFP Requirements
Screening Methods:
• Conservative/High level checks to initially identify issues
• Element-by-Element Method
• Conservative Method
25 October 2017 7
Determination of PFP Requirements
Strength Level Analysis:
• Based on global structure
• Employs Linear elastic methods combined with checks of utilization with respect to a critical temperature
• Generally applied offshore
• Less Conservative
25 October 2017 8
Structural Response
• Determine a structure’s behavior given it is subjected to fire loading.
• Identify Global Collapse Fire/Load Limits using Finite Element Analysis (FEA)
• Identify the integrity of structural supports for safety critical elements
• Identify potential for escalation
• Identify PFP and other mitigation requirements
25 October 2017 9
Identifying Thermal Loading
25 October 2017 10
Identifying Thermal Loading
• First Step in PFP optimization is identification of the thermal loads.
• This builds on existing safety studies routinely produced as part of design process:
– Fire and Explosion Analysis
– Quantitative Risk Assessment
25 October 2017 11
Fire and Explosion Analysis
25 October 2017 12
Value
• Specification of minimum fire/ explosion ratings for buildings and/or critical structures
• Assist in optimization of fire and explosion protection and design
• Identify the potential need for Additional Analysis (QRA, FEA, Computational Fluid Dynamics (CFD) analysis)
Purpose
• Identify Major Accident Hazards
• Identify of potential fire and explosion scenarios
• Assess potential consequences arising from these Fire and Explosion events
Data Requirements
General arrangements and Layouts, P&IDs, PFDs, Heat and Material Balance, Blowdown and Isolation Data, Cause and Effects, Inputs from HAZOP & HAZID for outlier events, Structural analysis to determine survivability criteria.
Quantitative Risk Assessment (QRA)
25 October 2017 13
Value
• Determine current, future, and sensitivities to the facility risk profile
• Determine how to address any recommendations for changes to the layout or the process in order to reduce the facility risk (Assess these recommendations -Goal)
• Identify high risk equipment, process, activities
• Influence the design – reduce critical elements
• Inherently safe design
Purpose
• Evaluate the current state of the design
• Identification and classification of all hazards (hydrocarbon, non-process, environmental, transportation, etc.)
• Identify potential cases of structural and process impairment (Offshore)
• Classify Individual Risk, Facility Risk, Societal Risk (Risk Profile)
Data Requirements
Population data and distribution across the site, potential external hazards (HAZOP, HAZID), operating philosophy, safety design measures, FEA results, General Arrangements and layouts, Heat and Material Balance, Blowdown and isolation data, ESD philosophy, Critical outlying questions?
Fire Events
25 October 2017 14
3D modelling from Phast
25 October 2017 15
Fire Impinged Areas/Durations
25 October 2017 16
Identify impinged structural members
Associate a heating duration (heat-flux time profile)
Structural Assessment and PFP Optimization
25 October 2017 17
Overview
• Establish the minimum PFP coating requirements while satisfying the following criteria:
- No global collapse,
- No disproportionate escalation
• Convert linear structural model e.g. STAAD to NLFEA model
• Heat flux applied to the entire structure to determine failure time
• Develop initial PFP scheme based on experience and failure time
• Iterate analysis until PFP minimized and criteria is met
25 October 2017 18
Example, PFP on Piperack
• Generated detailed Abaqus FEA model• PFP’d members and pipes temp limited to
400 °C• Non-PFP’d members were removed and
their load was redistributed to protected members
• PFP’d members are highlighted in red
25 October 2017 19
Thermal Loads and Structural Members
Example, PFP on Piperack
• Screening method required to PFP entire structure
• The figures show the optimized PFP scheme (PFP coated members shown in magenta)
25 October 2017 20
A B
Example, PFP on Piperack
• Plastic utilization plots
• Critical members are PFP’d
25 October 201721
A B
Example, PFP on Piperack
25 October 2017 22
Deflections and Strain
Vertical DeflectionsPlastic Strain
Assessment of Vessel Failure under Thermal Load
25 October 2017 23
Thermal Load on Vessel
25 October 2017 24
Phase Plots (Propane)150 kW/m2
250 kW/m2 350 kW/m2
Initial
LiquidVapor
Thermal Load on Vessel
25 October 2017 25
Vessel Failure
Failure of vessel in less than 6 minutes.
PFP Detailing
25 October 2017 26
• PFP termination on top flange of lateral members. The exposed top flange causes the section stiffness and capacity to decrease.
• To be conservative, the top flange is reduced from the section in the extreme condition analysis.
Detailing
25 October 2017 27
Exposed Top Flange
Detailing
25 October 2017 28
Coatback
Detailing
25 October 2017 29
Coatback
Thank you, Questions?
If you’d like to find out more visit:www.atkinsglobal.com
© Atkins Limited except where stated otherwise.
The Atkins logo, ‘Carbon Critical Design’ and the strapline‘Plan Design Enable’ are trademarks of Atkins Limited.
25 October 2017 30