Optimizing PFP through Risk Based Structural Analysis

Transcription

1 Optimizing PFP through Risk Based Structural Analysis James Loudoun Onder Akinci, Mike Stahl 25 October

2 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

3 What is PFP and When Do We Apply It? 25 October

4 Passive Fire Protection 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. 25 October

5 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

6 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

7 Determination of PFP Requirements Screening Methods: Conservative/High level checks to initially identify issues Element-by-Element Method Conservative Method 25 October

8 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

9 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

10 Identifying Thermal Loading 25 October

11 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

12 Fire and Explosion Analysis Purpose Identify Major Accident Hazards Identify of potential fire and explosion scenarios Assess potential consequences arising from these Fire and Explosion events 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) 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. 25 October

13 Quantitative Risk Assessment (QRA) 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) 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 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? 25 October

14 Fire Events 25 October

15 3D modelling from Phast 25 October

16 Fire Impinged Areas/Durations Associate a heating duration (heat-flux time profile) Identify impinged structural members 25 October

17 Structural Assessment and PFP Optimization 25 October

18 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

19 Example, PFP on Piperack Thermal Loads and Structural Members 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

20 Example, PFP on Piperack Screening method required to PFP entire structure The figures show the optimized PFP scheme (PFP coated members shown in magenta) A B 25 October

21 Example, PFP on Piperack Plastic utilization plots Critical members are PFP d A B 25 October

22 Example, PFP on Piperack Deflections and Strain Plastic Strain Vertical Deflections 25 October

23 Assessment of Vessel Failure under Thermal Load 25 October

24 Thermal Load on Vessel Phase Plots (Propane) Initial 150 kw/m2 Vapor Liquid 250 kw/m2 350 kw/m2 25 October

25 Thermal Load on Vessel Vessel Failure Failure of vessel in less than 6 minutes. 25 October

26 PFP Detailing 25 October

27 Detailing Exposed Top Flange 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. 25 October

28 Detailing Coatback 25 October

29 Detailing Coatback 25 October

30 Thank you, Questions? If you d like to find out more visit: 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