Design Explosion Load Specification for large floating facilities L. Paris, A. Dubois Process & Technologies Division, Technip France

Transcription

1 Design Explosion Load Specification for large floating facilities L. Paris, A. Dubois Process & Technologies Division, Technip France

2 Contents 1. Introduction 2. Derivation of effective DELs from «raw» results 3. Explosion loads for SCEs 4. Conclusion and way forward 2

3 1. Introduction 3

4 Introduction The purpose of the explosion analysis is to: Evaluate the contribution from explosion to the overall risk picture. Specify the accidental loads for the proper design of the installation according to the explosion mitigation strategy. Explosion analysis (especially with CFD) produces a large amount of data Results shall be properly interpretated in order to provide useful inputs to engineering disciplines and vendors 4

5 Other disciplines Safety discipline A multi-disciplinary work process Explosion Mitigation Strategy (from safety objectives) Targets (Systems) Performance Criteria Explosion (Risk) analysis Design Explosion Loads specification Explosion Response 5

6 A system oriented work process Main Safety Functions Preventing Escalation Safety Critical Systems Flare Safety Critical Elements Flare header, Drum, Structures Purpose of the design process shall be fully understood by all to ensure consistency. 6

7 Performance criteria Different levels according to SCEs type Examples of SCEs Resistance (Stability) Integrity (Containment) Operability Primary Structures Buildings (Refuge, CCR) Local loading (integrity) Large HC, cryogenic or pressurized vessels Piping - Flare header - Fire Water ring main Doors, safety valves Global loading (Resistance) Dedicated explosion load cases shall be defined in order to justify each requirement (Local vs global loading) 7

8 Example: the flare system (SCS) Keep a global view of the performance criteria for the whole system, not only individual SCEs. 8

9 2. Derivation of DELs from raw results 9

10 Derivation of DELs from raw results Specific items (Type, geometry, Location) Explosion (Risk) analysis Design Explosion Loads specification Results at specific target location Evaluation of missing blast parameters Derivation of effective explosion loads considering geometry Performance Criteria Local loading Global loading Explosion Response 10

11 Local loading for integrity check Interaction of blast waves with obstacles Each face of an obstacle will experience a different blast load depending on the orientation of the incoming blast wave. 11

12 Local loading for integrity check (cont.) Simple rule-sets for projects Small obstacles (D < 0.3 m) : Stagnation pressure P stag = P so + P dyn Large obstacles (D > 3 m) : Reflected overpressure P ref Medium obstacles (0.3 < D < 3 m) : Combination of P stag and P ref with respect to transverse size of obstacle (clearing time) Coarse approach. but what is the alternative today? Only tests trials may provide enhanced answers. 12

13 Global loading for stability check Components of resultant forces Form Drag Direct Load Measurement Global loading is considered as a combination of Form Drag and Differential Pressure (from DLM). 13

14 Global loading for stability check (cont.) Direct Load Measurement (DLM) method Accuracy depends on ratio mesh/target size Time consuming if number of targets is high Simplied DLM based on: Mean overpressure, dynamic pressure in area Reflection coefficients Wave speed Etc. Both includes Pressure Distribution Factor (PDF) DLM from CFD Results considered not relevant for medium size obstacles (~1-2 m) as grid size is usually 1 m in FLACS 14

15 Global loading for stability check (cont.) Simple rule-sets for projects Small obstacles (D < 0.3 m) : «Form Drag» based on dynamic pressure (P dyn ) and drag coefficient (C d ). Large obstacles (D > 3 m) : Direct Load Measurement (DLM) or simplified DLM to measure Pressure difference (P diff ). Medium obstacles (0.3 < D < 3 m) : Combination of Form Drag and DLM or simplified DLM. 15

16 3. Explosion loads for SCEs 16

17 Raw results The required inputs at a given frequency (from FLACS ) are: Local/Global Panel overpressure for walls / plated decks Mean/Max overpressure in module (NPMAX) over all CVs (30000) Mean/Max dynamic pressure in module (NDMAX) over all CVs Computation of effective local/global Design Explosion Load on each critical item based on: Location within the module (especially for drag) Size, geometrical shape Explosion load cases in the 3 directions (considering possible ignition locations) for global loading 17

18 Geometrical classification of SCEs Each individual SCE to be associated with one of 5 categories of shapes Shape Template Examples Beams and Pipes (BP) Planes (PLAN) - Pipework network - Frame structure with cylindrical cross section - Frame structure with other cross section - Decks - Blast wall Boxes (BOX) Horizontal cylinders (HCYL) Vertical cylinders (VCYL) - Buildings - Cold boxes, enclosures - Plate heat exchanger - Drums, bullets - Shell and tube heat exchanger - Column, Vertical drum - Stack - Crane pedestal Complex SCEs : Break-down into simple shapes 18

19 The facility is broken down into DEL sheets 19

20 DEL sheets are containing the required inputs A table summarizes MSF, SCEs, owners and associated sheets Target Identification Main Safety Function (MSF) System Items Tag Location Discipline Verification Sheet Sheet Rev Performance criteria Preventing escalation EDP System (Flare) HP Flare KO Drum V-01 Area 1 Equipment HCYL1 LP Flare KO Drum V-02 Area 1 Equipment HCYL2 Blow Down valves Area 2 Instrumentation BP1 Area 1 Piping BP1 Flare Header and associated piping Area 2 Piping BP2 Explosion Load cases (Local/Global) Piperack Area 1 Structures BP1 Area 2 Structures BP2 Flare stack Area 1 Structures BP2 Loads combinations Flexible (each sheet may be used several times), high traceability, but time consuming activity. 20

21 Examples Building (e.g. Temporary Refuge) Integrity : Individual components (walls, roof, doors) Local loading from BOX DAL sheet. Stability : Foundations (global check against sliding, overturning) Global loading from BOX DAL Sheet. Local effects Global effect (resultant) Structure support Structure support 2 sets of design explosion loads (P local, P global ) shall be defined. Each load could be transient or equivalent static. 21

22 Examples (cont.) Equipment (Column) Integrity of vessel wall, skirt Local loading from VCYL DAL sheet. Stability against sliding, overturning Global loading from VCYL DAL sheet. Integrity of nozzles based on drag loads (P drag ) applied on connected piping Global loading from BP DAL sheet. 3 sets of design explosion loads (P local, P global, P piping ) shall be defined. Each load could be transient or equivalent static. 22

23 4. Conclusion and way forward 23

24 Conclusion The Design Explosion Load Specification is issued in order to: Ensure a clear and efficient interface between the safety discipline and other engineering disciplines. Provide only the necessary data for the verification of SCEs to blast. Avoid misinterpretation regarding the definition of effective loads with respect to performance criteria. Issue of a new Technical guidance from FABIG expected soon Interpretation requires both safety & structural expertise in order to provide useful explosion load cases to disciplines. 24

25 Way forward Direct coupling between CFD and NLFEA : Calculation of explosion response and damage exceedance frequency. No more DAL Specification required 1 CFD with frequency 1 NLFEA with frequency Some challenges to overcome Huge computational power : Compliance with engineering projects Geometry completeness : Ok for brownfield, Not for new projects Damage acceptance criteria for global collapse??? 25

26 Thank you