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폭발해석 결과의 설계 반영폭발해석 결과의 설계 반영

20082008년년 1212월월 1111일일

현대중공업㈜현대중공업㈜

BHN 폭발/화재 (2005.7)

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Piper Alpha 폭발/화재 (1988.6)

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165 people killed

Lord Cullen Survey

Explosion

Explosion

Combustion of a premixed gas cloud containing fuel and oxidizer that can result in a rapid rise in pressure.

Explosion occurs at a gas cloud with a concentration between the UFL and LFL.

Deflagration / Detonation

Combustion wave propagating at subsonic/supersonic velocity

Overpressure of # mbar ~ # bar / upto 20 bar

Definition of typical parameters (time-pressure history)

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Explosion Loads

Overpressure loads: result from increases in pressure due to expanding combustion products

Drag loads: result from the flow of air, gases, and combustion products past an object.

Shock loads: a very small duration compared to the whole blast.

Global reaction loads: result from differential pressure loading, have same time scale as the pressure variation.

Explosion Load Parameters:

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Gas Cloud Size, Ignition Location, Congestion, Confinement, Ventilation

Explosion Design Loads

Main & Secondary Structural Members: Overpressure & Drag load

Piping or Equipment (Support): Drag Load, Pressure Difference & deflection /acceleration

Blast Wall, Deck & Panel: Overpressure

Blast Loads

Drag Load: ACLoadDynamicAvCF DDD ⋅⋅=⋅⋅⋅= 2

21 ρ

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Pressure Difference Load:

where, PDF = Pressure Distribution Factor

PDFAreaWindagePFPD ⋅⋅Δ=

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Blast Load for Piping & Vessels

Large obstacles (Dia. > 2 m): The force is determined from the Differential Pressure

Force,

For cylinders, PDF = 2/π.

)FactoronDistributiPressure(PDFAreaWindagePFPD ⋅⋅Δ=

Intermediate obstacles (0.3 m < Dia. < 2 m): Both Drag and Pressure DifferenceLoads are significant in the flow direction.

Small obstacles (Dia. < 0.3 m): Drag loads dominate for obstacles in particular in regions of high gas velocity near vents.

Drag Load, ACACvF DDD ⋅⋅=⋅⋅⋅⋅= PressureDynamic21 2ρ

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If the general level of Dynamic Pressure loads is not known then it is acceptable to take a load equal to 1/3 of the overpressure at the location for the DLB load case.

Direct Load Measurement (DLM) Method

DLM for Piping & Vessels

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Interaction Flow - Explosion

Layout

l d l

Safety Structural

3D Model (Layout)

Structural Layout1

Explosion Modeling1 (CFD)

Response Analysis*

Structural Details/Layout2

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Implement CAD Model

Explosion Modeling2 (CFD)

* For Structure, Blast Wall, Decks, Vessels, Equipment, Piping/Support, etc.

Explosion Design Loads

Design Principles

Deterministic Design

Probabilistic Design

Risk Based Design (RBD)Risk Based Design (RBD)

Calculation of Explosion Loads

Empirical Models - Experimental data

Phenomenological Methods - Physical processes & experimental

work

Numerical Models - Computational Fluid Dynamics (CFD)

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p y ( )

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Explosion Risk Analysis

Probabilistic Analysis

Ventilation Simulation

Geometry 3D Model

Explosion Simulation

Dispersion Simulation

Ventilation Conditions

l

Ignition Intensity

Weather Data

L k

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Explosion Load Explosion Probability

Explosion Risk (Frequency vs. O.P curves)

Leak Data

Input Data

Geometry

CAD geometry (3D)

Anticipated Congestion Model (ACM)

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Ventilation Simulation

Calculate the internal ventilation distribution - combinations of wind direction/speed (typically 12 simulations).

Establish the ventilation conditions in the areas of concern

Air Change per Hour (ACH)

Flow Pattern

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Dispersion Simulation

Calculate an equivalent stoichiometric cloud size distribution

Combinations of variables: 100-200 simulations

Leak locations

Leak directions

Leak rates

Inventories

Ventilation conditions

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Explosion Simulation

Calculate the explosion loads and impulses from the different cloud sizes

Necessary data to establish the probability of exceedance curve for explosion risk: 70 – 150 simulations.

Cloud sizes

Cloud locations

Ignition locations

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Explosion Simulation

Ignition Location Frequency of Exceedance Curve

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Criticality of SCEs

Safety Critical Elements (SCEs): any component part of structure, equipment, plant or system whose failure could cause a major accident events (MAEs).

Criticality 1: Elements which must resist to an “extreme event”. Items whose failure due to gas explosion would lead to major/catastrophic fire escalation or major impairment of escape possibilities.

Performance Standard – These items must not fail during the Ductility Level Blast (DLB) or Strength Level Blast (SLB), ductile response of the support structure is allowed during the DLB.

Example:

Primary structures,

Blast Wall

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Blast Wall,

critical equipment (Separator, Risers, ESDVs, LQ/Muster Shelter, Flare Header, FW ringmain, etc.)

Criticality of SCEs

Criticality 2: Elements which must resist to a “low-level event”. Items whose failure due to gas explosion would contribute to significant fire escalation locallybut not of such magnitude as to be outside the fire design scenario.

Performance Standard – These items must have no functional significance in an explosion event and these items and their supports must respond elasticallyexplosion event and these items and their supports must respond elastically under the SLB. Equipment and pipes designed for a less severe but non-the-less substantial explosion event.

Example:

Secondary structures,

HC containing equipment/supports,

HC piping,

SDVs

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SDVs,

2nd FW network/deluge skid,

Piperack,

E&I buildings, etc.

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Criticality of SCEs

Criticality 3: Equipment not designed or assessed for explosion. Items whose failure in an explosion event would contribute to minors effects.

Performance standard – These items have no functional significance in an explosion event and must not become or generate projectiles.

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Blast Load Levels

Ductility Level Blast (DLB):

Design level blast load

A low-probability, high-consequence event: 10-4/yr frequency of exceedance

Extreme design event, progressive collapse analysisg , p g p y

Ductility Ratio (μ),

Strength Level Blast (SLB):

Reduced blast load

A higher-probability, lower-consequence event

Elastic response

F t d i t

limitelasticatdeflectiony,deflectiontotalδwhere,, el ===elyδμ

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Frequent design event

Equivalent Static Load,

γ : Dynamic Amplification Factor (DAF),

If computations are not available for overpressure for SLB, then 1/3 of the blast loading from the DLB may be used for SLB.

peakstatic LL ⋅= γ

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Effect of Loading Regime

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Blast Load Levels

Ductility Ration (μ): limitelasticatdeflectiony,deflectiontotalδwhere,, el ===elyδμ

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References

[1] Jerzy Czujko, Design of Offshore Facilities to Resist Gas Explosion Hazard Engineering Handbook, 1st Ed. 2001

[2] UKOOA, Fire and Explosion Guidance, Part 1: Avoidance and Mitigation of Explosion, Issue 1, Oct. 2003

[3] API, RP 2FB, Recommended Practice for the Design of Offshore Facilities against Fire and Blast Loading, 1st Ed., Apr. 2006

[4] FABIG, Technical Note on Protection of Piping Systems subject to Fires and Explosions, Technical Note 8

[5] NORSOK, S-013, Risk and Emergency Preparedness Analysis, Rev. 2, Sept. 2001

[6] Gexcon, Explosion Modeling Reports, 2008

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