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Path Forward

Introduction

Advantages

Layout & Location

Foundation Types

Mechanical Design Aspects

Stress Analysis

Design Guidelines

Corrosion Protection

Safety Aspects
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Introduction
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What is Mounded Bullet ?
• Mounded LPG Bullets are large, horizontal cylindrical steel vessels used
for storage of pressurized gases (i.e. LPG) at ambient temperature.
• Installed above the highest ground water level and the soil cover
usually protrudes above grade, as an Earth mound, hence the term
“Mounded Storage”.
• Bullets sizes ranges between 3.5 to 7.0 meter diameter and lengths of
35 to 70 meters or more.
• Mounded bullets allow storage of large quantities of LPG - up to 2,000
MT or more in a single location!
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Typical Detail of Mounded Bullet
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BLEVE (Boiling Liquid Expanding Vapour
Explosion)
If a system catches fire due to leakage or there is any fire in the near by
surroundings, the liquid inside the container starts expanding due to heat
radiation. This will lead to rise in internal Pressure continuously and the
container may explode causing huge damage. This can be avoided by
using mounded storage concept.
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Why Mounded Bullets ?
•
Mexico LPG Gas Terminal Incidence : 1600 m 3 LPG was stored after
first BLEVE, Fireball Dia 350m,debris 1.2 km, 500 died, 7000 injured
• Main Causes of Disaster : Close Spacing of Vessels within Plant Populated
Built-Up Area within 300-400m of Plant Orientation Plant/ Layout not
Conducive to good Safety.
•
Conclusion: Avoiding aboveground storage : A BLEVE would not have
occurred & catastrophe could have been avoided: (NEED FOR MOUNDED
STORAGE)
BLEVE (Boiling Liquid Expanding Vapour Explosion)
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Advantages
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Advantages
•
BLEVE (Boiling Liquid Expanding Vapor Explosion) can be totally
avoided.
•
Protection of equipment against.
1.
Heat radiation from a nearby fire
2.
Pressure wave originating from an explosion
3.
Impact of flying objects.
4.
Sabotage
•
It results in reduced site area due to less stringent inter-spacing
requirements.
•
The safety distance to the site boundary can be reduced
considerably.
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Layout & Location
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Layout & Location
Vessels shall be located so that:
· They do not affect, and are not affected by, other nearby underground
structures (e.g. foundations, pipelines, sewers);
· They are not subjected to loads from vehicles;
· They are not affected by other hazards such as power cables and
cathodically protected pipelines.
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Typical Layout of LPG storage vessels
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Safe distances for mounded LPG pressure
Storage vessels
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Foundation Types
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Foundation Types….
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Mechanical Design Aspects
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Design Codes & Standards
•
ASME Sec VIII or PD 5500.
•
EEMUA
(Engineering
Equipment
&
Materials
Users
Association)
Publication No.190:00
•
OISD (Oil Industry Safety Directorate) - 150 : Design & safety
requirements for LPG mounded storage facility
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Material of Construction
Components
MOC
Shell and Heads
SA 516 Gr. 60 / 70
(Impact tested)
SA 537 Cl1
Nozzles necks
SA 333 Gr. 6
Nozzle flanges
SA 350 LF2
External studs / nuts
SA 320 Gr. L7 / SA 194 Gr. 4
Pipe fitting
SA 420 Gr. WPL6
Gaskets
SS 304 SPWD
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Weight of Mound
•
Weight of empty vessel (metal weight)
•
Weight of stored liquid
•
Weight of hydrotest water
•
Internal design pressure
•
Internal vacuum
•
Hydrotest pressure
•
Weight of Mound
q  q0 cos ,
2Qe
q0 
R
Qe = Weight of mound per unit length
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Mound Load on Vessel
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Distribution of Bed Reaction & Mound
Pressure
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Pressure Exerted by Mound
•
Pressure by mound on domed ends
p =C.gs.h
C = Soil pressure coefficients,
h = Depth below top of mound
C depends on slope of mound and movements of domed ends
For mound slope of 30o and end movements  0.02 m:
Cneutral = 0.3, Cactive = 0.2, Cpassive = 1.7
•
Axial frictional loads
Soil friction exerted when the vessel expands or contracts due to
temperature or pressure Friction coefficient of 1.0 may be considered
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Pressure due to uneven support
•
Pressure due to uneven support
Two cases of uneven distribution of soil reaction considered
•
1)
Settlement of mid point wrt two end points
2)
Settlement of ends wrt mid point
Soil reaction pressure
1)
Radially inward soil pressure follows cosine distribution.
2)
Bed angle depends upon preparation of soil bed below vessel.
For properly prepared sand bed, bed angle is 120o
3)
For hydrotest condition, bed angle of 60o-90o may be taken
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Pressure due to uneven support
•
Pressure due to uneven support
1) Horizontal Force = Horz. Seismic coefficient  weight
(loads a, b, f).
2)
Vertical Force = Vert. Seismic coefficient  weight.
(Weight is increased proportionally.)
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Load Combination
Operating
condition
Hydrotest
condition
X
X
Weight of the liquid in the vessel.
X
X
Internal Pressure.
X
X
Loads
Design Cases Empty condition
with vacuum
Dead weight of the vessel.
X
Internal Vacuum.
X
Loads due to the mound
X
X
Loads due to uneven support by the
foundation
X
X
Loads due to variation of the
vessels length
X
X
Loads due to earthquake
X
X
X
Loads due to an external explosion
X
X
X
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Stress Analysis
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Stress Analysis
•
Detail stress analysis using FEM Software Packages
•
Integrated model of vessel, domed end and stiffeners
•
All Possible load combinations (12 load cases) are considered for stress
analysis.
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Stress Analysis
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Stress Analysis
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Stress Analysis
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Stress Analysis
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Stress Analysis
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Settlements in Sand Bed
Sagging Type (Settlement at Mid Span)
Hogging Type (Settlement at Ends)
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Design Guidelines
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Design Guidelines
•
The vessels should be installed at least 0.6 m above the highest ground
water level in a sand foundation of at least 1 m thickness in order to obtain
proper bedding.
•
The foundation of the bullet shall be constructed such that for the
operational lifetime of the bullet, its longitudinal slope shall be in 1 : 200
minimum and 1 : 50 maximum.
•
The thickness of the mound shall be 1 meter minimum.
•
Longitudinal weld seams shall be avoided in the bottom 120 deg.
•
The ratio of distance between internal stiffeners to bullet diameter is in the
order of 1 : 2.
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Design Guidelines…..
•
Minimum 2 no. manholes shall be provided, one at each end of the
bullet.
•
All plates, welds, HAZ shall be impact tested . Impact test temperature
shall be determined as per design code.
•
PWHT shall be carried out for the complete bullet.
•
Radiography shall be full.
•
There are two methods of arranging nozzles :
1) All nozzles except manholes and large size nozzles (liquid inlet)
shall be grouped and shall be installed on a dome and not directly
on the shell.
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Design Guidelines…..
2)
All nozzles except manholes and large size nozzles (liquid inlet) shall
be grouped on the shell. Rectangular box shall be provided around
the grouped nozzles, manholes and large size nozzles . This
construction is called BOX TYPE CONSTRUCTION.
•
Settlement of soil bearing foundation :
1) Immediate settlement shall be limited to 50 mm.
2) Long-term settlement shall be limited to 25 mm.
•
Min. Factor of safety for foundation design is 2.0
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Corrosion Protection
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Corrosion Protection
•
Mound & Foundation are potentially Corrosive Environment
External Coating: glass fibre reinforced bitumen coating/epoxy
/urethane based coating
•
Internal Coating: for refinery services: bottom 90o is coated if
water/H2S ingression in LPG
•
Cathodic Protection: Impressed Current System: NACE RP - 0169
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Safety Aspects
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Protection system for situations in which filling/delivery rates are
based on alarms and corrective actions are manually implemented
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Suggested Alarm Priorities
SUGGESTED ALARM PRIORITIES
Priority
Alarm
Record
Low
High
Suggested Action
Emergency
PIA/HH
PIA/LL
X
X
X
X
Stop Supply
Stop Offtake
LA/HH
X
X
Stop Supply
LIA/HH
LIA/H
LIA/L
LIA/LL
X
X
X
X
HZ
X
X
Stop Supply and Offtake
XA
X
X
Call-out Instrument Maintenance
X
Stop Supply
Re-route Supply
Re-route Offtake
Stop Offtake
X
X
X
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Protection system for situations in which filling/delivery rates
are high and corrective actions are automatically implemented
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Suggested Alarm Priorities
SUGGESTED ALARM PRIORITIES
Priority
Alarm
Record
Low
High
Emergency
X
X
Suggested Action
PIZA/HH
PIZA/LL
X
X
PIA/H
PIA/L
X
X
LZA/HH
X
LIA/H
LIA/L
LISA/LL
X
X
X
HZ
X
X
Stop Supply and Offtake
XA
X
X
Call-out Instrument Maintenance
X
X
Trip Supply Valve
Trip Offtake Valve
Re-route Supply
Re-route Offtake
X
X
X
Trip Supply Valve
Re-route Supply
Re-route Offtake
Trip Pump
X
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Photographs
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Photographs
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Thank You
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