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7/15/2019 Ppt Emergency for Internal Pressure - Morovich
http://slidepdf.com/reader/full/ppt-emergency-for-internal-pressure-morovich 1/34
Emergency Release of
Internal Pressuresfrom
Aboveground StorageTanks
By George L. Morovich
TANK and ENVIRONMENTAL
TECHNOLOGIES, INC.
13 Flower Tuft Ct.
The Woodlands, Texas 77380
PH: +1-979-247-4812
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Emergency pressure release
alternatives.The causes, frequency and risks of
emergency internal pressure
incidents.
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Methods for providing emergency release of
internal pressure from within aboveground
storage tanks are desired as a safety
precaution to prevent shell uplift.
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Shell uplift may cause failure of the bottom
to shell joint along with damage to piping,
sumps and appurtenances; thereby,resulting in a release of a tank’s contents.
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There currently are three basic approachesfor emergency release of internal
pressure.
1. Emergency venting per API 2000
2. Weak roof to shell seam (Frangible roof)
3. Floating roof with open circulation
venting
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Emergency Venting
Per API 2000 applies only for relief of internal pressures resulting from
exposure to an external fire.
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Frangible Roof Joint (weak roof seam)
Based on completed research (allowing minimal
shell uplift), this approach is not reliable for tanks
below 50’ diameter.
Current API research investigated relative strength
of roof-to-shell and bottom-to-shell joints along with
allowable uplift .
Results of research expected to allow frangible joint
down to 30’ diameter (with improved bottom joints
and consideration of tank uplift , similar to Appendix
E earthquake design for uplift requiting flexibility inpiping and attachments).
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Frangible Roof Joint (weak roof seam)
1. Applicable to Cone Roofs only, based on specifiedroof slope, top of shell section detail and maximum
weld size.
2. Subject to workmanship (such as excessive welds),
3. Subject to changes that weaken the relative strength
of the bottom joint (such as bottom settlement and
corrosion).
4. Incident results in roof damage (typically requiring
removal from service).
5. Not suitable for certain incidents (such as overfill).
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Floating roof tanks with open venting or
other means to avoid combustiblemixture
Considered exempt from the condition that
API 2000 provides protection for.
1) The floating roof minimizes exposed product.
2) Circulation vent area wil l exceed the area required
in API 2000.
3) Circulation vents or other means used to minimize
the potential hazard of combustible mixtures from
developing within the tank.
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Domed External Floating-Roof Tank
Internal Floating-Roof Tank
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Internal Floating-Roof Tank
Fixed roof Floating roof
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Internal Floating Roof Tank --- Internal deflagration reported due to lightening strikeduring filling
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Over Pressure Event
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Over Pressure Event
Areas of bottom plate lifting.
Area of top shell
course damage.
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TYPES OF EMERGENCY INTERNAL
PRESSURE EVENTSOverfillSteam Release
Gas Injection
Product Reactions
External fire exposureInternal deflagration
Earthquake
Other
Of course other causes of roof / shell failure occur,
such as incidents involving excessive wind or
exposure to an external deflagration.
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Overfill incidents appear to be the most common and
preventable cause of emergency pressure related
damage to tanks. Minimum emergency vents or a
frangible joint cannot be expected to relieve pressure
prior to uplift. Product level control is the best means
to avoid this type of incident. Tank design with low
profile floating roofs and rim vents can avoid damage.
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Aluminum dome peripheral venting facilitates overfill with minimal damage or nodamage to the dome roof. Any resulting damage to the dome roof can typicallyrepaired without removal of the tank from service. Overfill slots are not desired dueto reduced operating capacity.
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OVERFILL in a cone roof tank causes damage to frangible roof.
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Steam Release is primarily a concern on heated
tanks.
Gas Injection
These types of incidents can also damage theinternal floating deck; however, if the tank is
equipped with circulation venting the damage is
typically limited to the floating deck.
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Over Pressure Event
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Product Reactions storing certain products, such as
Styrene, that can polymerize with release of
significant pressure. These tanks are often equipped
with dome roofs and tank shells are anchored to acounterweight to prevent uplift.
External fire exposure is the basis for the NFPA
minimum requirement.
Internal deflagration within an aboveground storage
tank is the most severe but also a very rare incident.
API research should produce a program to determine
vent requirements based on product storage
variables.
Internal deflagration within an aboveground storage tank is
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Internal deflagration within an aboveground storage tank is
the most severe but also a very rare incident.
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Earthquake is only a risk in certain areas but the
damage effects can be substantial. The sloshing of
product can cause uplift on the fixed roof and this may
damage or cause failure of the frangible joint, fixed
roof support structure (cone roof columns, rafters, and
aluminum dome supports and framing) and shell.
Sh ll d b d l i f i i
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Shell and bottom damage resulting from seismic event.
Note the plastic deformation due to uplift.
(submitted by John Lieb, Tank Industry Consultants)
PRESSURE RELEASE ALTERNATIVES
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PRESSURE RELEASE ALTERNATIVES
Alternate Frangible Roof Joint Details for small tanks are
offered; however, cost to document these will likely prohibit
adding these to the Standard.
Counterweight Anchorage of the tank shell and reinforced
shell to bottom joints.
PRESSURE RELEASE ALTERNATIVES (CON’T)
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PRESSURE RELEASE ALTERNATIVES (CON T)
Relative Strength of Roof-to-Shell and Bottom-to Shell Joints
research completed will likely allow for further reduction of
the 50’ diameter l imit. Allowable uplift and impact on attachedpiping wil l also be considered.
PRESSURE RELEASE ALTERNATIVES (CON’T)
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PRESSURE RELEASE ALTERNATIVES (CON T)
API 650 G “ Structurally Supported Aluminum Dome” roof
peripheral flashing (not sealed to tank) may be documented
to provide vent area contribution.
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PRESSURE RELEASE ALTERNATIVES (CON’T)
API 650 G “ Structurally Supported Aluminum Dome” roof
peripheral flashing uplift (resulting in no shell damage) may
be repaired without removal of tank from service.
PRESSURE RELEASE ALTERNATIVES (CON’T)
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PRESSURE RELEASE ALTERNATIVES (CON T)
Deflagration Venting research conducted with oversight from
the PVRC and support from API provides a mechanism to
evaluate venting of partial volume deflagrations.
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CONCLUSION
To minimize the impact of internal over pressure
incidents, attention should be paid to the causes,
frequency and resulting damage.
Some causes can be efficiently avoided.
Fixed and floating roof types and details allowing forinternal pressures to be safely vented with minimal
damage are preferred.
Attention must be made to tank operation, tank condition
and modifications.
Determine vent requirements based on product storage
variables and operating risks.