Ppt Emergency for Internal Pressure - Morovich

7/15/2019 Ppt Emergency for Internal Pressure - Morovich

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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

[email protected]



Emergency pressure release

alternatives.The causes, frequency and risks of

emergency internal pressure

incidents.



Methods for providing emergency release of

internal pressure from within aboveground

storage tanks are desired as a safety

precaution to prevent shell uplift.



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.



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



Emergency Venting

Per API 2000 applies only for relief of internal pressures resulting from

exposure to an external fire.



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).



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).





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.



Domed External Floating-Roof Tank

Internal Floating-Roof Tank



Internal Floating-Roof Tank

Fixed roof Floating roof



Internal Floating Roof Tank --- Internal deflagration reported due to lightening strikeduring filling



Over Pressure Event



Over Pressure Event

Areas of bottom plate lifting.

Area of top shell

course damage.







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.



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.



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.



OVERFILL in a cone roof tank causes damage to frangible roof.



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.



Over Pressure Event



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



Internal deflagration within an aboveground storage tank is

the most severe but also a very rare incident.





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



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



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)



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.





API 650 G “ Structurally Supported Aluminum Dome” roof

peripheral flashing (not sealed to tank) may be documented

to provide vent area contribution.




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.





Deflagration Venting research conducted with oversight from

the PVRC and support from API provides a mechanism to

evaluate venting of partial volume deflagrations.



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.

Documents

Ppt Emergency for Internal Pressure - Morovich