baker floatingroofworksafety
DESCRIPTION
floating roof designTRANSCRIPT
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Floating Roof Work Safety
2006 Storage Tank Conferenceand Safe Entry Workshop
Presented by Mark Baker
Types of Floating RoofsPan Roof
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Internal Steel Pan Roof
Types of Floating RoofsSteel Annular Pontoon
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Internal Steel Pontoon Roof
Types of Floating Roofs
Internal Steel Annular Open Pontoon
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Types of Floating RoofsSteel Double Deck Floating Roof
Internal Double Deck Roof
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Types of Floating RoofsInternal Aluminum Skin andPontoon Floating Deck
Types of Floating Roofs
Internal Aluminum FullContact Floating Deck
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Types of Floating Roofs
There are many other types
Floating Roof Work Safety
o Incidents have occurred workingunder floating roofs
o People who work around floatingroofs need to be aware of propersafety procedures
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API RP 2016
Guidelines and Procedure for Entering andCleaning Petroleum Storage Tanks
First Edition, August 2001
API RP 2016
o Covers potential hazards associatedwith internal and external floatingroofs
o Potential failure mechanismso Highly divergent riskso Procedures to prevent or mitigate
roof collapseo Procedures for inspecting floating
roofs
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Applicability
o Flat bottom, vertical cylindricalstorage tanks with internal orexternal floating roofs
n Built to API Std. 650 or API 12 C
n Repaired to API Std. 653
Applicability
o All types of:
n Aluminum
n Steel pan
n Steel annular pontoon
n Double deck
n High center deck roofs
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Floating Roof Stability
o Supportn Adequately attached to the floating roof
n Pins capable of carrying roof weight
n Legs should be:
o Straight
o Free from severe corrosion
o Pinned properly
n Roof in reasonable condition
Floating Roof Stability
o Lateral Movementn Small lateral movements increase risks
n Typical rim gap is 6 to 12 inches
n Lateral movement restrained by:
o Certain types of seals
o Wedges
o Bracing
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Floating Roof Stability
o Rotationn Roof must be stabilized against rotation
n Rotational stability may be provided by:
o Sampling well pipe (typically 6 –10 inch)
o Antirotation cable (aluminum decks)
o Other devices
Floating Roof Stability
o Legsn Typically 3 to 4 inch diameter pipesn Some have holes drilled in the pipe for
setting the heightn Roof design can impact leg stability
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Floating Roof Stability
o Pan or single deck
Floating Roof Stability
o Pan or single deck
Note: Deck is weak inbending and allows easylateral deflection of thesupport leg.
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Floating Roof Stability
o Double deck or Annular Pontoon
Note: To deflect a leg in thissection requires actual failure ofthe support leg by bending.
Floating Roof Stability
o Other IFR Decksn Aluminumn Composite
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Roof Failure and Collapse
o Excessive Loading
n External Floating Roofs 25 lb/ft2
n Internal Floating Roofs –12.5 lb/ft2
n IFR with roof drains –5 lb/ft2
o The roof at weakest state when onlegs
Roof Failure and Collapse
o Excessive Loading
n Liquid in Pontoons
o Product
o Water
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Roof Failure and Collapse
o Excessive Loading
n Leg Pinning
o Not Pinned
o Not Uniformly Pinned
Roof Failure and Collapse
o Stability
n Dependant upon vertical support
n Rotational resistance
o Seals
o Antirotation device
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Roof Failure and Collapse
Roof weight is directedvertically down the roofleg
Roof Failure and Collapse
Roof weight is directeddown the roof leg and ahorizontal component offorce is generated
The magnitude of thehorizontal force is dependantupon the weight of the roofand the angle of the leg
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Roof Failure and Collapse
o Stability
n Antirotation deviceo Corrosiono Weld Failureo Missing
n Work on top of the roofo May add excessive weighto May add excessive movement
Roof Failure and Collapse
o Stability
n Roof Sealso Wiper Sealso Foam Logo Mechanical Shoe Seals
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Inspections
o Above the roof Inspections
n At the top of the tank
n Without entry into the confined space
Inspections
o Inspect:n Water or Product on the Roofn Floating Roof Legso Check for vertical alignmento All pinned properly
n AntiRotation Systemo Verify working antirotation deviceo Check floating roof fitting for damage
n Rim Sealso Check seal condition
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Inspections
o Below the roof Inspections
n From outside the tank
n Without entry into the confined space
Inspections
o Inspect:n Floating Roof Legso Misalignmento Bucklingo Corrosion
n AntiRotation Systemn Rim Sealso Check primary sealo Check for wiper seals
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Before Cleaning Tanks
o Minimize Exposure Atmosphere isHazardous
o Condition of the roof is often unknowno Install a temporary roof support
After Cleaning Tanks
o Inspect Leg Condition
n UT, Hammer
o Cribbing
n Ensures that the entry manhole will remain clearand open during a roof collapse
n Serves as a guide to the exit
n Protects personnel inside the tank within ~30 ftradius of the manhole
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After Cleaning Tanks
o Cribbing (Baker Comments)
n The strength of wood timbers isdependant upon type of wood and itscondition
n Compressive strength ranges from 200PSI to 1,000 PSI.
n Engineer should design a cribbing stack
After Cleaning Tanks
o Lateral Movement Backup
n Wedges
n Radial steel beams
o Extending to within 1inch of the shell
o Used only on clean andgas freed tanks
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After Cleaning Tanks
o AntiRotation Backupn Required unless a guide pole is present,
the seal is a shoe seal and in goodcondition
n Wooden wedges –4 placesn Other systems may be required
Cable Suspended Roofs
o Not specifically covered in API RP 2016
o Principles can beapplied
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Cable Suspended Roofs
o Risks Reduced forn Lateral Movementn Rotation
o Other Concerns which should bechecked:
Cable Suspended Roofs
o Condition of the cableo Condition of fixed roof node
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Cable Suspended Roofs
o Excessive Loading of the Fixed Roofn High external loads may reduce load
carrying ability of the roof
o Excessive loading of the floating roofn Trapped productn Water on the roof
o Damage or deterioration of the RoofStructure
Other Standards
o API Publication 2026, “SafeAccess/Egress Involving FloatingRoofs of Storage Tanks in PetroleumService”
o Confined Space Entry –29 CFR1910.146
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Conclusions
o The risk of incidents can beminimized implementing API RP 2016
o The likelihood of a failure is not thesame for all roof designs
o Backup protection schemes should bereviewed to determine applicability