8. FloatingRoofWorkSafety

Floating Roof Work Safety

2006 Storage Tank Conference and Safe Entry Workshop

Presented by Mark Baker

Floating Roof Work Safety 

Incidents have occurred working under floating roofs



People who work around floating roofs need to be aware of proper safety procedures

Floating Roof Work Safety 

Incidents have occurred working under floating roofs



People who work around floating roofs need to be aware of proper safety procedures

API RP 2016 Guidelines and Procedure for Entering and Cleaning Petroleum Storage Tanks

First Edition, August 2001

API RP 2016 

   

Covers potential hazards associated with internal and external floating roofs Potential failure mechanisms Highly divergent risks Procedures to prevent or mitigate roof collapse Procedures for inspecting floating roofs

Applicability 

Flat bottom, vertical cylindrical storage tanks with internal or external floating roofs 

Built to API Std. 650



Repaired to API Std. 653

Applicability 

All types of: 

Aluminum



Steel pan



Steel annular pontoon



Double deck



High center deck roofs

Floating Roof Stability 

Support 

Adequately attached to the floating roof



Pins capable of carrying roof weight



Legs should be:





Straight



Free from severe corrosion



Pinned properly

Roof in reasonable condition


Lateral Movement 

Small lateral movements increase risks



Typical rim gap is 6 to 12 inches



Lateral movement restrained by: 

Certain types of seals



Wedges



Bracing


Rotation 

Roof must be stabilized against rotation



Rotational stability may be provided by: 

Sampling well pip (typically 6 – 10 inch)



Anti-rotation cable (aluminum decks)



Other devices


Legs   

Typically 3 to 4 inch diameter pipes Some have holes drilled in the pipe for setting the height Roof design can impact leg stability


Pan or single deck


Pan or single deck

Note: Deck is weak in bending and allows easy lateral deflection of the support leg.


Double deck or Annular Pontoon

Note: To deflect a leg in this section requires actual failure of the support leg by bending.


Other IFR Decks  

Aluminum Composite

Roof Failure and Collapse 

Excessive Loading 

External Floating Roofs - 25 lb/ft2



Internal Floating Roofs –12.5 lb/ft 2



IFR with roof drains – 5 lb/ft2


The roof at weakest state when on legs



Liquid in Pontoons 

Product



Water



Leg Pinning 

Not Pinned



Not Uniformly Pinned


Stability 

Dependant upon vertical support



Rotational resistance 

Seals



Anti-rotation device

Roof Failure and Collapse

Roof weight is directed vertically down the roof leg Leg is long and acts as a slender column which may bow under large loads

Roof Failure and Collapse

Roof weight is directed down the roof leg and a horizontal component of force is generated

The magnitude of the horizontal force is dependant upon the weight of the roof and the angle of the leg


Stability 

Anti-rotation device   



Corrosion Weld Failure Missing

Work on top of the roof  

May add excessive weight May add excessive movement


Stability 

Roof Seals  Wiper Seals  Foam Log  Mechanical Shoe Seals

The following photographs are curtsey of Phil Myers

Inspections 

Above the roof Inspections 

At the top of the tank



Without entry into the confined space

Inspections 

Inspect:  

Water or Product on the Roof Floating Roof Legs  



Anti-Rotation System  



Check for vertical alignment All pinned properly Verify working anti-rotation device Check floating roof fitting for damage

Rim Seals 

Check seal condition

Inspections 

Below the roof Inspections 

From outside the tank



Without entry into the confined space

Inspections 

Inspect: 

Floating Roof Legs   

 

Misalignment Buckling Corrosion

Anti-Rotation System Rim Seals  

Check primary seal Check for wiper seals

Before Cleaning Tanks   

Minimize Exposure - Atmosphere is Hazardous Condition of the roof is often unknown Install a temporary roof support

After Cleaning Tanks 

Inspect Leg Condition 



UT, Hammer

Cribbing 

Ensures that the entry manhole will remain clear and open during a roof collapse



Serves as a guide to the exit



Protects personnel inside the tank within ~30 ft radius of the manhole


Cribbing

(Baker Comments)



The strength of wood timbers is dependant upon type of wood and its condition



Compressive Strength ranges from 200 PSI to 1,000 PSI.



Engineer should design a cribbing stack


Lateral Movement Backup 

Wedges



Radial steel beams 

Extending to within 1 inch of the shell



Used only on clean and gas freed tanks


Anti-Rotation Backup 

 

Required unless a guide pole is present, the seal is a shoe seal and in good condition Wooden wedges – 4 places Other systems may be required

Cable Suspended Roofs 

Not specifically covered in API RP 2016



Principles can be applied


Risks Reduced for  



Lateral Movement Rotation

Other Concerns which should be checked:

Cable Suspended Roofs  

Condition of the cable Condition of fixed roof node


Excessive Loading of the Fixed Roof 

High external loads may reduce load carrying ability of the roof


Excessive loading of the floating roof  



Trapped product Water on the roof

Damage or deterioration of the Roof Structure

Other Standards 



API Publication 2026, “Safe Access/Egress Involving Floating Roofs of Storage Tanks in Petroleum Service” Confined Space Entry – 29 CFR1910.146

8. FloatingRoofWorkSafety

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