lifting a steel pan roof - nistm - national institute for storage
TRANSCRIPT
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Lifting a Steel Pan
Roof
Presented by: Warren L. Hall
A. R. Watson, Inc.
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Tank
100 ft diameter by 48 ft high cone roof tank
Service: Crude Oil
Tank removed from service for cleaning and
inspection
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Situation
Contractor found roof was on low legs with less than 3 ft of clearance
Excessive sludge also present in the tank
Two door sheets were cut into the tank shell for access to the roof.
Contractor attempted to jack the roof
Due to roof flexibility, the process would be very slow
Prolonged exposure of workers to sludge
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Plan
A. R. Watson was contacted to assist the contractor in a plan to move forward.
Watson considered many options and ultimately decided to lift the roof using a cable system suspended from the tank fixed roof
The floating roof is a 100 ft diameter steel pan roof
Weight – approximately 60,000 lbs
48 legs arranged in 4 radial rows
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Engineering
The roof was designed to support a load of 25
psf
The IFR has a weight of approximately 10 psf
Run a cable from each leg to the roof where it
will then be run to a series of come-along to lift
the roof
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Engineering
Rafters are W12 x 16 I-Breams 50 ft long – only
a center column.
The rafters and structure was analyzed assuming
loads are point loads along each rafter
corresponding to leg location.
Also include weight of roof plates
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Engineering
Found maximum deflection of a rafter was
0.207%
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Cables
½” galvanized steel
Working load of 6,000 lbs
½” Thimble
3 cable clamps with a torque of
68 ft-lbs
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Execution
Cable locations were identified on the roof.
Pipes located such that the cable loads were distributed
over two to three rafters for additional safety.
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Execution
Cables run to the shell
and attached to a
come-along
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Execution
Once cabling completed – the
roof was leveled
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And The Roof Lifted
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Conclusions
Roof was lifted in 2 hours after cabling
completed.
The cable lift system was successful for this type
of floating roof.
Cable support of a steel floating roof is not
practical as most of the roof strength is required
to support the floating roof and little left for
other loads.
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Questions?