Title: Behavior of Storage Cells in Condeep Structure under Hydrostatic Pressure

Author(s): Amr I. I. Helmy and Michael P. Collins

Publication: Structural Journal

Volume: 113

Issue: 4

Appears on pages(s): 839-850

Keywords: offshore structures; shear strength; water pressure

DOI: 10.14359/51688824

Date: 7/1/2016

Abstract:
To investigate the structural safety of the storage cells of some existing Condeep concrete offshore oil and gas platforms built in the 1970s, a 1:13 scale model of a typical upper dome-cell wall junction of a storage cell of such a platform was loaded to failure by increasing the external water pressure in the Hydraulic Testing Facility at the University of Toronto, Toronto, ON, Canada. A number of the early Condeep platforms use an internal pressurization system to restrict the pressure differential to approximately a 50 m (164 ft) head of water at the critical dome-cell wall junction. If this internal pressure system fails, the pressure differential across the domes and walls of the cells will approximately double. The question then becomes whether this increase in differential pressure will result in the failure of the structure. In the experiment, the model resisted a maximum pressure differential equivalent to a 147 m (482 ft) head of sea water. Immediately prior to failure, radial cracks could be seen near the base of the dome and water was flowing into the specimen at a rate of 139 L/min (37 gal./min). The final failure was abrupt and involved a brittle shear failure encompassing one half of the circumference of the cell wall. At failure the dome displaced downwards approximately 25 mm (1 in.) and the top of the cell wall was pushed approximately 10 mm (3/8 in.) outwards.