NATURE OF DEFECT
The tank had suffered from corrosion under insulation (CUI) to the vertical tank shell. This resulted in corrosion patches and pitting of various sizes and depths. The client required composites repairs to prevent further corrosion and restore the strength of the tank wall. Various defects were present on the tank shell with differing sizes and depth. These were evaluated by the client against the requirements of EEMUA-159 above ground flat bottom storage tanks: A guide to inspection maintenance and repair.
SOLUTION
Metalyte Pipeworks produced a composite repair method using Herculyte epoxies to fair the defects with an overwrap of Dragon-Quad-Std composite system. The number of layers required varied depending on the defect dimensions and elevation on the tank wall.
REPAIR METHOD
The substrate was prepared using an MBX machine to gain a surface profile to SSP.SP11. Surface defects within the immediate repair area were repaired using Herculyte resins and 500 microns of Dragon resin was applied as a bonding coat to the entire repair area prior to application of the Dragon composite. The repair area was patch wrapped in engineered Dragon-Quad-Std composite and allowed to cure until a minimum of 74.5 “Shore D” hardness was achieved.
