Tank Roof Inspection
Corrosion of roofs is seldom uniform. Both internal and external corrosion usually take the form of isolated attack that is governed by roof geometry, construction method, plate flatness and coating condition. Visual inspection is essential, but ultrasonic gauging can give useful information.
At all times care needs to be taken when working on both fixed and floating roofs. Special care is required if the roof is visibly corroded. The internal compartments of floating roofs should only be gauged when the tank is empty and gas free.
Ultrasonic thickness measurements of roof plates may be performed along the radial grid lines (extension of vertical grid lines) at 200 mm from shell, at 2/3 radius and at 1/3 radius. In addition, thickness measurements should be taken at locations where significant external corrosion is observed.
Method of ultrasonic gauging / screening is with remote access crawlers such as the range of
Scorpion crawlers or manual thickness gauge’s such as the
T-Scan 100 and T-Scan300.
The Silverwing HandScan system may also be used on fixed roofs to give an improved POD when conditions allow for the safe use of the system.