Procedure for monitoring the safety and security of steel tanks using ground surveying techniques

Measuring surveying control system for storage steel tanks farm has been developed for frequent measuring settlement and deformation of tank. The described system depends on soil investigation and design of precise surveying measurement procedure. The system included construction of permanent ground control points to be used for both vertical and horizontal measurements. These points are protected from any move; therefore they were constructed on stable soil strata at about 40m deep and kept isolated to avoid the influence of the surrounding soil. Markings for settlements (50x50x5x100 angles) were fixed to the base and for deformation (2x2cm surveying stickers) were fixed on every tank ring (11 horizontal shell rings) along 48 vertical sections. The system is designed to be permanent and give accuracy for settlement measurements of 0.005 mm and for deformation 2mm. Precise ground surveying measuring procedure was employed for settlement measurements and deformation measurements. The system was applied to petroleum tank farm at Portsaid region in Egypt. Results show deformation behavior at each ring of the tank wall which varied along the vertical section and position on ring. Two figures of deformations were measured. The first was due to the manufacture and construction quality which reached 14.5 cm at some position as initial figure before tanks filling. The second figure of deformation measurement was that generated due to the effect of filling the tank with fuel and was expected to be influenced by the characteristic of the tank wall steel material; that figure reached 5.3 cm at various locations. For settlement two measurements were observed. The first was to indicate the instant settlement that took place due to loading effect, and reached 2.7cm in some tanks. The second was for determining the rate of settlement per year after operating the site, that figure reached 3.76 cm/year for some tanks with total settlement after 42 months of 13.16 cm. Measurements were taken at different loading conditions and along a period of time with loading and unloading fluctuation. The designed system allows for precisely monitoring settlement and deformation over years, thus help in continuously indicate safety and reliability of the tanks and help in the repair or reconstruction decision which may be considered for continuing in service.Dr. Ayman Soliman Hassan Aguib, Associate Professor in Surveying Engineering, Civil Engineering Department, College of Engineering, King Saud University P.O. 800, Riyadh-11421, Saudi Arabia. Email: aaguib@ksu.edu.s