Structural Assessment of Steel Storage Tanks in Petroleum Depot Facilities in Rivers State

Steel storage tanks at petroleum depot facilities in Rivers State in the South South geopolitical zone are critical infrastructure whose structural integrity directly affects operational safety, environmental protection, and regulatory compliance. This study assesses the structural condition of above-ground atmospheric steel storage tanks at three petroleum depot facilities in Port Harcourt, Rumuola, and Eleme, using a combined visual, non-destructive, and analytical evaluation approach. Tank shell plate thickness was measured using ultrasonic pulse echo gauging at over two hundred points per tank, and the results were compared against minimum thickness requirements of API 653 for continued service. Floor plate integrity was assessed using a magnetic flux leakage scanner. Settlement surveys using a precision level were conducted around the perimeter of each tank to characterise annular plate distortion and foundation performance. Results indicate that shell corrosion in the lower shell courses, within 1.5 metres of the tank floor, had reduced plate thickness below the API 653 minimum in eleven of the fourteen tanks assessed, with the most severe remaining thickness of 3.2 mm compared to a minimum acceptable of 5.0 mm. Floor plate pitting corrosion above the repair threshold was identified in seven tanks. Two tanks exhibited differential settlements exceeding API 653 limits, indicating inadequate foundation performance. The study recommends immediate out-of-service repair for the most critically thinned tanks, implementation of a cathodic protection system for all floor plates, and a structured 5-year inspection programme aligned with API 653 and the Nigerian Department of Petroleum Resources regulatory requirements. Keywords: steel storage tanks, petroleum depot, structural assessment, API 653, corrosion.