In-Service Above Ground Storage Tanks Inspection Robotics Technology Update

Introduction

A unique technique for inspecting the floors of aboveground storage tank’s (AST) emerged in the late 90’s based on in-service robotic technology. The technology has come a long way since then, with new inspection and tank cleaning capabilities, greater operational efficiency and a much broader user base. The number of tanks inspected using in-service robotics has now exceeded the 700 mark. Industry now has an alternative to determining the minimum floor thickness of tanks in order to determine the next optimum time for an out-of-service inspection without emptying the tank. And this can often be accomplished without taking the tank out of service. Compliant with API Std 653 (Ref 1) guidelines for determining tank floor corrosion rates, and when combined with complimentary inspection technologies and activities such as statistical analysis and an API 653 external survey, one can apply this methodology to provide the tank owner with a snaphot of the AST’s condition without taking it out of service. Using this same logic, where the floor scanner and other complimentary approaches are combined as part of an overall tank floor inspection strategy an inspection effectiveness could be properly assigned for a Risk-Based Inspection, i.e. “A” (highly effective = 80-100% damage detection effectiveness), “B” (usually effective = 60-80% damage detection effectiveness), “C” (fairly effective = 40-60%) as shown in API RBI BRD 581. Although there is a population of tanks that require out-of-service inspections because of the tank’s condition, age and inspection history, there is a growing population of tanks that will benefit from the introduction of this technology.

This article discusses specific technical capabilities for the use of in-service, high density, ultrasound scanning for assessing the condition of AST floors. Topics such as safety and environmental risk reduction are also covered as well as the technology’s cost-savings performance.