Tank bottom life, risk-based inspection and corrosion

What it takes to implement corrosion prediction of tank bottoms. INDUSTRY tank standards set limits on how long flat bottom tanks may be operated before being internally inspected [sidebar 1] based on tank bottom corrosion rates. But many companies are not collecting sufficient data or even the right kinds of data that would actually save them significant costs or even provide them with good optimal operating intervals. Moreover, without appropriate data collection, tank bottom life estimating methods such as ‘similar service’, ‘risk-based inspection’, and statistical methods cannot be properly used. The purpose of this paper is to deliver the following key points: 1. It is critical to collect the right kinds of corrosion data according to a formal protocol. 2. While linear corrosion rate theory may be used for tank bottoms, the corrosion rates are actually nonlinear with time. This provides an opportunity for longer tank inspection intervals while decreasing risk. 3. Standards development organisations and corporate joint industry projects should sponsor data collection and assessment programmes that would allow for more accurately applying corrosion rates to increase...