Recent projects, notably in the US, are now showing the benefits of incorporating integrity operating windows (IOWs) into risk-based inspection (RBI) programmes and revealing key learnings. They also open up the advantages of this approach to the wider industry; it need not be a case of all or nothing with IOWs.
Across oil and gas streams over the last two decades, RBI methodology has been enhancing asset integrity by focusing inspection and the associated costs on the most critical equipment. RBI uses past operating conditions and inspection data to make strategic future predictions, capturing a ‘risk snapshot’ in time. The approach involves the determination of a probability of failure, combined with the consequence of failure. At some point in the future, when a risk tolerance is expected to be exceeded, an inspection is recommended to better quantify the state of the component. The inspection itself does not reduce risk, but it mitigates the uncertainty that is associated with the current degradation state. This enables operators to better quantify the current damage present in the component and helps engineers make more accurate projections on the asset’s remaining life.
Past performance is not future performance
What happens, however, when the road ahead deviates from what is expected? An obvious example is the change in process conditions as plant infrastructure ages. Equipment will degrade during its years of in-service operation. Mature assets cannot be expected to perform as they did before the process conditions altered. The risk associated with failure will inevitably increase. In this scenario, looking back at historical data is a little like using only the rear view mirror when driving a car. That check is essential, but what about seeing ahead to navigate the new roads? IOWs can help keep operations safe and on track.
IOWs are allowable operating limits for a process variable that can affect equipment integrity as a result of corrosion or the impact of other damage mechanisms. These IOWs can then be used with a framework that captures these process changes as they happen, in real time. If limits are exceeded, an IOW programme can facilitate a timely response to prevent the onset of rapid asset deterioration, or raise a flag or alert to trigger a response, addressing long-term integrity concerns. Operating within an IOW does not mean that no degradation should be expected; the resulting degradation is acceptable for the equipment’s expected remaining life, and should be manageable based on current inspection plans. When combined with an RBI programme, IOWs’ proactive approach helps to increase asset reliability, decrease risk and prevent a potential incident in the short to near-future term.
Written by Vishal Lagad, Lloyd's Register, USA.