Influence of Inspections on the Risk Evaluation of a Subsea Manifold by a Top Logical Model

We present a preliminary risk analysis of a typical subsea manifold for the Brazilian oil basin through a top logical model (TLM) developed by considering initiating events and their respective event trees. A total of seven initiating events have been identified, including: loss of containment in the section between the connector and the flowline, loss of containment in the section between valves, spurious valves closure, and pipe plugging in the sections between valves. For each of these initiating events, an event tree was developed, defining some barriers and identifying risk sequences. Additionally, for five initiating events, namely, Loss of containment in pipelines before valves, Loss of containment in at least one valve, Loss of insulation at Manifold input connectors, Loss of containment in ducts prior to manifold inlet connectors, and Structural Deficiency in the Manifold Protective Structure, no barriers were identified. From these event trees and using fault trees, the system TLM was developed, which is very useful for assessing the influence of inspection plans on equipment risk evaluation. This model allows for considering sensitivity analyses such as initially considering the existing standard inspection plan followed and no inspection plan. Other important variables to consider include failure detection probabilities associated with the inspection techniques used to assess the system. These results are valuable for decision-making regarding the definition of inspection plans.

Keywords: Offshore oil and gas industry, Risk analysis, Top Logical Model (TLM), Initiating events, Consequences, Equipment inspection, Detection probability.