API 581 is a recommended practice document published by the American Petroleum Institute (API) that provides a quantitative risk assessment (QRA) methodology for assessing the likelihood and consequences of potential failures in pressure vessels, piping, tanks, and other equipment in the oil and gas industry.

Here are the key features of API 581:

• API 581 provides a comprehensive and systematic approach to evaluate the risk of equipment failures by considering the likelihood and potential consequences of such failures.
• The document includes guidelines for establishing inspection intervals, defining damage mechanisms, determining the remaining life of equipment, and prioritizing inspection and maintenance activities.
• API 581 uses a risk matrix to prioritize equipment based on the severity and likelihood of potential failures. The matrix uses a numerical risk ranking system to prioritize equipment for inspection and maintenance.
• The document provides a framework for implementing a risk-based inspection (RBI) program, which allows for more effective and efficient use of inspection resources by focusing on higher-risk equipment.
• API 581 covers a wide range of equipment types, including pressure vessels, piping, tanks, heat exchangers, and other types of equipment commonly found in the oil and gas industry.
• The document includes detailed information on various damage mechanisms that can affect equipment, such as corrosion, fatigue, and cracking.
• API 581 provides guidance on the selection of appropriate inspection and monitoring techniques based on the type of equipment and the identified damage mechanism.
• The document emphasizes the importance of ongoing data collection and analysis to support the RBI program and improve the accuracy of risk assessments.