API 580 is a standard published by the American Petroleum Institute (API) that provides guidelines for managing risk in the petroleum industry. It outlines a risk-based inspection (RBI) methodology for determining the inspection frequency and evaluating the risks associated with corrosion and other damage mechanisms.

To calculate the risk per API 580, you will need to consider the inspected rate of corrosion and the predicted rate of corrosion. The risk calculation involves comparing these two rates and assessing the consequences of failure. Here’s a general approach to calculating risk using API 580:

  • Determine the Inspected Rate of Corrosion (IRC): The IRC is the corrosion rate observed during inspections or monitoring activities. Visual inspections typically determine it, as non-destructive testing techniques like ultrasonic thickness measurements or analyzing monitoring data such as corrosion coupons or probes. However, the IRC indicates the actual corrosion rate experienced by the equipment.
  • Determine the Predicted Rate of Corrosion (PRC): The PRC estimates the future rate of corrosion based on various factors. These factors may include operating conditions (e.g., temperature, pressure, fluid composition), material properties (e.g., corrosion resistance, susceptibility to cracking), environmental factors (e.g., exposure to corrosive substances, humidity), and historical data (e.g., past corrosion rates, trends). In addition, corrosion modeling techniques, such as empirical, mechanical, or statistical models, can be used to estimate the PRC.
  • Compare the IRC and PRC: Comparing the IRC and PRC helps determine whether the corrosion accelerates, decelerates, or remains relatively constant. In addition, you can identify any deviations or trends by assessing the difference between the observed and the expected corrosion. This information is essential for understanding the equipment’s current condition and predicting future degradation.
  • Assess the Consequences of Failure: The consequences of failure involve evaluating the potential impact if the corrosion were to lead to a failure of the equipment or system. This assessment typically includes considering factors such as safety risks (e.g., the potential for leaks, fires, or explosions), environmental impact (e.g., pollution, contamination), production losses (e.g., downtime, reduced throughput), repair costs, and potential for business interruption. The consequences can be qualitative or quantitative, depending on the available data and analysis techniques.
  • Calculate the Risk: Risk calculation combines the likelihood of failure with the consequences of failure. The possibility of failure can be determined by considering the difference between the IRC and PRC. Various approaches can be used to quantify the likelihood, such as probabilistic analysis, expert judgment, or semi-quantitative methods. The consequences of failure, as assessed in step 4, are typically expressed in monetary terms or qualitative scales. Multiplying the likelihood and consequences provides an estimation of the overall risk associated with the corrosion damage mechanism.
  • Determine Risk Mitigation Measures: Appropriate risk mitigation measures can be identified based on the calculated risk. These measures aim to reduce the risk to an acceptable level. They may include adjusting inspection frequencies to monitor the equipment more closely, implementing corrosion control strategies such as coating systems or cathodic protection, considering material upgrades or modifications to improve corrosion resistance, or implementing process changes to mitigate corrosion risks. The selection of risk mitigation measures should evaluate the effectiveness, feasibility, and cost-effectiveness of each option.

It’s important to note that API 580 provides more detailed guidance on each of these steps, including specific methodologies and tools that can be used for risk assessment. Additionally, industry-specific standards and regulations may influence the risk calculation process.