RBI Background

The American Petroleum Institute (API) recommends to develop an inspection program using risk-based methods. You can use ReliaSoft RBI to record the data relating to the potential damage to specific equipment and components, and then forecast future physical and economic consequences of failure as well as the probabilities of failure for individual components, equipment and entire plants. In addition, you will be able to better plan when to inspect, maintain and replace weak components before failure occurs.

The program is primarily based on two publications: API RP 580 and API RP 581. Both provide guidance on developing a risk-based inspection program for fixed equipment in refining, petrochemical and chemical process plants. The documents are written to include RBI methods for pressurized fixed equipment such as pressure vessels, piping, tanks, pressure relief devices and heat exchanger tube bundles, among others.

Note: RBI corrects several errors that are present in the API RP 580 and API RP 581 standards so the results obtained in the RBI software may differ from those calculated using other methods. These changes included correcting several property values in tables (e.g., the nominal boiling point of NO2 is 22°C and not the 135°C shown in the standard), correcting inconsistencies in equations and correcting some theoretical inconsistencies.

Introduction

The RBI software calculates the probability of failure and the consequence of failure for given components in a pressurized environment. These calculations are used to help plan inspections and reduce the risk of failure.

The API defines failure as the loss of containment from a pressure boundary resulting in leakage to the atmosphere or a rupture of the pressurized component. Throughout a given period of time, damage will accumulate within a pressured environment. That damage causes increased risk of failure to equipment and components. After a significant amount of damage, a predetermined risk target is exceeded and an inspection of that component is recommended to better understand and measure the damage.

Consequences of Failure

Within RBI, there are two types of consequence analyses: area and financial. The loss of containment by leakage, rupture or other causes can cause damage to nearby equipment, the environment and/or be harmful to personnel. Some components must have both types of consequence analysis performed, while others do not. The consequence properties help to rank components based on risk.

The consequence analysis in the RBI software is modeled after API RP 581’s Level 1 consequence analysis, which is a method used to evaluate the consequences of fluid or gas release.

Probability of Failure

In an RBI assessment, the probability of a component failing is based on several factors:

Program Parts

The API RBI program can be broken down into three parts:

Date Definitions

In a risk based inspection, the following dates are used:

The following graphic shows the risk vs. time curve (i.e., the risk increases as time increases). When you perform an inspection, the risk should go down.

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