Introduction to Risk Based Inspection

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The consequence of failure is calculated as the combined values of the consequences for

damage to the failed equipment, damage to the surrounding equipment, loss of production,

the cost due to personnel injury and the damage to the environment. The consequence of

failure can include both a financial consequence (FC) and an area (safety) consequence

(CA).

FC = FCcmd + FCaffa + FC prod + FCinj + FCenviron

CA = max (CAequip, CA personnel )

FCcmd is the financial consequence to failed equipment.

FCaffa is the financial consequence to surrounding equipment.

FC prod is the financial consequence due to production downtime.

FCinj is the financial consequence due to personnel injury.

FCenviron is the financial consequence due to environmental damage/cleanup.

CAequip is the area consequence to surrounding equipment.

CA personnel is the area consequence to nearby personnel.

For further detail on calculating probability of failure and/or consequence of failure, please

consult API RP 581. [1]

Introduction to the RBI Software

ReliaSoft’s new RBI software tool has all of the functionality of RCM++ and facilitates risk

based inspection (RBI) analysis for oil & gas, chemical and power plants in adherence to the

principles and guidelines presented in the American Petroleum Institute's recommendationsin the API RP 580 and RP 581 publications, as well as the American Society of Mechanical

Engineers’ recommendations in the ASME PCC-3-2007 publication. RBI also includes all of the

standard features available in RCM++, such as being able to perform a functional failure

analysis on an item and/or create a DFR planner.

The RBI interface is identical to RCM++, with the addition of RBI specific options on the

System Hierarchy tab.

The equipment and component types that are available for RBI analysis are currently limited

to those addressed API RP 581. The available equipment types are shown below.

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Each equipment type also has associated components. For example, the Vessel-FinFan

equipment has the specific components shown below available for analysis.

While the system hierarchy can contain items that are not RBI-related, those items will be

ignored when performing an RBI analysis. For example, in the following picture the system is

the hydrogen generation unit, which has several items that receive RBI analysis and several

that do not.


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Once you create the assets, you must answer questions and fill out the relevant properties

for the asset to be analyzed. All of these inputs are used to create a failure model that

determines the probability of failure, and calculates the consequences of failure. The

results also include the recommended inspections, if any, that should be performed to keep

the asset under the maximum allowable risk.

Example

A small town wants to do a risk analysis on a proposed high pressure 24-inch pipe carrying

crude oil for which the oil transportation company is willing to pay a rent of $500,000 inadvance for the next 20 years. The company will also perform an inspection on the pipe

halfway through the rental period. Since the city is self-insured and is not willing to take any

financial chances, the city council would like to know if the $500,000 offsets the possible

risk associated with the pipe. The city has requested the required information from the oil

transportation company to conduct its own RBI analysis of the pipe.

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24-Inch Pipe Specifications

The pipe is composed of carbon steel. The heavy crude, which contains 100ppm H2S, is being

pumped through at an operating temperature of 25 Celsius with a pressure of 4.5 MPa.

The only two damage mechanisms expected are general thinning and external corrosion.


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For their analysis, the city assumed that the effectiveness of the performed inspections was

average. All other property values were estimated based on other similar pipes used

elsewhere.


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The city based the financial portion of the consequences on the current population density

and the property values around the proposed pipe area. For the initial estimate, the city did

not take into account inflation or any possible losses associated with property value

changes, nor possible resident dislike of the pipeline across city land.


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Results

The analyzed results show that in case of a containment failure of the pipe, the expected

cost associated with a failure would be almost $4.9 million. This far exceeds the $500,000

payment to be received. However, the probability that a failure will occur within 20 years

under normal circumstances is estimated to be only 0.7%. Therefore, the expected financial


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risk is the product of the two, or a little over $36,000. This is well under the $500,000

payment to be received.

In terms of a cost analysis of the risk, and not including the potential loss in property value

by having the pipe run across city property, the city council recommended that thecommunity accept the proposed pipeline as an additional revenue source with minimal risk.

References

[1] American Petroleum Institute, API RP 581 Risk-Based Inspection Technology 2nd ed.,

Washington, D.C.: American Petroleum Institute, 2008.

Introduction to Risk Based Inspection

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