About Risks

When you connect elements to each other in a series, every element has one preceding connection and one succeeding connection, with only one path from the Start element to the End element. For example, in the following image of Scenario A in the System Reliability Analysis example, the elements in the Diagram for Scenario A root subsystem are connected in a series: every element between the Start and End elements has one connection from an element and one connection to an element, and you can reach the End element from the Start element in only one way.

When you connect elements in parallel to one another, one or more elements will be connected to multiple elements, and there will be multiple paths from the Start element to the End element. For example, in the System Reliability Analysis example, the Bottling Line elements in the Bottling Subsystem root subsystem are connected in parallel. In this case, the Start element and the Linkelement are connected to three Subsystem elements: Bottling Line 1, Bottling Line 2, and Bottling Line 3. Therefore, there are three different paths from the Start element to the End element, depending on which of the three Bottling Lines that you pass through.

When a Risk will be reset automatically is determined by the failure type of that Risk. A Risk whose failure type is Failure With Replacement will be reset automatically when any of the following scenarios occur:

• An unplanned correction takes place following the occurrence of a Risk.
• A planned correction takes place to mitigate the occurrence of a Risk.
• Preventive Maintenance is performed against a piece of equipment to mitigate the occurrence of a Risk.
• A Special Action with a TTF replacement is performed against a piece of equipment to mitigate the occurrence of a Risk.

A Risk whose failure type is Failure Without Replacement will be reset automatically when any of the following scenarios occurs:

• Preventive Maintenance is performed against a piece of equipment to mitigate the occurrence of a Risk.
• A Special Action with a TTF replacement is performed against a piece of equipment to mitigate the occurrence of a Risk.

Suppose that the following Risks with a failure type of Failure With Replacement are defined in your simulation for a Water Pump:

• Bearing Failure
• Impeller Failure
• Seal Failure

In the simulation, after unplanned correction is completed following the occurrence of the Bearing Failure Risk , the time in-service for the Bearing will be reset automatically to zero (0) to indicate that you will replace the Bearing after it fails so that the Bearing Failure Risk will not occur again until the defined TTF Distribution is reached.

In addition to Risks being reset automatically as described in the preceding scenarios, you can specify that additional Risks be reset following the planned or unplanned correction of a given Risk. In other words, you can specify a Risk as a source Risk, whose planned or unplanned correction triggers additional Risks to be reset at that time. This means that the time in-service for the components associated with the additional Risks will be changed to zero (0), indicating that the additional components were also replaced (or repaired to as good as new) following the planned or unplanned correction of the source Risk.

Throughout the documentation we will use the term source Risk to refer to a Risk whose planned or unplanned correction triggers the resetting of additional Risks. We will use the term additional Risk to refer to Risks that are reset by the planned or unplanned correction of a source Risk.

You can specify that additional Risks should be reset only when:

• An unplanned correction takes place following the occurrence of a source Risk.

  -or-

• A planned correction takes place to mitigate the occurrence of a source Risk.

Source Risks that are mitigated as a result of Special Action with a TTF replacement or Preventive Maintenance will not trigger any additional Risks to be reset.

Suppose that:

• You will replace the Seal, in addition to the Bearing, when the Bearing Failure Risk occurs.

  -or-

• The planned correction that you perform to mitigate the occurrence of the Bearing Failure Risk will also mitigate the occurrence of the Seal Failure Risk.

In this case, you want to indicate in your simulation that the Bearing Failure Risk (i.e., the source Risk) should reset the Seal Failure Risk (i.e., the additional Risk). In other words, the time that the Seal has been in-service will also be changed to zero (0) to reflect that the Seal will be replaced (or repaired to as good as new) following the planned or unplanned correction of the Bearing Failure Risk.

You can specify any Risk that is defined for an Asset as a source Risk or an additional Risk, with a few exceptions. When you set up a simulation to include source Risks and additional Risks, you must follow these rules:

• You can specify a Risk as a source Risk if the failure type for that Risk is:

  • Failure With Replacement

    -or-

  • Failure Without Replacement
• You can specify a Risk as an additional Risk only if the failure type for that Risk is Failure With Replacement.

In the simulation, only Risks whose failure type is Failure With Replacement are reset following a planned or unplanned correction. Risks whose failure type is Failure Without Replacement are not reset following planned or unplanned correction because the components associated with these Risks are not replaced (or repaired to as good as new). Specifically, this means that a Risk whose failure type is Failure Without Replacement:

• Can be specified as a source Risk. In other words, the planned or unplanned correction of these Risks can trigger additional Risks to be reset, if the failure type of the additional Risks is Failure With Replacement.
• Cannot be specified as additional Risks. The rows containing Risks whose failure type is Failure Without Replacement are disabled.

Suppose that the following Risks with the following failure types are defined for a Shell and Tube Heat Exchanger:

• A Tube Bundle Failure Risk whose failure type is Failure Without Replacement.
• A Shell Head Failure Risk whose failure type is Failure With Replacement.
• A Seals (gaskets) Failure Risk whose failure type is Failure With Replacement.

Now suppose that when you complete planned or unplanned correction for the Tube Bundle Failure Risk, though you will not replace (or repair to as good as new) the Tube Bundle, you will replace (or repair to as good as new) the Seals (gaskets). In this case, you want to indicate in your simulation that the Tube Bundle Failure Risk is a source Risk that should trigger the resetting of the Seals (gaskets) Failure Risk (i.e., an additional Risk). In other words, the time that the Seals (gaskets) has been in service will be changed to zero (0) to reflect that the Seals (gaskets) will be replaced (or repaired to as good as new) following the planned or unplanned correction of the Tube Bundle Failure Risk.