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Corrective Tasks

Preventive Tasks

Inspection Tasks

On Condition Tasks


 ReliaWiki: Imperfect Repairs

Tasks

To properly analyze repairable systems, we first need to understand how components in these systems are restored (i.e., the maintenance activities that are performed on the components). In general, maintenance is defined as any action that restores failed units to an operational condition or keeps non-failed units in an operational state. For repairable systems, maintenance plays a vital role in the life of a system. It affects the system's overall reliability, availability, downtime, cost of operation, etc.

In ReliaSoft applications, maintenance activities are represented using tasks, which are resources that can be shared among analyses and can be managed via the Resource Manager. There are two basic kinds of tasks, which comprise four task classes:

Tasks are assigned to URDs, which are in turn used to represent a set of properties that can be applied to standard blocks in RBDs and to events in fault trees.

The Maintenance Task window allows you to create, view and edit all classes of maintenance tasks. It can be accessed by clicking the Create New or View/Edit icon in the Task wizard, which is accessed from Task fields in properties windows (e.g., the Corrective Maintenance Task field in the Universal Reliability Definition window).

  

It can also be accessed from the Corrective Tasks and Scheduled Tasks pages of the Resource Manager by choosing Home > Edit > Add, by selecting a task and choosing Home > Edit > View or by double-clicking a task.

For a new resource, a name will be proposed automatically based on the default naming criteria established for the current database (see Default Name Formats window). You can replace this with your own name of up to 150 characters, if desired. Remember that the name and identifiers are the primary way in which your team will be able to find the resources you need for your analyses.

The following options must be configured for all classes of tasks. Configuration options that are specific to particular task classes are presented in the corresponding sections.

If no crew is assigned, it is assumed that the work will be done by some undefined crew that is always available.

For simulation, the application uses the restoration factor to determine the new age of the block after the maintenance action.

For example, consider an automotive engine that fails after 6 years. If the engine is rebuilt and the rebuilding task has a 50% restoration factor:

The engine fails again after 3 years (when it again reaches the effective "age" of 6 years), but the rebuild this time affects only the age accumulated after the first rebuild. Thus the engine has an effective age of 4.5 years after the second rebuild (3 + 3 x (1 - 0.5) = 4.5).

After the second rebuild, the engine fails again after a period of 1.5 years (when it again reaches the effective age of 6 years) and a third rebuild is required. The effective age of the engine after the third rebuild is 5.25 years (4.5 + 1.5 × (1 - 0.5) = 5.25).

The engine fails again after 3 years (when it again reaches an effective age of 6 years) and another rebuild is required. This rebuild also rejuvenates the engine by 50%, thus making it effectively 3 years old again.

After the second rebuild, the engine fails again after a period of 3 years (when it again reaches the effective age of 6 years) and a third rebuild is required. The effective age of the engine after the third rebuild is 3 years.

Compare the following tables to see how the two options differ.

Only Damage Accumulated Since Last Repair

Time

Time Since Last Repair

Effective Age Before Repair

Effective Age After Repair

Start = 0

0

0

0

6 years

6

6

3

9 years

3

6

4.5

10.5 years

1.5

6

5.25

 

All Accumulated Damage

Time

Time Since Last Repair

Effective Age Before Repair

Effective Age After Repair

Start = 0

0

0

0

6 years

6

6

3

9 years

3

6

3

12 years

3

6

3

 

The ReliaWiki resource portal has more information on restoration factors at: http://www.reliawiki.org/index.php/Repairable_Systems_Analysis_Through_Simulation.

 

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