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Equipment Production Loss Contribution

  • 462 Words, 15 Min Read

    AssetStudio's AeROS software was used in this article

This presentation shows how to assess production loss due to equipment unreliability for equipment arranged in: series, parallel and standby configurations.

Consider a production system consists of equipment operating in series.

Fig.1 Equipment operating in series

The reliability models, corrective maintenance downtimes and flowrate (production rate) of each equipment are assumed as follow:

Fig.2 Reliability and Corrective Maintenance settings for each equipment

Equipment Production Loss Contribution analysis is imperative for plant operation.

We wish to rank the equipment performance based on its production loss.

The simulation results are obtained through a 365-day simulation with 1000 executions.

Fig.3 Simulation results for each equipment (Regular Node)

The simulation results table provides the downtime of each equipment. The loss due to each equipment can be estimated by multiplied its Total Downtime by its Flowrate.

Fig.4

Note that C and D have a maximum flowrate of 2 units/hour, but its actual flowrates are constrained by equipment A and B maximum flowrates.

Consider a production system with the following construct, where the reliability models, downtime behaviors and flowrates are the same as last example.

Fig.5

A simulation results is obtained through a 365-day simulation with 1000 executions.

Fig.6

The loss due to each equipment is its downtime multiplied by flowrate.

Fig.7

The downtimes can be obtained from the simulation results. When estimating the equipment production loss, analyst will have to decide the correct flowrate base on the production flow design.

In the above 2 examples, the losses are calculated based on the fact that the downtime of each item directly contribute to the system loss.

Consider a scenario which involves equipment in standby configuration.

Fig.8

The system operates with 3-by-2 standby configuration, and switching occurs every 200 hours. If 2 units fail, the system operates with 1 unit, as such it operates with half the load.

The 3 pumps are identical, with Exponential failure distribution (mean = 200 hours), and each takes 50 hours to repair upon failure. The individual flowrate (production throughput) is 1 unit per hour. Therefore, the system flowrate is 2 unit per hour.

A simulation results is obtained through a 1000-hour simulation with 1000 executions.

At the system level, the Efficiency is 0.9817, and the production is 1963 units (over 1000 hours). We can deduce that the loss is 37 units.

Fig.9

At the equipment level (Regular Node tab):

Fig.10

Note that when an item fails in a standby situation, its failure may not contribute to loss (as long as standby is available). Therefore, we cannot use the downtimes of individual equipment to deduce the total loss as we did in the previous two examples.

Since these 3 pumps are identical, and the total loss is 37 units. We can therefore conclude that each pump contributes a loss of 37/3 units over 1000 hours operation.


Conclusion

In summary, for series or parallel (or combination) network, we can use the simulation downtime information of individual item to deduce its loss contribution. For the case of standby system, first deduce the losses at system level, then ascribe the losses to each item equally. This works only for the case that all items are identical. In the next article, we will look at loss contribution for standby system ( RAM Analysis for an Offshore Platform).

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