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For These Reasons, Don’t Calculate Availability from Work Orders

Ahmed Kotb | Asset Strategy and Standards Engineer, TRANSCO

For These Reasons, Don’t Calculate Availability from Work Orders

During my work experience, the source of data for calculating the asset availability was discussed several times on different levels and in many meetings.

In most cases, I found that there’s a common belief that the maintenance work orders in CMMS are the data source for calculating the availability, considering that the duration between actual job start (date and time) and actual finish (date and time) represents the asset downtime.

If we refer to the below figure (published by SMRP), it shows clearly that the above-mentioned time (actual start to actual finish) recorded on the work order is the asset “repair time” NOT the asset “downtime”, and as you can see, asset repair time represents a small portion of the asset downtime and hence can’t be considered for calculating the asset availability.

Total Asset Downtime

As you know, the simplest formula for calculating the availability is:

Availability % = Uptime ÷ (Uptime + Downtime) x 100


Uptime = Total Available Time – Downtime

Downtime = Scheduled Downtime + Unscheduled Downtime

Scheduled Downtime is the time required for completing the planned maintenance (PM, PdM,etc.) and unscheduled downtime is the time an asset is down for repairs or modifications that are not on the maintenance schedule.

The question now is, if the maintenance work orders in the CMMS are not the correct data source for the asset downtime, where can we find it?

The answer is that the only accurate source for the actual downtime of an asset and its category (i.e. for PM, PdM, CM, BD, Standby, etc.) is the operations daily asset operating time log.

Operations normally have a daily log for each main asset that records the categorized downtime plus the uptime.

Table 1 shows an example of a simple daily asset operating time log for one month that is updated on daily basis by Operations:

Table showing accurate asset availability calculations

From this table, the availability can be easily and accurately calculated for each asset, as all required figures for the availability calculation formula are available and accurate.

The repair time on the work order not only can’t represent the asset total downtime but also in many cases is not accurate even for the repair time itself, as most likely (but of course this is not a good practice) the technician/trade will fill this time in the work order after going back to the workshop and by that time they will not be able to remember exactly what time the job started and finished.

Asset availability also can’t be calculated automatically from the SCADA system because the SCADA system will not categorize the downtime according to its reason; it’ll show only when the asset was up and when it was down/tripped but will not show the type of maintenance that was carried out on the asset while it was down. Also, SCADA system will not show the operations preparation work to put the asset back to service, which is part of the asset downtime.

In brief, I believe that the only accurate source for calculating the asset availability is the operations asset operating time log NOT the work orders.

I hope that this article has helped you.

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About the Author

Ahmed Kotb Asset Strategy and Standards Engineer, TRANSCO

Asset Management and Reliability Team Leader with more than 33 years of experience in Maintenance and Reliability, Maintenance Planning and Scheduling and Asset Management fields. More than 26 years of experience in the Oil and Gas industry in international leading companies (Shell, BP and Total) including more than 22 years in Maintenance Planning and Scheduling.

Certified Asset Reliability Practitioner (ARP CAT-I) from Mobius Institute. Certified Trainer from the International Training & Consultancy Forum (ITCF).

Led several CMMS/AMS system Implementations. Experience of EPC Mega Projects where Led the Asset Management Team and one of the largest Asset Management System implementation projects in the Middle East for ADNOC Offshore new fields (EPC mega projects in UAE) that involved more than 180,000 assets.

Experience involved leading several Teams such as Maintenance Planning and Scheduling Teams (3 times), Asset Management Team, Asset Management System Project Team and Reliability and Data Management Team (in Shell/BP/Total joint-venture companies). Planned more than 40 major Shutdowns / Turnarounds and several major overhauls.

Public speaker who conducted presentations, workshops, masterclasses and webinars in major international conferences around the world. Course instructor who conducted several courses (real and virtual classes) in Maintenance and Reliability (RCM, RCFA, etc.), Maintenance Planning and Scheduling, and Asset Management fields in several countries.

Member of Egyptian Engineering Syndicate (EES), the Society for Maintenance and Reliability Professionals (SMRP), Gulf Society for Maintenance and Reliability (GSMR) and ITCF. Published Author on website powered by Mobius Institute.