Why Mechanical Run Test shall be done 4hours?

Ever wondering the reason why 4hours duration of mechanical run test being adopted all these years?

Several code standards mention this and as engineer in charge you shall either specify or not, depend on your judgement

I take sample from API 610, for pumps, on since the old edition this already stated as, if specified pump shall be mechanically run at rated flow for 4h

Why not 2 or 3 or 6 or 8hours? at the beginning you may question why, because not much explanation or the explanation quite confusing and not straight forward see API 610 ed 11th talk about ambient 43centigrade etc., not many people will understand.

However, in edition 12th, it is easier to understand, as long as temperature rise relative to ambient not more than 1centigrade, you able to claim, it already run at stable temperature, in my perspective, if you have a bearing that cold or same as ambient temperature, then you run for 10minutes, 20 minutes, 1 hours, if you measure the temperature it keep goes up until there is balance between heat generated = heat dissipated.

Heat generated comes from the friction

Heat dissipated comes from convection, radiation and conduction (sometimes negligible for conduction for air cooled).

Back to topic why 4hours, I tried to give my opinion on this, after several times doing FAT for centrifugal pumps, positive displacement pump, diesel engine.

This 4-hours run give a good judgement whether our equipment in real case that it will run 24/7 365days, it will cycle the same, without risk of deteriorating effect of temperature, means the cooling system is correct. Same as us human, mechanical equipment does not like too hot or too cold temperature.

Some COMPANY spec for diesel engine ask for 8hours run test, which in my personal opinion it is too much and not easy to execute, imagine during the day of the test, how you will manage practically let say the run test start at 9AM(ideal), because normally people start work at 7-8AM, they do preparation first before do FAT, to verify the safety and all auxiliary ready, sometimes waiting for another 3rd party or equipment principal, then you start the test when everyone already get the briefing of today test, 9AM +8hours = 17.00 or 5PM, then need to debrief, before of that, we need to agree on how many times data shall be taken and what data, if all data is acquisition by digital means, it is easy, but, several data is manually taken, such as noise, handheld vibration, local pressure gauge or temperature, sometimes let say you want 15-minutes cycle, it cannot be completed because operator will take time to rotate to all location, sometimes, 2teams is made for consistency and redundancy, so it will came to 30-minutes cycle for more humane way of execution. However, sometimes for complex package I do 15-minutes data cycle for first 1-hours, then after that 30minutes, since generally after 1 hour 90%stable temperature is reached.

I do a deviation proposal during my time as contractor to lower down diesel engine test from 8hours to 4hours, considering above struggle and also minimize carbon footprint, yes, the deviation was accepted, they like the reason to save carbon for 4hours. While the engine will run for a lifetime producing carbon, but you can picture the message. (thinking about Prophet Moses and ant's story). I bought total 4units 1MW EDG, and 2 small unit EDG less than 1MW, each unit done 1-day 4-hours running test, it is tiring but also exciting. I do squeeze this equipment to show it true potential and verify the design robustness.

Finally, to conclude reason why 4-hours being used in my opinion

1. It already shown the stability of the system
2. Stable temperature which defines as no more than 1centigrade raise in 10minutes interval reached
3. More practical in term of execution to manage the available day working time, preparation, spare time, data acquisition etc.

Case: if during FAT you measure several temperatures, for instance Diesel Engine Generator, you will measure engine oil temperature, engine coolant temperature, engine air intake temperature, fuel temperature, exhaust temperature, alternator bearing DE NDE and winding U V W. Which one you take as reference temperature to define; "yes, this equipment reaches stable temperature"?