String Testing of a Lube Oil System

[RogerSAM]

Hello everyone,

I have a specific case that I needed some insight on since I am a relatively new engineer who is still learning.

We conducted a string test to check the response of a lube oil system that consisted of two pumps - 1 main and 1 standby. The main turbine driven pump was manually tripped and the system transient response during the stand-by's cut-in period was verified. The test was successful and header pressure did not drop to alarm levels during the test.

Now the question is around 5 minutes or so before the test, both the pumps were operational. The stand-by pump was then shutdown to conduct the test. My senior is telling me that since the stand-by pump was just recently shut off, it doesn't simulate the real behaviour because during the normal operation, the stand-by would be off for a long time. So although in the test, it generated pressure fast, it wont necessarily do it in the actual real world scenario. He's talking about breaking of the inertia of the fluid etc. that just doesnt make sense to me.

Is he right?

 

[seuenergy]

hi,
Could you provide the P&ID of the lube oil system?
Currently, I could not get your senior's point. Is he talking about the filling conditions of the inlet pipeline of stand-by pump is different for long term shut down and short term shut down?

 

[RogerSAM]

hi,
Could you provide the P&ID of the lube oil system?
Currently, I could not get your senior's point. Is he talking about the filling conditions of the inlet pipeline of stand-by pump is different for long term shut down and short term shut down?

Please find the P&ID attached.

Both are the same.

Here is the full breakdown of the problem:
We recently experienced a tripping on the main lube oil pump motor. This led to the whole machine tripping within 1.5s while the standby pump recovered the pressure within 1.8s.

So obviously we suspected problems with the accumulator and turns out they only have an oil capacity of 21 liters while being responsible for both the hydraulic oil and the lubricating oil. Not to mention, their location is not very ideal as their oil will have to go through a bunch of filters and exchangers before serving their purpose.

We conducted the string test back in 2022 which somehow passed so we were looking for reasons as to why the transient response of the LO system was adequate then but it isnt now. Thats when my senior mentioned the reasoning that standby pump had been recently taken offline before the test which could contribute to the overall pressure recovery in 2022.

Are there any other deficiencies that I am missing in the P&ID that may be contributing to such an erratic transient response of the LO system? Something that is not in line with industrial best practices?

p.s for your convenience, i have highlighted the LO lines in the P&ID