Reciprocating compressor piping vibration

[fespindola]

A client asked us to perform a stress and vibration analysis of a reciprocating compressor piping system, because they were concerned with vibration level (34 mm/s) - which is high - and believed that it was taking place only by bad piping supports.

The plant is 40 years old and they had just modified "something" to make the discharge pressure go from 30 bar to 80 bar, without changing the suction pressure. After some time studying the case we discover that our client had no idea what was the problem and neither had drawings or detailed information about the machine and its system. Till now, we just know that the discharge piping was changed for a smaller diameter (NPS 4).

We did a process study for this new operating conditions, which concluded that the flow speed in the discharge piping is adequate and that there are some two-phase flow, after the air-cooler, but not enough to led to pipe vibration.

Now, we believe that the pulsation bottles may not be effective anymore, as the discharge pressure and the discharge pipe dia. has changed. We will use the API 618 design approaches to evaluate them.

Has anyone dealt with a problem like this?
The change in discharge pressure and piping dia. is enough to led to this high vibration level?
Are the pulsation bottles undersized?

Thanks,
Fespindola

 

[BigInch]

Yes to all.
That was a pretty dumb move by your client.
There is nearly 3 times the mass running through that system and at least twice the velocity before reducing the discharge pipe size. Be sure that the natural frequency of the pipe & span is not a resonance multiple of speed x number of cylinders.


I hate Windowz 8!!!!

 

[fespindola]

Thanks, BigInch.
As the design approach 1 of API 618 is just a reference for pulsation bottles sizing, do you know any other reference or sizing criteria that we could use, besides the acoustical simulation?