Emerson Exchange 365

Do you have more information that you could provide?  It would be helpful to have the full operating conditions as well as a valve serial number to ensure the valve is appropriately sized and selected for how this application is currently operating.  Have you worked with your local sales office to have them review this application in detail?  I'd be happy to get you in touch with someone local to help solve your problem.

In reply to Janine McCormick:

Hi Janine

the valve data sheet 

In reply to Jim Cahill:

Just looking at the data sheet, this looks like a very high pressure drop application (>18 bar). With such high pressure drop, cavitation would be a problem that eats away your valve trim. I'm not sure what's the pressure drop in your actual application, but with 15 barg upstream, you would expect cavitation if you have more than 8 bar pressure drop across your valve. In order to avoid cavitation, I would suggest you to add a second stage control valve downstream of your current valve to reduce the pressure drop across your first stage.

In reply to Eric Tam:

Hi Etam

yes the pressure drop is about 15 bar

In reply to Jim Cahill:

Hi Mohsen,

In your original post, you stated that the pressure is 15 bar, so I assumed it’s the inlet pressure. However, in the datasheet that you posted, the inlet pressure is 20 barg and the pressure drop is about 18.7 bar. So, which is the inlet pressure and which is the pressure drop across the valve?

Nevertheless, assuming that the inlet pressure is 20 barg, you would expect cavitation at pressure drop greater than 10 bar, so with 15 bar drop across the valve, you’ll definitely have cavitation and the erosion is caused by the shockwaves from the gas bubbles that are imploding on your valve trim.

In this case, you’ll have to lower the pressure drop across your valve by adding another control stage upstream or downstream of your existing valve, assuming that the pressure drop across your control elements has to be retained at 15 bar.

Cheers, Eric

In reply to Eric Tam:

Thanks so much for your post, Mohsen and for your insight, Eric. Working through the problem on this forum, ensures others can learn from your experience, Mohsen. Please keep us updated on Emerson Exchange 365 as to whether this information has helped you solve your problem.  Cheers!

Best Regards,

Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast

Hello,

My name is Shawn Fagen.  I am a Sales Engineer for Emerson - Fisher Division in Marshalltown, IA.  I am in the Refining group here and Janine McCormick is my manager.  She had me take a look at this and there are a few specific things I want to review.  If possible, can you send me the serial card for this valve?  If you would not like to post it on the message board, you can send it to me at [email protected]

In reply to Shawn Fagen:

Hi

Thanks or your answers

the inlet pressure of valve is 15 Bar (working Pressure), and the outlet is atmosphere.

the valve is installed in out of site battery limit, and i have to go there and check the serial number, i try to go there and write it, but if need another data to help me, I would appreciate  it  if you could let me know

Best Regards,

Mohsen

In reply to Jim Cahill:

Hi Mohsen,

As mentioned in my previous post, if your inlet pressure is 15 barg, then cavitation is expected at 8 bar pressure drop. From your valve data sheet, it appears that you’re using an anti-cavitation valve that typically prevent cavitation by dissipating the energy through three stages. If the limit of design is not exceeded, cavitation would only occur in the centre of the seat cage and the fluid exist through the radial holes of the cavitation sleeve (as shown in your original post) without phase change. However, if the pressure drop across the inner and outer part of the cavitation sleeve exceed the vapour pressure, cavitation would still occur as the fluid travel through the cavitation sleeve, causing erosions on the outer part of the sleeve.

The only way to resolve this issue is to increase the number of pressure reduction stages so that the pressure drop across each stage does not exceed the limit at each stage.

Cheers, Eric

In reply to Eric Tam:

Hello Mohsen,

Considering the possible cavitation-problem it could be worth looking into the possibility to, as described above, add another pressure reducing stage.

One option that could be worth to look closer into is to use a diffuser disc (restriction orifice but with multiple small holes) to take a part of the pressure drop from the valve.

This could be clamped (wafer style) between the valve outlet flange and the pipe flange, this disc would take the last part of the pressure drop protecting the control valve and if it is damaged by cavitaion despite the extra pressure stage it is easily replaced and not to expensive.

Though it is important that it is sized together with the control valve, taking 1/2-1/3 of the pressure drop at max flow without making the valve to small or out of good control range.

Then you need to look at the complete flow range and calculate the disc dP as this decreases with the flow.

This is just a second input to the problem and I have not made any calculations of my own only adding another idea worth looking closer at.

Regards Niklas

I think Niklas has made a very good suggestion. This reminds me of the good old diffusor that's fitted on the outlet of every water faucet. The only thing to watch out is the reduction of Cv of your flow control valve after installing the diffusor, as this reduces the differential pressure across your valve and therefore the Cv. However, your 12" valve seems to have plenty of capacity for the flow you need. Actually, looking at the erosion mark on the valve trim, it appears that the valve is only used at partial capacity most of the time.

In reply to Eric Tam:

Thanks Niklas and Eric

I would appreciate  it , if you find another idea

Mohsen,
The pictures suggest that this might be a result of stagnant sea water on one side of the cage to which Monel is known to be susceptible. Does it happen that the valve is exposed to stagnant sea water?

Regards,

Nishanth N