7 replies to this topic

[Linus Van Pelt]

I'm looking for some discussion or advice please on installing two rupture discs in series on a vessel emergency vent line.

 

Due to space constraints I cannot install a double disc assembly, so the disc locations will be about 4m apart on the 10" line.

 

The purpose of the second disc is to provide backup in case of corrosion of the first disc.

 

I'm wondering if there are restrictions on the set pressure of the downstream disc?

 

Is it acceptable to set the pressure the same as the first disc? should I be concerned about some sort of back-pressure effect? or will it simply burst simultaneously with the first disc?

 

I'm used to installing a second very low pressure disc where a sub-header joins the main header, but not two-discs in series at similar set pressures.

 

I know I'll need to vent the space between the discs and use an excess flow valve, etc. but is there anything else I need to be aware of?

 

Thanks in advance for any pointers.

[fallah]

Hi,

 

They should have the same set pressure...

 

The pipe segment between two RD's should be equipped with a pressure gauge and a pressure transmitter (with high pressure alarm) to announce the operator when the first RD would be failed... 

[Linus Van Pelt]

Thanks for taking the time to respond Fallah.  

 

Can you elaborate on why its acceptable to set the second disc at the same pressure as the first?  

 

I know that if the discs are close-coupled, such as in a 'double disc assembly' then they would be set at the same set pressures, but I presume if the second disc was to be positioned, say, at the end of the line then it would not be acceptable to set it at the same pressure (?).  

 

So, my question is: is there a location along the vent line (with its pressure profile) where it becomes not acceptable to have the discs set the same? and how does one identify this location?

 

Thanks for any responses.

[breizh]

Hi ,

 

http://webwormcpt.bl...-in-series.html

 

Similar to what Fallah said .

 

A customized system :

 

http://www.contdisc....c-Assembly.html

 

Note : go to literature on this web page .

 

 

Breizh

Edited by breizh, 07 February 2016 - 10:35 PM.

[fallah]

 

So, my question is: is there a location along the vent line (with its pressure profile) where it becomes not acceptable to have the discs set the same? and how does one identify this location?

 

 

It should be investigated case by case...
 

[Linus Van Pelt]

Thank you, but it is precisely *how* to do this investigation that I am not clear on.

[fallah]

Luis,

 

As long as the "double discs assembly" is set in order to avoid the main disc (latter one) would be subject to corrosion or other similar damages, regardless of the distance between two discs, there is no reason based on which two discs being set at two different pressure values...

[Ganesh Buddha]

they should be set at the same pressure...

 

the criteria is if the discs are to burst on a positive pressure then the header pressure i.e if they are to rupture at high pressure for venting, then the alarm as explained by Mr Fallah would experience relatively high pressure for a momentary notice only. as both the discs should rupture at the same time in the case of pressure escalation. the alarm set up would be eligible only in case of rupture due to corrosion of first disc.