3 replies to this topic

[MechTech2010]

I am fairly new to relief system design, and was hoping this forum could provide some clarification on the following issue.

 

When a R.D and R.V are installed in a series configuration (R.D upstream of R.V inlet) is it acceptable, required, or forbid for the burst pressure of the R.D to be lower than the set pressure of the R.V?  For example; the R.D has a burst pressure of 150 psig (0% manufacturing tolerance) and the R.V has a set pressure of 145 psig, protecting a vessel with a MAWP of 150 psig.

 

ASME UG-127 footnote 52 states: "Use of a rupture disk device in combination with a pressure relief valve shall be carefully evaluated to ensure that the media being handled and the valve operational characteristics will result in opening of the valve coincident with the bursting of the rupture disk."

 

However, API 520 section 4.3.2.2.2 states that:" When a R.D is installed at the inlet of a R.V, the devices are considered to be close coupled, and the specified burst pressure and set pressure should be the same nominal value."

 

Could one of the more experienced members shed some light on this?

Thank you in advance.

[fallah]

Hi,

 

As far as i know, as per various guidelines in API and ASME for a R.D./R.V. combination, the marked burst pressure of the R.D cannot be higher than the marked set pressure of the R.V., but can be lower.

For example in ASME UG-132 (a)(4)(a), for R.D./R.V. combination capacity testing, it is mentioned that: "...The marked burst pressure shall be between 90% and 100% of the marked set pressure of the valve."

[flarenuf]

hi

i agree with Fallah here

 

from National Board Pressure Relief Department

1. Confirm the marked disk set pressure is equal to or less than the vessel MAWP.
    
2. Look at the marked disk temperature and confirm it has been specified so that it is the temperature of the disk when it is expected to burst, and not the vessel design temperature. Normal operating conditions, upset conditions, and environmental effects should all be considered.
   
   the latter is very important as burst pressure is related to temp , if disc is colder than designed for  then burst pressure could be higher than PSV set pressure
    
3. flarenuf

[MechTech2010]

Fallah & Flarenuf, Thank you for the replies.

 

I will have to re-read UG-132.  I was under the impression that section specifically addressed the requirements that the valve and/or disk manufacture must following to certify the capacity of their product.  I do not have the code in front of me, but I will be sure to check that section tomorrow morning.

 

Thanks again.