6 replies to this topic

[JKM]

Dear All,

 

As per the API 521 Sixth Edition "Table 9- Typical K-factor for Pipe Fittings" it has been specified as below:

a. Rupture Disc, sub critical flow: 1.5

b.  K-Factor, open                       :  0.21

 

1. Please clarify what are the typical value of K-factor(rupture disc) for the Critical Flow case.

2. Please clarify why K-factor of rupture disc is nearly 8 times that of Gate Valve. If I understand it correctly then after bursting the inside dia will be  equal to the pipe diameter. So there should be no resistance. And for conservative approach it could be equal to resistance offered by Gate valve(open) but not 8 times higher. On assuming the rupture disc K-factor equivalent of 8 gate valve, our inlet pipe size increases to meet the criteria of 3% pressure drop.

 

 

 

Regards

JKM

Edited by JKM, 22 June 2016 - 09:58 PM.

[breizh]

Hi ,

You may consider the document attached with examples .

Hope this helps

Breizh

 

[S J]

JKM

 

Why do you need K value at critical flow ?

It may not critical flow at PSV inlet line.

[JKM]

Dear Briezh,

Thanks a lot for your reply. However my 2nd question is still not answered. In our team we are discussing API data. For us K- factor of 1.5 compared to 0.21 of gate valve seems too high.  Please share your thought on this.

 

SJ

As per our calculation the flow shall be critical.

[latexman]

Some reasons that I have seen.  The opening does not tear or break into a perfectly round, smooth opening as a full open gate valve.  There are pieces of the metal/graphite remaining in the flow path.  Comparing a PSE to an open butterfly valve is more fair.

[S J]

JKM

 

Is rupture disc installed at inlet of PSV ?

If so, it's not possible that pressure drop through rupture disc exceeds critical pressure ratio.

Reaching critical flow means that pressure drop is much higher than 3%.

 

Otherwise, are you clarifying rupture disc installed alone ?

[breizh]

http://www.cheresour...ngineers-part-2

 

Take a look .

Breizh