4 replies to this topic

[chemks2012]

Dear all,

 

Need your help again please.

 

I have designed a valve using PSG8 [which more or less uses same formulas as that of API520] and supplier quoted a ASME VIII valve.

As we know the actual orifice area of ASME valves are larger than API valves. However, supplier is trying to explain that both valves are one and the same.

1. However, I do not agree with supplier as orifice area of both valves are different e.g.  ‘L’ orifice in ASME equates to 2118mm2 while that in API equates to 1840mm2. And I am wondering how can these two valves are same? I understand that it is better to install a valve with bigger orifice [ASME] valve but not sure if this is allowed?
2. Also, I am checking pressure relief documents prepared by someone if past and it seems that he designed valve based on PSG8 and valve supplier has supplied ASME valve. Is this OK?
3. Also, to my surprise, supplier has quoted ASME ‘L’ orifice area of 2078.06mm2 which is again different to standard ASME orifice L area stated above.
4. Similarly, supplier has quoted ASME ‘J’ orifice area of 937.417mm2 instead of standard ASME area of 940mm2. Not sure how and why?

Any help please.

Thanks a lot.

Edited by chemks2012, 17 February 2014 - 06:19 AM.

[fallah]

Hi,

 

To compare the capacity of the API and ASME valves you should compare the product of the orifice area multiplied by coefficient of discharge for each valve not orifice area itself. All you need is ensuring the certified capacity of the PSV not to be lower than the required relief load for that PSV...

[chemks2012]

Hi Fallah,

 

Thanks for your reply.

Yes, agree with you - I have multiplied Kd with orifice area and as expected ASME VIII valve has larger effective orifice area.

 

But are you saying that though I designed the valve based on API 520 formulas, I can have ASME VIII valve?

 

Also what do you think the reasons for point 3 and 4 in my original post? [i.e. ASME orifice area quoted by supplier is different],

 

Thanks in advance.

KS

[fallah]

Hi,

 

API method is a way to get a preliminary estimate of the PSV size. Obviously, final sizing must be done using the ASME orifice area and certified coefficient of discharge.

 

It might the supplier has quoted two different PSVs from two different manufacturers. If so, ASME orifice area for two valves could be different while orifice area multiplied by coefficient of discharge for two valves are almost equal...

Edited by fallah, 18 February 2014 - 01:57 AM.

[chemks2012]

Thanks Fallah.

Much appreciated your help.

Edited by chemks2012, 18 February 2014 - 03:29 AM.