Hi All,

When calculating a nozzle reinforcement in a 2:1 ellipsoidal head the min required thickness for the head is needed in order to specify the reinforcement areas. The formula for that is

t = (P*(D+2*CA)*K) / (2*S*E-0.2*P)

We received a calculation done by one of our subcontractor (using Compress) and the K factor they were using is 0.9.
We ran our own calculation in PVElite and the K factor has come out as 1.
To check which is right we've calculated the same with Finglow which used 0.9 as well.
We had a look in ASME and in UG37 it states 0.9 for 2:1 heads but in 1-4 it states 1. We cannot decide which is right and which is wrong. As I see it now, it should be 0.9, but I'm not sure. And if it's 0.9 then I don't undestand why we're using 1 to specify the required head thickness, and 0.9 to specify the same thing in the nozzle reinforcement calculation.

Please someone explain this to me.

Thank you.
Istvan

Please read the forum on the link below:

K factor

Please notice that this is a new feature on PV Elite 2009

Istvan,

The use of 0.9 or 1.0 in the formula depends on the location of the nozzle in the head. If the nozzle and its reinforcement limit lie within the spherical part of the head, the required thickness of the ellipse (spherical portion) can be computed as a sphere (K = 0.9), otherwise the nozzle or its reinforcement lies within the knuckle region and the value of tr is computed as if the head were a regular ellipse. So, you need to check the input and make sure all of your calculations are "on the same page".

By reinforcement, I mean the "diameter limit" that was used. In the 2009 version of PV Elite the "K" value is taken in the corroded condition, so it might be a slightly smaller value than 0.9 or 1.0. But this makes very little difference. That is what Luis was acutally referring to above.

Thanks for the answers.
I'm getting there to undestand it. :-)
So as our shell diameter D (as stated in ASME the inside diameter) is 914.4, 80% of that is 731.52.
PVElite, Compress and the Finglow calculations all agree that the reinforcement radius limit of our nozzle is 387 which is 774 in diameter which is greater than 731.52 therefore they all should be using 1 as factor K. (PVElite is using 1)
As per UG37, Table UG37 can only be used when the opening and its reinforcement are located entirely within the 80% of the head diameter.

Is this correct?

This is a bit scary because with K=1 this reinforcement is insufficient, with K=0.9 it's sufficient to code.

BTW even if the diameter was the o/d, the wall thickness is 12 so o/d is 938.4, 80% of that is 750.72 which is still smaller that the diameter limit 774.

Hi Istvan,

You have the right idea. Review the definition of tr in UG-37. An undocumented feature of PV Elite is the use of the semicolon ";" in the nozzle description. If you have a semicolon present in the Nozzle description field, the following 2 lines will print out in the nozzle report.

Distance from Head Center to Knuckle Curvature 38.4000 in.
Distance from Head Center to Edge of Diameter Limit 30.0110 in.

You can also reduce the diameter limit (if possible) where it does not cross into the knuckle. In this manner, you get the extra area in the shell using the 0.9 factor.

I hope this helps.

Scott,

Thank you for your help. I've learned something again. :-)

Thanks again

Istvan