6" nozzle set into manway cover - PD5500

[TomRob142]

Hello all,

I'm having some problems designing a manway cover modification, where the client requires a 6" nozzle (c/w instrument) adding to an existing manway cover. Design code is PD5500, and most other threads cover this same activity in ASME code only. The main problem seems to be caused by a (potential) discrepancy in PVelite software - screen shot of which is attached. Assessing the requirements for an unstayed end with opening using section 3.5.5.3 of the PD5500 code, the calculations are relatively straightforward, however pvelite spits out a required thickness (e1) of almost 3x the required thickness for an un-pierced version (e).

Has anyone else noticed this?

I feel like it's wrong to rush to point out an 'error in the software', however comparing the results to the same when completed manually, I can't think of any other reasoning?

 

[CuMo]

How big is the opening in comparison to the cover? Does it fully satisfy the dimensional requirements of PD 5500?
One way to eliminate a potential error in the software is to either run the same calculation by another software or at least change the method.
You can try and go to settings, Nozzle Analysis option and activate the "Compute areas for PD 5500 3.5.4.9 - which is the Pressure Area method from EN 13445 and see if this makes any difference.
Just double check that this alternative method is acceptable for your client & Notified Body.

Or you could try to design your cover as a reverse flange geometry where your nozzle becomes your shell...

Making the cover as thick respectively rigid as the code wants it to be is to prevent any deflection that could cause weld failure at the joint with the nozzle. /My interpretation, not necessarily true/.

 

[DriveMeNuts]

Your bolted cover sketch is 35-35(c)?
The minimum thickness for this type of bolted cover (without an opening) is calculated per equations (3.5.5-3) and (3.5.5-3), which equals 251mm. The 108mm figure in your calcs seems to be wrong. sqrt(0.3*666.75[sup]2[/sup]*88/186.673) = 250.68mm
Even the 64.380mm number is wrong. If you put in effort to use your calculator you would have got 0.41*666.75*(88/186.763)*1.059 + 1.5 =137.91mm.

The opening factor Y1 = 1.059. So, the opening only increases the cover thickness by 5.9%.

Final minimum thickness is (251.471 x 1.059) + 1.5 = 267.808mm. So, PVElite seems to under calculate the correct thickness.

There are so many errors in this PVElite calc. Did you actually do your own calc, or run straight to EngTips? Like you say, it is straight forward.

PVElite is an awful piece of software. I have never trusted it.