Weld Flange To Dish Head Directly

[wcw1985]

Dear All,

I have 1 question which cannot be solve and would like to ask for dear forum members's opinions:

Design condition:
Internal pressure : 10 bar

Torispherical Dish Head: OD1300mm ( around 51")

SORF 20" Flange Ansi 150 -->OD about 700mm (27.5")

I would like to open an opening in center of the dish head and weld this flange directly on it using welding method just like Fig UW-16.1(c) without any nozzle.

How do i calculate to know if the opening is properly reinforced?

I checked UG-36 (b) (2) but i see none of the figure in Fig UG-36 similar to my case.
I checked Appendix 1-7 (LARGE OPENING IN CYLINDRICAL AND CONICAL SHELL) but it was for opening in shell not head.
I checked Appendix 1-10 (ALTERNATIVE METHOD FOR DESIGN OF REINFORCEMENT FOR OPENING S IN CYLINDRICAL AND CONICAL SHELLS UNDER INTERNAL PRESSURE) still was for shell not head.

I really hope for a reply that could help me. Thanks in advance.

The flange will be closed with blind flange in the end of the fabrication.

 

[wcw1985]

doct9960,

1st: To cut cost. I may be suffer from engineering calculation initially but if i can cut cost by saving the cost of the project, i will try my best to do it.

2nd: The bottom of the tank required a manway because there is a baffle plate near the bottom of the tank which to be bolted with some bolting equipment require human to do servicing ( unbolting the nut from the bottom of the tank) in the future.

3rd: It does not require U-stamp by the client but the local government require us to submit a valid calculation based on ASME code in the fabrication of this vessel.

4th: This vessel will go many places (a lot of units in the future) but particularly in the asia like singapore,indonesia,malaysia, and thailand.

 

[SnTMan]

wcw1985, I don't see how you could consider a, say, 6" long piece of pipe to be more costly than your various schemes to seal the flange bolt holes.

Regards,

Mike

 

[wcw1985]

Hi Mike,

The way to seal the bolt hole is an idea only,after long discussion in this forum ultimately i think cutting a plate, drill and tap hole would be more practical and faster than sealing a bolt hole and using flange. I would like to thanks gr2vessels for his idea.

 

[gr2vessels]

wcw1985,
The following are pressure vessel regulations stipulated in current codes:
Plate cannot be used for the size of your flange, it has to be a forging, fully tested in fabrication. You have to design the flange as per ASME VIII-1 Appx. 2 or similar code. You cannot drill through the flange and tap the hole, exposing the thread to the internal pressure. You must design it with a minimum thickness under the bolt hole to withstand the design conditions. In other words, you have to reinvent a standard flange, called studding outlet. You might make it a bit thinner and lighter, based on your particular design conditions, but the cost of fabrication will make it impractical.
Cheers,
gr2vessels

 

[steakman911]

Why would you not use a Std or Long RFWN Flg and be done with it.? That would be very cost effective and realtively easy to install with plenty of advice/guidance from Sect VIII. If there is no room beneath the vessel, I would suggest that you lengthen/strengthen the vessel supports/saddles to allow human ingress/egress. Any anncillary piping connecting to the vessel can easily be adjusted to accomodate a taller vessel.

It concerns me that you are in a jurisdiction that allows pressure vessels to be manufactured without U stamp certification. There is a reason for U-Stamps and there is a reason for codes and recommended practices: They save lives. Why try to change or go around years and years of knowledge/experience.? Cost saving..?? Cheap products are just that, CHEAP and 99% of the time not worth the money spent. In this case potentially deadly.

You came here for opinion, this is mine.

Build it right and promote that fact.

stk