Help needed on design of a rectangular to circular cone section.

[tjh78]

Hi everyone first time poster here wondering if any of you could help me out on a little problem I am having. I am currently trying to design a conical section that goes from a rectangular cross section with radiused corners on one end to a circular weld neck flange on the other end. I am having a hard time finding any clear cut way of designing this section.

Appendix 13 in Section VIII of the ASME code doesn't have any mention of even rectangular cones let alone one with a transition to circular at the end. The pressure in the cone is only about 3 psig so I know that it won't be a really thick section but I am thinking that if I just assume that it is a regular rectangular section and not a cone that may be making it too thick.

Does anyone have any experience with this kind of section? Any help you could give me would be very appreciated, thank you.

 

[SnTMan]

tjh78, when designing a circular cone, the Code approach is to design the thickness for the large end, and I would expect a similar approach for a transition section. I am assuming the rectangular end is the large end here. Typically, for internal pressure only cases, the length is of no interest.

Unfortunately, Appendix 13 is probably going to give you something thicker that you really want, or perhaps even need. You do not say whether any Codes or standards apply, and this willl need to be considered in your design approach. FEA may be an option, as may be some kind of simplified analysis. It depends.

Regards,

Mike

 

[tjh78]

Yeah that is what I am afraid of. Would a circular cone analysis using a diameter on the large end that produces an equivalent to the area of the rectangular section be of any use to me from a design standpoint. The unit is being designed per ASME but as always on something like this we could use U-2(g).

 

[SnTMan]

tjh78, it might be of use to you, but as an owner, it wouldn't be any use to me

There is a little too much going on there.

Regards,

Mike

 

[TGS4]

I've designed these types of transitions before. Your only option is U-2(g).

 

[racookpe1978]

First, remember to design for strength and safety during operation - not merely "easiest way I can use to justify using the absolutely lightest weight imaginable." In particular, for this case of a rectangle to circular transition, fabrication and welding costs of the transition are going to override material cost, where in a simple round duct or square duct with square corners, material is of more importance.

Your biggest stress will be across the largest flat area: the round end is going to have lowest hoop pressure and the lowest stress from fluid flow transient stress, and will be best able to resist that stress through its internal shape.

So your safest design is to assume a rectangular PV (flat sides) at your highest internal (?) pressure. Are you positive there is no chance of ever pulling a vacuum in there? If 3 PSIG is the operating pressure, potential vauums might be much higher than pressures.