Welding Flange To Plate

Why did anyone choose to build a pressure vessel shell whose outside diameter failed to match a standard flange inside diameter, if a flange was meant to be used?

It was better at the 1^st step of design to select the diameter of the vessel to be the same diameter of the standard flange. Otherwise, you have to procure a nonstandard flange with diameter matching the diameter of the vessel.

And tapered transition by 18^o or ratio 1:3 (l ≥ 3) is only required when you weld unequal thicknesses, where there must a taper transition of the thicker part to adjust the two welded thicknesses (see UW-9 and Fig. UW 13.1 of ASME BPVC, Section VIII, Div.1).

And the permissible misalignment between two parts with different thicknesses shall be ≤ 1/2(t₁-t₂), where t₁ = thicker part thickness & t₂ = thinner part thickness of a welded parts as per Fig. UW-13.1.

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Note. A new nonstandard welded-neck or slip-on or socket-weld flange can be designed to match with the diameter of the vessel, depends on the design pressure and design temperature. Otherwise, if it is possible you can modify the diameter of the vessel to match with the diameter of the standard flange.

Thanks Mr.Abdul Halim for your kind explaination.

As per Mr.Tornado said, i don't know what do you mean by "outside diameter of shell failed to match inside diameter of shell'..sometime, client wants id of shell to be flushed with id of flg. And then, i only need to adjust OD of flg which is A value to fit with shell OD. ID of shell need to fix due to process internal attachment constraint.

As far as i know, in B16.47, the bore of flg is determined by purchaser as note (f). As long we are not exceed max bore, B of flg, then you don't have to run Appndx 2 cal which is still claim as a std flg. Please refer to clause 2.7 in B16.47 for the max value of B.

However, if i insist to maintain the flg as a std, i need to maintain the A value and try to use fig 1-3 in order to match OD of the shell. Am i right?

Dear Mr.Abdul Halim,

Did you mean diameter of the vessel is the inside diameter or outside diameter? i only can guess that is for outside diameter since A value in B16 is a fix value, which is same as pipe nominal size..but in my case, client fix the ID. Since i decide to roll by plate (lower cost and the schedule for this project too short to order pipe with big size) , we will not always get the OD same as pipe OD.

Could anyone please advice me on this issue?

Thanks in advance..

Inform the client that his awkward choice of i.d. leads to an o.d. that does not match a standard pipe/flange size.