WELD NECK FLANGE DIMENSION NOT UNDER ASME B16.5

[rajat84]

I have designed a shell of 406.4 mm and there is no weld neck flange having nominal bore of that dimension.

The closest I can find is flange dimension if nominal bore 387.4 mm, I donot want to machine the flange as it will reduce the strength.

Please advice me as to machine the entire flange from round bar or is there any other solution for non stantard flanges.


Rem: Every view counts

 

[vesselfab]

I have no idea what you are designing, so this may not fit.

When deciding on shells that must be flanged, you have 2 choices.

1. Use OD to match standard pipe size and modify your ID as pressure dictates.

2. Design and use special flanges.

In this case not knowing your wall thickness/pressure, could you go to a 18" b16.5 flange with a heavy wall to get towards your 16" i.d. ?

 

[rajat84]

Thanks vesselfab on your guidance,
Here is the complete information

406.4 mm (16") is the inside diameter of the shell and the wallthickness is 10 mm.

Design conditon and flange rating
MAWP = 10 bar @ 150 (degree) celcius
Flange material = 2.2 austic stainless steel (316L)
Flange rating 150 lb
Flange type - weld neck flange.

VESSELFAB, AS PER THE COMMENTS,
"1. Use OD to match standard pipe size and modify your ID as pressure dictates."
-Did you mean Machine out weldneck flange from 16" blind flange and also check the thickness to appendix 2 (ASME)

"2. Design and use special flanges.
same as above.

I would not like to go to that route as it will be costly and time consuming, is there any other solution i can go with. Please suggest

Apologies for writng long essay

 

[vesselfab]

No

i meant, start from the beginning with an 18" or 16" o.d. design to fit standard pipe and fittings
or
design and manufacture special flanges

 

[proinwv2]

I guess this is about what vesselfab said, but this is what I suggest.

1. Use a B16.5 flange of a larger, or smaller ID, and weld a reducing section between the vessel and flange.

2. Design a flange, using Sec.VIII, Div.1, App.2 (assuming this codes applies).

3. If you modify the B16.5 flange, then it is no longer to that code, and you are back to my (2) above. I have used modified flanges in a similar manner and was able to meet App.2 requirements because our application did not require full P&T ratings. These were both class 150 and 300 flanges.

In general I recommend always using the B16.5 flange as they are proven and usually the most economical.

Paul

http://www.ostand.com

 

[doct9960]

rajat84,

Have you considered using lap joint flanges instead of welding necks?

Weld "lap" on vessel shell. Look at Fig. 328.5.5 of ASME B31.3 to see some typical fabricated laps. The lap should be thicker than your vessel shell (say 5 mm thicker) as you need to machine the front and back. The front needs to meet gasket contact face requirements, while the back needs to be level with the LJ flange.

Use 16"-300# LJ flanges (SA-105). Machine the flange bore to accommodate your vessel OD and fabricated lap. Check design of modified LJ flange to ASME VIII-1 Appendix 2.

 

[saplanti]

rajat84,

There is no standard welding neck flange with internal diameter of 406.4 mm. Normally, flange neck outside diameters are equal to the nominal pipe outside diameter. Therefore you do not have any chance to use standard welding neck flange. If you definitely need to use welding neck flange this has to be special as proinwv2 suggested.

The flanges to have internal diameter is slightly larger than the external dimater of the pipe are SLIP-ON or SOCKET WELD flanges. You need to check your specification if you can use them.

Ibrahim Demir

 

[rajat84]

Thank you ALL
Flange material will be SA182F 316L (because the design requirement is stainless steel) and there is a good website from where I got the information on flanges.

http://www.texasflange.com/Dimensioncutsheet.htm

I totally agree with your point guys and from my understanding on flanges, I should be able to use Slip on flange with long neck. I will check for the strength of flange from Appendix 2 (ASME). Attach to this is website discussing on LWN

http://www.red-bag.com/engintools/flange_dimension.php

Long weld neck (LWN) flange is butt welded to shell at an angle of 37.5 (degree) and outside diameter of weld neck is ‘MACHINED at an angle of 14 degree’ for smooth exterior.
( Attach to this is the dxf (Autocad 2000 format). If any difficulty in opening let me know)

Will I need to recheck flange to Appendix 2 (ASME) as I am machining the flange for smooth exterior and if I do how will I work out thickness??

Please advice

 

[vesselfab]

WOW

yes that will work even though will be quite expensive and time consuming, not to mention a lot of unneccessary weight and stainless steel added that has absolutely no value to the integrity of the vessel.

You have not checked the price of that T316l long weld neck have you?

 

[rajat84]

I do not understand, stainless steel is the design requirement plus having F316L provides more strength and corrosion allowance.

Which material are you conmparing F316L against. please elaborate.

My query was
Will I need to recheck flange to Appendix 2 (ASME) as I am machining the flange for smooth exterior and if I do how will I work out thickness??

 

[vesselfab]

sorry was not comparing materials

I was thinking cost differential between standard wn flange and a Long Weld Neck and it's machining

 

[david97]

Rajat84,

This might be helpful on welding LWN to shell

http://www.eng-tips.com/viewthread.cfm?qid=127814&page=3

I would not worry about recalculating the thickness but won't you be spending money on buying LWNF and than machining it to achieve the taper length for welding. Why not prepare a special flange.

Anyways, I think UW-13 might talk about the taper length for welding flange to shell. But please check it as I have out of touch on ASME vessel.

Hope it helps