There are no limitations on the lower limit on ID. If you want to provide a hole less Forging it is also permitted so long as it is designed properly.

ANSI B 16.5 does not address Long weld neck forging.

yann16-

I agree with the previous posts as far as codes not directly addressing the design of long weld neck flanges. However, traditionally, a long weld neck would have an ID equal to the nominal diameter, and the neck would typically be quite thick to provide for some integral reinforcement. There are several LWN fabricators out there, I use an old catalog from Lenape Forge http://www.lenapeforge.com for details about their design of LWN flanges.

jt

I agree with jte and others. To add my own info: It's been my experience that the neck thickness of these forgings may vary with the manufacturer (since there is no "standard" that addresses these forgings). So be wary of any calculations based on the LWN.

ASME B&PV Code Section VIII Div 1 added new paragraph UCS-66(c)(4) a couple years ago to address equivalence of LWN flanges to standard flanges when considering MDMT, there are some restrictions placed on the dimensions so be certain that the LWN forging meets this rule if designing to Section VIII.

Tylor forge is another generally used LWN forging.

Good Luck
B.Moorthy
moorthykar@yahoo.com

There are 3 types of forged flanges under the LWN banner.  They are LWN (Long Welding Neck); HB( Heavy Barrel); FB (Full Barrel).   All of these are covered by the code under UW 16 and figure UW16.1.  

We used these connections on vessels at every opportunity and especially the figure Q1-Q4 were we needed RT.  There is no problem in the design and use of these flanges and they make installation and inspection much easier.
It is just an easy way to install a penetration into PV.   Our PV designers had some FEA done on some large LWN and the stress at the penetration were several orders of magnitude less with this type nozzle.


The LWN or Long Weld(ing) Neck Flange is available through 24" sizes meeting the ASME B16.5 standard (all pressure classes).  FVC can also meet the specifications of ASME B16.47, Series A & Series B. FVC maintains a large inventory of SA105 and some inventory of SA350-LF2, SA182-F1, and SA182-F11. Modified versions of the LWN can also be furnished as a "custom" product.

http://www.fvc.cc/index.htm

Here are the standard weight flanges class 150-2500

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


ASME has incorporated most of the MSS-SP44 specification into B16.47 Series A and most of the API 605 Specification into B16.47 series B. They have also added Blinds to these two specs. You may note that these specs include only Weld Necks and Blinds. For Slip-On’s over 24” you must refer to either Industry Standard (which are not automatically covered by ASME) or Boiler Code Flanges. If you need help deciding which flange best suits your application feel free to contact us.