Opening in knuckle of formed head
3

Question

Opening in knuckle of formed head

GIGI72 (Mechanical)

(OP)

20 Sep 04 11:35

We are going to manufacture some covers for heat exchangers with drain and vent threaded connections placed on the short radius of the knuckle of the formed head.
Can someone tell me if ASME VIII div. I accept this openings in this position? Consider also that the coupling is always less then 1" dia. NPT-F, welded with fillet as per UW16.2.
Thank You.

jte (Mechanical) · Answer 1 · 2004-09-20 12:13:52

GIGI72-

The simple answer is yes. Provided that your couplings are installed radially and that the cut in the head is not skewed longer as in a hillside nozzle. On the other hand, I'd avoid it based on engineering judgement (read the Foreward) even if it is simply to avoid an argument (ok, "discussion") with another engineer.

A search of this site for "knuckle" produced a bunch of results:

Thread794-98923 is related but different.

Thread794-67661 is directly related but gets off track.

jt

codeeng (Petroleum) · Answer 2 · 2004-09-20 15:13:46

Code permits nozzles in the knuckle region. For the size mentioned they will be except from nozzle reinforcement (see UG-37(c)(3)). If hillside then the opening is based on the major axis.

MJCronin (Mechanical) · Answer 3 · 2004-09-30 13:25:45

GIGI,

I would just like to add that, many corporate guidelines meant for pressure vessel design and specification suggest avoiding placement of any type of nozzle in the knuckle area. (in my opinion, if you can avoid this... it is a good idea)

You probably already know that the knuckle area is the weakest area of an ASME flaged and dished head.

MJC

bvi (Mechanical) · Answer 4 · 2004-10-07 19:39:39

If you use the code case that permits thinner heads, 2286 if I recall the number correctly, you will be limited in the knuckle region due to a fatigue concern. With the thinner heads, more flexure in the knuckle region is expected. So if you are going to put an opening in the knuckle region, don't use the alternative rules in the code case.

JoeTank (Structural) · Answer 5 · 2004-10-08 02:40:02

Just an additional comment to Mr. Cronin's comment. The knuckle region of an F&D head is indeed the most highly stressed region on the head. So, in that regard it could be considered the weak link. Nevertheless, in a properly designed head, the knuckle region meets all of the ASME Code requirements and is as strong as most other componenebts on a vessel that also meet the Code requirement.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

PVGuy (Mechanical) · Answer 6 · 2004-10-08 10:31:33

The code allows the user an advantage if they place the opening in the dished portion of the head (see paragraphs a and c under the definition of tr in UG-37). Also it is my understanding that if the opening is placed in the knuckle that you need to be extra careful about your tr value if Appendix 1-4(f) calcs apply to the host.

jte (Mechanical) · Answer 7 · 2004-10-08 12:13:16

PVGuy-

I didn't remember anything about that so I pulled my (marked up) copy of the Code to read up on it... Definition (3) of tr was highlighted. Thanks for the reminder! Gotta check the definitions more often.

jt

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Opening in knuckle of formed head
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