Nozzle locations in F&D Heads 2

[MJCronin]

To all,

For pressure vessels built to the ASME Code:

1) Is the location of nozzles in the "knuckle" region of an ASME torospherical (flanged & dished) head acceptable ?

This area, as I understand, is the weakest area of the F&D head.

2) Are there any limitations on the locations of nozzles in elliptical heads ?

( assume nozzles are oriented parallel to the axis of the vessel)

No opinions !!!!....... please be specific about your reasons and any references you may have.

Thank You

MJCronin

 

[ab1234]

Please note that ASME code do not impose any restriction on the position of opening on dished ends. However, generally the consultant specifications limits that opening and its reinforcemnt shall be in the crown area for both Torrispherical and Ellipsoidal dished ends. Probably the reason being knuckle having high radius of curvature is highly stressed and any opening and welding in it will further increase the stresses and hence this is being avoided.

ab

 

[aybee]

ASME V111 UG37a) cls 3 pg 48 sets out the relationship between the location of nozzles and diameter of the head in ellipsoidal heads.refe also appendix L for example
The knuckle is the highest stressed area when under pressure

 

[ab1234]

aybee,
please note that the clause you referred only tells that if nozzle and reinforcement located in the specified area then thickness of Dished End shall be as per specified guidelines. It does not mention that Nozzles can not be located in knuckle area. The reason being if nozzles are in crown area then reinfocement requirement of spherical shell (with crown radius) needs to be satisfied.

Nevertheless, as you mentioned knuckle being highly stressed it shall be avoided. But in case it is unavoidable due to some constarint, it can be located in knuckle area as per code.
thks

 

[MJCronin]

To all,

We all agree and acknowledge that the "knuckle area" is the highly stressed area of the head and that installing nozzles in this area is not the best idea..

But, does any Code or regulation prohibit this practice ?

AB1234, what do you mean by:

" However, generally the consultant specifications limits that opening and its reinforcemnt shall be in the crown area for both Torrispherical and Ellipsoidal dished ends"

and, in your second respose:

"But in case it is unavoidable due to some constarint, it can be located in knuckle area as per code."


MJC

 

[TomBarsh]

The applicable Section VIII Div 1 paragraphs would be UG-36 and UG-37. There is nothing in there to preclude locating a nozzle at any particular location. There are provisos about the shape, size, and proportions of openings; but no qualifications for location.

A related issue, probably often overlooked, is the statement of UG-36(a) that elliptical/obround openings that exceed an aspect ratio of 2:1 (long chord/short chord) shall have the reinforcement increased "as necessary...". This may likely occur for non-radial nozzles in knuckle area. Worst case I've seen was someone had 2" weld necks tangential to a large diameter cylinder, resulting in 2" x 20" long slits in the shell (with external loads and a WRC-107 analysis).

Regarding nozzles in the knuckle, since the reinforcing area required is based on the formula for the head thickness (not the possibly lesser thickness permitted by the definitions of 'tr' in UG-37(a)) then presumably the head knuckle is properly reinforced per Code. Of course there may be some unusual and undesirable deformations resulting from the distribution of stress/strain at that location.

But just because something is not mentioned in the Code, such as nozzles in knuckle, doesn't mean that the careful engineer need not investigate it.

By the way, for what it's worth, I have seen probably hundreds of vessel designs with nozzles located in knuckles of heads (I imagine most of these designs eventually got built). It seems that as design software becomes more commonly used (and maybe common sense less used) the process designers are adding nozzles in locations and orientations that are not the best for the vessel.

Tom

 

[ab1234]

Hi MJCronin,

I feel your question addressed to me have been replied by Tom.

In brief I would conclude following. ASME code do not put any restriction to location of opening in dished ends. Properly reinforced opening is acceptable even in crown area.

I do not remember consultant/clients specifications restricting Nozzle and its reinforcemnt in Crown area. You may check up Kellogs & EIL.

ab

 

[LSThill]

Hi MJCronin (Mechanical) and Team Member's

I total agree with Mr. Tom Barsh (Structural), Codeware Technical Support, the Home of "COMPRESS".

http://www.codeware.com

Leonard Thill
Leonard@thill.biz

http://www.thill.biz

 

[roca]

Check BS 5500 or PD 5500 as it is now called
All nozzles and their reinforcing pads shall be located outside of the knuckle area or within 0.8 x Head Diameter (taken friom the head centre line)
If you give me your e-mail address I can send you the details

 

[PVGuy]

If you put the nozzle in the knuckle region of a torispherical head or the ellipsoidal Head (outside 0.8D) you need to consider the buckling phenomenon discussed in the new addenda in App. 1-4(f). If this case applies to your head then it may increase the tr value you need to use for your nozzle reinforcement calculations.

 

[unclesyd]

Though I’ve been in and around numerous discussions as to the merits and demerits of putting a nozzle in the KR area of a head, but as previous posts have stated it wasn’t prohibited by the ASME codes and the A.I. This type nozzle was always called “hill-side nozzles”. We used them in vessels were a minimum number of nozzles were desired due to crevice corrosion problems on gasket surfaces. Most of heads on these vessels were purchased thicker than required and with a longer flange. These nozzles had to be close to sidewall of the vessel to facilitate entry for inspection. The only problem that I’ve seen is when a change in the process causes corrosion of the head. Usually the KR thickness will fall out first creating reinforcement problems.
All ASME pressure vessel and nozzle design programs I’ve seen will allow them with or with out warning.

If there is any question as to the design of a nozzle a good source of information is Paulin Research. Tony Paulin and his group have done a lot research on nozzle design above and beyond what is required by code.

To the Compress Group; I wrote a purchase order for Compress when it was only Les Bildy and John Migliavacca, more Les than John.

 

[MJCronin]

To all,

Thank you for your comments, observations and experiences...

It has been my experience that process chemical companies are demanding more and more flexibilty in thier equipment design. A pressure vessel may serve many process purposes, and may be configured for the future with spare nozzles....

This all translates into crowded top heads and radial nozzles installed in the knuckle region.

I find it interesting that the British Pressure Vessel Standard, BS 5500, puts limits on nozzle locations, but our ASME VIII does not.


MJC

 

[roca]

PVGuy
Which edtion of ASME VIII are you refering to as I must be out of date.
I have a copy of the 2002 Edition incorporating Addenda July 1 2002. In Appendix 1 there is no section 1-4(f).
It only goes as far as 1-4(e)
Thanks

 

[PVGuy]

roca,

It is the latest addenda, Addenda July 1 2003. The buckling phenomenon is only a concern if your t/L ratio is less than .002.

 

[workermonkey]

To all,

In my own limited experience it seems that the biggest problem with putting nozzles in the knuckle radius is that its harder to weld and causes the head to warp. It takes the welders longer to prep the joint and nozzle and increases the heat effected area.


To MJCronin (Mechanical),

"I find it interesting that the British Pressure Vessel Standard, BS 5500, puts limits on nozzle locations, but our ASME VIII does not."

i'm 4 months into learning the ASME code and i can't believe how many problems there are with it. As a young engineer i would love to see some engineers and not politicians write these codes. (no offense to anyone intended).

 

[bvi]

Note that if you use the Code Case (I forget the number) that provides alternative rules for ellipsoidal and toriscpherical heads (resulting in lower wall thickness), there is a restriction on putting nozzles in the knuckle region. This restriction is in because, with the thinner heads, there is a concern about fatigue in teh knuckle caused by the stress concentration of the nozzle in the flexing knuckle region.

 

[GatorOne]

Workermonkey: Your comment: "As a young engineer i would love to see some engineers and not politicians write these codes. (no offense to anyone intended)." needs a clarification. All rules in the ASME code are written by engineer volunteers. No politicians here. You may want to inform yourselve better before making a post.

 

[workermonkey]

GatorOne,

sorry but its been my experience so for that most of these codes are written by lawyers. It would seem as though an engineer did the actually technical writing because so much of it is detailed and just plain "jargon". There are also enough loop holes in the whole thing to make me sick. I've also done some of my own calculations and from what i've been able to do on my own it would appear that the code is costing us money on materials. If some states didn't require code stamped vessels i'd say drop the whole thing because of all the costs and problems it creates. those damn inspectors are expensive! and i'm not so sure they care about the code anymore then i do. i've noticed a lot of errors by previous engineers in my position and the inspectors have simply signed off on a lot of it. Sorry but from what i've seen the code is a useful tool but isn't always right.

 

[GatorOne]

Thanks for the reply. Perhaps you may want to joint the ranks of volunteers and work to make the Code better.

 

[workermonkey]

i'd love to, if i decide to stay in this industry. i've asked my inspector multiple times what it would take to get on these boards or have some kind of say on these things. When i have a problem with something that thouands of people use every day i'd like to fix it.