Figure UG 37

[Cluain]

Firstly, I must apologize for asking multiple questions. If anyone has the time to respond, I would be most grateful!

Can someone explain why the correction factor “F” in UG -37 is not mandatory?

Also, if one inserts, say, a hill side nozzle (tangentially& integrally) into a cylindrical shell and the long axis of the nozzle is greater than twice the short axis. Then as per UG 36(a) (1) the reinforcement across the short dimension shall be increased as necessary to provide against excessive distortion.

What code paragraphs should one use to verify that the reinforcement across the short dimension has been increased adequately? Is it here, that one uses the correction factor when calculating the short dimension?

In regards to the longitudinal shell axis; I am having difficulty understanding what the code is trying to communicate in Fig UG 37. It appears that the angle theta and the referenced correction factor have a direct relationship to the circumferential stress in a vessel. Upon initial viewing of Fig UG 37 the “X”(longitudinal shell axis) and “Y” axis are not to be confused with the “Z” axis which would typically be parallel to the long seam of a vessel.

If this were so, then a nozzle tilted 45 degrees in the “Z” axis direction( long dimension of opening parallel to long seam) would have a correction factor of "1" because the angle theta would be “0” in respect to longitudinal shell axis “X” of figure UG 37.

 

[rww88]

I am a technical writer by vocation. I have under preparation a commercial technical publication the subject of which is pressure vessel opening reinforcement. I have reproduced some of the raw, unverified, unedited portions of the preliminary manuscript that refer to the F correction factor. One preliminary illustration on this subject has been prepared. I hope this may help.

“What is the F factor mentioned in UG-37 and when is it applicable? The factor F is in essence a required replacement area (A) correction factor which gives credit for the compensating variation in pressure stresses associated with different planes with respect to the axis of the vessel. It might be best to think of F as an area reduction factor. A value of F = 1.0 (no area reduction allowed) must be used in all pressure vessel opening configurations except those that employ integrally reinforced nozzle designs in cylindrical shells and cones.”

“How is the correct value of F selected? A conservative design approach is to always consider the value of F as unity. The value of F can be determined from the formula: [later]
Alternatively, it can be estimated from the ASME Code Figure UG-37 which is reproduced below:"

”Much confusion seems to prevail regarding the F correction factor. Much of this is believed in part to stem from the lack of any supplemental text information provided within Figure UG-37.1. An important point that must be considered before giving a disproportionate amount of consideration to this correction factor is the fact that it is materially irrelevant except with regards to integrally reinforced nozzles that manifest in non-circular openings. Realizing any meaningful benefit from the fact that a weak plane and strong plane exists through radial appurtenance in a cylindrical shell or cone that result in circular opening, is questionable."

“Unless there exists a production situation where a large volume of identical vessels are being fabricated, any significant monetary savings derived from the avoidance of excess material through the use of the F correction factor, as would be the case for a single vessel, is questioned. In the event of a large volume production scenario, an appurtenance is used known as a variable area integrally reinforced nozzle that varies the amount of reinforcement in relation to the opening's major axis relative to the longitudinal axis of the vessel. Continuously integrally reinforced nozzles have a constant amount of reinforcement area about the nozzle centerline while those reinforced with a variable area of reinforcement do not. This lack of symmetry is usually developed through additional weld buildup on either the shell or nozzle neck or with a larger fillet on the attachment weld.”

“When is the simplified version of the formula for A (the required replacement area) applicable? When the allowable stress of the nozzle material is equal to or greater than that of the penetrated shell or head material, or when the nozzle only abuts the vessel wall, and when consideration for the area reduction factor F is not warranted. These exclusions are indicated in red in the Figure UG-37.1 equation for A which is reproduced below:”

 

[TomBarsh]

Also see threads:

http://www.eng-tips.com/viewthread.cfm?qid=119465

http://www.eng-tips.com/viewthread.cfm?qid=233189

 

[Cluain]

Thanks Tom.

Obviously, I should have done a key word search, which would have saved us both a great deal of time. I did do a thread search but didn't see the ones you referenced.

I appreciate your descriptive notes and I’m relieved with the fact that I’m not the only person who has been confused by Fig UG 37.

More annoying is the fact that I confused the unit circle thingeee, thinking it was a plan view of a vessel and took the origin or “Z” axis to run parallel with the long seam of the vessel. Anyway, the attached threads cleared this up for me along with your elegant posting.

Very much appreciated.

Your humble servant.

Cluain