Nozzle reinforcement questions 3

[JStephen]

A couple of quick questions on nozzle reinforcement in a formed head per ASME B&PV Section VIII:

If I understand UG-37 right, when a nozzle is not radial in the head, then the dimension "d" is the chord across the nozzle, rather than the nozzle diameter. Is this correct? The definition seems to indicate this, but none of the illustrations in either ASME or the vessel books I have actually show this.

In UG-40, the limits of reinforcement are described as being measured "parallel to a vessel wall". For a curved head, does this mean it is an arc measurement along the head or just an offset distance from the nozzle centerline?

 

[CodeRef]

Yes,
See ASME Section VIII-1 NONMANDATORY APPENDIX L EXAMPLES ILLUSTRATING THE APPLICATION OF CODE FORMULAS AND RULES paragraph L-7.7.1.

 

[JStephen]

That answers it, thanks!

 

[Shmulik]

CodeJackal,
I have to admit that I couldn't understand this example of L-7.7.1. and how it comes together with UG-37 nomenclature definition of 'd': "finished diameter of circular opening or finished dimension (chord length … EXCLUDING excess thickness available for reinforcement)….

As far as I can understand the meaning of this definition: excess area available in shell (A1) is calculated acc. to nozzle's diameter only.
Area required for reinforcement (A) has to be calculated twice:
1- for longitudinal direction using nozzle's diameter.
2- for circumferential direction using chord length (multiplied by F factor in case the nozzle is self reinforced).

Namely: you can't credit extended chord length in order to gain larger value of A1.

 

[JStephen]

I took the part about excess thickness in the definition of "d" to be defining the radius at which d is measured. And it would seem to me that you can credit the extended chord length in the one plane, not in the other.

 

[CodeRef]

Here is an interpretation of Fig UG-37 that might aid your understanding and use of the F correction factor. It may cause more questions, but that is a good thing.. right?

Interpretation: VIII-1-01-90
Subject: Section VIII, Division 1 (1998 Edition, 2000 Addenda); UG-37 and Fig, UG-37
Date Issued: September 25, 2001
File: BC01-639

Question (1): Is it mandatory to use the factor F, as given in Fig. UG-37 of Section VIII, Division 1, for determining the reinforcement requirements of integrally reinforced openings in cylinders and cones?
Reply (1): No, the value of F = 1.0 may be used, at the designer's option.

Question (2): May the factor F, as given in Fig. UG-37, be used in determining the reinforcement requirements for integrally reinforced nozzles in cylinders and cones when the nozzle is oblique or tangential to the vessel surface?
Reply (2): Yes.

Question (3): Is the angle theta, as shown in Fig. UG-37, measured with respect to the cylinder or cone's longitudinal axis whereby a plane cut through the opening in the vessel's longitudinal direction results in F = 1.0, and a plane cut through the opening in the vessel's circumferential direction results in F = 0.5?
Reply (3): Yes.

I believe the reply to the first question reflects Shmuliks approach. Specifically when stating the value of F = 1.0 may be used, at the designer's option. Such as when using it in two planes/directions and going with the most restrictive/punitive value.

As far as the definitions given in the nomenclature, I prefer the following:
d= Diameter of opening along the longitudinal plane or chord of opening in the non-radial circumferential plane based upon the sketches in Fig. UG-40
A= Total area of reinforcement required in the plane being examined.
F= Correction Factor for calculation of stresses on different planes with respect to the longitudinal plane.

 

[Shmulik]

To my understanding it is obvious that using of 'F' correction factor is optional only. Nomenclature definition says "Fig. UG-37 MAY BE USED…"

I would come a step farther and dare saying that the example of L-7.7.1. is somehow a misleading one (don’t forget it is NONMANDATORY!).
This example ignores the most clearly nomenclature definition of 'd': "finished diameter of circular opening or finished dimension (chord length ... EXCLUDING excess thickness available for reinforcement)...

I believe that the best approach of using the area replacement method is to provide the replaced area as close as you can. (This way of understanding reflects in factor 'F' nomenclature definition).
The fact that VIII-1 allows us using uniaxial area replacement method for openings is already a significant minimizing of requirements. Taking it away towards excess thickness available according to chord length of opening is way to far from a liable design.

 

[doct9960]

The article below may enlighten you on nozzle openings...

http://www.pdhonline.org/courses/m205/m205content.pdf