Appendix 1 Supplementary Formulas

[chaulklate]

Reference Appendix 1-4(c), the formula has a value "k" which is taken from Table 1-4.1. Note post script note 1 which starts "Ellipsoidal heads designed under K > 1 ..." Also refer to Example 1. There, the ID is indicated to be 40, and value h is indicated to be 9. If this is a 2:1 head with 40 ID, should the h value not be 10?? The way I see it, for a 2:1 head, the D/2h ratio should always be 2 and therefore the "k" factor should always be 1. This seems like basic stuff, what am I missing here?

1. What are the scenarios where the D/2h ratio can be any other value than 2 for a 2:1 head?

2. Does the Code recognize ellipsoidal heads with ratio other than 2:1?

 

[TomBarsh]

1- I have seen some "standard" 1.5:1 ratio heads for some applications. But I would guess that 2:1 is by far the most widely used.

2- Table 1-4.1 (as you referenced) stipulates K factors for other head ratios. So, yes, the Code recognizes other ratios for ellipsoidal heads.

This may be something of an "over refinement" but assuming that the head has a 2:1 SE ratio on inside surface in the new condition then it will have a slightly different ratio in the corroded condition*. For small diameter, thin heads this may make a difference.

*Actually, the inside surface in the corroded condition will no longer be an ellipsoid; ie: a curve drawn 'parallel' to an ellipse such that it is at all points equidistant from the ellipse is not itself an ellipse. But accounting for the slight change in topology is even less worthwhile than accounting for the change in head ratio.

 

[LSThill]

TEAM MEMBERS

Reference to ASME Pressure Vessel training CD Module 4 Designing Vessels Under Internal Pressure

4-9 Design Thickness of a 2:3-1 Ellipsoidal Head


PER Appendix 1-4:


t = PRK/SE – 0.2 P where K= 1/6[2 + (D /2h)^2]
= 430 x 48.2 x 1.2/20,000 x 1.0 – 0.2 x 430 or read the value of K from Table
=0.628 in 1-4.1 based upon D/2h

Design t = 0.628 in + 0.10 = 0.73 in

Given a ration of 2:3:1, D/2h is 2.3. the value of K (1.21) may then be calculated or read form Table 1-4.1.

All dimension are in the corroded condition per UG-16(e)

 

[JStephen]

Note that in the body of the code, it defines a "standard" F&D head, but then the equations in Appendix 1 allow you to design heads of other profiles. Similarly, the code defines a "standard" elliptical head as 2;1.

 

[chaulklate]

So, can we agree then that a standard 2:1 head in the new and uncorroded condition has a k value of 1? And also agree that same head has a k value somewhat less than 1 in the corroded condition?

 

[JoeTank]

A 2:1 ellipsoidal head has a D/2h ratio of 2

Joe Tank

 

[JStephen]

Seems to me that a 2:1 elliptical head would go by the formula in the body of the code, which doesn't use a K value. I'd use the same formula for the head, whether corroded or not.