How To: Determine Openings In Shells, Headers, And Dished Heads

The objective of this post is to help you learn How To: Determine Openings In Shells, Headers, And Dished Heads. We will review the formula(s) required to complete the calculations. Then define the different variables in each of the formulas. Wrapping everything up with a couple of practice questions for you to work on.

All referenced page numbers are from the 2007 ASME Boiler & Pressure Vessel Code

We Will Cover The Following

How to determine the minimum allowable distance between the centers of two unreinforced openings
Review and provide variable definitions for the formulas provided in the Boiler & Pressure Vessel Code
Review practice questions to determine the minimum allowable distance between the centers of two unreinforced openings

Formulas

PG-32.1.3 page 19 Single Openings. Single openings are defined as openings that have a minimum center-to-center distance between adjacent openings not less than Lh or Ls. The minimum allowable distance between the centers of two unreinforced openings is determined by the following equation:

The formula to determine the variable K found in the equation above is under PG-32.1.1 page 19.

Formula Variables

A, B = The finished opening diameters of any two finished openings under consideration, in. (mm) (see d below)

D = The outside diameter of the shell, header, or dished head containing the opening, in. (mm)

d = Diameter of a finished opening, in. (mm) (see PG-32.1.2)

K = PD/1.82St (where K shall not exceed 0.990)

Lh = The distance between centers of the two openings measured on the surface of the dished head.

Ls = The distance between centers of the two openings measured on the surface of the shell or header

P = The maximum allowable working pressure

S = The maximum allowable stress value, taken from Tables 1A and 1B of Section II, Part D

t = The nominal thickness of the head, shell, or header in. (mm)

[table id=1 /]