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Reg. 580, Reg. 581

Pitch of tubes

 
The spacing of tube holes shall be such that the minimum width in inches of any ligament between the tube holes shall be not less than:-

D + ½
8

alternatively,

the thickness and cross-section of the plate between the tube holes shall be not less than

0.125D+0.2=minimum thickness in inches.
0.17D+0.025=minimum cross-section in square inches where D is diameter of the tube holes in inches.

In no case shall the minimum thickness of any tube plate in the tube area be less than the following limits:-

T=1/2 inch, Where the diameter of the tube holes does not exceed 2 inches.
T=9/16 inch, Where the diameter of the tube hole is greater than 2 inches.




Reg. 581

Stay tubes


Stay tubes shall be of steel seamless or electrically resistance welded.
a) Minimum thickness of stay tubes – The minimum thickness of stay tubes shall be as per regulation 148.
b) The maximum working pressure for screwed in stay tube shall be calculated by the following formula:

WP = 5900         1.28
[(D---------------/N )² - D1²]
Equation XII/16
A

D is diameter of the stay tube over threads in inches.
D1 is internal diameter of the tubes under the threads in inches.
N is number of threads per inch.

A is the area in square inches supported by one Stay tube, measured from centre to centre of stay tubes. When the area contains tubes or parts of tubes their aggregate area, calculated from their smallest external diameter of body when in tension and smallest internal diameter when in compression, shall be deducted from the area of the containing figure and the remainder used as A in the formula.

Where stay tubes have their thickness increased at the screwed, ends to provide for plus threads the increased thickness shall be obtained by up-setting and not by welding, and the tubes shall be subsequently annealed.

Stay tubes may be attached to the tube plates either by screwing or by metal arc welding.

Where stay tubes are screwed into the tube plates they shall be screwed with a continuous thread not finer than 11 threads per inch at both ends and shall be expanded into the tube plates, by roller expander and, if desired, may be seal welded.

Welded attachment of stay tubes be as shown in Figure XII/67,XII/67A,XII/68, ,XII/68A and XII/69.
 
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