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Reg. 193
FLAT PLATES


Flat plates supported by solid screwed stays, marginal seams or flanges

a) For plain flat plates supported by solid screwed stays or riveted marginal seams or flanges, the maximum working pressure shall be as follows : -

 

W.P. = C ( t - 1 )2 Eqn.(28)
A2 + B2

In this formula and in those following in the succeeding regulations relating to "Flat Plates" unless otherwise specified

W. P. is the working pressure in lbs. per square inch.

t is the thickness of the flat plat in 32nds of an inch,

t1 is the thickness of the washers, strip or dublings employed in 32nds of an inch ,

A is the horizontal pitch of stays in inches,

B is the vertical pitch of the stays in inches,

C is a co-efficient which varies in value with method of vexing the stays and nature of the support.

Where the plates are exposed to the direct impact of the flame the following of C shall be reduced 12-1/2 per cent-

C = 60 for stays screwed into the plate with their ends riveted over,

C = 90 for stays screwed into the plate and and fitted with nuts on the outside,

C = 100 for stays passed through the plate and fitted with nuts inside and outside

C = 110 for a riveted seam or flange, in the flat plate securing it to the shell side plate, end plate, furnace or uptake.

Where portions of plate are supported by stays or riveted seams or flanges having various values of support, the value of C, shall be taken as the mean of the points of support concerned.

The support of a riveted seam shall be assumed to be at the line through the centres of rivets in the nearest row and of a flange at the commencement of curvature. In the latter case, if the inner radius of curvature of the flange exceeds 2-1/2 times of the thickness of the plate, the support shall be assumed to be at a distance of 2-1/2 times the thickness of the plate from the inner side of the flange.
b) For portions of plate where the stays are irregularly pitched D2 shall be used instead of A2 + B2, D being the diameter in inches of the largest circle which can be drawn passing through not less than three points of support, viz., the centres of stay or rivets or the commencement of the curvature of flanging whichever is applicable.
c) For the tops and sides of combustion chambers and fireboxes the distance between the rows of stays nearest to the back tube plate, or the back or firehole plate respectively, and the commencement of curvature of these plates at their flanges shall not be greater than the maximum pitch of the stays.
d) For the tops of combustion chambers and fireboxes where they are joined to the sides by curved portions, if the outer radius of the curved portion is less than half the allowable distance between the girders, the distance between the first girder and the inner surface of the side plates shall not exceed the allowable distance between the girders. If the radius of curvature is greater than half the allowable distance between the girders, the width of the flat portion measured from the centre of the girder shall not be more than half the allowable distance between the girders.
e) Where stay tubes are not fitted in nest of tubes, as in tube plates of locotype boilers, and parts of plate outside the space occupied by tubes are supported, in accordance with Regulation 212 (b), by screwed stays each stay in the row nearest the tube shall be of sufficient strength to support the plate up to the edges of the tube holes in addition to its share of the plate on the opposite side of the line of stays.

The working pressure for the plate between tubes and stays shall be determined by Eqn.(28).  A being the horizontal pitch of the stays in the nearest row, B twice the distance between the centre line of stays and a line touching the tubes opposite them and C the co-efficient appropriate to the kind of stay.
 
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