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Reg. 408

Dished End Plates with pressure on concave side

Where an end plate is dished to semi-ellipsoidal or partially spherical form, the inside radius of dishing shall be not greater than the outside diameter of the flange(see Fig 23).

Wherever practicable, the inside corner radius shall be 12.5 per cent, of the inside diameter and in no case shall be less than 6 per cent. of the inside diameter.

For ends of semi-ellipsoidal from the ration of the major axis to the minor axis shall be not greater than 2.

Where an end plate is dished to semi-ellipsoidal or partially spherical form and has a flanged-in-manhole or access opening, the thickness shall be increased by not less than 15 per cent. of the thickness computed by the formula for an end plate without an opening, but in no case shall this increase be less than 1/8 inch.

The depth in inches of the flange G (see Fig 23) forming the access opening measured from the outer surface of the place at the minor axis of the opening shall be not less than:

 Where ________                    G=ÖT x W T=thickness of the end plate in inches W=length of minor axis in inches.

The corner radius of the manhole flange vm (see Fig. 23) shall be not less than 1 inch.

In case where full compensation is provided for an un-flanged opening cut in a dished end plate, no additional thickness is necessary.

Where it is not practicable to make a dished end plate in one piece, fusion welded seams welded from each side of the plate may be employed provided the appropriate constraints as given below are introduced into the formula for obtaining the thickness. The limits of pressure and diameter specified in Regulation 416 shall, however, apply.

The maximum working pressure shall be determined by the following formula but in no case shall the thickness at the edge of the flange for connecting to the shell be less than the thickness of the unpierced seamless shell as determined by Equation (1).

 W.P.= (t-2) x C x S Equation (97) D x K
Where,

t = thickness of plate in thirty-seconds of an inch.
WP = working pressure in pounds per square inch.
D = outside diameter of the flange in inches.
K = a factor dependent upon the ration h / D
Generally obtained from the curve shown in Figure 22 or by Equation 75 In no case shall K be taken as less than:

 1.15 R or 0.12 D D R
S = minimum ultimate stress of plate in tons per square inch.
C = constant as follows:
a. Where the end plate is in one piece.
C = 35
b. where the end plate is not one piece.
C = 32 where Class I requirements are complied with.
= 27 where Class II requirements are complied with.

The thickness to be used in the formulae is the thickness of the end after manufacture and is applicable over the whole area of the end up to the point where for ends of partially spherical shape, the dishing radius joins the corner radius; from this point a gradual thinning is permissible up to a maximum of 10 per cent. of the thickness ‘t’ at the point where the corner radius joints the straight portion of the flanged end. A similar gradual thinning is permissible for ends of semi-ellipsoidal shape. This permissible reduction in thickness also applies to the flange for the manhole opening.

Where a dished end plate is pierced with more than one opening for electrodes or other fittings, the openings shall be so arranged as to provide an unpierced annulus not less than 2 in. wide measured from the center of the corner radius.

Where the diameter of such opening is not greater than 1-1/2 inches and the value of t

 the ligament p-d is not less than I compensation is not required P K

 Where d is greater than 2-1/2 inches or p-d is less than I full compensation shall be P K

provided where-

p = pitch of opening in inches.
d = diameter of openings in inches.
K = factor (see Equation above).

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