Where an end plate is dished to semiellipsoidal 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 semiellipsoidal from the ration of the
major axis to the minor axis shall be not greater than
2.
Where an end plate is dished to semiellipsoidal or
partially spherical form and has a flangedinmanhole
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 unflanged
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.= 
(t2)
x C x S 
Equation
(97) 
D x K 
Where,
t = thickness of plate in thirtyseconds 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:

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 semiellipsoidal 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
11/2 inches and the value of t
the ligament 
pd 
is not less than 
I 
compensation is not required 
P 
K 
Where d is greater than
21/2 inches or 
pd 
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). 