

Reg. 276, Reg. 277
General

The
thickness T specified in equation 74 of Regulation
278 is the thickness of the end plate after manufacture
and is applicable over the whole area of the end plate
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 maximum
of 10 per cent of the thickness T at the point where the
corner radius joins the straight portion of flanged end
plate. A similar gradual thinning is permissible for end
plates of semiellipsoidal shape. This permissible reduction
in thickness applies also to the flange for the manhole
opening. In no case, however, when the end plate is but
welded to the drum shell, shall the thickness of the edge
of the flange for connection to the shell be less than
the thickness of an unpierced seamless shell of the same
diameter and material, determined by equation 72. 
Reg. 277
Dished End with Opening
a) 
Heads with openings:
i) 
Holes cut in the heads
(manholes or tube holes) should be round or elliptical. 
ii) 
Small size openings complying
with conditions of subregulation (c) do not require
any additional thickness of head or reinforcement
of opening. 
iii) 
Large size openings require an increase in thickness
of the head, according to subregulation (b) or
a reinforcement of the opening according to subregulation
(d).


b) 
Shape factor K for
heads with large unreinforced openings: The shape factor
K to be used in calculating the thickness of heads varies
depending on the height of the head H and on the dimensions
of the largest opening. The value of K is indicated in Fig.
23D, by means of curves, each of which corresponds
to a value of the ratio.
where,
d = diameter of the largest opening in the head (in the
case of an elliptical opening, the larger diameter of
the ellipse);
D = outside diameter of the head; and
T = minimum thickness after dishing.
In addition, the following conditions shall be satisfied:
The same condition and the same curves apply for openings
simply cut in the plate of the head as well as to those
which are flanged inwards. In the latter case, the radius
r’ of the flanging (see Fig.
23C) should not be
smaller than 25 mm (1 inch). The thickness of the flanged
portion may be smaller than the calculated thickness T.
Unreinforced openings and flangedin openings in dished
heads shall be arranged so that the distance from the
edge of the head is not less than as shown in Fig.
23E.
In all cases the width of the band separating two adjacent
openings should, in projection, be at least equal to the
diameter of the smallest opening as shown in Fig.
23E. 
c) 
Small openings which
do not require any reinforcement:
Figure 23D
indicates that for a given ratio of H/d,
the shape factor K of a plain head corresponds to a
certain values of the ratio,
Piercing of holes with a diameter smaller than or equal
to that which corresponds to this value can thus be
made without any reinforcement in a head, the thickness
of which is equal to the minimum required for a plain
head.
The position of those openings shall however comply
with the conditions stated in subregulation (b).

d) 
Reinforcement of
large openings:Large holes may be cut without increasing
the thickness of the head, provided they are sufficiently
reinforced.
The reinforcement may consist either of a welded nozzle
or one or two reinforcing welded plates, or of a combination
of these two procedures.
To determine the strength of the construction, one shall
proceed as follows (see Fig.
23F). Let the imaginary
diameter d’ of the opening be given by the formula
where,
d = actual diameter of the opening in the head (outside
diameter of the nozzle);
T = minimum thickness of the head; and
A = effective crosssection of reinforcement.
This effective area A corresponds, within the Limits given
below, with the actual crosssection of the reinforcing
plates and with the crosssection of the nozzle decreased
by the crosssection necessary to support the pressure,
for those parts of the nozzle situated outside the internal
surface of the head.
The shape factor K can then be read corresponding
to the ratio
The maximum limits for the are of reinforcement that
should be taken into account are
(a) L_{1} = (2 RT)^{1/2}. for the width of a reinforcing
plate;
(b) L_{2} = (d Tt)^{1/2} for the length of a nozzle.
where,
R = internal radius of the spherical part of the head
(or for elliptical heads the internal radius of curvature
of the meridian at the centre of the opening)
Tt = actual thickness of the nozzle,
L_{1} and L_{2} = dimensions given in Fig.
23F.
The position of the outer edges of the reinforcement
shall comply with the provisions of subregulation (b)
and Fig. 23E.
In cases where the allowable stress of a part of the
reinforcement is lower than that of the head, the corresponding
area A should be multiplied by the ratio:
allowable stress of the reinforcement
material

allowable stress of the head material


