Section
4 Dished ends subject to internal pressure
4.1 Minimum thickness
4.1.1 The
thickness, t, of semi-ellipsoidal and hemispherical unstayed
ends, and the knuckle section of torispherical ends, dished from plate,
having pressure on the concave side and satisfying the conditions
listed below, is to be determined by the following formula:
4.1.2 For
semi-ellipsoidal ends:
the external height, H ≥ 0,18 D
o
where
D
o
|
= |
the external diameter of the parallel portion of the end, in
mm. |
4.1.3 For
torispherical ends:
the internal radius, R
i ≤ D
o
the internal knuckle radius, R
i ≥
0,1D
o
the internal knuckle radius, R
i ≥ 3t
the external
height, H ≥ 0,18D
oand is determined
as follows:
Figure 10.4.1 Shape factor
4.1.4 In
addition to the formula in Pt 5, Ch 10, 4.1 Minimum thickness 4.1.1 the
thickness, t, of a torispherical head, made from more
than one plate, in the crown section is to be not less than that determined
by the following formula:
4.1.7 The
minimum thickness of the head, t, is to be not less than
6,0 mm.
4.1.8 For
ends which are butt welded to the drum shell, see
Pt 5, Ch 10, 1.8 Allowable stress, the thickness of the edge of
the flange for connection to the shell is to be not less than the
thickness of an unpierced seamless or welded shell, whichever is applicable,
of the same diameter and material and determined by Pt 5, Ch 10, 2.1 Minimum thickness.
4.2 Shape factors for dished ends
4.3 Dished ends with unreinforced openings
4.3.1 Openings
in dished ends may be circular, obround or approximately elliptical.
4.3.2 The
upper curves in Figure 10.4.1 Shape factor provide
values of K, to be used in Pt 5, Ch 10, 4.1 Minimum thickness 4.1.1, for ends with unreinforced openings. The selection of
the correct curve depends on the value and trial calculation is necessary to select the correct
curve,
where
d
|
= |
the
diameter of the largest opening in the end plate, in mm (in the case
of an elliptical opening, the larger axis of the ellipse) |
t
|
= |
minimum
thickness, after dishing, in mm |
D
o
|
= |
outside diameter of dished end, in mm. |
4.3.3 The
following requirements must in any case be satisfied:
4.4 Flanged openings in dished ends
4.4.2 Where
openings are flanged, the radius, r
m of the
flanging is to be not less than 25 mm, see
Figure 10.4.2 Typical dished ends. The thickness of
the flanged portion may be less than the calculated thickness.
4.5 Location of unreinforced and flanged openings in dished ends
4.5.1 Unreinforced
and flanged openings in dished ends are to be so arranged that the
distance from the edge of the hole to the outside edge of the plate
and the distance between openings are not less than those shown in Figure 10.4.3 Opening in dished ends.
4.6 Dished ends with reinforced openings
4.6.1 Where
it is desired to use a large opening in a dished end of less thickness
than would be required by Pt 5, Ch 10, 4.3 Dished ends with unreinforced openings,
the end is to be reinforced. This reinforcement may consist of a ring
or standpipe welded into the hole, or of reinforcing plates welded
to the outside and/or inside of the end in the vicinity of the hole,
or a combination of both methods, see
Figure 10.4.4 Limits of reinforcement. Forged reinforcements
may be used.
Figure 10.4.3 Opening in dished ends
Figure 10.4.4 Limits of reinforcement
4.6.2 Reinforcing
material with the following limits may be taken as effective reinforcement:
-
The effective
width, l
1 of reinforcement is not to exceed or 0,5d
o whichever is the lesser.
-
The effective
length, l
2 of a reinforcing ring is not to
exceed
- where
R
i
|
= |
the internal radius of the spherical part of a torispherical
end, in mm, or |
R
i
|
= |
internal radius of the meridian of the ellipse at the centre
of the opening, of a semi-ellipsoidal end, in mm, and is given by
the following formula: |
= |
|
4.6.5 If
the material of the ring or the reinforcing plates has an allowable
stress value lower than that of the end plate, then the effective
cross-sectional area, A, is to be multiplied by the ratio:
4.7 Torispherical dished ends with reinforced openings
4.7.1 If
an opening and its reinforcement are positioned entirely within the
crown section, the compensation requirements are to be as for a spherical
shell, using the crown radius as the spherical shell radius. Otherwise
the requirements of Pt 5, Ch 10, 4.6 Dished ends with reinforced openings are
to be applied.
|