HEAD TYPES
There are different
types of dished heads and cones to shapes and standards. This contains Tori
spherical, 2:1, Semi-Ellipsoidal, Hemispherical, Shallow Head, Cones and
Cones for Pressure Vessels, Flat, Inverted Dish and Inverted
Cones.
Tori
spherical heads are the most common type of head used for the manufacture
of pressure vessels and usually the most cheap to form.
The I.C.R is equal to the I.D of the head or less.Normally suggest allowing the
I.C.R to be between 90% to 95% of the I.D of the head.
The I.K.R needs to be between 6% and 10% of the I.C.R of the head.
The S.F is normally between 10mm and 30mm depending on the diameter and
thickness of the head to be formed.
2:1 Semi-Ellipsoidal
heads are deeper than a tori spherical head and therefore sturdier
and able to resist greater pressures. These heads are more difficult to
form possessing to the greater depth required. As a result these are more costly
to form than a tori spherical head, but may allow a reduction in
material thickness as the strength is greater.
The I.C.R is 0.8 of
the O.D of the head.
The I.K.R is 0.154 of
the O.D of the head.
The S.F is normally
between 10mm and 30mm depending on the diameter and thickness of the head to be
formed.
Hemispherical heads allow extra pressure than
any other head. However, the hemispherical head is the most expensive to form,
as they consists of a number of petals or gores. The number of which depends on
the size of the head and the thickness of the plate to be used. The depth of
the head is half of the diameter.
Hemispherical heads are also used in
architectural applications by joining two hemispheres together to form a
spherical ball. Other common applications are for stainless steel cooking
kettles with steam jackets.
Shallow heads are the most common type of head
used for the manufacture of atmospheric tanks and vessels and usually used on
horizontal tanks fabricated to AS1692. These heads are not suitable for
pressure vessels and not recommended for tanks or vessels with external loads.
I.e. agitators, nozzles with high loads. If unsure, you should have the design
checked.
I am normally suggest allowing the I.C.R to be
between 1.5 to 2.0 times the I.D of the head.
This can be adjusted if you require a specific depth of head.
The I.K.R for these heads is usually 32mm, 51mm or 76mm depending on the
diameter and customer requirements.
The S.F is normally between 10mm and 30mm depending on the diameter and
thickness of the head to be formed.
Cones are the most common type of head used
for the manufacture of atmospheric tanks and especially stainless steel tanks.
However they can be used in the manufacture of pressure vessels subject to
certain criteria as listed below. (Cones for pressure vessels)
Cone angles are variable and are at the discretion of the customer.
The I.K.R for most cones is usually 25mm, 32mm, 51mm, 76mm or 102mm depending
on the diameter, thickness and customer requirements.
CONES FOR PRESSURE VESSELS
The maximum internal apex angle for cones to
be used in the fabrication of a pressure vessel is 120 Degrees.
The I.K.R for cones to be used in the fabrication of a pressure vessels need to
be a minimum of 6% of the inside diameter of the vessel.
The S.F is normally between 10mm and 30mm depending on the diameter and
thickness of the head to be formed.
A flat end with a knuckled outer edge.
Typically used as bases on vertical atmospheric tanks and lids for smaller
tanks.
The I.K.R for most flat ends is usually 25mm, 32mm and 51mm depending on the
diameter, thickness and customer requirements. The S.F is normally between 10mm
and 30mm depending on the diameter and thickness of the head to be formed.
Dished only heads are generally used for
atmospheric tanks and vessels and for bulk heads or baffles inside horizontal
tanks or tankers.
Typically the I.C.R is equal to the diameter or dished to a nominated I.C.R by
the client.
INVERTED DISH
Inverted Head. Generally used on tanks and
vessels requiring the strength of a dish whilst minimizing the depth. Useful in
the construction of tanks and silos by providing a sloping, fully draining base
with radius corners. Can be used in pressure vessel applications. More
expensive to form and knuckle than a regular tori spherical head.
Generally used on tanks and silos requiring a
sloping, fully draining base with radius corners. Can be used on large
stainless steel milk silos in lieu of a flat sloping base to protect against
oil canning and subsequent stress cracking of weld seams during the hot / cold
CIP process. More expensive to form and knuckle than a regular cone.
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