In the United States it
is common to build
cylinders using ASTM
tubing and pipe
specifications.
However ASTM
Standards do not include
any recommended burst
pressure requirements
that would help an
Engineer design a
cylinder.
Barlow's formula is one
method commonly used in
the industry to
approximate or predict
the bursting pressures
of cylinder tubing.
Barlow's Theory is a
theoretical calculation that
predicts where a failure is
likely to occur.
From here an Engineer
will look at a variety of
factors such as temperature,
environment and application
and use a safety factor to
come up with a material
grade and wall thickness
that will allow a cylinder
to operate safely.
Safety factors vary greatly
as do environments,
temperatures and
applications.
The greater the risk
for injury if a failure
occurs the more likely a
higher safety factor will be
used for a cylinder. As a
rule of thumb a safety
factor of 4 is common but
could be as high as 10 or
more if personal injury is
at risk.
Many Engineers will use
Tensile or UTS to determine
theoretical bursting
pressure estimation. Tensile
strength is the point where
material will break.
However many
Engineers will use the yield
strength of the material and
a safety factor for
determining a safe working
pressure.
The yield point with a
safety factor of 1 is the
theoretical value where the
tube will begin to
plastically deform
permanently.
I have a spreadsheet built
that that will generate
theoretical burst pressures
using Barlow's Theory for a
variety of common cylinder
grades and wall thicknesses
using yield, tensile and
safety factors from 1
through 10.
If you would like a copy of
this spreadsheet please send
an e-mail request to
BobRick@CommercialFluidPower.com
and I will forward a copy.
Note: Spreadsheet is built
in Excel 7.0.
Please advise if an
earlier version or different
format is needed.
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