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* DIN: Deutsches Institut für Normung e.V.
Gas Permeability
DIN* Designation: 3535
This standard provides a means of measuring leakage
of a gas through a gasket. This test is designed to com-
pare the leakage rates of different products.
The fluid used is nitrogen gas at an internal pressure
of 580 psig (40 bar) and a gasket loading of 4,640 psi (32
N/mm2). The apparatus is considerably more versatile
than that used in ASTM F37. The sample gasket size can
be varied; much higher internal pressures can be used.
Normally measurements are made at room temperature.
However, we have the ability to test at elevated tempera-
tures.
The test measures the effects on leakage rates due
to changes in gasket products themselves, in gasket
thicknesses, in gasket flange widths, in varying internal
pressures, in varying gasket loads, and at varying tem-
peratures.
Helium Mass Spectrometer Test
The ability to control and detect leakage on an ever-
decreasing scale is a requirement of industry today. Mass
spectrometer technology is used where stringent leak
detection is needed, such as in the manufacture of devices
used in body implants, nuclear vessels and cathode ray
tubes.
The Helium Mass Spectrometer Leak Detector
(HeMSLD) develops a high vacuum, which enables it to
detect trace amounts of helium that are present. Helium
gas is used as a test media in standard flange fixtures
on the DIN 3535 gas permeability fixture. The HeMSLD
detects the helium leakage through the gasketed joint
by way of a hand-held "sniffer" probe or by a hard-piped
connection from the DIN 3535 fixture or equipment where
other leak detection systems are used. Leakage as low as
1 x 10-9 standard cc He/second can be detected.
Other ASTMTests
Purchasers may want to consider the use of the fol-
lowing ASTM test methods, depending on their gasketing
needs:
F147 Test Methods for Flexibility of Non-Metallic Gasket
Materials
F607 Test Method for Adhesion of Gasket Materials to
Metal Surfaces
Sealability of Gasket Materials
ASTM Designation: F37
Test methods A and B provide a means of evaluating
fluid sealing properties at room temperature. Method A
is restricted to liquid measurements and Method B (most
common) can be used for both gas and liquid measure-
ments.
These test methods are suitable for evaluating the
sealing characteristics of a gasket product under differing
compression flange loads. Since this physical property is
so important to the proper function of a gasket, it should
be used as an acceptance test when test methods are
agreed upon between supplier and purchaser as follows:
fluid, internal pressure of fluid, and flange load on the
gasket specimen.
The most commonly used fluids are isooctane and
nitrogen gas. Gasket load, fluid and internal pressures can
vary according to customer needs. However, our experi-
ence indicates a strong preference for nitrogen gas, with a
gasket load of 3,000 psi (20.7 N/mm2) at an internal pres-
sure of 30 psig (2 bar).
These precise measurements of leakage rates are
designed to compare gasketing products under controlled
conditions. The leakage measured comes either through
the gasket, or between the gasket and the flange faces,
or both. Our experience over many years with thousands
of test samples indicates that, in most cases, the leakage
measured is a result of leakage through the gasket.
It is not a question of whether or not any fibrous type
gasketing product allows leakage through the gasket, but
how much leakage, under any set of given conditions of
time, temperature and pressure.
Questions? Call Gasket Applications Engineering
at 1-800-448-6688