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Pressurized, Accelerated Life Testing of Polymeric Materials
Touchstone built multiple test apparati to test various types of
organic polymer materials with exposure to the following test media
at pressures to 100 psi and temperatures up to 300 deg F. In most
cases dry nitrogen has been used as a cover gas, although testing
has been performed with a hydrogen sulfide atmosphere. Other atmospheres
are possible including; Methanol, CO2 gas, Water, Diesel fuel, Oil
well condensate, H2S gas, Methane gas, Drilling muds, HCl (34%),
and Crude oil. Samples are exposed for a specified period after
which they are inspected and mechanically tested.
Pressurized SWAAT Testing
The standard practice in the manufacture of brazing sheet is to
produce a coil of sheet for plant trials. A group of heat exchangers
are produced during this trial and evaluated to determine the performance
of the units in various ways including static burst, cyclic pressurization
(fatigue), SWAAT corrosion, and thermal flow. The pressurized sheet
fixture was developed to allow pressurized SWAAT testing of candidate
material prior to plant manufacturing trials to determine whether
the brazing sheet is unusually susceptible to corrosion before the
expensive trials are undertaken.
The test coupon consists of a 3.5" disc of brazing sheet that
has been formed into a cup using an Olsen cup tester to simulate
the extreme cold work effect of stamping, for instance. After forming
the test specimen is brazed following conventional procedures and
then installed in the test fixture. The fixture can then be pressurized
to simulate use conditions (100 to 400 psi) typically using either
N2 or He gas. After placing in a SWAAT test cabinet and pressurizing,
the fixture is monitored until a drop in pressure occurs indicating
a failure. The specimen can then be removed and evaluated metallographically.
This system allows evaluation of experimental or production trial
lots of sheet without the necessity of actually manufacturing heat
exchangers and collapsing the time-to-market for a new product..
If the SWAAT life is acceptable the next step is to product actual
parts for evaluation.
Index of Accelerated Life Testing