a.
Physical Properties. The physical and mechanical properties for
acrylic plastic are given in Table 3-1. The type of acrylic generally chosen
for pressurized windows is the utility grade, defined by Federal
Specifications L-P-391B. If the acrylic plastic is not certified by the
manufacturer as having the typical physical properties in Table 3-1, the
castings must have the minimum physical properties in Table 3-2 as determined
by acceptance tests by the manufacturer or an independent materials testing
laboratory with certified test results furnished by the fabricator to the
user.
(1) Construction. Acrylic windows must be made from monolithic
cast material. Commercial acrylic plate is available up to 4 inches thick
and special shapes can be cast to order.
(2) Forming. Machining is best performed with sharp tools and
slow feed at high surface speed. A water-base coolant is helpful.
(3) Annealing. Annealing will remove residual stresses after
machining or sawing. Manufacturer's instructions should be followed.
Dimensional changes may occur during annealing.
(4) Surface Finish. It has been found that a 32- to-64 rms finish
on sealing and bearing surfaces of the window seat is satisfactory. The
viewing surfaces, if machined, must be polished. Annealing should follow
final machining and polishing.
b.
Fabrication Certification. The window fabricator must certify that
only approved methods and materials were used for all forming, machining,
polishing, heat treatment and inspection processes.
c.
Design Certification. The window designer must certify compliance
of the window design with the requirements of ANSI/ASME PVHO 1 (Reference I)
and include engineering calculations and/or a description of the experimental
method and data used to verify compliance.
d.
Pressure Testing Certification. The window supplier or an approved
testing laboratory must certify the results of the window pressure test and
include pressure, temperature, pressurization rate, duration of sustained
loading and viewport flange used.
e.
Identification. Identification of each window must be on the
window seating surface in letters and numbers 0.125 inch (3.2 mm) high with
an indelible felt marker through a paper stencil. The identification must
contain the information as shown in the following example.
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