f. When a viewport is subjected to pressurization from both sides, the
thickness of the window must be selected on the basis of the highest design
pressure, regardless of whether this pressure is external or internal to the
a. The window seat cavity in the viewport flange must be dimensioned to
provide the window bearing surface with support during hydrostatic testing
and subsequent operation at maximum design pressure. The dimensions of
window seat cavities for standard window geometries are shown in Figures 3-16
b. The surface finish on the window seat cavity must be at least 64 rms.
c. The surface of the window seat cavity must be protected against
corrosion, preferably by a weld overlay of corrosion resistant material prior
to final machining. Painting of seat cavity surface, anodizing it, or
plating it with electroless nickel is also an acceptable means of preventing
a. Because of the large mismatch between the moduli of elasticity in the
plastic window and the metallic flange, it must be assumed in stress
calculations that the window does not provide any reinforcement for the hull
material around the penetrations.
b. Any of the analytical, or empirical, methods for stress and
displacement calculations acceptable to the applicable ASME Code may be used
for dimensioning the thickness, width, and location of the flange around the
c. Reinforcements for pressure vessel penetrations meeting the
requirements of the applicable ASME Code will be considered acceptable for
viewport flanges without further engineering calculations.
d. The following minimum requirements must be met by viewport flanges
shown on Figures 3-16 and 3-17 with a finished diameter opening in excess of
24 in (635 mm).
(1) Radial deformation of the window seat at maximum internal or
external design pressure must be less than 0.002 x Di.
(2) Angular deformation of the window seat at maximum internal or
external design pressure must be less than 0.5 degrees.