(1) The dimensions of a standard window in the O to 10,000 psi (0
to 60 MPa) design pressure range should be based solely on the basis of the
window's short term critical pressure (STCP) and the approved conversion
factor (CF) for the given maximum ambient temperature. Minimum STCP values
of some standard window geometries, based on tests conducted by the U.S.
Navy, referenced in ANSI/ASME PVHO 1 (Reference 1) are given in Figures 3-12
through 3-15. CF values for the standard window geometries are given in
Tables 3-3 and 3-4. Calculations of STCP on the basis of these figures
satisfy the requirements of this Standard under paragraph A.3.c. However, it
is also acceptable to have the designer establish the STCP with his own
destructive tests of full scale, or model scale windows performed according
to procedure in C-5 providing such tests are witnessed by and are acceptable
to the Authorized Inspector.
(2) The dimensions of windows in the 10,000 to 20,000 psi (69 to
138 MPA) design pressure range, should be based solely on nondestructive
tests in the form of long term and cyclic pressurizations. Dimensions of
approved windows for this design pressure range (based on tests conducted by
the U.S. Navy, referenced in ANSI/ASME PVHO 1 (Reference 1) are given in
Table 3-5.
c.
STCP of an acrylic plastic window is, for the purposes of this
Standard, defined as the pressure at which catastrophic failure of the window
takes place (window disintegrates releasing pressurized fluid into, or from
the chamber) when subjected to hydrostatic pressure increasing at a constant
rate of approximately 650 psi (4.5 MPA) per minute. The pressurization must
take place at ambient temperature range of 70 to 77 deg. F (21 to 25 deg. C)
in a flange that satisfies the requirements of paragraphs 8, 9, and 10. The
CF is an empirical ratio of short term critical pressure to design pressure
specified on the basis of long experience as the safe relationship between
the two variables for a given temperature.
(1) The evaluation of a design is to be conducted on a minimum of
five full-scale windows and the results are considered representative only if
the lowest critical pressure is AT LEAST 75% of the mean critical pressure of
the other four windows. In such a case, the STCP value of the window design
is to be taken as the lowest critical pressure among the five tests. In case
the lowest critical pressure does not meet this criterion, the STCP value of
the window design is to be equal to the single lowest critical pressure among
the five tests multiplied by a factor of 0.75.
(2) Model scale windows may be substituted for full-scale windows
in c (1) tests, if in addition to the five model scale windows at least one
full-scale window is tested. The test data (STCP calculated according to c
(1)) generated by testing of model scale windows is considered acceptable
only if the critical pressure of the full scale window is equal to, or above
the single lowest critical pressure among the five tests. In case that the
critical pressure of the single full scale window does not meet this
criterion, four more full scale windows should be tested and the STCP value
of the window design should be calculated according to c (1) on the basis of
full-scale windows alone.
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