Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC

Photographs of the DM Test Piping and its components are shown in Figure 2-9 through Figure 2-14.
The system was instrumented with accelerometers, displacement sensors, and strain gages at critical
locations as shown in Figure 2-15 through Figure 2-18. The Ultimate Strength Test piping specimen had
an identical piping configuration with the same piping components. Since this test was designed to stress
the pipe to failure, it was modified by the addition of another 1000 kg (2200 lb) mass and the removal of a
lateral support as illustrated in Figure 2-19. As shown, one of the two-directional supports was replaced
by a vertical support. Photographs of the US Test Piping and its components are shown in Figure 2-20
through Figure 2-22. This system was also instrumented with accelerometers, displacement sensors, and
strain gages at critical locations as shown in Figure 2-23 through Figure 2-25
A series of test load cases were carried out for each piping test specimen. A summary of the test cases is
presented in Table 2-1. The design method confirmation tests included preliminary tests (DM1),
allowable stress tests (DM2), and elasto-plastic response tests (DM4). Preliminary tests included
horizontal and vertical low-level sine sweep tests (DM1-1) to determine the frequencies and modal
damping values as summarized in Table 2-2, and seismic tests (DM1-2) in which seismic input motions
were applied separately in the horizontal and vertical directions. The seismic input motion was selected
based on the Japanese “S2” seismic wave for a PWR. For each test, the seismic wave was adjusted to
achieve the desired maximum stress limits. The input motion for the DM2-1 test was selected to induce a
maximum stress equal to the Japanese Code primary stress limit of 3Sm (JEAG 4601-1984 Edition). For
the DM2-2 test, the input motion was to induce a maximum stress level equal to 1.5 times the Code limit
or 4.5Sm. Seismic table motion was applied simultaneously in the horizontal and vertical directions. In
this series of tests, the dominant input motion frequency was not close to the fundamental piping system
frequency (off-resonance). The DM4 series of elasto-plastic response tests applied higher input motions
to achieve plasticity with stress levels from 2 to 4.5 times the primary stress limit (6Sm, 10.5Sm, and
13.5Sm). In order to achieve these high levels, the seismic waves were adjusted so that the dominant input
motion frequency was close to the fundamental piping system frequency (on-resonance). In all of these
tests, the piping system was internally pressurized to induce a hoop stress equal to the design stress
intensity Sm. The tests were conducted at room temperature and no evidence of pipe failure was observed.
JNES/NUPEC provided the results of the Design Method Confirmation tests shown in Table 2-1 as
digitized acceleration, displacement, support load, and strain time histories. Frequencies and damping
ratios at high levels of seismic acceleration were also calculated by JNES/NUPEC and are shown in Table
2-4. Representative time history results are shown in Figure 2-26 to Figure 2-28. Horizontal and vertical
seismic acceleration input motions for the DM4-2(2) test are shown in Figure 2-26. Maximum piping
response displacement time history is shown in Figure 2-27. The maximum strains were measured at the
flanks of piping elbow 2. Hoop strain time history at this elbow for the DM4-2(2) tests is shown in
Figure 2-28
The Ultimate Strength Test was designed to fail the pipe. As indicated in Table 2-1, this test series
included preliminary low-level sine sweep tests (US1) to determine the frequencies and modal damping
values as shown in Table 2-3, and ultimate strength seismic tests (US2). The seismic input motion was
designed to induce a maximum stress level equal to 8 times the Code limit or 24Sm. In order to achieve
this high stress level, the seismic waves were adjusted so that the dominant input motion frequency was
close to the fundamental piping system frequency (on-resonance). In these tests, the seismic table motion
was applied only in the horizontal direction. The piping system was internally pressurized to a design
stress intensity of Sm and the tests were conducted at room temperature. The seismic input motion was
repeated until failure occurred. During the fifth test run, a longitudinal through-wall crack developed in
elbow 2. A photograph of the failure is shown in Figure 2-29. A close-up of the longitudinal crack in the
elbow is shown in Figure 2-30. An examination confirmed that the failure was the result of fatigue
ratcheting.
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