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36 HYDRO REVIEW / July 2017 www.hydroworld.com
spillway located on the right abutment.
Te spillway has four gates, each of which
is 6. 1 m wide and rated to pass 3.77 cubic
meters per second of water. Te gates are of
the Stoney roller design and were originally
operated one-at-a-time by a gantry crane until
1979, when a dedicated winch system was
installed, allowing the four gates to be opened
simultaneously. In 1998, the staunching bars
were replaced with music note seals and the
gates were reinforced for seismic events.
In late 2014, Gate 2 was removed from
service for installation of bird netting. After
removing the gate, personnel with Mercury
determined that the lower section had undergone permanent deformation. Corrosion was
also reported on the gate’s internal and external surfaces, prompting an FFS assessment,
which was undertaken by Quest Integrity.
Inspecting the gate
Two on-site visits were carried out by Quest
Integrity engineers, with the aim of quantifying the level of superfcial corrosion, using a
Panametrics 36DL-Plus U T thickness meter.
Tese measurements (see Table 1 on page
38) were taken at four locations between the
spillway gate’s seven girders, designated A, B,
C and D, with A being the lowest location
and D being the top section of the gate (see
Figure 1 on page 34).
Location A showed the highest level of
metal loss with respect to the nominal gate
thickness of 15.875 mm. Meanwhile, location
D showed the minimum metal loss, with a
value very close to the skinplate nominal
thickness. It was found that the magnitude of
metal loss was related to the location of the
skinplate section with respect to the spillway
gate height. Te bottom sections showed
higher degrees of metal loss compared to
the top sections.
Finite element analysis
A fnite element analysis (FEA) was per-
formed by Quest Integrity with the purpose of
estimating the stresses at the spillway gate due
to hydrostatic loading. Two diferent scenarios
— Deformation load: To determine the
possible maximum loading that caused the
current defection in the gate. An as-designed
model with no corrosion was used; and
— Fitness for service: To demonstrate
the current gate is ft for service in accor-
dance with the plastic collapse and local
The von Mises distribution of the converged solution, with a load factor of 3. 6.
Figure 2 — 2014 Analysis of Gate No. 2
● Peer Reviewed Tis article
has been evaluated and edited in accordance
with reviews conducted by two or more
professionals who have relevant expertise.
Tese peer reviewers judge manuscripts for
technical accuracy, usefulness, and overall
importance within the hydroelectric industry.