Figure 1 — Spillway Gate No. 2
Method for Assessing a Deformed Spillway Gate
When permanent deformation was found on a gate at Mercury’s
Karapiro plant, Quest Integrity performed a number of assessments to
determine whether it needed to be replaced, or if it still met criteria to
be ft for service.
By Vitor Lopes Garcia and David Osuna
This schematic shows the position of Spillway Gate No. 2’s seven horizontal girders in relation to the four locations selected for measurement.
When personnel at the 96-MW Karapiro hydropower plant removed one of the four spillway gates from service in late
2014, they discovered the lower section of the
gate had undergone permanent deformation and
had sufered corrision on the internal and external
gate surfaces. Concerned about the ability of the
gate to operate reliably when returned to service, plant
owner Mercury (formerly Mighty River Power) commissioned a
ftness-for-service (FFS) assessment. Tis article covers the methods
used to determine if the spillway gate was ft for continued service
and the results of the assessment.
Background on the situation
Commissioned in 1947, the Karapiro hydro plant is the last in a
series of nine power stations located on the Waikato River on the
North Island of New Zealand. Te facility houses three vertical
Kaplan turbine-generator units and has a net head of 30 m. Te
dam is a 52-m-tall, 335-m-long concrete arch structure, with a