| Dams
AMERICA’S HISTORY IS INTRINSICALLY linked to its vast water resources. Managing and harnessing those resources ensures a reliable and sustainable source of water for agricultural irrigation, industrial processes, and potable drinking water. In the process, food security and economic growth became certainties. Additionally, dams contribute to flood control, safeguarding communities from devastating natural disasters and providing navigational waterways for commercial shipping. Beyond water management, the capacity of dams to generate clean and renewable hydropower drives innovation and supports diverse energy production. The recreational opportunities and tourism potential they offer also add significant value, contributing to both local economies and the preservation of natural habitats. As the backbone of water management and energy generation, it becomes even more evident that dams stand as vital assets in enhancing national resilience and fostering sustainable development. Dams utilize various styles of water control
gates which are commonly referred to as hydraulic structures. The style of these gates is quite diverse from tainter gates, also known as radial gates, used for smooth water regulation while minimizing erosion to miter gates which are used for navigational locks. Additionally, there are sluice gates, stop logs, bulkheads, vertical lift gates and so on. One common element with all hydraulic structures is the significant amount of fatigue loading they must withstand during their service life. Hydraulic structures will shake themselves apart while in service. Because of these high fatigue loads, as well as many hydraulic structures being considered fracture critical, many are now designed and built to the AWS D1.5 bridge code. This ensures designs with fatigue life in mind, reinforces material toughness requirements and puts a higher emphasis on quality.
Nondestructive testing (NDT) One of the techniques employed to evaluate the
gates’ structural integrity and detect any signs of wear, corrosion, or fatigue is nondestructive testing (NDT). These inspections provide engineers with critical data
on the gates’ condition, allowing them to address any potential issues promptly. Quality in steel construction is a primary focus for hydraulic structures. NDT is one of the primary methods for verifying both the quality of construction as well as the structures performance while in-service. NDT is the process of inspecting, testing, or evaluating materials, components, or assemblies for defects without damaging or destroying the object being examined. There are currently 16 recognized NDT Methods, those most commonly used for welded steel construction of hydraulic structures are Ultrasonic Testing (UT), Radiographic Testing (RT), Magnetic Particle Testing (MT), Liquid Penetrant Testing (PT) and Visual Testing (VT). Of these, only two are considered volumetric test methods, Ultrasonic Testing and Radiographic Testing. Volumetric test methods are capable of examining the through thickness of a test object regardless of the objects thickness. This becomes incredibly important especially with structural welding where because of the nature of the welding process many types of discontinuities can occur deep within the weld which if left undiscovered can result in failure. Ultrasonic Testing utilizes high frequency soundwaves which propagate through the test object. Because of the short wavelength associated with higher frequencies used with UT ,the soundwaves are incapable of transmitting through gases or low-density materials due to their significant difference in acoustical impedance. This results in soundwaves reflecting from air voids or materials of significant density differences back to the transmitting transducer providing a signal on the display. UT is incredibly sensitive to locating cracks and other linear discontinuities. Examinations can be performed relatively quickly, accurately, cost-effectively, and there are no safety issues, in addition only one side of the test object needs be accessible when using the pulse- echo technique. Radiographic Testing utilizes ionizing radiation either in the form of gamma radiation from a decaying radioisotope or X-radiation from an X-ray generator. The ionizing radiation penetrates through the test object and is received by either a radiographic film for conventional RT, by a digital detector array (DDA) for digital radiography, or an imaging plate (IP) for computed radiography. Regardless of the image
Above: Miter Gate Leaf during fabrication
Left: Tainter Gate in operation
www.waterpowermagazine.com | October 2023 | 35
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