Enhanced Techniques and Technology for Sensing Cavitation Damage and Crack Initiation in Hydraulic Equipment
* Can we identify cavitation damage using acoustic technologies in a new innovative way?
* With a similar sensor arrangement, is detection of fatigue cracking and crack propagation possible for broad application to hydraulic structures and equipment?
Need and Benefit
* Cavitation Damage Detection: There are currently two systems commercially available that tout cavitation detection in hydromachinery as their purpose. Reclamation has been involved in evaluating these systems side-by-side at Grand Coulee Powerplant for the past couple of years. The results of the systems have been inconclusive. The two system's responses do not correlate well with each other. One manufacturer has provided extensive interpretation of the results and the feeling is that they may be valuable.
In order to better serve Reclamation's powerplants, a trend toward condition-based maintenance has been suggested. Many plants normally schedule outages in order to repair cavitation damage to the turbine runner and draft tube. If a sensor package was available to alert operators when the units were in a damaging zone, closer records of time in the zone could be collected or--preferably--the unit could be adjusted to operate outside the damaging area. Plant managers could make a better determination of when outages are necessary for repairs if damage is monitored. To date, the available systems have not provided this type of information and probably will not without extensive calibration with unit damage on a specific basis.
* Crack Detection and Propagation: There are many instances throughout Reclamation that detection of cracking in structures or equipment is vital to the performance of critical hydraulic equipment and machinery as well as structures. There have been many instances where cracking of turbine runner blades have resulted in major damage or extensive test programs in order to satisfy concerns. Internal tie rods in piping bifurcations are another area where there has been documented damage and the potential for much more (e.g. catastrophic failure). Acoustic emissions have been used in nondestructive testing (NDT) scenarios to evaluate structures for cracking, both in concrete and steel reinforcement bars and wires. Use of the same type of equipment, crack initiation and growth has been accurately measured. It has even been used successfully to locate termite activity in wood structures.
The complex geometries present in hydraulic machines pose some interesting problems for application of this technology, however it appears achievable. Using this same type of technology, it may be possible to continuously monitor high-hazard locations and detected initial cracking prior to complete failure. Also, crack propagation could be monitored in order to evaluate whether the cracking possibly stops prior to failure as many times can happen in turbine runners.
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