Detecting Cavitation in Centrifugal Pumps

ently Nevada Corporation is continually investigating methods to help our customers protect and manage all their machinery. This includes integrated solutions to address machines of all sizes, speeds, and criticality. Within two of the largest markets that we serve, Hydrocarbon Processing and Power Generation, the most common machine type is the process pump. The vast majority of these pumps are small – less than 200 hp (150 kW) in size – and operate at speeds below 3600 rpm. They use rolling element bearings and mechanical seals. Our pump lab is a direct result of industry’s need for improved knowledge and solutions for this important class of machines. Traditionally, the types of pumps described above have been categorized as “low business risk.” If they are monitored at all, it is generally with a portable data collector at intervals rarely more frequent than once per month. Permanently installed online systems are almost never employed because it is argued that the costs of such pumps do not justify the cost of permanent monitoring. Interestingly, this long-held paradigm is changing. The focus on these “smaller” machines is intensifying, because there are often so many of these machines in a plant that they can collectively comprise a significant portion of the maintenance budget. As has been said, “many drops make an ocean,” and this is often true with maintenance costs in a typical plant – it can be the many small expenditures that eclipse the few expensive ones. Increasingly, online monitoring is justifiable, particularly for certain malfunctions. The subject of this article – cavitation – is one such phenomenon that can be very damaging to pumps, is a direct result of improper operating conditions, and can only be effectively detected and mitigated in an online environment. Because operating conditions are what cause a pump to cavitate, the condition needs to be measured in real time and conveyed to Operations personnel so that they can stop the pump from cavitating – in effect, stopping the pump from damaging itself. Portable data collection informs Operations after cavitation has occurred. In contrast, permanent monitoring informs as it is occurring, allowing Operations Detecting Cavitation in Centrifugal Pumps Experimental Results of the Pump Laboratory