What are some methods for monitoring corrosion in a pump?
Corrosion in pumps is a serious concern that can lead to catastrophic failure of a pump if it is not properly monitored. Selecting the proper material for the pump is extremely important in addressing this concern. Material selection depends on numerous conditions such as the fluid being pumped or speed of rotation of the pump.
Choosing the incorrect material for an application will accelerate the effects of corrosion. Similarly, choosing the best-suited material for an application will dramatically reduce the effects of corrosion.
Because of the dangers of corrosion in pumps, it is necessary that pumps applied in systems where corrosion is a known risk are frequently checked to ensure normal operation. Several methods for corrosion monitoring exist.
A visual inspection of the pump is the easiest and can reveal corrosion damage occuring in the pump.
A drawback to a visual inspection is that it requires the pump to be shut off and taken apart. Additionally, stress cracking could have no visible signs in the visual check, yet the results can be sudden and catastrophic.
General corrosion can be detected by using a metal probe to measure the electrical resistance.
As the cross section is reduced by corrosion, the measured electrical resistance will increase.
Metal probes can also be used to measure the linear polarization resistance. A voltage is applied using the probes, and the resulting current is proportional to corrosion rate.
Finally, ultrasonic thickness measurement can determine the thickness of an area on the pump and show if thickness is being lost due to corrosion.
For more information on corrosion monitoring, refer to HI 9.6.5 Rotodynamic Pumps Guideline for Condition Monitoring at pumps.org.