Failure analysis and guidelines for further exploitation of centrifugal slurry pumps used for copper flotation waste transport: A case study

Abstract

High power slurry pumps are the core element of copper flotation waste transport. Pump failure can lead to shutdowns of the flotation process and high financial losses. This paper is a case study of three high power, split case, rubber lined, closed impeller, tangential discharge slurry pump failures, where all failed pumps were located at the first stage of three different pumping sections. Analysis of the material strength of each pump housing showed a strong reduction in the ultimate tensile strength to 25 %, 39 % and 46 % of the specified min value of 241 MPa for ASTM A48 Class 35 Gray Iron Castings. Microstructure analysis showed numerous micro cracks formed along with casting defects such as cementite, phosphorus eutectic and porosities. Vibration analysis identified interference between pump stages that led to low frequency beat phenomena that consequently could cause cyclic load on the castings. Detailed FEM modeling of the pump housing assembly, including main bolted connections, indicated that tightening the pump housing bolts with the correct torque or operation at a nominal pressure of 0.69 MPa could cause the pump housing to fail due to strongly reduced material properties. Further investigation showed that the ASTM A48 Class 35 Gray Iron and cast stainless steel bodies A743 CA6NM did not show overload both when the housings are properly bolted together and when a 30 % overload is introduced on one of the fasteners, given the proper material properties.