Pump Case Studies
|Pump Case Study Session 1B||
CSP3: The 'Repair or Replace' Decision of Boiler Feed Pump Impellers
Authors: Joseph A. Silvaggio, Jr. and Carolyn B. Smith (Siemens)
In the course of a boiler feed pump's operating life, it is periodically disassembled and its components are inspected. Most boiler feed pump impellers are made of 17-4 or CA6NM type materials, which allow for magnetic particle inspection. When pump impellers wear or cracks or damage are discovered, the decision to either repair or replace the impeller(s) needs to be made. This decision is required to assure pump reliability and longevity at the required performance levels. This case study explores what is involved in making this decision.
CSP4: Morton-Like Effect in a Centrifugal Pump
Author: Maki Onari (Mechanical Solutions, Inc.)
Two single-stage double-suction type pumps were installed in a nuclear power plant in reactor feed service (two 50% pumps). The pumps are driven by steam turbines. In February 2011, Pump B indicated a large step change in the vibration at the running speed accompanied by a significant deficiency in performance. This vibration issue was a result of a broken impeller vane causing imbalance and internal rubbing. Pump B was completely refurbished during a major outage in spring 2012, but Pump A was not refurbished. After the outage, Pump B began increasing shaft vibration at the inboard and outboard ends. This time the vibration amplitude was not constant (Morton-Like Effect); it was oscillating (0.5 to 4.5 mils pk-pk) with a period between 10 to 60 seconds for the synchronous speed component of vibration. In summer 2012, plant personnel tried different ways to eliminate this phenomenon and detected a strong influence of the condensate seal water temperature (seasonal) or by changing the seal water injection flow. However, the results were not always consistent and sometime without any effect (not repeatable). Thorough investigation revealed that the Morton-Like Effect was continuing, caused by severe binding / deformation of the pump casing while all four foot hold-down bolts were tightened during the outage in 2012. Over-torquing caused deformation of the pump casing as well as the shaft seal cavities during the thermal expansion process. This deformation allowed a light rub or a “near rub” between the seals and the shaft setting the stage for the slowly associated shaft cyclic bow deformation of the Morton-Like Effect.
CSP5: Drive Shaft Failure Analysis on a Multistage Vertical Turbine Pump in River Water Supply Service in a Nickel and Cobalt Mine in Madagascar
Authors: Juan Gamarra (Mechanical Solutions, Inc.), Paul Behnke (ITT Industries)
This case study demonstrates the effectiveness in machinery root cause investigations of thorough vibration testing including strain gauging, Operating Deflection Shape (ODS), Experimental Modal Analysis (EMA), and Finite Element Analysis (FEA) rather than traditional troubleshooting approaches, which had not detected a inter-related problem, and would not have provided such clear visual evidence for decision makers.
|Location Level Three, Room 370F|