Abstract: FMEA is an Engineering technique used to define, identify and eliminate known and potential failures, problems and errors from the system, design, or process before they reach the customer. The generic nature of the method assisted the rapid broadening of FMEA to different application areas and various practices fundamentally using the analysis method were created. An attempt is made to analyze the failures in Centrifugal Pump using Failure mode and effects analysis INTRODUCTION: The centrifugal pumps find a wide application because of their capabilities to adapt to variable operating conditions, and their ability to discharge different kinds of fluids. The designers of pump attempt to develop high quality and efficiency of pump with a high reliability. Hence it is important, the designers to know the different failure modes of the components, which are occurring most frequently and which will affect the system performance. The FMEA is an effective tool for this purpose. 1.1 Failure Mode and Effects Analysis (FMEA) - Overview 1. Quality 2. Reliability 3. Failure cause 4. Failure mode 5. Failure effect 6. Failure Mode and Effects Criticality Analysis (FMECA) 7. Analysis approach 8. Hardware approach
9. Functional approach 10. Risk Priority Number (RPN) 11. Severity 12. Occurrence 13. Detection 14. Corrective action 15. Single failure point 1.2 Purpose of FMEA A systematic thinking promoted by FMEA is relevant when a new product or system is developed. The purposes of FMEA as follows: To identify the potential design and process related failure modes. To find the effects of the failure modes. To find the root causes of the failure modes. To prioritize recommended actions using the risk priority number. To identify, implement, and document the recommended actions. To assess the safety of various systems and components. To highlight any significant problems with a design. To avoid expensive modifications to designs by identifying potential failures and preventing them.
1.3 Main Phases of FMEA
the risks due to the identified failure modes.
1.4 FMEA Process
The main phases of FMEA are illustrated in Fig.1.3. The analysis process starts from the identification of the scope of the system and the functions the FMEA is to be applied on. After the subject for the FMEA is confirmed the next step is to identify the potential failure modes in a gradual way. The technique of brainstorming has often proven to be a useful method for finding failure modes. There exists many different worksheets to support the brainstorm procedure and the documentation of FMEA overall. In the following phases, the effects and causes of potential failures are determined and so called cause and effect diagrams can be used to help in these phases. The final step is to document the process and take actions to reduce
FMEA is an inductive process that examines the effect of a single point failure on the overall performance of a system through a "bottom-up approach" as shown in Fig.1.4. Since the FMEA concentrates on identifying possible failure modes and their effects on the equipment, design deficiencies can be identified and improvements can be made.
Identification of potential failure modes leads to recommendation for an effective reliability program. Priorities on the failure modes can be set according to the FMEA's risk priority number (RPN) system. 1.5 The role of FMEA in a Quality System
1.6 Centrifugal pump
The Fig.1.3. Illustrates the role of FMEA in a typical quality system. FMEA is an integral part of any QS 9000 compliant quality system. In 1988, the International Organization for Standardization issued the ISO 9000 series of business management standards. Advanced Product Quality Planning (APQP), QS 9000 compliant automotive suppliers must utilize Failure Mode and Effects Analysis (FMEA) in the Advanced Quality Planning process and in the development of their Control Plans.
A side cross-section of a centrifugal pump indicating the movement of the liquid is shown in Fig.1.6. The first phase of Failure mode and effects analysis is to study the basics of component which is taken for analysis. Hence the basics of centrifugal pump is presented in this section. Components of a Centrifugal Pump A centrifugal pump has two main components: I. A rotating component comprised of an impeller and a shaft. II. A stationary component comprised of a casing, casing cover, and bearings.
1.7. General components of centrifugal pump
1.8.Impeller types (Based on Mechanical Construction)
1.2 Principal Causes affecting the Operation of the Pump: The general components, both stationary and rotary, are shown in Fig.1.7. Rotating Components Impeller Based on major direction of flow in reference to the axis of rotation a) Radial flow b) Axial flow c) Mixed flow Based on suction type a) Single-suction: Liquid inlet on one side b) Double suction: Liquid inlet to the impeller symmetrically from both sides Based on mechanical construction (Fig.1.8.) a) Closed: Shrouds or sidewall enclosing the vanes b) Open: No shrouds or wall to enclose the vanes c) Semi-open or vortex type
Photograph of cracked location of feed water pump casing
design FMEA. But the deficiencies in the process, assembly and service may also be considered using the process, assembly and service FMEAs. The output from the design FMEA may be utilized as an input to the process FMEA and service FMEA. The finite element analysis, computer simulation and laboratory tests can be included in the detection methods. The design FMEA operates under the assumption of a single-point failure. But it is possible to take multiple point failures to improve the quality and reliability of the Centrifugal pump.
CHAPTER -5 Survey on failures in centrifugal pump METHODOLOGY 5.1. Solid model generation using preprocessor: In ANSYS there are three stages. They are pre-processor, solution and post processor. So before doing analysis, the geometry of the model should be created. Modeling is done in ANSYS through pre-processor. There we have lot of option through which the geometry of the model is created. 5.2. Meshing contours: After generation of the solid model using pre-processor, the model should be meshed properly. That is the model should be disecritised into number of small elements. For meshing of the model, we should generate meshing contours. 5.3. Meshing of areas: After generation of contours for proper meshing we should go for meshing of the model. There are two
FUTURE WORK In centrifugal pump it is essential to improve the quality and reliability of the designs continuously. The following are the suggestions for further development. Current project considers only the deficiencies in the design, using
types of meshing. They are free mesh and mapped mesh. So in free mesh we can solve it and get the results but it wont be accurate. 5.4. Defining material: So after completing modeling and meshing we have to define the material of the model. So there are different properties which will define a material that is density, youngs modulus, Poissons ratio. For different materials this values are different. By using these properties the material can be define in pre-processor. 5.5. Choosing appropriate element for analysis: The basic concept of FEA is to discritise the model into finite number of smaller elements. There are different element types available in ANSYS preprocessor. Based on the model the element types vary. We have to choose a appropriate element for analysis. 5.6. Attributing equivalent and actual boundary: After discritising and defining material of a model, we have to apply the boundary conditions and the loads wherever we required for the analysis. First, constraints should be applied. So wherever required, the degrees of freedom should be arrested. After applying constraints, the loads are applied on nodes or element for the analysis. 5.7. Solving the problem using solver: Solution is the second stage in ANSYS where the solution of the given problem is done. So here we wont do anything the solution module generate the element matrices and find the stress and deflections according to the parameters we applied.
5.8. Viewing results: The results are viewed in post-processor. Where the stress and deflection can be plotted on the screen. So different colours are plotted for different stress value. We can view both the maximum and minimum stress. 5.9. Studying the parameters stress and deflection for existing design: The above steps are done for the original design and stress value and deflection for original design can be studied.
CHAPTER -6 MODELING 6.1. LOADING OF SHAFT
Fig.6.1. Loading of Shaft 2.2. LOADING OF IMPELLER
Fig.6.2. Loading of Impeller 6.3. MESHING OF SHAFT
Fig.6.4. Meshing of Impeller 6.5. MAPPED MESH: Mapped mesh is generated for the model which is shown in fig.
Element type used for meshing the model is SQUAD ELEMENT.
6.6. SOLUTION: After completing modeling and giving boundary conditions the problem has to be solved using the ANSYS-SOLUTION utility.In the solution utility all the element matrices are formed and it is solved to find the stress and deflection for the applied boundary condition. Fig.6.3. Meshing of Shaft 6.4. MESHING OF IMPELLER
CHAPTER-7 RESULTS AND DISCUSSIONS 7.1 STATIC ANALYSIS: The stress distribution and the deflection of the impeller are found. The stress distribution and the deflection plot for the various components of the impeller are plotted in the figures. 7.2. RESULTS FOR SHAFT WITH ORIGINAL MATERIAL: Fig.7.2.Maximum Shear Strain for En16 Steel Shaft
Fig.7.1.Maximum Shear Stress for En16 Steel Shaft
Fig.7.3.Total Deformation for En16 Steel Shaft 7.3. RESULTS FOR SHAFT WITH OPIMIZED MATERIAL:
Fig.7.4.Maximum Shear Stress for En16 Steel with bronze Shaft
Fig.7.6.Total Deformation for En16 Steel with bronzeShaft
Fig.7.5.Maximum Shear Strain for En16 Steel with bronze Shaft Fig.7.7.Maximum Shear Stress for En16 Steel with brass Shaft
7.4.
RESULTS FOR IMPELLER WITH ORIGINAL MATERIAL:
Fig.7.8.Maximum Shear Strain for En16 Steel with brass Shaft
Fig.7.10.Maximum Shear Stress for Cast iron impeller
Fig.7.9.Total Deformation for En16 Steel with brass Shaft
Fig.7.11.Maximum Shear Strain for Cast iron impeller
Fig.7.12.Total Deformation for Cast iron impeller 7.5.. RESULTS FOR IMPELLER WITH RUBBER COATED MATERIAL:
Fig.7.14..Maximum Shear Strain for Rubber coated Cast iron impeller
Fig.7.15.Total deformation for Rubber coated Cast iron impeller Fig.7.13..Maximum Shear Stress for Rubber coated Cast iron impeller
7.6. RESULTS FOR STEEL BEARING: 7.8. COMPARISON FOR THE SHAFT MATERIAL S.N O 1. 2. SHAFT MATERI AL En 16 Steel En 16 Steel with bronze En 16 Steel with brass TOTALDEFORMAT ION 0.0018701 0.0011981
3.
0.00073762
7.9. COMAPRISON FOR THE IMPELLER MATERIAL Fig.7.16..Heat flux on steel bearing 7.7. RESULTS FOR LEAD ALLOY STEEL BEARING: S.N O IMPELLE R MATERI AL Cast iron Cast iron with rubber coated TOTALDEFORMAT ION
1. 2.
0.02048 5.3564e-5
7.10. COMAPRISON FOR THE BEARING MATERIAL S.NO 1. 2. BEARING MATERIAL Steel bearing Lead alloy steel bearing HEAT FLUX 1.2821e-6 4.3211e-7
Fig.7.17.Heat flux on lead alloy steel bearing
CHAPTER-8 CONCLUSION AND SCOPE FOR FUTURE WORK 3. In this work, effort has been made to increase the pump efficiency by optimizing the material of the various components in the pump by analyzing the stress distributions in them. Pre -stress conditions are applied to this model, therefore the strengthening and weakening of the parts is predicted. Optimization of the parts of Shafts, Bearings, Impeller leads to decrease in deformation. SCOPE FOR FUTURE WORK 6. In centrifugal pump it is essential to improve the quality and reliability of the designs continuously. The following are the suggestions for further development, 1) Current project considers only the deficiencies in the design, using design FMEA. But the deficiencies in the process, assembly and service may also be considered using the process, assembly and service FMEAs. The output from the design FMEA may be utilized as an input to the process FMEA and service FMEA. 2) The design FMEA operates under the assumption of a single-point failure. But it is possible to take multiple point failures to improve the quality and reliability of the Centrifugal pump.
from a impeller
centrifugal
pump
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