Project Title: Pressure Vessels Designation by Fracture Analysis
Importance and Statement of Topic:
Pressure vessels are main group of equipment used in the power station and refinery resources and their designation and manufacture relates to their mechanical engineering domain. A pressure vessel includes different part which its most important parts are: the pressure vessel’s head and its shell. The head and shell of vessel are important and influential elements on the efficiency of vessel. Therefore the research has paid special attention to these two parts.
In this research we decide investigation stress analysis methods and criteria of fracture mechanic obtain optimum designation of pressure vessels. Optimum designation has certain goals, which are: predicting cracks in pressure vessels and its different parts and also find optimum relationship for the diameter and thickness of vessel’s head and shell.
Optimum thickness means to get an appropriate thickness for certain diameter with certain pressure in such manner that by investigating the fracture criteria for any diameter with least safety coefficient an obtain the thickness for that diameter. Because in the designation criteria of pressure vessels such as ASME the resulted formulas have been prepared with high safety coefficient and our purpose is that these coefficients and their protective degree reaches to the least amount in the designation in such as way that results in the wall thickness, consuming raw material and finally cost reduction.
Review of Literature and Relevant Topics:
Also it has been made so many researches about this subject and I has offered a summery of one of these researches which has been published in the Engineering Failure analysis 15 (2008) 208-219
(The application of design methods based on finite element analysis ‘‘Design by Analysis – Direct Route’’ as an alternative to the recommendations based on the experience and formulas ‘‘Design by Formula’’ allows removing the unnecessary conservatism of the current design codes. A finite element analysis (FEM) was used to calculate the behaviour of a pressure vessel (PV) made of high strength steel (P500) subject to the design loads and assuming the existence of the ‘‘worst case’’ crack allowed by the European standards in order to demonstrate the safe use of these steels and the too conservative design rules currently applied by the PV manufacture codes. It was demonstrated that the presence of cracks on pressure vessels made of high strength P500 steel non-detected during non-destructive tests, do not endanger the safety of the vessel, so its application can be fully successful and safe even under the worst allowed conditions, given way to significant reductions of wall thicknesses, weights.)
Also my researches titled proficiency project currently concentrates on stress analysis of different pressure vessels head and comparison those with results obtained from tension analysis by using of finite element methods with designation standards (ASME).
Aims and Hypothesizes:
This research has several aims which are:
A: according to the static pressure entered on pressure vessel, predicting the points that crack will occur in them most potentially.
B: the most important aim is that in this research based on the stress analysis and fracture mechanic we obtain the appropriate criteria for the thickness of different parts of vessel such as vessels head and …according to the diameter, pressure and materials, in such a way that for the certain diameter based on the fracture mechanic criteria can get the optimum thickness in such a way that has least safety and protective coefficients and offer proportions of diameter to thickness for any material and certain pressure as tables and diagrams and if possible as formulas.
At final, it results in the wall thickness, weight and cost reduction.
The most important used method in this research is stress analysis by finite element methods through software such as ANSYS, and if necessary can perform pressure tests on different parts of pressure vessels such as shell and head and compare the results of these stage i.e. practical results with the results of finite element stress analysis.
-ASME Section 8 -Pressure Vessels
-Fracture analysis of a pressure vessel made of high strength steel (HSS)
(Engineering Failure Analysis 15 (2008) 208–219)
Practical Guide to Pressure Vessel Manufacturing
(New York, NY, USA: Marcel Dekker Incorporated, 2002.)
-ANSYS version 11.0