Study On Analysis Methods To Protect Against Plastic Collapse Of Pressure Vessel

Design by analysis (DBA) of pressure vessels, as a method may be used to replace design by formulae (DBF), is becoming more and more appreciated for designers. It is widely used especially in designing of components works under high pressure or high temperature and non-standard equipments which could not be designed by formulae. An important task of DBA is protecting against plastic collapse of pressure vessels, however elastic-plastic analysis methods of different standards are different too.In this thesis a research on six major elastic-plastic analysis methods has been carried out by using numerical analysis, mainly includes the following contents:1. An introduction of gross plastic deformation design check of the direct route in European standard EN 13445-3 and its applications is presented in this paper. After comparing two ways of quadratic extrapolation the following conclusions can be drawn:when using EN13445, in order to obtain principal structural strains, strain components of hot spot shall be determined by quadratic extrapolation with surface pivot points.2. A method based on strain linearization is proposed to calculate principal structural strains. There are six evaluation methods of structural strain because of difference of modeling, after comparing two ways of quadratic extrapolation the following conclusions can be drawn:the deviation of results calculated by strain linearization and quadratic extrapolation is minimum; strain linearization is capable of treating such problems, for which the EXTRA method is meaningless, because it can evaluate the structural strain at any location of pressure vessel components.3. A maximum equivalent structural strain criterion is presented in this thesis for the GPD design check. It is more available for the ductile materials, which are widely used in the pressure vessels.4. A zero curvature criterion procedure is accomplished and the judgment of load-strain or load-deformation (P-w) is given. It is accurately and quickly to judge one point in P-w curve is whether zero curvature or not, or determine the location of zero curvature point on curve. So the load and resistance factor design (LRFD) can be used to design check.5. After comparing six elastic-plastic analysis methods by using limit analysis and elastic-plastic analysis the following conclusions can be drawn: zero curvature criterion is the best method to calculate limit load; the difference of allowable load determined by collapse load and limit load is related to effects of non-linear geometry, thus the minimum could be seen as the final allowable load of considered structure.