Research On Fatigue Behavior Of Welded Aluminum Pressure Vessels

Welded aluminum pressure vessels are widely used in fields such as petrochemical industry and energy. The conspicuous progress of domestic technology on smelting, welding, non-destructive testing and so on in the recent years objectively makes the increment of the allowable stress of aluminum and the light-weight of welded aluminum pressure vessels possible. Light-weight of welded aluminum pressure vessels not only meets the needs of energy conservation and emission reduction, but also is good for the improvement of competitiveness of domestic welded aluminum pressure vessels in the world. Light-weight of welded aluminum pressure vessels has become an inevitable trend, and to increase the allowable stress is one of the valid ways to realize light-weight. The increment of the allowable stress of aluminum leads the reduction of thickness and the fatigue strength of pressure vessels. This study is supported by the Research Projects of Quality Inspection System in Zhejiang Province (20080225), focused on the question whether realizing the light-weight of welded aluminum pressure vessels by increasing the allowable stress is valid, to research the fatigue behavior of welded aluminum pressure vessels. The main tasks of this study are listed as below:1) Several groups of domestic welded joint fatigue data are processed respectively by hot spot stress extrapolation method and structural stress method, differently processed data shows that, hot spot stress extrapolation method is superior to nominal stress method in the aspect that it can reduce the classes of fatigue curves, but the classes are still needed; Structural stress method can correlate fatigue behaviors of differently loaded different types of welded joints with a single line, namely the master S-N curve, it is superior to its two rivals in reduction of classes of fatigue curves. What’s more, by comparing the domestic welded joint fatigue data processed by structural stress method and the master S-N curve provided by ASME BPVC Section Ⅷ Rules for Construction of Pressure Vessels Division 2-Alternative Rules, the applicability of this master S-N curve for fatigue assessment of domestic aluminum pressure vessels is proved to be possible.2) Fatigue experiments of welded aluminum pressure vessels have been done to provide basic data for researches on fatigue behavior of welded aluminum pressure vessels which have similar structure with experimental vessels. Since experimental results basically accords with the results of fatigue assessments of welded aluminum pressure vessels by structural stress method, it is reasonable to predict the fatigue life of domestic welded aluminum pressure vessels with structural stress method. Furthermore, by comparing fatigue life prediction results calculated by structural stress method and local strain method, the superiority of structural stress that the results are not affected by human factor is demonstrated.3) The influences of increment of allowable stress on the fatigue failure mode of internal pressure cylinders and the reason of the line between static strength dominated area and fatigue dominated area’s moving to the left is demonstrated; What’s more, the fatigue life of cylinder made of5A05, of which the allowable stress is the largest when taking2.4as the tensile safety factor, and6A02of which the allowable stress increases most when taking2.4as the tensile safety factor, is predicted by structural stress method.