Asme’s research while affiliated with University of Vic - Central University of Catalonia and other places

Welding residual stresses have important consequences on the performance of engineering components. High residual stresses lead to loss of performance in corrosion, fatigue and fracture but as yet these consequences are poorly quantified. The major cause of this is that residual stress often remains the single largest unknown in industrial damage situations since they are difficult to measure or estimate theoretically. One of the key issues in the study of residual stress is that the detail of the stress distribution on a small scale (in the order of millimetres) can be important. In this paper, the neutron diffraction technique is used which while it is a very expensive technique, is capable of non-destructively measuring residual stresses at this scale up to a depth of 35 mm. The investigation reported compares the residual stress characteristics due to various restraints for a single bead and in fully restrained samples with different numbers of beads. The findings have important consequences with respect to design of welding procedures and fitness for purpose assessments.

There is now much interest in the development of risk based strategies for maintenance planning including assessing appropriate inspection strategies and making economic life estimates of critical components. This study examines this problem from a practical point of view by studying a significant body of tube thickness inspection data collected in a power station. This data naturally has all sorts of difficulties. For example there are issues related to the accuracy and correctness of the measurements. Then there is the issue of how to use the data to determine deterioration rates and life expectancy. This paper examines this data using center dot a method developed by the authors: a procedure based on a "warning level" approach and center dot a suggested interpretation of the American Petroleum Institute's technique of "risk based inspection".

Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly it is not directly covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However not all thermal shock cracks lead to failures (such as rupture, leak or in more brittle material fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.