C.J. Liu

Local Mechanical Properties and Microstructures of Alloy52M Dissimilar Metal Welded Joint between A508 Ferritic Steel and 316L Stainless Steel

The local mechanical properties and microstructures in a real dissimilar metal welded joint (DMWJ) of nuclear power plant were investigated. Results show that the distributions of mechanical properties in the DMWJ are very inhomogeneous. Especially in the three interface regions of A508/Alloy52Mb, Alloy52Mb/Alloy52Mw and Alloy52Mw/316L, the inhomogeneous characteristics are most prominent, and some local softening and hardening zones are formed. This non-uniform distribution on mechanical properties is mainly caused by the different microstructures in the DMWJ. The local dramatic variations in mechanical properties and local mismatch effect in the softening and hardening zones have significant effects on macroscopic fracture mechanics parameter, local crack initiation and growth behavior. But they are not considered in present structure integrity assessment codes and Leak-Before-Break (LBB) analysis. For assessing integrity and conducting LBB analysis on the DMWJ accurately, it is necessary to determine the local mechanical properties and their local mismatch ratios. In addition, the new integrity assessment and LBB analysis methods based on local damage and fracture need to be developed.

Determination of Material Degradation at Various Environmental Conditions

There are growing interests in materials and system degradation at various environmental conditions, especially for structures in fossil fuel power station, nuclear power plants and petrochemical industry. Several testing and simulation approaches have been developed to determine the degradation of material properties with the influence of corrosion environment. A simulation technology is introduced to investigate the effects of irradiation on mechanical properties for a degraded reactor pressure vessel steel. The degradation procedure combines the application of cold prestrain together with high temperature heat treatment. It is found from the results of Charpy impact tests for degraded material that there is an increase of ductile-brittle transition temperature and a trend to a decrease of upper shelf energy because of irradiation embrittlement. Evaluation procedures of temper embrittlement and hydrogen-embrittlement are described for reactor pressure vessel steel exposed to hydrogen environment. A regular coupon sample test is adopted to determine the material degradation of hydrogen processing reactors. Numerical analysis and experimental hydrogen charging technique are explored to simulate the process of hydrogen embrittlement. A critical parameter of hydrogen concentration is defined to evaluate the susceptibility of hydrogen induced cracking for reactor steels. A fatigue testing system is designed to obtain the degradation of fatigue strength for materials under the low oxygen steam environment. The system couples a steam chamber with an axial force-controlled fatigue testing machine. The fatigue tests are performed for a titanium alloy with tension-compression loading up to 107 cycles. Test results show that the fatigue strength is obviously influenced by the steam environment and the stress ratios.Copyright

On-Line Monitoring System for Hydrogenation Equipment in Petrochemical Plants

A life monitoring and assessment system of pressure vessels and piping in petrochemical plants has been developed based on the structural integrity theory and web technology. Two industrial cases of the monitoring system are given in this paper for hydrogen processing reactor, hydrogen pipeline and furnace tube of hydrogen reformer. The monitoring system is established to predict hydrogen embrittlement for the wall materials of hydrogenation reactor and pipeline in petrochemical plants. A critical description of hydrogen induced cracking is introduced to set up a criterion for the embrittlement. The electrochemistry hydrogen sensor is designed for its feasibility of real-time monitoring and assessment of hydrogen embrittlement for the equipment. It is pursued by the research to make a more impersonal judgment of safety of the hydrogenation reactor with real time tracing of operation. A remote inspection system is created based on computer network technology to monitor the plant subjected to hydrogen attack. The on-line system is also founded to monitor the operation of the furnace tube of hydrogen reformer and predict its residual life. The system executes in the remote server to assess the life of the tube and issue the information through the internet. Therefore remote users can monitor and manage the tubes on real-time. A non-contacting temperature monitoring technique is introduced into the system using CCD camera. An assessment method is introduced in this paper to create a correspondent relationship between remaining life and damage accumulation. It is significant for the method to describe the tube damage or materials degradation under unstable operations including varied pressure, varied temperature, over-heat or thermal fatigue, etc. A life fraction model related to damage accumulation is adapted into a real time monitoring system to calculate the residual life for a selected tube and work out an optimum preventive maintenance project.Copyright