Kenji Seo

DETECTION OF MATERIAL DEGRADATION ON CrMo STEEL DURING SERVICE OPERATION BY A CHEMICAL ETCHING TEST

ABSTRACT Mechanical properties of structural materials for high temperature use, such as CrMo steel, degrate during long-time service operation and it is important to detect these materials degradation by means of non-destructive technique from a structural integrity view point. In this study, a chemical etching technique is developed to detect temper embrittlement, one of the typical form of material degradation, caused by impurity segragation at grain boundaries. The material used in this work is Mo steel serviced for 8 years at 500–535°C in a petroleum refinery plant, which showed an increase in FATT, ΔFATT=35°C, and the shift in dynamic toughness(Kd)-temperature curve was 55°C. Clear difference in intergranular attack revealed by the picric acid etch was observed between embrittled and de-embrittled materials. The relation between ΔFATT and average width(w) of grain boundary grooving was examined. The change in toughness of materials can be detected through a measurement of w.

Thermal elasto-plastic analysis on stress and strain induced in weld metal during multi-pass welding

This paper is concerned with the elasto-plastic analysis of thermal stresses and strains in weld metal of multi-pass butt weld. Analysis is performed based on the incremental theory of thermo-elasto-plasticity under one dimensionaly distributed temperature. Numerical calculations are made for two kinds of weld joint as shown in Figs. 1(b), (c), each of which corresponds to the behavior of the transverse and longitudinal section of weld joint respectively.Assumptions are made for heat flow that a rectangular distribution of initial temperature is given at the start of each pass and heat flow occurs only in y-direction. Another initial condition is also applied to the calculations that a line heat source is given at the start of each pass as shown in Fig.9.From the calculations are estimated successfully transient thermal stress and plastic strain distributions. Effects of weld conditions on residual stress and strain are clarified. Relations between plastic strain in back surface and angular distortion under several weld conditions are also obtained.

Intensity of Restraint of Weld Joints Restrained by Shearing Force Through Fillet Welds (Part 1)

Measurements of the reaction stress and the intensity of restraint were undertaken and the results were compared with the analytical results in Part 1.Experiments were made for two types of specimens, H-type and T-type (see Figs. 14 (a) (b) ), in which bending moment by reaction forces may or may not be neglected respectively.Some analyses showed good agreement between test results and calculations (see Figs. 17 (a) (b)). It was found that the occurrence of weld joints might be estimated by comparison of the Kcr-value with the K-value. The necessary value of uncompleted fillet-weld length 2Δ to prevent weld cracking may be obtained from equation (14) for given values of joint geometry, size of fillet and welding heat input.