Amount Of Thickness Reduction Research Articles

Development of wall-thinning evaluation procedure for nuclear power plant piping - Part 2: Local wall-thinning estimation method

Flow-accelerated corrosion (FAC), liquid droplet impingement erosion (LDIE), cavitation and flashing can cause continuous wall-thinning in nuclear secondary pipes. In order to prevent pipe rupture events resulting from the wall-thinning, most NPPs (nuclear power plants) implement their management programs, which include periodic thickness inspection using UT (ultrasonic test). Meanwhile, it is well known in field experiences that the thickness measurement errors (or deviations) are often comparable with the amount of thickness reduction. Because of these errors, it is difficult to estimate wall-thinning exactly whether the significant thinning has occurred in the inspected components or not. In the previous study, the authors presented an approximate estimation procedure as the first step for thickness measurement deviations at each inspected component and the statistical & quantitative characteristics of the measurement deviations using plant experience data. In this study, statistical significance was quantified for the current methods used for wall-thinning determination. Also, the authors proposed new estimation procedures for determining local wall-thinning to overcome the weakness of the current methods, in which the proposed procedure is based on analysis of variance (ANOVA) method using sub-grouping of measured thinning values at all measurement grids. The new procedures were also quantified for their statistical significance. As the results, it is confirmed that the new methods have better estimation confidence than the methods having used until now.

Heavy Deformation of Patented Near-Eutectoid Steel

Evolution of microstructure in the patented near-eutectoid steel, forged under varying situations, is critically examined in the present investigation. Steel with 0.74 wt.% carbon is isothermally annealed at 500 °C to obtain fine pearlite microstructure. Steel samples, so patented, are subjected to mechanical deformation by forging at various temperatures with different amount of thickness reduction. Microstructural analyses have revealed that mechanical deformation by forging at lower temperatures brings about partial dissolution of cementite, which is followed by the formation of e-carbide in the microstructures. In contrast, cementite is precipitated within ferrite matrix upon warm or hot forging at higher temperatures. It is further observed that increasing deformation percent during low-temperature forging reduces interlamellar spacing of pearlite, whereas an opposite trend is noticed in case of deformation at higher temperature; moreover, deformation induced the change in interlamellar spacing and formation of fine carbide phases in microstructures has caused appreciable enhancement in hardness of the steel.

Effect of Rolling Reduction on Microstructure and Mechanical Properties of Plain Low Carbon Steel

In the present study, the effect of cold-rolling for the amount of reduction in thickness ranging from 25% to 75% on microstructure and mechanical properties of plain low carbon steel processed from dual-phase ferrite-martensite starting microstructure was studied. As the cold-rolling, the microstructure elongated to rolling direction and more compressed with increasing the rolling reduction and strength also increased. After annealing at warm temperature 500°C, the ultrafine grained was obtained in the 75% rolling reduction. Moreover, it was exhibited excellent strength of 82% and hardness of 66.1% higher than as-received condition with adequate uniform elongation 9.6%.

Influence of process parameters on grain refinement in AA1050 aluminum during cold rolling

The microstructure evolution during cold rolling of commercial purity AA1050 aluminum is investigated through numerical simulations. A finite strain elasto-viscoplastic constitutive model is employed, where the dislocation density and average grain size are taken as variables characterizing the deformed microstructure. Grain size evolution due to dynamic recrystallization is considered and the microstructure quantities are allowed to influence the macroscopic material behavior in terms of the flow stress and deformation-rate dependence. The effects of such process parameters as rolling friction, thickness reduction in each rolling pass and amount of rolling asymmetry are discussed. The results indicate that grain refinement due to dynamic recrystallization is most significantly affected by the amount of thickness reduction in each pass and the level of rolling friction and to a lesser extent by the asymmetry of the rolling process. An increasing degree of asymmetry will, however, reduce the variations in grain size through the sheet thickness and leave the material more homogeneously recrystallized.

Effects of rolling parameters on temperature distribution in the hot rolling of aluminum strips

A model for the study of hot strip rolling of aluminum alloys is proposed, and the approach is based on thermo-mechanical analysis using the Finite-Element Method (FEM). To assess the rolling behavior of materials during a pass, finite element program Abaqus/Explicit has been employed and the hot rolling process was modeled in three dimensions. The appropriate models for heat transfer mechanisms are considered and the temperature distribution along the rolled strip and the temperature variation during hot strip rolling process is predicted. The effects of various process parameters such as rolling speed, amount of thickness reduction, initial thickness of the strip and interface heat transfer coefficient are considered. To verify the validity of the model and predicted results, a multi-pass hot rolling program is used and a comparison is carried out between the predicted results by model with plant-recorded results.

Ultrasonographic Monitoring of Implant Thickness after Augmentation Rhinoplasty with Expanded Polytetrafluoroethylene

Expanded polytetrafluoroethylene (ePTFE), or Gore-Tex (W.L. Gore & Associates, Flagstaff, AZ), is widely used in augmentation rhinoplasty, and the histological changes that it undergoes in the human body have been studied for decades. However, changes in the thickness of ePTFE after its use in augmentation rhinoplasty with a noninvasive object method are not well understood. We report the results of 19 patients (10 male and 9 female patients) who had undergone an uncomplicated augmentation rhinoplasty with Gore-Tex. Ultrasonography was used to evaluate changes in the thickness of Gore-Tex implants and to detect inflammatory reactions around the implants 9-67 months after surgery. Gore-Tex implants were clearly distinguishable from the surrounding tissue with ultrasonography. The postoperative thickness of the implant was decreased by 29%. There was no significant correlation between the degree of change in implant thickness and the length of time after surgery. However, the amount of thickness reduction was associated with the implant's initial thickness at the time of the surgery (R = 0.448; p = 0.001). In addition, four patients (21%) showed fibrosis or granuloma formation around the implant that was detectable via ultrasonography. Gore-Tex implants lost thickness after nasal dorsal augmentation in proportion to their initial thickness, and ultrasonography was useful for evaluating changes in Gore-Tex thickness.

TEM observation of the internal structures in NbC containing Fe–Mn–Si-based shape memory alloys subjected to pre-deformation above room temperature

Abstract Shape recoveries comparable to those of the trained conventional alloys are obtained in Fe–Mn–Si-based alloys containing Nb and C by pre-rolling at 870 K and subsequent short ageing at 1070 K to produce NbC precipitates. In addition, when the amount of thickness reduction by pre-rolling is between 14 and 30%, these newly developed alloys attain recovery stresses high enough to make them useful for practical applications such as pipe joints. In this work, the microstructures resulting from the pre-rolling treatment at 870 K and subsequent ageing are investigated by means of transmission electron microscopy (TEM) in Fe–28Mn–6Si–5Cr–0.53Nb–0.06C and Fe–15Mn–5Si–9Cr–5Ni–0.53Nb–0.06C (mass%) alloys. Observations of the as-rolled microstructure indicate that the pre-rolling treatment produces a high density of stacking faults in the fcc matrix. A fine distribution of semi-coherent, nanometric scale NbC precipitates is obtained after ageing the pre-rolled samples. The amount of pre-rolling affects the size and distribution of precipitates and most of the precipitates are seen to be in close relation with stacking faults in the aged condition. The stress-induced hcp martensite is produced as lamella structure, probably due to the abundance of sites for its nucleation i. e., stacking faults and precipitates, and the width of martensite plates is extremely small. These thin martensite plates are highly recoverable, which is the indispensable condition for obtaining a large shape memory effect.

Modelling Work-Roll Temperature Variations in Hot Strip Rolling

Prediction of temperature distribution within work-rolls during the hot strip rolling process is of great importance to mill designers because of the significant role it plays in the product's dimensional accuracy and roll life. The present article employs the unsteady state heat transfer equation with time-dependent boundary conditions, as well as a two-dimensional finite element method, to determine work-roll temperature variations during continuous hot strip rolling. To achieve an accurate temperature field, the authors consider the effects of different factors, including work-roll and metal thermal relationship, idling work-roll revolutions, and the effects of various process parameters such as rolling speed, interface heat transfer co-efficient, and the amount of thickness reduction at each deformation pass. A comparison of the predicted and published experimental results shows the validity of the mathematical model.

Recovery and recrystallization of cold-rolled polysynthetically twinned (PST) crystals of TiAl

The recovery and recrystallization behavior of cold-rolled polysynthetically twinned (PST) crystals of TiAl with a nearly stoichiometric composition was investigated as a function of reduction in thickness and subsequent annealing time at 900 and 1000°C. The change in microhardness was found to occur in two stages regardless of the amount of reduction; the first stage associated with the decrease in dislocation density and the second stage related with the annealing-out of deformation twins introduced in TiAl lamallae during rolling. However, the recrystallization mode was found to vary depending on the amount of reduction in thickness. In specimens rolled to less than 20% reduction in thickness, the full recovery in hardness occurs preserving the lamellar structure. In contrast, in specimens rolled to more than 40%, a structure composed of equiaxed grains of TiAl is obtained after recrystallization. A mechanism is proposed to interpret the unusual recrystallization behavior of PST crystals of TiAl cold-rolled to less than 20%.

Deformation and Recrystallization Behaviour of the TiAl Phase Constituting the TiAl/Ti3Al Lamellar Structure of Ti-rich TiAl Compounds.

We have grown TiAl crystals of a nearly stoichiometric composition composed of a single lamellar grain as well as those composed of two lamellar grains and studied their deformation behaviour at room temperature. The deformation behaviour of lamellar grains depends strongly on their lamellar orientation. Yield stress is high for uniaxial loading perpendicular or parallel to the lamellar boundaries (the hard mode of deformation), while it is low for uniaxial loading at an intermediate angle (the easy mode of deformation). The tensile elongation for the easy mode of deformation can be as large as 20% at room temperature. By utilizing such easy mode of deformation, TiAl can be rolled up to 59% reduction in thickness at room temperature. Microstructures resulted from annealing of cold-rolled TiAl have been found to depend on the amount of reduction in thickness. This paper summarizes the results of a systematic study on the deformation and recrystallization of TiAl crystals with the lamellar structure.

Effects of prior plastic deformation on the martensitic transformation in oriented single crystals of Au-47.5 at.% Cd

Oriented single crystal samples ofβ phase Au-47.5 at.% Cd were progressively compressed along [110], [111] and [112] axes, causing each sample to deform with a different {110} 〈001〉 slip multiplicity and, therefore, develop a different defect substructure. The effects of the existing substructure upon subsequent martensite and reverse transformation were studied as a function of deformation for each sample, using a resistance technique. It was observed that for small amounts of reduction in thickness (≤ 5%), the greater the work-hardening rate associated with deformation, the greater the enhancement of the martensite nucleation (increase inM s temperature). It is suggested that {110} 〈1¯10〉 slip band intersections, produced during prior deformation, are responsible for this enhancement. For larger amounts of reduction in thickness (>5%), for the [110] and [111] samples, martensite nucleation becomes less enhanced, and finally inhibited. Deformation of the [112] sample has little effect upon martensite nucleation behaviour for any amount of reduction in thickness, because it undergoes almost single slip and presumably, few slip band intersections are formed. There is no apparent correlation between prior deformation andA s temperature. The greater the work-hardening rate associated with deformation, the greater the increase in difficulty of propagation of both the martensite and the austenite as a function of reduction in thickness. Defect pinning of the transformation interface is suggested as a possible mechanism to explain this observation. Also, practically the same increase in difficulty of propagation is observed for the A → M and M → A transformations for any sample, suggesting that the defects responsible for pinning are not erased after the two cycles that the sample is subjected to during testing.