Development of an Integrity Evaluation System on the Basis of Cooperative Virtual Reality Environment for Nuclear Power Plant

Since early 1950’s fracture mechanics has brought significant impact on structural integrity assessment in a wide range of industries such as power, transportation, civil and petrochemical industries, especially in nuclear power plant industries. For the last two decades, significant efforts have been devoted in developing defect assessment procedures, from which various fitness-for-purpose or fitness-for-service codes have been developed. From another aspect, recent advances in IT (Information Technologies) bring rapid changes in various engineering fields. IT enables people to share information through network and thus provides concurrent working environment without limitations of working places. For this reason, a network system based on internet or intranet has been appeared in various fields of business. Evaluating the integrity of structures is one of the most critical issues in nuclear industry. In order to evaluate the integrity of structures, a complicated and collaborative procedure is required including regular in-service inspection, fracture mechanics analysis, etc. And thus, experts in different fields have to cooperate to resolve the integrity problem. In this paper, an integrity evaluation system on the basis of cooperative virtual reality environment for reactor pressure vessel which adapts IT into a structural integrity evaluation procedure for reactor pressure vessel is introduced. The proposed system uses Virtual Reality (VR) technique, Virtual Network Computing (VNC) and knowledge based programs. This system is able to support 3-dimensional virtual reality environment and to provide experts to cooperate by accessing related data through internet. The proposed system is expected to provide a more efficient integrity evaluation for reactor pressure vessel.

Influence of Stress on Degradation and Life Prediction of High Strength Ferritic Steels

Influence of stress on creep deformation and degradation behavior has been investigated. Corresponding to inflection of stress vs. time to rupture curve, difference in recovery phenomena, that was homogeneous in short-term and inhomogeneous in long-term, was observed. Inflection of stress vs. time to rupture curve took place at the stress condition corresponding to half of 0.2% offset yield stress at the temperature. Elastic limit stress of Grade 91 steel was evaluated to be 150MPa at 600°C and 100MPa at 650°C, by means of stress abrupt change test. These stresses were found to be almost the same as half of 0.2% offset yield stress at the temperatures. Inflection of stress vs. time to rupture curve is caused by transient of applied stress from higher level than elastic limit to within elastic range. It has been concluded that long-term creep strength of ferritic creep resistant steels should be predicted from the selected creep rupture data under the stresses lower than elastic limit by considering half of 0.2% offset yield stress at the temperature, by means of Larson-Miller parameter with a constant of 20.

Computational Models on Graphs for the Nonlinear Hyperbolic System of Equations

The problems in the form of nonlinear partial derivative equations on graphs (nets, trees) arise in different applications. As the examples of such models we can name the circulatory and respiratory systems of the human body, the model of heavy traffic in the big cities, the model of flood water and pollution propagation in the large river systems, the model of bar structures and frames behavior under the different impacts, the model of the intensive information flows in the computer networks and others.

Load Bearing Capacity of Through Wall Cracked Elbows: Comparison of Test Results With Calculation

Integrity assessment of piping components with postulated cracks is very important for safe and reliable operation of power plants. Pipe bends or elbows are one of the very important piping components in any power plant. The existing equations of limit load of elbows have various shortcomings. Additionally, the test data on elbows are not so abundant in the literature. Against this backdrop, a comprehensive experimental and analytical program has been undertaken at Reactor Safety Division (RSD) of Bhabha Atomic Research Centre (BARC) to carry out fracture tests on through wall cracked elbows and also to propose new limit load formulas of through wall cracked elbow. The present paper describes the elbow test specimens, test set-up, test results, brief description of elastic-plastic finite element analysis, newly proposed collapse moment equations for through wall circumferentially cracked elbows and the comparison of test results with theoretical predictions.

Buckling of Composite Laminates Using Higher Order Deformation Theory

Response of composite laminates under in-plane compressive or shear loadings is of interest to the analyst and designers. Since they are thin, they are prone to instability under in-plane loads. Transverse shear effects are important even for thin laminates since elastic modulus and shear modulus are independent properties. For very thick laminates neglecting transverse shear effects leads to completely erroneous results. A number of different theories have been suggested by different investigators to account for transverse shear effects. In this investigation, an attempt has been made to take into account transverse shear effects for the stability analysis of moderately thick/very thick composite laminates under in-plane compressive and shear loading using a “SIMPLE HIGHER ORDER SHEAR DEFORMATION THEORY” based on four unknown displacements instead of five which is commonly used for most of the other higher order theories. A C1 continuous shear flexible finite element based on the proposed HSDT is developed using the Hermite cubic rectangular element. The analytical results obtained have been compared with the available results in literature. Effect of various parameters like aspect ratio, thickness to side ratio, fiber orientation and material properties have been studied in detail.

Fabrication, Construction, and Operation Problems for Grade 91 Fossil Power Components

The use of creep strength enhanced ferritic alloys, such as Grade 91, in fossil power plants has become popular for high temperature applications. Since Grade 91 has higher stress allowables than Grade 22, a designer can specify thinner component wall thicknesses, resulting in lower through-wall thermal stresses during transient events and lower material and pipe support costs. During the past two decades, Grade 91 has been used successfully in fossil power plants. However, this alloy has had some incidents of premature failures. Case histories discuss such factors as excessively hard material, extremely soft material, overheating failures, and improper mill processing. This compilation also discusses likely root causes and solutions to avoid these potential Grade 91 problems.

Analytical Determination of Material JR and Fracture Toughness Transition Curves Using Micro-Mechanical Modelling

Local approach has been used to compute a) Jinitiation and JR curves at different temperatures and b) fracture toughness transition curves for German Reactor Pressure Vessel Steel 22NiMoCr37. Ductile fracture has been analyzed using Gurson material constitutive model and probability of cleavage failure is calculated using Beremin’s model. A variation of Gurson parameter q2 near crack tip region as a function of charpy energy is suggested to obtain Jinitiation as well as complete JR curve accurately at different metal temperatures.

Full Size Internal Pressure Creep Test for Welded P91 Hot Reheat Piping

In order to establish the life assessment method for the welded modified 9Cr-1Mo steel hot reheat piping, an internal pressure creep test is conducted with a full size test component. As a result, the fracture mode of the component is clarified and the life prediction method is established. Furthermore, the creep damage detection procedures are proposed.

Creep Failure Behavior of Creep-Strength Enhanced Ferritic Steels

Creep-strength enhanced ferritic steels such as Gr.92, Gr.122, Gr.23 and Gr.91 have recently been introduced for power plant applications, and some of these have experienced creep failure in boiler tubes and thick wall components after several years of operation. In order to use these steels safely in power plants, understanding of creep failure behavior is essential. In this study the creep failure of Gr.91 and Gr.92 boiler tube base metal and Type IV cracking of Gr.92, Gr.122, Gr.23 and Gr.91 welds were reproduced in test piece of actual components size. Creep failure mode was investigated, as was microstructural morphology during creep, particularly in the weldment, with discussion based on evidence of void formation and changes in the physical damage in terms of creep life.

Creep Stability of High Strength 9% Cr-W Ferritic Heat Resistant Tube Gr.92 After 15 Years in Service

High strength 9%Cr-W ferritic heat resistant steel (ASME SA213 T92, KA-STABA29) was developed as the materials for high temperature application in USC plant with a temperature at 600°C and higher pressure than 25 MPa in steam conditions. The Gr.92 contains much W, and therefore, its creep property is attained by solute dragging of W on the dislocation gliding motion and also Nb and V forms concerning MX the precipitation strengthening mechanism. This material was installed as tertiary super heater of Tobata Co-operative Thermal Power Plant, and the plant had been operated about 15 years without any trouble. In this report, stability of several properties of ex-serviced Gr.92 steel was evaluated [1,2].