Comparison of the Limit Loads Between Defected Pressure Pipes With an Internal Pit and an External Pit at High Temperature

High temperature pressure pipes are widely used in power stations, nuclear power plants, and petroleum refinery, which always bear combined effects of high temperature, high pressure, and corrosive media, so the local pits are the most common volume defects in pressure pipe. Due to various reasons, the defects usually appear on the internal or external wall of pipe. In this paper, the dimensions of a defect were characterized as three dimensionless factors: relative depth, relative gradient and relative length. The main objects of study were the pipe with an internal pit and pipe with an external pit. Orthogonal array testing of three factors at four different levels was applied to analyze the sequence of the influence of three parameters. In present study, when the maximum principal strain nearby the location of the defects reaches 2%, the corresponding load is defined as the limit load, which is classified as two kinds of load type: limit pressure and limit bending moment. According to this strain criterion and isochronous stress strain data of P91 steel, the limit load of high temperature pipe with a local pit was determined by using ABAQUS. And in the same load condition of the pipe with the same dimensionless factors, the limit load of the internal defected pipe was compared with that of the external defected pipe. The results of this study can provide a reference for safety assessment and structural integrity analysis of high temperature creep pressure pipe with pit defects.

Brittle Fracture Analysis of a Dissimilar Metal Weld

One important part of the integrity demonstration of large ferritic components is based on the demonstration that they could never undergo brittle fracture. Connections between a ferritic component and an austenitic piping (Dissimilar Metal Weld — DMW) have to respect these rules, in particular the Heat Affected Zone (HAZ) created by the welding process and which encounters a brittle-to-ductile transition. Within that frame, the case considered in this article is a Ni base alloy narrow gap weld joint between a ferritic pipe (A533 steel) and an austenitic pipe (316L stainless steel). The aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material. The bases of this study rely on a stress-based criterion developed by Chapuliot et al., using a threshold stress (σth) below which the cleavage cannot occur. This threshold stress can be used to define the brittle crack occurrence probability, which means it is possible to determine the highest loading conditions without any brittle fracture risk.

ASME Section III Stress Analysis of a Heat Exchanger Tubesheet With a Misdrilled Hole and Irregular or Thin Ligaments

A stress analysis is described for a nuclear steam generator tubesheet with a thin or irregular ligament associated with a mis-drilled hole using the rules of ASME B&PV Section III and Non-Mandatory Appendix A, Article A-8000 for Stresses in Perforated Flat Plates. The analysis demonstrates the proper application of the NB-3200 rules for this special application with discussion of the differences between an actual tube hole deviation from what is assumed in ASME Appendix A. This is a companion paper to “Technical Justification Supporting Operation with a Tube Installed in a Mis-Drilled Hole of a Steam Generator Tubesheet”.

Parametric Study of the Coupling Power Factor for the Statistical Energy Analysis of Piping Acoustic Vibration

Energy-based finite element model is utilized for the evaluation of the Statistical Energy Analysis (SEA) coupling factor and the dependence of the coupling factor on the different system parameters is studied. Previous research has shown that the coupling factor is largely dependent on the modal densities of the fluid and pipe subsystems, which depend on the pipe dimensional parameters. The coupling factor depends also on the spectrum of the acoustic power generated, which in turn depends on the mass flow rate, the pressure reduction ratio and the characteristics of the pressure-reducing device. This study is concerned with the piping system parameters, downstream of the pressure-reducing valve. The system parameters selected for consideration are the pipe diameter to thickness ratio D/T and the pipe length to diameter ratio L/D. The study presents the effect of the variation in these two dimensionless parameters on the coupling factor. The results of the analysis can be used directly in the formulation of SEA power flow equations for large piping systems with multiple sources of acoustic energy as part of the fatigue life evaluation in critical services.

Development of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part I

Thermal fatigue may develop in piping elbow with high temperature stratified flow. To prevent the fatigue damage by stratified flow, it is important to know the distribution of thermal stress and temperature history in a pipe. In this study, heat conduction inverse analysis method for piping elbow was developed to estimate the temperature history and thermal stress distribution on the inner surface from the outer surface temperature history. In the inverse analysis method, the inner surface temperature was estimated by using the transfer function database which interrelates the inner surface temperature with the outer surface temperature. Transfer function database was calculated by FE analysis in advance. For some patterns of the temperature history, inverse analysis simulations were made. It was found that the inner surface temperature history was estimated with high accuracy.

Application of the Bayesian Updating to the Load and Resistance Factor Design (LRFD) Method

The present study has attempted to apply the Bayesian updating to the LRFD, or Load and Resistance Factor Design method. The LRFD method takes into account the statistical distribution of the material resistance and those of the applied loads. The LRFD method can reflect the degrees of different uncertainties of the resistances of the materials and the loads. Thus, the LRFD method can attain the optimal design which can keep up an adequate reliability level of the components designed, whereas the conventional allowable stress design (ASD) method cannot. The LFRD method, however, requires vast amount of statistical data for the material resistances and the applied loadings of different kinds. The present study proposes the Bayesian updating scheme which requires only a small amount of statistical data for the material resistance and the various load item distributions to calculate the values of the partial design factors used in the LRFD method. It is revealed that the median of the updated distributions of the estimated standard deviations can give adequate reliability index values higher than the target reliability index value corresponding to a fracture probability of 0.01% even for a small number of the statistical data, say, less than 20. This paper also compares and discusses the LRFD method with the updating scheme and the conventional ASD method, showing that the updated LRFD method can maintain the reliability index value higher than the target index value whereas the ASD method cannot.

Application of Gurson Model to Ni-Based Alloy Weld Joint Pipe With an Axial or a Circumferential Surface Flaw: Phase II

The previous paper ASME PVP2012[1] reported application of Gurson model to the fracture test results using pipe models with part-through wall cracks on the dissimilar metal (DM) welds. The predicted maximum loads and the crack behaviors after penetration did not agree well. These results may originate from improper parameter values of Gurson model. This paper revised these parameters and improved the estimated fracture behaviors of the pipe models. A suitable fitting process of Gurson parameters was also proposed.

Influence of Variable Amplitude Fatigue Loading on AISI 304L Stainless Steel

The aim of this work was to study the influence of variable amplitude loading on the fatigue crack initiation and propagation. Low Cycle Fatigue (LCF) tests are conducted, on an AISI type 304L austenitic stainless steel, at different total-strain-amplitudes, in laboratory air at room temperature and with a constant strain rate of 3.10−3 s−1. Two types of signal were used: a conventional signal and a complex signal. The first one was triangular in shape with a negative strain ratio (Rε = −1). The second one is still triangular in shape with Rε = −1, but between the maximum of the total-strain (εmax = +0.6%) and the minimum (εmin = −0.6%), several cycles with a smaller total-strain-amplitude are introduced (with values ranged from 0% to +/− 0.3%). From these tests, several conclusions can be drawn on Cyclic Stress Strain (CSS) behaviour, fatigue life and fracture characteristics.

Interfacial Blister Evolution of Coated Surfaces Under Severe Thermal and Pressure Transients

The effects of severe thermal- and pressure-transients on coated substrates with indentation-induced, blister defects were analyzed using experimental and finite-element methods. An explicit FEA approach was first used to assess the transient thermal- and stress-states and the propensity for fracture related damage and evolution, under uniform convection and pressure transients across the surface; cohesive zone properties were evaluated in a previous study before being applied in an implicit indentation simulation. The indentation simulation results then served as the initial conditions for explicit modeling of interfacial flaw evolution due to thermal and pressure transients. Various conditions were analyzed including thermal and gun tube boundary conditions, and the effects of coating thermal capacitance. Given the need for robust coatings, the experimental and modeling procedures explored by this study will have important ramifications for coated tube design.

User’s Design Specification Preparation for 2¼Cr-1Mo-¼V Reactors in Accordance With ASME Section VIII, Division 2 Code and Code Case 2605

Today’s hydroprocessing reactor manufacturers use 2¼Cr–1Mo–¼V steel to build lighter reactors than conventional Cr-Mo reactors. Manufacturing even lighter hydroprocessing reactors has been enabled with the introduction of the new ASME Section VIII Division 2 Code, initially released in 2007. The higher allowable stresses in the new Division 2 for these Vanadium-modified steels permits even lighter reactors to be built while maintaining suitable design margins. The new Division 2 Code requires additional engineering to ensure safe design. One of the challenges the engineer is faced with, is preparation of the User’s Design Specification (UDS) including new and more stringent requirements for fatigue evaluation. As the operating temperature of the rector is higher than 371°C, engineers have to evaluate the fatigue life of the reactor in accordance with Code Case 2605 (CC2605). CC2605 requires inelastic analysis and evaluation effects of creep. Vanadium-modified reactors require additional care during fabrication to prevent higher hardness around weld areas, reheat cracking, and reduced toughness at lower temperatures in the “as welded” condition. This paper provide guidance for the preparation of an ASME Section VIII Division 2 User’s Design Specification including process descriptions of all the cycles expected for the life of the rector and analysis requested by CC2605. An example of such an analysis, including finite element analysis results, is provided in this paper. Requirements to provide the material specification is also discussed with an emphasis on prevention of reheat cracking, hardenability, and temper and hydrogen embitterment.