Minimum design metal temperature of Q345R determined by exemption curve in ASME VIII-2 and its derived methods

The Ni-Mo-Cr alloy (HAYNES® 242™) is an age-hardenable alloy that can be significantly strengthened by a simple aging heat treatment at 650°C (1200°F). Long-term thermal exposures at moderate temperatures increase the strength and decrease the ductility and Charpy V-notch impact toughness. Tensile ductility and Charpy impact toughness have traditionally been used to study the effect of long-term thermal exposure on mechanical properties. However, there has been little or no work reported on the effect of long-term thermal exposures on the fracture toughness of nickel-base alloys. The room temperature fracture toughness (KJc) properties have been evaluated for Ni-Mo-Cr plate material in the annealed, annealed and aged, and annealed plus long-term thermal exposed condition. The microstructural and fracture mode characteristics of this alloy were examined as well. The tensile ductility, impact toughness and fracture conditions of the toughness properties were decreased by a long-term thermal exposure at 650°C (1200°F). The fracture toughness test data revealed the crack extension during the KJc tests to be stable throughout the test. The mechanical property data suggest a strong relationship between fracture toughness and tensile ductility. The microstructures and fracture surface morphologies for three metallurgical conditions of the Ni-Mo-Cr alloy are presented.

Q345R steel is the most commonly used material in fabrication of the pressure vessels and boilers in China, due to its excellent properties. In 2010, ASME code case 2642 accepted Q345R steel for use in construction of pressure vessels. The code case specified impact test exemption curve A for the impact test requirements for Q345R. However, this provision severely limits the application of this material at low temperature, since most of the minimum design metal temperature (MDMT) of curve A is above the freezing point. In this paper, a series of tests (such as uniaxial tensile test, impact test, and fracture toughness test) were carried out at low temperature to investigate the mechanical properties of Q345R steel plates with thickness of 36–80 mm. This study of low temperature usage of Q345R steel was conducted using the fracture mechanics assessment procedure of API 579-1/ASME FFS-1. The fracture toughness is given by master curve (MC) method in the transition regime. The results show that Q345R can be used at lower temperature and that classifying Q345R steel into curve D is appropriate.

Recently, ceramics was used extensively as structural materials and ceramics components became larger and more complex. Fracture sometimes occurs during firing because of large and complex shape, and this fracture interrupts manufacturing process. The simulation of sintering has been studied to prevent this fracture. However, it was difficult to simulate fracture process because there was little data on strength of green compact. It is necessary to measure strength during sintering in order to perform a useful simulation. In this study, we measured strength of two kind of alumina green compact during sintering. Three point bending test at elevated temperature was performed and strength was estimated at each temperature. A model for strength at relative low temperature was also proposed using the temperature dependence of specific surface area. Furthermore, fracture toughness test was performed and the relationship between strength and fracture toughness was obtained. Strength at relative low temperature increased with temperature. Fracture toughness was proportional to strength at the temperature range where materials demonstrated brittle fracture manner. Strength of each alumina was analyzed using this model.

The current approach in evaluating the Pressurized Water Reactor (PWR) inlet and outlet nozzle corner regions with respect to plant heat-up and cool-down pressure-temperature limit curves contains a number of conservatisms. These conservatisms include postulation of a large ¼ thickness flaw at the nozzle corner region and use of RTNDT (reference nil-ductility temperature) or an estimation of RTNDT. The paper herein discusses generic fracture toughness of nozzle forging material SA-508 Class 2 for use with postulated smaller surface flaws in developing pressure-temperature limit curves for nozzle corners for nuclear power plant operations. ASME Appendix G uses the lower bound KIC curve, which has inherent margin since RTNDT is a conservative method for locating the KIC curve. RTNDT is based on the drop weight test, which is a crack arrest transition temperature measurement, and the Charpy impact test, which is a blunt notch impact test. These data are conservatively bounded by the KIC curve, which is a lower bound crack initiation toughness curve. In contrast, the master curve method is based on an initiation transition temperature fracture toughness test technique per ASTM E1921. The master curve index temperature (T0) provides a more accurate measure of the material fracture toughness than KIC indexed with RTNDT. Since many of the nuclear pressure vessels were fabricated to ASME Code editions prior to 1972, RTNDT was not measured for the nozzles. In many cases, RTNDT has been estimated. Therefore, for this work, the fracture toughness was generically established based on conservative T0 measurements of 22 representative forgings with a margin of two standard deviations to ensure a conservative lower bound toughness using ASME Appendix G, G-2110. The properties of a forging are better near the surface due to the faster cooling rate during heat treatment. The difference in reactor pressure vessel fracture toughness was established for forgings near the surface at the postulated flaw location as allowed by ASME Section III, NB-2223.2 relative to the traditional ¼ thickness location. The near-surface forging toughness was conservatively determined through evaluation of 31 near-surface and approximate ¼ thickness location fracture toughness measurements.

Abstract XABO 355 (minimum yield strength of 355 MPa, or 51 ksi, for thicknesses up to 35 mm, or 1.4 in.) is a thermomechanically rolled structural steel. This datasheet applies to thermomechanically rolled flat plate products in thicknesses up to 60 mm (2.4 in.). This steel grade is distinguished by testing by notch-bar impact test to –20 deg C (-4 deg F) minimum. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on forming and joining. Filing Code: SA-777. Producer or source: ThyssenKrupp Steel Europe AG.

The wedge splitting test specimens with three series of different relative crack length were used to study the influences of relative crack length on the fracture toughness of common concrete. The suitable formulation for fracture toughness of concrete with different relative crack length was gotten on comparing between fracture toughness test results and computation results of the model developed from Hu formula.