Investigating of Strain Effect on Cleavage Fracture for Reactor Pressure Vessel Material

Failure mechanism of 20MnMoNi55 steel in the lower self of ductile to brittle transition (DBT) region is considered as brittle fracture but it has been observed from the experimental analysis of stress-strain diagram that clear plastic deformation is shown by the material before failure. Therefore, strain correction is implemented in the cleavage fracture model proposed by different researchers in the lower self of the DBT region with the help of finite element analysis. To avoid a huge number of experiments being performed, Monte Carlo simulation is used to generate a huge number of random data at different temperatures in the lower self of the DBT region for calibration of the cleavage parameters with the help of the master curve methodology. Fracture toughness calculated after strain correction through different models are validated with experimental results for the different probability of failures.

Application of mathematical modelling in the process of design and production of pressure vessels

The paper presents the engineering practice, which the company “Regeneracija” Ltd. Velika Kladuša – Bosnia and Herzegovina uses to perform preliminary experimental testing and measurements, followed by mathematical modeling of critical pressure of these vessels, in order to obtain the projected quality of pressure vessels made of composite materials. The paper will confirm the hypothesis that it is possible to relate mathematical connection and dependence of the critical pressure of vessels of composite materials (Pkr) with mechanical characteristics of vessel material (σM), vessel diameter (D), and vessel wall thickness (s). In this way, by varying the mentioned parameters, it is possible to achieve the desired product quality in the production of composite material containers by achieving the projected critical and thus working pressure. Generally speaking, the mathematical model of critical pressure obtained in this way will be a good indicator for design engineers to know how much critical pressure a given vessel can withstand, and based on that to take quick control of working or projected pressure, but also for designing completely new vessels made of composite materials as a substitute for the expensive experimental testing.

Influence of long-term high-temperature action on impact toughness of base metal and weld metal of 22K steel welded joint

One of the applications of construction low-carbon 22K steel (AISI 1022 type) is as a material for the vessel of a core catcher (CC) for nuclear power plants with VVER reactors. In the event of severe beyond design basis accident, the CC-vessel will be under conditions of prolonged hightemperature impacts, which can significantly change the structural state and lead to degradation of mechanical properties of the vessel material. Data on the effect of such actions on the mechanical properties and fracture resistance of welds (the properties of which usually differ from those of the base metal) from low-carbon steels are very limited in the literature. This makes it difficult to guarantee the reliability and safety prediction of CC. The purpose of this work was to carry out the comparative Charpy V-notch impact tests of the samples of base metal and weld metal of the 22K steel welded joint before and after long-term high-temperature heat treatment, simulating the thermal effect on the reactor vessel material of nuclear power plants during severe accidents. Welded joints of 22K steel sheets were obtained by the method of automatic argon-arc welding with a consumable electrode (welding wire SV-08G2S was used) in accordance with PNAE G-7-009–89. Based on the test results, the ductile–brittle transition curves were plotted and analysis of fracture surfaces after tests was carried out. The influence of structural factors on the impact toughness has been studied. It is shown that prolonged high-temperature exposure leads to an increase in the temperatures of beginning and end of the ductile-brittle transition by 30 – 50 °C and to the expansion of range of the ductile-brittle transition temperature by 15 – 25 °C of both base metal and weld metal of the welded joint.

Failure Modes for Acrylic Polymers in Section VIII Pressure Vessels

Section VIII of the Boiler and Pressure Vessel Code is introducing the use of acrylics as a pressure vessel material. The design method is specified in ASME PVHO-1, Safety Standard for Pressure Vessels for Human Occupancy. The current method relies upon an empirical method developed in the 1960–70’s. It does not use “allowable stress” or other mechanical properties traditionally used to calculate design dimensions, but instead uses a fixed range of dimensions for specific shapes and determines the wall thickness using a curve. Understanding the PVHO-1 design assumptions and typical failure modes is important for a non-PVHO pressure vessel designer using acrylics. An ASME Codes & Standards task group is developing a “design by analysis” method (DBA) for acrylics and other glassy polymers for pressure vessel components. The proposed DBA methodology uses Verification and Validation (V&V) techniques and Finite Element Method (FEM) as the design method framework in order to advance the use of glassy polymers as pressure vessel materials.

The effect of household storage tanks/vessels and user practices on the quality of water: a systematic review of literature

Background Household water storage remains a necessity in many communities worldwide, especially in the developing countries. Water storage often using tanks/vessels is envisaged to be a source of water contamination, along with related user practices. Several studies have investigated this phenomenon, albeit in isolation. This study aimed at developing a systematic review, focusing on the impacts of water storage tank/vessel features and user practices on water quality. Methods Database searches for relevant peer-reviewed papers and grey literature were done. A systematic criterion was set for the selection of publications and after scrutinizing 1106 records, 24 were selected. These were further subjected to a quality appraisal, and data was extracted from them to complete the review. Results and discussion Microbiological and physicochemical parameters were the basis for measuring water quality in storage tanks or vessels. Water storage tank/vessel material and retention time had the highest effect on stored water quality along with age, colour, design, and location. Water storage tank/vessel cleaning and hygiene practices like tank/vessel covering were the user practices most investigated by researchers in the literature reviewed and they were seen to have an impact on stored water quality. Conclusions There is evidence in the literature that storage tanks/vessels, and user practices affect water quality. Little is known about the optimal tank/vessel cleaning frequency to ensure safe drinking water quality. More research is required to conclusively determine the best matrix of tank/vessel features and user practices to ensure good water quality.

Modelling the Constraint Effect on Reference Temperature with Finite Element Parameters for Reactor Pressure Vessel Material 20MnMoNi55 Steel

A series of experiments were performed in the ductile to brittle transition region on three-point bending specimens of different thicknesses and a/W ratio of 20MnMoNi55 steel. master curve and reference temperature (T0) are obtained as per ASTM E1921-02 with different thickness and a/W ratio of the specimen and a variation of T0 is obtained, which indicates constant dependent on T0. Mathematic models are formulated to correlate T0 with Q-stress, T-stress and Triaxiality ratio to count for the constraint loss. Both the average value and also the maximum value of the finite element parameters are considered to predict T0 at different constraint label and compared with the experimental results.

An Update on the Investigation of Fracture Toughness Properties of the High Flux Reactor Vessel From Surveillance Test Campaign in 2017

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154-O alloy grade with a maximum Mg content of 3.5 wt. %. The vessel experiences large amount of neutron fluences (notably at hot spot), of the order of 1027 n/m2, during its operational life. Substantial damage to the material’s microstructure and mechanical properties can occur at these high fluence conditions. To this end, a dedicated surveillance program: SURP (SURveillance Program) is executed to understand, predict and measure the influence of neutron radiation damage on the mechanical properties of the vessel material. In the SURP program, test specimens fabricated from representative HFR vessel material are continuously irradiated in two specially designed experimental rigs. A number of surveillance specimens are periodically extracted and tested to evaluate the changes in fracture toughness properties of the vessel as function neutron fluence. The surveillance testing results of test campaigns performed until 2015 were published previously in [1, 2]. The current paper presents fracture toughness and SEM results from the recent surveillance campaign performed in 2017. The fracture toughness specimen tested in this campaign received a thermal neutron fluence of 13.56 x1026 n/m2, which is ∼8.9 × 1025 n/m2 more than the thermal fluence received by the specimen tested in SURP 2015 campaign. These results from this campaign have shown no change in the fracture toughness from the values measured in the previous SURP campaign. The SEM observations are performed to study the fracture surface, to measure (by WDS) the transmutation Si formed near crack tip and to investigate various inclusions in the microstructure. SEM fracture surface investigation revealed a tortuous (bumpy) fracture surface constituting micro-scale dimples over majority of the fracture area. Islands of cleavage facets and secondary cracks have been observed as well. EDS analysis of various inclusions in the microstructure revealed presence of Fe rich inclusions and Mg-Si rich precipitates. Additionally, inclusions rich in Al-Mg-Cr-Ti were identified. Finally, changes in mechanical properties of Al 5154-O alloy with an increase in neutron fluence (or transmutation Si) are discussed in correlation with SEM microstructure and fracture morphology observed in SEM. TEM investigation of precipitate microstructure is ongoing and those results will be published in future.

Impact of Patient-Specific In Vivo Vessel Material Properties on Carotid Atherosclerotic Plaque Stress/Strain Calculations

Patient-specific vessel material properties are in general lacking in image-based computational models. Carotid plaque stress and strain conditions with in vivo material and old material models were investigated (8 patients, 16 plaques). Plaque models using patient-specific in vivo vessel material properties showed significant differences from models using old material properties from the literature on stress and strain calculations. These differences demonstrated that models using in vivo material properties could improve the accuracy of stress and strain calculations which could potentially lead to more accurate plaque vulnerability assessment.