Investigation of seal effects according to axial compression variation of metal seals for transport and storage casks

Abstract

Casks for the transport and storage of heat generating radioactive waste in Germany are normally provided with screwed lid systems, which are in most cases equipped with double jacket metal seals with an inner spring wire to provide long term resistance to the seal compression force. Preservation of the high sealing quality of those seals under operational and accidental stress conditions is essentially important to the safety of those casks. Relative displacements of the lid system surfaces caused by specific impact scenarios cannot be excluded and have to be evaluated with respect to a possible increase in the leakage rate.

To get representative data for such metal sealed lid systems, BAM has developed a special conceptualised flange system placed in an appropriate testing machine for relevant mechanical loading of the metal seals under static and cyclic conditions. Furthermore, the flange system enables continuous measurement of the standard helium leakage rate during each test.

The primary aim of the investigation is to identify the correlation between variation of installation conditions (axial displacements) caused by external loads and the standard helium leakage rate. An essential parameter in this case is the useable resilience r_u of a metal seal under relevant stress conditions. The useable resilience r_u is the vertical difference in the cross-section between the seal's assembling status and the point where the leakage rate, by means of external load relieving, exceeds the quality criterion of 10^–8 Pa m³ s^–1. Load relieving can instantly occur due to modification of the seal groove dimension caused by accident impacts and deformation of the lid system. Furthermore, component specific basis data for the development of finite element calculation models should be collected. In the tests, seals are subjected to static and cyclic loads. All tests are performed at ambient temperature.

This paper presents the test configuration, different test series and results of the current experiments. Typical load–displacement–leakage rate correlations are presented and discussed.     

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Abstract

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.     

Effect of Sr on primary α-Fe phase in liquid Al-11.5Si-0.4Mg cast alloy

Abstract

The effect of Sr on the sedimentation of primary α-Fe phase has been investigated at superheating temperatures of 760 and 900 °C. A convection free experimental technique was used to aid in quantifying the primary α-Fe particles sedimented at 600 °C for 4 h. Sr marginally decreases the formed particle weight at normal melting temperature (760 °C), but greatly increases the particle weight at the superheating temperature of 900 °C. Sr refines primary α-Fe particles at both temperatures, causing the increase of the number of primary α-Fe particles, especially when superheated at 900 °C. In addition, Sr causes a decrease in the particle volume fraction but an increase in the number of the sedimented particles, and a great increase in the depth of the sediment in the mould at higher superheating temperatures. These observations are interpreted in terms of the precipitation of Fe rich particles on suspended oxide films, and the rigidisation of suspended films at higher temperatures, possibly as a result of their change in chemistry, but especially as a result of inflation of their doubled-over form by hydrogen, and the effect this has on the multiplication of growing iron rich precipitates as a result of their mechanically unstable substrate.     

Method for welding highly crack susceptible magnesium alloy ZK60

Abstract

The highly crack susceptible magnesium alloy ZK60 plates of 2 mm thickness were successfully welded by laser beam welding (LBW) with filler strip, which has the advantages of low heat input and capability of adjusting the compositions of weld metal to a less susceptible level. The effects of the compositions of filler strips on the microstructures and mechanical properties of the joints were investigated. Compared with autogenous LBW, LBW with filler strip can produce a narrower joint and avoid the cracks and pits, which severely worsen mechanical properties of the joints. When the filler strip of ZK40 alloy is employed, the grains in fusion zone can be refined, and a high quality joint, with the ultimate tensile strength of 322 MPa up to 90·7% of the base metal, is obtained.     

Neural network model of heat and fluid flow in gas metal arc fillet welding based on genetic algorithm and conjugate gradient optimisation

Abstract

Although numerical calculations of heat transfer and fluid flow can provide detailed insights into welding processes and welded materials, these calculations are complex and unsuitable in situations where rapid calculations are needed. A recourse is to train and validate a neural network, using results from a well tested heat and fluid flow model to significantly expedite calculations and ensure that the computed results conform to the basic laws of conservation of mass, momentum and energy. Seven feedforward neural networks were developed for gas metal arc (GMA) fillet welding, one each for predicting penetration, leg length, throat, weld pool length, cooling time between 800°C and 500°C, maximum velocity and peak temperature in the weld pool. Each model considered 22 inputs that included all the welding variables, such as current, voltage, welding speed, wire radius, wire feed rate, arc efficiency, arc radius, power distribution, and material properties such as thermal conductivity, specific heat and temperature coefficient of surface tension. The weights in the neural network models were calculated using the conjugate gradient (CG) method and by a hybrid optimisation scheme involving the CG method and a genetic algorithm (GA). The neural network produced by the hybrid optimisation model produced better results than the networks based on the CG method with various sets of randomised initial weights. The CG method alone was unable to find the best optimal weights for achieving low errors. The hybrid optimisation scheme helped in finding optimal weights through a global search, as evidenced by good agreement between all the outputs from the neural networks and the corresponding results from the heat and fluid flow model.     

New approach to determination of maximum temperatures in welding using travelling heat sources

Abstract

The present paper considers methods of calculation of maximum temperatures in welding using a constant welding speed and a point heat energy source. A comparison of theoretically obtained times for the occurrence of maximum temperatures with those obtained experimentally shows slight deviations. The latter are dependent only on the accuracy of temperature measurements and the workpiece size (i.e. plate size in the present work). In the present case, the limitations refer only to the workpiece size. The advantage of this new approach is in the determination of a plane curve which is an envelope of all the points in the workpiece that are simultaneously at the maximum temperature in arc welding.     

Preliminary studies on friction welding of sintered P/M steel preforms to wrought mild steel

Abstract

Continuous drive friction welding studies on sintered powder metallurgical (P/M) steel preforms–wrought mild steel combination are reported in the present study. The work is a preliminary study to optimise the friction welding parameters and data generated by the present work is expected to contribute to friction welding of dissimilar and similar sintered P/M preforms to wrought metals or sintered P/M preforms – a planned future research work. Sound welds were obtained with all welding parameter combinations studied. The mechanical properties of welds were comparable to those of sintered P/M steel. Sintered P/M preforms deformed to a greater extent than wrought mild steel due to their low flow stress and thermal conductivity. The sintered density and other properties of the P/M preforms were found to dictate the deformation at the interface and consequently the weld strength. The results indicate that the current approach can be extended to other combinations of sintered P/M preforms.     

Role of reinforcement in sintering of SiC/316L stainless steel composite

Abstract

Austenitic stainless steels with improved corrosion resistance are gaining wide popularity. However, their applications are limited because of their poor tribological properties. The present work was undertaken to improve the overall performance of 316L stainless steel by reinforcing it with SiC. During the processing of the 316L SS composite, the 316L SS matrix was found to interact strongly with the SiC at 1100°C resulting in the formation of low melting Fe–SiC phase. An attempt to process SiC/316L SS composite above this temperature resulted in complete melting of the composite compact.     

Holistic model for atmospheric corrosion Part 7 – Cleaning of salt from metal surfaces

Abstract

This is the seventh paper outlining a holistic model of atmospheric corrosion. Previous papers have outlined how airborne salinity can be estimated at any given location, how salt deposition onto a surface can be modelled and what forms moisture can take on a plate surface. The present paper develops a model for rain induced cleaning of deposited aerosols from metal surfaces. The individual phenomena of splash and wash off are modelled, and then the effect of these processes on salt retention is discussed. The results of the models are compared with data from field exposures and laboratory tests. Simplified rules to allow the process to be incorporated into the holistic model framework are proposed.