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.     

Solidification cracking in low alloy steel welds

Abstract

The high solidification cracking susceptibility of low C steel weld metals was investigated using pure Fe model alloys containing 0–0·23%C, 0–5%Ni and 0–0·0144%B. In addition, a few Fe–C–Ni ternary alloys were also tested. Solidification cracking susceptibility was tested using longitudinal varestraint and transvarestraint tests. Cracking was evaluated using crack length and brittleness temperature range criteria. The Fe–C alloys showed high cracking tendency in two regimes, the first in the ultralow carbon range of 0·03–0·05%C and the second in a narrow band close to 0·1%C. The cracking was much more than that attributable to solute segregation. In Fe–Ni and Fe–B alloys, cracking was a function of alloy content. Solidification cracking due to C and Ni was higher in the ferritic mode of solidification compared to the austenitic, unlike in stainless steels, where the ferritic mode provides high resistance to cracking. In Fe-C-Ni ternary alloys, cracking could be better related to composition in terms of a variable coefficient for C in the Ni equivalent. In the vicinity of 0·1%C, cracking was attributable to shrinkage due to solid state transformation from δ to γ in the brittle temperature range, and is similar to that occurring during continuous casting of steel. However, this factor did not appear to play a role in cracking in the ultralow C range of 0·03–0·05%C.     

Influence of Mo in the structure of rapidly solidified Fe–Mo–Cr–Mn–Si–C alloy

Abstract

An Fe–Mo–Cr–Mn–Si–C alloy was prepared in an induction furnace and was cast into cylindrical rod in a copper mould in castmatic equipment (low pressure casting). A single phase non-equilibrium featureless (no visible microstructures after deep etching) phase was observed over a certain range of thickness of the rod. In this present work, the extent of the featureless phase was studied with different concentrations of Mo (5–25 wt-%) for 5·5 mm diameter of cylindrical rod at a cooling rate of 1100 K s^–1. Light optical microscopy, scanning electron Microscopy and Vickers hardness tests were used to analyse the samples. The amount of the featureless area varies as the Mo content changes and the maximum featureless area was obtained for 7 wt-% of Mo. This single phase featureless structure exhibits very high hardness (>1350 HV) which can be used in many interesting applications with or without suitable heat treatments.     

Effects of particle size on deformation behaviour of metal matrix composites

Abstract

By incorporating the dislocation strengthening effect into the Mori–Tanaka method, a new hybrid approach is developed in the present paper for calculating the deformation response of SiCp/Al composites. The diameters of the particles are 1, 5, 20 and 56 μm. Both numerical and experimental results indicate a close relationship between the particle size and the deformation behaviour of the composites at a constant particle volume fraction. The yield strength and plastic work hardening rate of the composites increase with decreasing particle size. The predicted stress–strain behaviour of the composites is in qualitative agreement with the experimental results. By incorporating Weibull statistics for particle fracture, the results simulated are agreed well with the experimental results for particle size >5 μm.     

Impact properties of sintered and wrought 17–4 PH stainless steel

Abstract

Charpy V notch (CVN) impact testing was conducted on full size and subsize specimens of sintered and wrought 17–4 PH stainless steel (17–4 PH SS) in the as sintered and H900 heat treated conditions. Test geometries correspond to the American Society for Testing and Materials (ASTM) and Metal Powder Industries Federation (MPIF) impact testing standards. Merits of a notched specimen compared with an unnotched specimen were analysed for both the wrought and sintered materials. The notched ASTM standard bars had a lower coefficient of variance for impact energy than the unnotched MPIF standard bars and displayed greater toughness. Porosity and grain size have a detrimental synergistic effect on impact toughness for the sintered material. Following a discussion about the differences in the wrought and sintered microstructures, it is recommended that impact testing of the injection moulded and sintered specimens should be evaluated according to the ASTM test specifications.     

Adhesive bonding of aluminium with structural acrylic adhesives: durability in wet environments

The durability of EN AW 6082-T651 aluminium alloy joints bonded with a toughened acrylic adhesive was investigated upon exposure to wet environments (humidity, water immersion and salt water immersion). Environmentally-friendly surface treatments were used to avoid hexavalent chromium. Single lap shear tests were used to determine the durability of the adhesively bonded joints. Specimens were exposed to 31% and 95% relative humidity and submerged in deionized water and 3 wt% sodium chloride solution at 25°C and 50°C, for 10, 30 and 90 days. The data collected in the experiments showed that the durability was higher for surfaces treated with γ-methacryloxypropyltrimethoxysilane (γ-MPS) and sulfo-ferric etchant (P2 etch) than other surface treatments. Both these treatments improved considerably the durability in all environments tested. The results indicate that specimens even without surface treatment maintained a significant residual strength after exposure to low humidity environment (room temperature at 31% RH). The joints exposed to a high humidity environment showed a higher reduction in adhesive strength than those immersed in deionized water and saline solution.     

Developers for High Speed with Low Gamma

77B-4 melol hydroquinone developer ensures considerable speed gain as compared to the D-76 developer (both developers with 6 gr.ll potassium bromide) due to a higher reduction potential value of the former. 17B-4 renders higher speed thon a similar developer with a pH 9-6 buffer solution especially when developing intensive short exposures. The reduction potential value besides the processing time is of paramounl importance for obtaining high speed with low gamma.