29 research outputs found
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Solid-state resistance upset welding: A process with unique advantages for advanced materials
Solid-state resistance upset welding is suitable for joining many alloys that are difficult to weld using fusion processes. Since no melting takes place, the weld metal retains many of the characteristics of the base metal. Resulting welds have a hot worked structure, and thereby have higher strength than fusion welds in the same mate. Since the material being joined is not melted, compositional gradients are not introduced, second phase materials are minimally disrupted, and minor alloying elements, do not affect weldability. Solid-state upset welding has been adapted for fabrication of structures considered very large compared to typical resistance welding applications. The process has been used for closure of capsules, small vessels, and large containers. Welding emphasis has been on 304L stainless steel, the material for current applications. Other materials have, however, received enough attention to have demonstrated capability for joining alloys that are not readily weldable using fusion welding methods. A variety of other stainless steels (including A-286), superalloys (including TD nickel), refractory metals (including tungsten), and aluminum alloys (including 2024) have been successfully upset welded
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Helium embrittlement model and program plan for weldability of ITER materials
This report presents a refined model of how helium embrittles irradiated stainless steel during welding. The model was developed based on experimental observations drawn from experience at the Savannah River Site and from an extensive literature search. The model shows how helium content, stress, and temperature interact to produce embrittlement. The model takes into account defect structure, time, and gradients in stress, temperature and composition. The report also proposes an experimental program based on the refined helium embrittlement model. A parametric study of the effect of initial defect density on the resulting helium bubble distribution and weldability of tritium aged material is proposed to demonstrate the roll that defects play in embrittlement. This study should include samples charged using vastly different aging times to obtain equivalent helium contents. Additionally, studies to establish the minimal sample thickness and size are needed for extrapolation to real structural materials. The results of these studies should provide a technical basis for the use of tritium aged materials to predict the weldability of irradiated structures. Use of tritium charged and aged material would provide a cost effective approach to developing weld repair techniques for ITER components
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Upset welded 304L and 316L vessels for storage tests
Two sets of vessels for tritium storage tests were fabricated using upset welding. A solid-state resistance upset weld was used to join the two halves of each vessel at the girth. The vessels differ from production reservoirs in design, material, and fabrication process. One set was made from forged 304L stainless steel and the other from forged 316L stainless steel. Six vessels of each type were loaded with a tritium mix in November 1995 and placed in storage at 71 C. This memo describes and documents the fabrication of the twelve vessels
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Welding tritium aged stainless steel
Stainless steels exposed to tritium become unweldable by conventional methods due to He buildup within the metal matrix. With longer service lives expected for new weapon systems, and service life extensions of older systems, methods for welding/repair on tritium-exposed material will become important. Results are reported that indicate that both solid-state resistance welding and low-heat gas metal arc overlay welding are promising methods for repair or modification of tritium-aged stainless steel
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Weldability of general purpose heat source iridium capsules
Two weldability tests developed by ORNL for plate material have been demonstrated on iridium (Goodwin 1987 and David 1987), but neither test is applicable to underbead cracking in a capsule configuration. As a result of underbead cracking of welded iridium capsules at SRP, a weldability test was designed and demonstrated on capsules to measure the susceptibility of different batches of iridium to underbead cracking. The capsule weldability test and its use to determine the relative weldability of the ORNL new-process iridium is presented in this paper. 6 refs., 1 fig., 1 tab
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Resistance upset welding for vessel fabrication
Solid-state resistance upset welding has been successfully applied to fabrication of small vessels. The process has advantages compared with the fusion welding processes currently used to join the two halves of such vessels. These advantages result from the improved metallurgical properties of the weld zone and the simplicity of the welding process. Spherical and cylindrical shapes have been fabricated using the upset welding process. Nondestructive and destructive tests have shown excellent weld strength. Storage tests have demonstrated long term compatibility of the welds for cylindrical parts made from 304L stainless steel that have been in storage for eight years. Spherical vessels and reinforced desip vessels made from forged 21-6-9 stainless steel have been prepared for storage
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Microstructural analysis of solid-state resistance welds
No melting is present in solid-state welds and the microstructure is therefore very different from the solidification structures found in fusion welds. Improved properties of the weld result from the solid-state metallurgical structure. Solid-state resistance welding therefore has advantages compared to fusion welding processes. Different types of solid-state resistance welds have been developed for several unique applications ranging from small tube closure welds to vessel fabrication welds. Solid-state resistance upset welds have a hot worked microstructure, usually with recrystallization near the mating surfaces. Quality of the weld can be related to the metallographic appearance of the bond line at the mating surfaces. Impurities such as oxidation effect both the appearance of the bond line and weld quality. Microstructural examination of flow lines can provide a remarkably clear picture of the deformation pattern, or upsetting, that occurs during welding. Unusual effects such as multiple interfaces can be clearly seen from microstructural examination. Hardness traverses across metallographic sections are used to relate weld area strength to microstructural characteristics. Solid-state weld and heat-affected zone strengths have been compared to base metal and to fusion weld strengths using hardness data
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Welding tritium aged stainless steel
Stainless steels exposed to tritium become unweldable by conventional methods due to He buildup within the metal matrix. With longer service lives expected for new weapon systems, and service life extensions of older systems, methods for welding/repair on tritium-exposed material will become important. Results are reported that indicate that both solid-state resistance welding and low-heat gas metal arc overlay welding are promising methods for repair or modification of tritium-aged stainless steel
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Remote reactor repair: GTA (gas tungsten Arc) weld cracking caused by entrapped helium
A repair patch was welded to the wall of a nuclear reactor tank using remotely controlled thirty-foot long robot arms. Further repair was halted when gas tungsten arc (GTA) welds joining type 304L stainless steel patches to the 304 stainless steel wall developed toe cracks in the heat-affected zone (HAZ). The role of helium in cracking was investigated using material with entrapped helium from tritium decay. As a result of this investigation, and of an extensive array of diagnostic tests performed on reactor tank wall material, helium embrittlement was shown to be the cause of the toe cracks