Stainless Steel Flange Research Articles

Process Development for Vacuum Brazed Niobium–316L Stainless Steel Transition Joints for Superconducting Cavities

The paper describes process development for producing sound, strong, and ductile Nb pipe–316L stainless steel (SS) flange brazed joint suitable for application in superconducting radiofrequency (SRF) cavities. The developed transition joints, made with BVAg-8 braze filler metal (BFM), were free of brittle intermetallic compounds, in contrast to the existing global brazing practice of using oxygen-free electronic copper as BFM which results in the formation of a continuous layer of Fe–Nb brittle intermetallic compound at Nb–braze interface. In view of the large difference in the mean thermal expansion coefficients between niobium and 316L stainless steel, a new design for manufacturing and assembly (DFMA) has been developed to ensure achievement of desired joint thickness with uniformity in circumferential and longitudinal directions. An environment-friendly prebraze cleaning procedure has been qualified and implemented. DFMA has resulted in (i) significant reduction of the out-of-roundness errors (≤10 μm) while machining of the niobium pipe, (ii) simplified clearance fit prebraze assembly at room temperature (RT), and (iii) uniformity of joint thickness. A process flow chart has been developed to ensure repeatability of joint characteristics. The brazed joint, of niobium pipe and 100CF knife edge 316L SS flange made by standardized practice, displayed helium leak tightness better than 5 × 10−10 mbar l/s at RT and at liquid helium temperature (LHT). The braze-joint sustained 873 K/10 h postbraze hydrogen degassing treatment and thermal cycling between RT and LHT without any loss in hermeticity.

Design and fabrication of a window for the gas Cherenkov detector 3.

The gas Cherenkov detector 3 was designed at Los Alamos National Laboratory for use in inertial confinement fusion experiments at both the Omega Laser Facility and the National Ignition Facility. This instrument uses a low-Z gamma-to-electron convertor plate and high pressure gas to convert MeV gammas into UV/visible Cherenkov photons for fast optical detection. This is a follow-on diagnostic from previous versions, with two notable differences: the pressure of the gas is four times higher, and it allows the use of fluorinated gas, requiring metal seals. These changes force significant changes in the window component, having a unique set of requirements and footprint limitations. The selected solution for this component, a sapphire window brazed into a stainless steel flange housing, is described.

Development of a Test Conduction-Cooled MgB2Coil

We are now developing conduction-cooled MgB 2 coils toward the realization of magnets with 1-MJ magnetic energy. We devised a new fabrication method, which is based on the wind and react method. A bobbin in the react process is made of stainless steel. To improve cooling performance, one of the stainless steel flanges of the bobbin is replaced with an oxygen-free copper (OFC) one after the react process. To prevent winding collapse, these flanges consists of several pieces, and these pieces are replaced in sequence. The OFC flange and the coil winding are bonded with epoxy impregnation. To validate this new method, we fabricated a test coil with an inner diameter of 100 mm and a self-inductance of 8.3 mH by using a multistrand MgB 2 wire. We cooled the test coil by a two-stage GM cryocooler and measured its critical current (I c ) at 25 K. The difference between the temperature of the OFC flange and that of the winding surface was within 2 K. The I c was about 263 A, which had been expected to be 275.8 A in accordance with its load line and short-sample measurements. These results support the validity of our fabrication method.

Failure Analysis of a 304 Stainless Steel Flange

An investigation for the cracking mechanism of a 304 stainless steel flange was carried out. The flange was installed in a (NH4)2SO4 tank . Optical microscopy examination shows that the cracking is intergrainular. SEM examination shows that the brittle nature of the cracked surface morphology. EDS analysis shows that chloride exists on the cracked surface. Electrolytic etching of the stainless steel in oxalic acid solution reveals that it has intergrainular corrosion sensitivity. The results show that poor welding operation caused to form defects in the weld. Corrosion occurred preferentially in the defect area and cracks propagated circumferentially in the weld seam. The crack propagation direction changed at a point where there was a large circumferential stress.

A novel ceramic chamber prototype

A novel ceramic chamber prototype has been designed and fabricated which is described in this paper. The manufacture procedure of the ceramic test chamber is original. For the novel ceramic chamber, the uniformity of its inner deposited Ti film is improved to have a thickness variation of approximately 1%, and the average wall thickness error of the chamber (length 650 mm) is developed to be less than 55 μm. The manufacture procedure is explained below. The two halves of ceramic chambers were first cleaned, the metal films were then deposited on the inner surface by sputtering and, finally, the two halves were joined with a fixture to become a ceramic tube using glass powder colloid at ∼250 °C. The glass powder colloid can be used for the vacuum-assembled parts because the outgassing rate is measured to be 4.8 × 10−9 Pa m s−1 after baking. For a novel ceramic chamber prototype, the ceramic tube was connected to the stainless steel flange by glass powder colloid and tungsten inert gas (TIG) welding. The ceramic chamber prototype was leak tight after the rapid temperature cycle test. Thus, it is feasible to fabricate the novel ceramic chamber prototype.

Metallurgical Analysis on a Cracked Super Duplex Stainless Steel Flange

A flange-to-pipe weldment in a seawater-intake-return-line suffered from cracking on its flange portion after in service for 4 months. The flange was fabricated from S32750 super duplex stainless steel. The cracked flange was investigated by visual inspection and fractographic examination on the crack surface, metallographic examination, hardness measurement, and chemical composition analysis of the flange-to-pipe weldment. The results of laboratory analysis showed that the flange had cracked in a brittle manner resulting from the presence of large amount of sigma phase in the flange material. Formation of such brittle second phase precipitates in the flange material was due to improper heat treatment.

Is adsorption an artifact in experimentation with Triclosan?

AbstractThis paper examines the effect of adsorption of Triclosan (TCS) onto labware on the results obtained during lab-scale experiments. Three sets of experiments were considered; two of them expose the problem in water or wastewater treatability studies and the other one in microbial susceptibility testings. In the former two sets, lab-scale systems; ozonation; and membrane filtration (NF/RO) that are commonly used in water or wastewater treatability studies were utilized and the distribution of TCS within the systems were followed. The ozonation labware tested was composed of a Pyrex reactor with plastic and glass tubings. The NF/RO system was composed of a stainless steel feed tank, a stainless steel membrane unit, stainless steel flanges, and stainless steel and plastic tubings. Ozonation system was operated without ozone gas, but air. Similarly, NF/RO system was without membrane in it. Both of the systems were rinsed with methanol before experiments to remove any possible earlier contamination. Dur...

Buckling capacity of welded stainless steel flanges by finite element analysis

This paper presents the development of a finite element analysis method to predict the buckling capacity of welded stainless steel unstiffened plates. Material and geometric nonlinearities, geometric imperfections, and residual stresses are included in the development. The resulting method is validated with experimental results on specimens of cruciform shape and is used to measure the sensitivity of the compressive capacity of plates, whose boundary conditions simulate the flanges of stainless steel plate girders, to local geometric imperfection, length-to-width ratio, and slenderness. When the slenderness parameter of a flange is greater than 1.0, as the mode value of the imperfection increases, the compressive capacity increases, and when the slenderness parameter is less than 0.5 the mode value has negligible effect on the compressive capacity. When a flange length, a, is less than twice its width, b, the value of a/b has a much greater impact on the ultimate load capacity of the flange than when it is greater than twice its width. The parametric study results are compared to American, European, and Japanese design specifications for unstiffened steel cross-sectional elements. For a given value of slenderness, the AISC nominal design buckling resistance is close to the average of the ultimate loads obtained from the parametric study and the Eurocode and JSSHB specifications are generally conservative.

Failure Analysis of Leaked Stainless Steel Housing of Electro Chemical Hydrogen Metre

The failure of the stainless steel housing of Electro Chemical Hydrogen Metre (ECHM) in the Steam Generator Test Facility resulting in a minor sodium fire has been investigated through systematic metallographic and fractographic analyses. The root cause of the failure was identified as caustic stress corrosion of the stainless steel flange that forms a part of the ECHM housing.

Fabrication of an Ultra High Vacuum Compatible Faraday Cup for Qualification of Electron Gun for 10 kW Industrial LINAC

In this paper, we report fabrication and testing of a unique Faraday Cup designed for qualification of Electron Gun for a 10 kW industrial LINAC. This is a compact device consisting of a tapered copper cavity electrically isolated by a ceramic cylinder metalized at both ends. Kovar tubes matching with the diameter of ceramic isolator were used at both ends to facilitate high quality UHV compatible joints with copper cavity at one end and standard knife edge stainless steel flange at the other end. The Kovar tube was flared at both ends to form a collar matching with the outer diameter of the ceramic isolator. The joint between Kovar collar and ceramic isolator was done by hydrogen brazing using copper silver eutectic alloy. All the joints were tested with helium leak detector and leak rates were found to be below 1 × 10−10mbar.litre/second.

A Proposal of New Fabricating Technique of Large MgB$_{2}$ Bulk by a Capsule Method

We proposed a new fabricating technique of a large superconducting bulk (20-30 mm in diameter) by a capsule method and measured the trapped field distribution for the bulks. The capsule consists of a couple of commercial stainless steel flanges, a stainless steel plate and a copper gasket. The bulks showed a superconducting transition at 38.3-38.6 K with a transition width of 0.6-1.1 K. The trapped magnetic field of the center of the bulk surface reached 1.65 T at 14 K for the bulk 30 mm in diameter. These results indicate that the capsule method is useful to produce the tesla-order large bulk magnet.

Note: Mounting ultra-high vacuum windows with low stress-induced birefringence

We have developed a way to mount ultra-high vacuum windows onto standard ConFlat(®) vacuum systems with very low stress-induced birefringence. Each window is sealed to a stainless steel flange with a compressed indium wire, and that flange is connected to a vacuum chamber with another indium seal. We find that deformation of a standard ConFlat flange during indium sealing dominates the stress on the window, so an extra-rigid flange is needed for minimal birefringence. With this mounting scheme, the typical residual birefringence is Δn = 2.3 × 10(-7) and is unchanged by a 120 °C bake.

Hydrogen permeability of Pd–Ag membrane modules with porous stainless steel substrates

Palladium-based membranes are attractive for their nearly perfect permselectivity to hydrogen. Membrane modules, consisting of a membrane foil, porous stainless steel substrate, test frame and flange were assembled and tested in an electrically heated vessel. Instantaneous hydrogen permeation flux was measured. Influences of operation conditions on the membrane performance were examined. Microstructure and morphology of the membrane surface and the cross-sectional surface of the substrate and membrane foil were characterized by scanning electron microscopy. It was observed that for an operation temperature higher than 755 K, the hydrogen permeation flux through the membrane module with 0.2 μm grade porous 316L stainless steel substrate decayed continuously due to the inter-metallic diffusion between the membrane and the substrate. For a temperature of around 869 K–943 K, a stable hydrogen permeation flux through the membrane module with 0.5 μm grade stainless steel substrate was observed. Pretreatment of the 0.5 μm grade substrate with polishing and etching helped to smooth the membrane foil surface. However, it changed the surface structure of the material and led to a decrease in hydrogen permeability. Under the conditions investigated, the permeation factor of the module increased by raising the hydrogen pressure in the vessel side and decreasing the membrane module temperature. By decreasing the hydrogen exit partial pressure by sweep gas, the membrane module permeation flux increased, while the permeation factor decreased.

Detection of scintillation light in liquid xenon by multipixel avalanche Geiger photodiode and wavelength shifter

A multipixel avalanche Geiger photodiode with a p-terphenyl wavelength shifter in front of it has been tested in the liquid xenon to detect the 175-nm scintillation light. The detection efficiency of about 10% is obtained. A poly-para-xylylene film was used for protection of the liquid xenon detection medium from p-terphenyl pollution. The film has shown very good and stable adhesion at the low temperatures both to the p-terphenyl surface and to the surface of the stainless steel flange.

Application of MO-Type Flange for Accelerator Beam Ducts 3

Based on experiences in the precedent stain-less steel case, a possibility of employing copper-alloy and aluminum-alloy Matsumoto-Ohtsuka (MO)-type flanges in a vacuum beam pipes for a particle accelerator is experimentally studied. They can mitigate the heating problems found in the case of stainless-steel flanges under high-intensity beams, and also simplify the manufacturing procedure of beam pipes. Copper-alloy flanges show a comparable vacuum sealing property to the stainless-steel one, and several beam pipes with the copper-alloy flange has been successfully installed in the KEKB B-factory positron ring. The R&D on aluminum-alloy flanges has just started, and a promising result is obtained. Any coatings or treatments to improve the hardness of sealing part can be omitted if duralumin-series aluminum alloys are used. However, further detailed investigations are required about the hardness and stiffness properties of the gasket and flange materials before applying the flanges to the real machine.

Development of copper-alloy Matsumoto–Ohtsuka-type vacuum flanges and its application to accelerator beam pipes

The possibility of employing copper-alloy Matsumoto–Ohtsuka-type flanges in a vacuum beam pipes with complicated apertures for a particle accelerator is experimentally studied. Copper-alloy flanges can mitigate the heating problems arising as a result of high-intensity beams more efficiently than stainless-steel flanges. Baking of beam pipes up to a temperature of 200 °C was acceptable with copper-alloy flanges. Moreover, direct electron-beam welding to a copper beam pipe became available, which made the manufacturing easy. In this study, several beam pipes with copper-alloy flanges were installed in the KEKB B-factory positron ring, and the performance was investigated using the high-intensity beams.

Design of a new UHV all-metal joint for CLIC

All-metal joints are widely used in the vacuum systems of particle accelerators. The most common ConFlat ® design consists of a flat soft copper gasket captured between two stainless steel flanges with sharp edges (knives). The gasket is plastically deformed and a high contact pressure develops around knives to obtain leak tightness. For large accelerators, a high reliability and a cost-optimized design are required. A smooth internal transition between flanges is needed for the RF waveguides of the compact linear collider (CLIC), with limited deformation of the inner part of the gasket. We present the study of a flange meeting these requirements. First the finite element analysis (FEA) of the Stanford linear accelerator center (SLAC) X-band all-metal joint, which has a similar specification, is shown. Some drawbacks, such as non-homogeneous sealing properties, are highlighted. Then, a new joint design is described. FEA results are presented and are compared with experimental measurements carried out on prototypes.

Structural analysis of Wendelstein 7-X magnet weight supports

The Wendelstein 7-X (W7-X) optimized stellarator is presently under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald. The goal of W7-X is to verify that the advanced stellarator magnetic confinement concept is a viable option for a fusion reactor. The W7-X coil system consisting of 70 superconducting coils of seven different types is supported by a massive central support structure (CSS), and thermally protected by the cryostat. The magnet system's weight is borne by supports (cryo-legs) which are bolted to the cold CSS. They reach down through the cryostat wall to the warm machine base which means that a small thermal conductivity is important to keep thermal losses at an acceptable level. Therefore, the design of the cryo-legs incorporates glass-reinforced plastic (GRP) tubes which are shrink-fitted into stainless steel flanges at the ends. In order to ensure free thermal shrinkage of the magnet system and to reduce stresses in the cryo-legs, sliding and rotating bearings are used as interfaces to the machine base. Tie rods between the machine base and the warm ends of the cryo-legs prevent toroidal movements of the magnet system with respect to the torus axis. Nevertheless, significant deformation of the CSS during operation results in tilting of the cryo-legs in such a way that toroidal movements of the whole magnet system take place. The number of cryo-legs and their stiffness are chosen such that the toroidal movement is kept within an acceptable range. All these restrictions, as well as requirements concerning simplicity and ease of assembly, make the cryo-leg design and structural analysis quite a complex and challenging task. The paper presents an overview of structural analyses of the W7-X magnet system with cryo-legs, local analyses of a cryo-leg under design loads, and FE simulation of the cryo-leg mechanical test.

Characterization of Vacuum Brazed Joints for Superconducting Cavities

Brazing is a process to join metallic and non-metallic materials, without any melting or plastic state of the base metals. The poor wettability of ceramic may be improved by the use of alloys containing an element capable of changing the chemistry of the ceramic surface (active braze). In this paper we propose the substitution of the Electron Beam welding with Vacuum Brazing in order to join the resonator components, Nb, Cu OFHC, and Al2O3, with stainless steel flanges, in superconducting resonant cavities. Several combinations of brazed joints have been tested. The characterization of the joints has been performed with SEM-EDS and MICROPIXE. All the joints fulfil the requirements.

Design of a high-power NMR probe for low-temperature studies.

A low-temperature, high-power NMR probe head design is described which eliminates the problem of electric arc discharge commonly experienced during radiofrequency pulse cycling in a helium environment. A polychlorotrifluoroethylene (Kel-F) coil former, fitted with a solenoid coil, is heat-shrunk onto stainless-steel flanges and spot-welded inside a stainless-steel probe head assembly connected to a hollow coaxial transmission-line probe shaft. By this means, the sample coil and all high-voltage elements can effectively be isolated in a vacuum, while at the same time permitting good thermal contact between the sample and cryogenic gas. This design was used in NMR studies in the 4.6 K < or = T < or = 77 K temperature range for RF pulse durations < or = 50 ms (and longer for low RF amplitudes) and amplitudes up to approximately 60 G.