Stainless Steel Flange Research Articles

Failure analysis on cracking and leakage of 304 stainless steel flange in petrochemical butyl device

Abstract During the pressure test process in a petrochemical butyl device in China, it was found that the 304 stainless steel flange of the ethylene pipeline appeared to be cracking and leakage. This article analyzed the reasons for failure using macroscopic inspection, chemical composition analysis, metallographic structure analysis, scanning electron microscope, energy dispersive spectroscopy, mechanical properties test, and intergranular corrosion test. The results show that the carbon content of the flange base material exceeds the standard, many carbides precipitate at the grain boundary, the material itself is seriously sensitized, and the intergranular corrosion resistance is reduced. At the same time, under corrosive media such as sulfur and chlorine and high stress, the flange displays stress corrosion cracking, which leads to cracking and leakage failure. This article reports the reasons for the failure of the flange, and some reasonable suggestions are put forward to avoid similar leakage accidents.

Design and performance of indium seals for size-constrained tunable laser spectrometers.

Indium seals have been used extensively in ultra-high vacuum and cryogenic applications. Typically, these seals use indium alongside or in place of other metal gaskets in stainless-steel vacuum flanges, with some custom applications for flanges sealing directly with glass (optics or tubes). Here, we present the design and performance of three pressed indium seals (99.99% In) between aluminum and 0.5 in. diameter sapphire optics and aluminum and gold coated Kovar semiconductor packages (TO-66 and TO-39). Test fixtures were designed to mimic those of future tunable diode laser spectrometers for Earth, planetary, and manned spaceflight environmental monitoring applications. Successful high-hermeticity seals [<10-10 atm cc/s (He)] were achieved for all seals formed with sufficient pressure applied to allow indium to flow between mating surfaces. The hermeticity of the seals was maintained after temperature cycling (-10 to +80 °C, 20 cycles), with the optical seals surviving extended duration tests (-55 to +85 °C, per MIL-STD-883). Semiconductor packages (TO-39) subjected to these extended tests saw a moderate increase in leak rate [∼5 × 10-9 atm cc/s (He)]; however, further testing showed that either the glass-metal package seals or the indium were affected (the sample size was too small to draw firm conclusions for future applications). Overall, these results suggest long-term survivability of indium seals for Kovar-aluminum and sapphire-aluminum interfaces [>10 years at 10-10 atm cc/s (He)], where the coefficient of thermal expansion differs by approximately four times.

Effect of gasket material on flange face corrosion

Bolted flanged joints play a crucial role in connecting pressure vessels and piping systems. The corrosion of the flange surface is one of the most common causes of leakage failure in bolted flanged joints. This research investigates the effect of three gasket materials on the corrosion behavior of 321 stainless steel flange material using a novel setup specially designed for corrosion quantification of such assemblies. The results show that graphite gaskets cause more corrosion to flange surfaces under the same working conditions compared to graphite gaskets with metal foil inserts and virgin polytetrafluoroethylene (PTFE) gaskets. The mechanism of flange face corrosion is that, for PTFE gaskets, corrosion propagation mainly occurs at the gasket inner diameter and propagates through the depth of the flange while, for graphite gaskets, corrosion occurs on the whole contact surface of the flange and the gasket.

Stress Corrosion Cracking Behavior of Welded Joints in 304 Stainless Steel Flange Neck on a Tandem Mixer

Stress Corrosion Cracking Behavior of Welded Joints in 304 Stainless Steel Flange Neck on a Tandem Mixer

Effect of gap size on flange face corrosion

AbstractBolted flanged joints play a critical role in offshore wind turbine tower structures, serving as integral components that connect various sections of the tower. This research study employs electrochemical techniques to investigate the effect of gap dimensions, which determine the crevice gap thickness and crevice depth, on corrosion behavior of 321 stainless steel flange sample plates in a 3.5 wt% NaCl solution at 50°C. Gaskets are used in this study to create gaps between two flange surfaces. A novel fixture is utilized to simulate the applied stress on the gasket, fluid flow within the fixture, and the geometric aspects of the gasket and flange. The findings reveal that increasing the gap thickness from 1.58 to 6.35 mm results in a rise in the general corrosion rate of the flange surface from 0.09 to 1.03 mm y−1, and crevice corrosion initiation time increases from 0.23 to 3.12 h. Furthermore, reducing the crevice depth (d) from 7.49 to 0 mm leads to a decrease in the general corrosion rate from 0.09 mm y−1 to 0.04 µm y−1, and cases with d = 3.81 and d = 0 mm show no observable crevice corrosion after potentiostatic tests.

Failure Analysis of Header Flange Cracking in Propane Dehydrogenation Unit

The boiler fault of propane dehydrogenation unit is investigated by macroscopic inspections, mechanical properties testing, chemical composition analysis, metallographic microstructure, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The experiments confirm the reason for cracks occurrence of SA182-F347H boiler that the stress corrosion cracking occurs. The sulfur injected into the device reacts with the flange metal to produce sulfide corrosion products. The improper control of flange manufacturing process and the operating temperature in the sensitized range lead to the sensitization of flange materials and reduce the corrosion resistance. During the equipment shutdown, the sulfide corrosion products on the surface of the flange reacted with air and water to form polysulfuric acid, and causing stress corrosion cracking and leakage of the sensitized F347H stainless steel flange.

Cryogenic bath-type heat exchangers for ultra-pure noble gas applications

Two cryogenic bath-type heat exchangers for ultra-pure noble gas applications were developed with particular emphasis on noble gas liquefaction in cryogenic distillation systems. The main objective was to construct heat exchangers for xenon from materials that do not emanate radon and that fulfill ultra-high vacuum standards. Therefore, only high-quality copper and stainless steel materials were used. Especially, large-area oxygen-free copper fins with high conductivity in a new design ensure efficient heat transfer. One bath-type Xe-Xe heat exchanger was designed with a diameter of 50 cm to achieve a xenon condensing capacity of at least 100 kg/h. In order to guarantee the necessary heat transfer between the two xenon reservoirs, this heat exchanger features a specially manufactured stainless steel flange with a copper plate welded inside. We first tested our concept on a dedicated bath-type heat exchanger with a reduced diameter of 30 cm using liquid nitrogen to liquefy the xenon. A model based on conservative assumptions such as film boiling on the nitrogen side and film condensation on the xenon side was developed and applied to caluclate the expected heat transfer for our design. We were able to demonstrate an adjustable xenon liquefaction rate of up to 113 kg/h limited only by our measurement procedure at a cooling efficiency of (0.98 ± 0.03) for the LN2-Xe heat exchanger.

Mitigation of parasitic losses in the quadrupole resonator enabling direct measurements of low residual resistances of SRF samples

The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF characterization of superconducting samples in a wide temperature, RF field, and frequency range. Its main purpose is high resolution measurements of the surface resistance with direct access to the residual resistance, thanks to the low frequency of the first operating quadrupole mode. In addition to the well-known high resolution of the QPR, a bias of measurement data toward higher values has been observed, especially in higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometers of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 nΩ at 2 K and 413 MHz. A constant correction based on simulations was not feasible due to deviations from one measurement to another. However, this issue is resolved given these new results.

Leakage rate detection of ConFlat seals in aluminum and stainless steel flanges under mechanical loads for quantum optical experiments in space

Several space missions, such as quantum optical experiments or quantum sensors, require ultrahigh vacuum (UHV) systems to perform their experiments and fulfill the scientific mission goals. Most of these experiments use standard ConFlat (CF) flanges for the design of the UHV system. One of the biggest challenges for these vacuum systems during a space mission is the mechanical loads. These loads are applied during launch, stage separation, etc., as a combination of static and dynamic loads. When loads are applied, the UHV system can experience an increased leakage rate, which decreases the vacuum quality. Investigation of the rise of the leakage rate due to static loads is an important step to allow a proper design process of space suitable UHV systems. In this paper, CF DN40 flange connections will be experimentally tested for standard aluminum (AluVaC) and stainless steel (316LN-ESR, 14429-ESU) tubes. Additionally, three different bolt pretension torques of 10, 12.5, and 15 N m are tested and compared. The presented results can be used to improve the design and assembly procedure for future UHV systems, such as the MAIUS (Matter-Wave Interferometry under Microgravity) sounding rocket missions.

RuO2 Nanorods as an Electrocatalyst for Proton Exchange Membrane Water Electrolysis.

A custom-built PEM electrolyzer cell was assembled using 6” stainless-steel ConFlat flanges which were fitted with a RuO2 nanorod-decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst. The current density–voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under constant water feed operation. The electrocatalytic behavior was investigated by making a series of physical modifications to the anode catalyst material. These experiments showed an improved activity due to the RuO2 nanorod electrocatalyst, resulting in a corresponding decrease in the electrochemical overpotential. These overpotentials were identified by collecting experimental data from various electrolyzer cell configurations, resulting in an improved understanding of the enhanced catalytic behavior. The micro-to-nano surface structure of the anode electrocatalyst layer is a critical factor determining the overall operation of the PEM electrolyzer. The improvement was determined to be due to the lowering of the potential barrier to electron escape in an electric field generated in the vicinity of a nanorod.

Monotonic and cyclic behaviour of a stainless steel cuff system for beam-to-column connections between pultruded I-section GFRP profiles

This paper presents an experimental study about the monotonic and cyclic behaviour of beam-to-column connections between pultruded GFRP profiles with I-section, joined by means of stainless steel cuff connection parts. This study pursues a previous investigation by the authors in which custom stainless steel cuff parts were proposed for beam-to-column connections between pultruded tubular GFRP profiles, which presented very satisfactory performance under both monotonic and cyclic loading. A similar concept is now investigated for joining profiles with I-section shapes, which are more often used in civil engineering applications. Four series of full-scale beam-to-column connections were tested under monotonic loading, using stainless steel cuffs of two different plate thicknesses and lengths. The results show that higher cuff thickness and length provided higher initial stiffness and strength, with the cuff thickness being the most influential parameter. Conversely, the ductility of the connections decreased with increasing cuff thickness: the series with thinnest cuff parts presented the highest ductility. The series with the most ductile cuff part was also tested under cyclic loading and presented significant capacity to dissipate energy, but showed marked pinching. These results were compared to those of a stainless steel flange cleated connection system previously tested using the same GFRP I-section profiles: the connections using cuff parts presented worst mechanical behaviour than the cleated connections. This indicates that the cuff connection system is more efficient to join tubular sections than open sections, such as I-sections.

Substantial and simultaneous reduction of major electron traps and residual carbon in homoepitaxial GaN layers

The presence of large amounts of electron traps together with residual carbon, as well as their trade-off relationship, is an obstacle to fabricating next-generation GaN-based power devices using the metal-organic chemical vapor deposition (MOCVD) method. Using the hydride vapor phase epitaxy (HVPE) method, we have overcome all of the aforementioned obstacles. In a previous study, we realized GaN homoepitaxial layers with greater purity than the best MOCVD-grown layers by removing quartz components from the high-temperature region of the HVPE apparatus. In the present study, the concentration of residual carbon was further reduced to less than 3 × 1014 cm−3 by removing carbon components near the wafer. In addition, the concentrations of major electron traps widely observed in homoepitaxial GaN layers were substantially reduced to the 1012–1013 cm−3 range via further modification of the HVPE conditions/apparatus to suppress etching of a stainless-steel flange of the HVPE reactor. The results imply that stainless-steel-related impurities such as Fe and Cr are the most likely cause of the major electron traps although native point defects have long been considered their origin. The resultant GaN layers, which showed substantially improved optical and electrical properties, did not exhibit a trade-off relationship between the concentrations of carbon and electron traps.

Study of Reasons for Pitting Corrosion Occurred on Flange Made of 1Cr18Ni9Ti Stainless Steel

When pickling the stainless steel flange made of 1Cr18Ni9Ti after welding process, rough pits were observed on the surface of the part. An investigation of occurrence mechanism and chemical composition of these pits has been carried out, which involved scanning electron microscope (SEM) and Energy Dispersive Spectroscopy (EDS). It was found that the flange suffering local corrosion called pitting corrosion during the pickling process, for the reason of that cavities occurred between the outer sleeve nut and the weld joint area blocked the movement of cations, mostly Fe3+ and Cr3+. These cations hydrolyzed to H+ absorbing Cl− outside the cavity in the pickling acid causing corrosion on the part surface. Adjusting purity of pickling acid and shafting the part during pickling process can obviously reduce the potential of occurrence of pitting corrosion.

Radio-frequency design and commissioning of a flexible waveguide for high-vacuum S-band applications

Flexible waveguides, which allow for greater deformation as compared to traditional hard waveguides, are highly useful for simplifying waveguide system assemblies. However, the peak powers of these waveguides have been limited to several megawatts in non-vacuum environments. Herein, a novel flexible waveguide was developed for the S-band (2856 MHz) with the aim of facilitating the interconnection of two hard waveguides. The flexible waveguide was composed of brass, and its surface was plated with oxygen-free high-conductivity copper for brazing with stainless steel flanges in a vacuum furnace. By connecting the stainless steel flanges together, it can be applied to a high-vacuum environment. The prototype exhibited good measurement results in low-power microwave tests; the results of a 72-h vacuum leak test showed satisfactory vacuum performance as well, and no obvious surface collapse was observed. High-power microwave commissioning was conducted between June and July 2019; the waveguide showed a maximum average power of approximately 2.7 kW. Unfortunately, the prototype was damaged after reaching that power level, which indicates the need for further optimization of the fabrication process. From our experiment, it is clear that the flexible waveguide cannot be used in large accelerators because of its average power limit.

Tool Wear, Surface Topography, and Multi-Objective Optimization of Cutting Parameters during Machining AISI 304 Austenitic Stainless Steel Flange

The application of AISI 304 austenitic stainless steel in various industrial fields has been greatly increased, but poor machinability classifies AISI 304 as a difficult-to-cut material. This study investigated the tool wear, surface topography, and optimization of cutting parameters during the machining of an AISI 304 flange component. The machining features of the AISI 304 flange included both cylindrical and end-face surfaces. Experimental results indicated that an increased cutting speed or feed aggravated tool wear and affected the machined surface roughness and surface defects simultaneously. The generation and distribution of surface defects was random. Tearing surface was the major defect in cylinder turning, while side flow was more severe in face turning. The response surface method (RSM) was applied to explore the influence of cutting parameters (e.g., cutting speed, feed, and depth of cut) on surface roughness, material removal rate (MRR), and specific cutting energy (SCE). The quadratic model of each response variable was proposed by analyzing the experimental data. The optimization of the cutting parameters was performed with a surface roughness less than the required value, the maximum MRR, and the minimum SCE as the objective. It was found that the desirable cutting parameters were v = 120 m/min, f = 0.18 mm/rev, and ap = 0.42 mm for the AISI 304 flange to be machined.

Preventing Casting Defects of Stainless Steel Flanges Using a Water-Soaking Method

High-precision flanges are used in conjunction with O-rings, bolts, and nuts in a variety of pipe connections to prevent the leakage of harmful fluids. Flanges require good hermeticity; i.e., without pores, cavities, blow holes, or other shrinkage defects. This study employed mold flow analysis to predict where and how defects are likely to occur during the casting process. In this study, we soaked the bottom of the casting system in cold water to direct the direction of solidification from the bottom upward. Simulation results indicate that this method significantly reduces the probability of shrinkage defects in castings.

Influence of Flange on Seismic Performance of 1,100-kV Ultra-High Voltage Transformer Bushing

Failures of the metal flange were observed in transformer bushings in previous earthquakes. In order to evaluate the influence of the flange on the seismic responses of 1,100-kV ultra-high voltage (UHV) bushing, two types of flanges were selected, which used different materials and layouts. The finite element (FE) and theoretical analyses were first carried out. The results indicate that there is an out-of-plane rocking effect at the flange bottom plate, and the flange will be damaged if the stiffeners are improperly designed. Then two identical bushings using different flanges were tested on the shaking table. The bottom plate of the cast aluminum flange cracked along the stiffeners accompanied by oil leakage. However, the UHV bushing with stainless steel flange survived in the test. It is concluded that the properly designed flange could improve seismic performance of UHV transformer bushings.

Buoyancy-driven air flow within plenum-to-plenum facility down-comer channel

Reliable measurements of thermal and velocity fields were experimentally investigated under different natural circulation intensities in a dual channel facility designed and developed with a representative geometry of prismatic modular reactor core. Experiments were conducted under steady state conditions to obtain statistically stationary time series signals of temperature and velocity. Insignificant radial temperature variation was observed along the down-comer channel implying that the majority of supplied heat is removed through the upper plenum. Velocity results obtained emphasize the delicate nature of natural circulation phenomena in terms of flow destabilization, and recirculation penetration length. Observed air velocity distribution reveals that downward velocity is proportional to the extent of cooling applied to the setup. The calculated values of the dimensionless group Froude number (Fr) in the range of 2 to 10 indicate that air is dominated by momentum and is exiting the channel as a jet. Quantification of turbulent intensities implies that flow destabilization is noticeable along the down-comer channel particularly for the case of high cooling intensity. For 5 °C cooling water temperature, turbulent intensity (vrms/v) peaks at the mid-channel (z/L = 0.5) reaching a value of 0.5. This value of turbulent intensity is much higher than the inlet (z/L = 0.96) and outlet (z/L = 0.04) turbulent intensities of 0.2 and 0.06 respectively. This destabilization is because of the flow reversal and heat conduction effects through stainless steel flanges connecting both channels. Current results provide detailed velocity and temperature variation which can be useful for validating computational fluid dynamics codes.

Failure of superduplex stainless steel flange due to inadequate microstructure and fabrication process

Abstract Flanges made of alloy steels used in the oil and gas platforms must be produced by hot forming (usually forging) in order to obtain a wrought product with refined microstructure and good toughness. In the present study, a flange of superduplex stainless steel, supposedly produced by forging (ASTM A-182 F53), has prematurely failed by pitting corrosion and cracking. The investigation was conducted to analyze the manufacturing processes, microstructures and properties of the failed flange. The analyses revealed that the flange has been produced by casting, and the chemical composition and microstructure were inadequate for the application in seawater conduction at room temperature. The failed flange was also analyzed by in situ double loop electrochemical potentiodynamic test (DL-EPR) and ferritoscope analysis. These two complementary non-destructive tests were able to detect the inadequate microstructure and corrosion resistance of the flange.

Investigation of vacuum properties of CuCrZr alloy for high-heat-load absorber

The Taiwan Photon Source (TPS) uses high-heat-load (HHL) absorbers to protect downstream ultrahigh-vacuum chambers from overheating. In this work, we propose to use the CuCrZr alloy (ASTM C18150) for the HHL absorber body and the ConFlat® flanges. We use the throughput method to measure the thermal outgassing rate and a helium leak detector to verify the vacuum seal between the CuCrZr alloy and stainless-steel flanges. The measured outgassing rate of the CuCrZr alloy was 5.8×10−10Pam/s after 72h of pumping and decreased to 2.0×10−10Pam/s after 100h of pumping. The leak rate through the vacuum seal between a CuCrZr flange and a stainless-steel flange was less than 1×10−10Pam3/s even after mounting and unmounting the flanges ten times and baking them at 250°C. These results indicate that CuCrZr alloy is suitable for integrating HHL components with ConFlat® CuCrZr flanges for the absorption of the synchrotron radiation generated by the TPS.