Austenitic stainless steel components

Since 1973 [3] and 1975 in Dresden 2 [4], on line measurements of redox potential have been performed in the BWRs (Boiling Water Reactors) primary coolant in order to verify the IGSCC (Intergranular Stress Corrosion Craking) susceptibility of austenitic stainless steel components. Such measurements turned out to be fundamental for estimating the effect of hydrogen addition as a remedy for IGSCC [5-6]. 

Another important development in forging technology is the use of austenitic stainless steel components for fast breeder reactors (FBRs). Components of the reactor vessel for Monju, the prototype FBR in Japan, were manufactured using type 304 stainless steel. Significant advances in production technologies were made to fabricate the austenitic steel... 

Pipe cracking has occurred in the heat affected zones of welds in primary system piping in BWRs since mid-1960. These cracks have occurred mainly in Type 304 stainless steel which is the type used in most operating BWRs. The major problem is recognized to be IGSCC of austenitic stainless steel components that have been made susceptible to this failure by being "sensitized", either by post-weld heat treatment or by sensitization of a narrow heat affected zone near welds. 

Evaluation of Thermal Aging Embrittlement for Cast Austenitic Stainless Steel Components in LWR Reactor Coolant Systems. , ML003727111 1997-09-30 86, PROJ0690 EPRI TR-106092, 1997-09-30, 2000-08-09 ML003736671+ EPRI TR-106092, EPRI Final Report, Evaluation of Thermal Aging Embrittlement for Cast Austenitic Stainless Steel Components in LWR Reactor Coolanf , Electric Power Research Institute, September 1997. 

Obviously, the best approach to the prevention of zinc embrittlement is to avoid or minimize zinc contamination of austenitic stainless steel components in the first place. In practice, this means using no galvanized structural steel, such as railings, ladders, walkways, or corrugated sheet metal, allocations where molten zinc is likely to drop on stainless steel components if a fire occurs. 

The stress intensification factors in Appendix D of ASME B31.3 have been developed from fatigue tests of representative piping components and assemblies manufactured from ductile ferrous materials. The allowable displacement stress range is based on tests of carbon and austenitic stainless steels. Caution should be exercised when using eqs. (la) and (lb) (para. IP-2.2.10) for allowable displacement stress range for some nonferrous materials (e.g., certain copper and aluminum alloys) for other than low-cycle applications. 

Non-metallic wear part materials, which are proven to be compatible with the specified process fluid, may be proposed within the above limits. See 5.7.4.C. Such materials may be selected as wear components to be mated against a suitably selected metallic component such as hardened 12 % Cr steel or hardfaced austenitic stainless steel. Materials may be used beyond these limits if proven application experience can be provided, and if approved by the purchaser. ... 

In order to achieve a favourable load curve, the stator casing is mostly made in the form of a thick-walled hollow cylinder as a semi-finished forging of material C22.8 (as per VdTUV 350) for temperatures up to 350°C or an austenitic stainless steel. Its cylindrical construction makes it easy to calculate the load curve as described in the AD data sheets (Figure 4). The add-on components, the spacer with the pump casing and the motor sealing cover are bolted to the motor by means of concentrically arranged high-pressure expansion bolts. 

Materials such as austenitic stainless steels, nickel-based alloys, and titanium alloys can be used as materials for pressure vessel components in cryogenic applications at temperatures as low as 200°C. Alloy steels have brittle transition points making their impact properties at low temperatures unsuitable for pressure applications. Closures and bolts must also be made of materials that remain ductile at low temperatures. 

Austenitic stainless steels like 31 OS, 316, or 316L are typically used for the construction of cathode and anode current collectors and bipolar separator plates. Corrosion of these steel components is a major lifetime-limiting factor in MCFC. The corrosion behavior of stainless steel components in molten carbonate conditions has been studied extensively during the past decade. Research is being aimed at increasing the corrosion resistance of these components by altering the alloy composition or by surface modification techniques. ... 

Stress corrosion cracking is a form of localized corrosion, where the simultaneous presence of tensile stresses and a specific corrosive environment prodnces metal cracks [157, 168]. Stress corrosion cracking generally occnrs only in alloys (e.g., Cn-Zn, Cu-Al, Cu-Si, austenitic stainless steels, titaninm alloys, and zirconinm alloys) and only when the alloy is exposed to a specific environment (e.g., brass in ammonia or a titaninm alloy in chloride solutions). Removal of either the stress on the metal (which must have a surface tensile component) or the corrosive environment will prevent crack initiation or cause the arrest of cracks that have already propagated. Stress corrosion cracking often occurs where the protective passive film breaks down. The continual plastic deformation of the metal at the tip of the crack prevents repassivation of the metal surface and allows for continued localized metal corrosion. 

The austenitic stainless steel A-286 has also been used in pressure vessels for hydrogen gas containment, although reported experience with this steel is limited to specialized laboratory components [27, 47] and not extensive commercial application. Nonetheless, the material has filled a unique niche, where relatively large diameter, seamless pressure vessels have been fabricated... 

As an industrial problem stress corrosion cracking is of considerable importance. There is a long history of major and minor failures, particularly in the chemical industry and in the transport industry, particularly of components in ships and planes. It is a major potential source of failure in the nuclear power industry in which, for excunple, austenitic stainless steels may fail in high purity water containing oxygen and chloride ions at the level of ppb. 

Iron-carbon-chromium-nickel alloy steels are used extensively in furnace applications such as heat treat containers, hearth components, drive chains, carburizing boxes, recuperators, regenerative burners, burner parts, and radiant tubes. The metal selection must consider the fact that the expansion rate of austenitic stainless steels is nearly twice that of ordinary steel. (See fig. 9.14.)... 

Metals are utilized for applications requiring high strength and/or endurance, such as structural components of heart valves, endovascular stents, and stent-graft combinations. Commonly used alloys include austenitic stainless steels (SS), cobalt-chrome (Co-Cr) alloys including molybdenum-based alloys, tantalum (Ta), and titanium (Ti) and its alloys. Elgiloy, a cobalt-nickel-chrome-iron... 

All raw austenitic stainless steel material, both wrought and cast, used in the fabrication of the major NSSS components in the RCPB, is supplied in the annealed condition as specified by the pertinent ASTM or ASME Code 1900-2050 F for 1/2 to 1 hour per inch of thickness and water quenched to below 700°F. The time at temperature is determined by the size and type of component. 

The unstabilized grades of austenitic stainless steels with carbon content of more than 0.03% used for components of the RCPB are 304 and 316. These materials are furnished in the solution annealed condition. Exposure of completed or partially-fabricated components to temperatures ranging from 800 F to 1500 F is prohibited. 

Homogeneous or localized heat treatment in the temperature range 800-1500°F is prohibited for unstabilized austenitic stainless steel with a carbon content greater than 0.03% used in components of the RCPB. When stainless steel safe ends are required on component nozzles, fabrication... 

Specific requirements for cleanliness and contamination protection are included in the equipment specifications for components fabricated with austenitic stainless steel. The provisions described below indicate the type of procedures utilized for NSSS components to provide contamination control during fabrication, shipment, and storage as required by Regulatory Guide 1.37. 

Contamination of austenitic stainless steels of the 300 type by compounds which can alter the physical or metallurgical structure and/or properties of the material is avoided during all stages of fabrication. Painting of 300 series stainless steels is prohibited. Grinding is accomplished with resin or rubber-bounded aluminum oxide or silicon carbide wheels which were not previously used on materials other than austenitic alloys. Outside storage of partially-fabricated components is avoided and in most cases prohibited. Exceptions are made for certain components provided they are dry, completely covered with a waterproof material, and kept above ground. 

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