Erosion resistance

Although thermal performance is a principal property of thermal insulation (13—15), suitabiHty for temperature and environmental conditions compressive, flexure, shear, and tensile strengths resistance to moisture absorption dimensional stabiHty shock and vibration resistance chemical, environmental, and erosion resistance space limitations fire resistance health effects availabiHty and ease of appHcation and economics are also considerations. 

Thermal spray processes can be used to give coatings of chromium carbide or nickel chromium for erosion resistance, copper nickel indium for fretting resistance, tungsten carbide cobalt for wear and abrasion resistance, and even aluminum siHcon polyester mixtures for abradabiHty. 

Naphthalenediol. This diol is made by the fusion of sodium 2,7-naphthalenedisulfonate with molten sodium hydroxide at 280—300°C in ca 80% yield. A formaldehyde resin prepared from this diol has excellent erosion resistance, strength, and chemical inertness it is used as an ablative material in rocket-exhaust environments (76). 

Another set of nickel aHoys, which have a high chromium content, a moderate molybdenum content, and some copper, are the ILLIUM aHoys. These cast aHoys are wear and erosion resistant and highly resistant to corrosion by acids and alkaHes under both oxidizing and reducing conditions. 

Niobium carbide is used as a component of hard metals, eg, mixtures of metal carbides that are cemented with cobalt, iron, and nickel. Along with tantalum carbide, niobium carbide is added to impart toughness and shock and erosion resistance. The spiraling rise in the price of tantalum has spurred the development of a hafnium carbide—niobium carbide substitute for tantalum carbide (68). These cemented carbides are used for tool bits, drill bits, shovel teeth, and other wear-resistant components turbine blades and as dies in high pressure apparatus (see Carbides). 

ASTM D2132, Test MethodforDust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials, Vol. 10.02, ASTM, Philadelphia, Pa., 1989. 

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

The metallurgy of the cyclone equipment has in recent years focused primarily on type 304 H stainless steel. The 304 H material is durable and easy to fabricate and repair, withstands the high regenerator temperatures, and is oxidation- and corrosion-resistant. Essentially all internal surfaces of the cyclone that are subject to erosion are protected with a 2 cm layer of erosion-resistant lining. When installed and cured, most refractory linings are highly resistant to erosion. 

FIG. 8-69 Ecc( ntric plii valve shown in erosion-resistant reverse flow direction, Shaded components can he made of hard metal or ceramic materials, Cm 1 li(isy Fislier-R/iseuimini. ... 

For inlet or outlet end erosion-corrosion, either extend tube ends 3 or 4 inches into the water box or install sleeves, inserts, or ferrules into the tube ends. These should be a minimum of 5 inches long. The ferrules may be nonmetallic or erosion-resistant metals, such as stainless steel, if galvanically compatible. The end of the ferrule should be feathered to prevent turbulence. 

For erosive wear. Rockwell or Brinell hardness is likely to show an inverse relation with carbon and low alloy steels. If they contain over about 0.55 percent carbon, they can be hardened to a high level. However, at the same or even at lower hardness, certain martensitic cast irons (HC 250 and Ni-Hard) can out perform carbon and low alloy steel considerably. For simplification, each of these alloys can be considered a mixture of hard carbide and hardened steel. The usual hardness tests tend to reflect chiefly the steel portion, indicating perhaps from 500 to 650 BHN. Even the Rockwell diamond cone indenter is too large to measure the hardness of the carbides a sharp diamond point with a light load must be used. The Vickers diamond pyramid indenter provides this, giving values around 1,100 for the iron carbide in Ni-Hard and 1,700 for the chromium carbide in HC 250. (These numbers have the same mathematical basis as the more common Brinell hardness numbers.) The microscopically revealed differences in carbide hardness accounts for the superior erosion resistance of these cast irons versus the hardened steels. 

There are size limitations. If large areas are surfaced by automatic welding, only tough alloys can be applied without cracking. The cracks tend to stop at the tougher base, but there is no simple answer to the question about the erosion resistance of a surface containing fine cracks. 

If the amount of metal removal by erosion is significant the surface will probably be continually active. Metal loss will be the additive effect of erosion and active corrosion. Sometimes the erosion rate is higher than that of active corrosion. The material selection judgment can then disregard coirosion and proceed on the basis of erosion resistance provided the corrosion rates of aetive surfaces of the alloys considered are not much different. As an example of magnitudes, a good high-chromium iron may lose metal from erosion only a tenth as fast as do the usual stainless steels. 

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

Soft rubber is obtained by adding 2-4% sulfur by adding extra sulfur (25-40%), the rubber can be made into ebonite, which is a hard, brittle material, having a wider range of chemical resistance than soft rubber. Soft ordinary rubber is chemical and erosion resistant, but its thermal resistance is not high (about 80 C). 

As a slight departure from the present classification scheme, oxide-based cermets can be either oxide particles in a metal matrix or metal particles in an oxide matrix. Such cermets are used in tool making and high-temperature applications where erosion resistance is needed. 

Greater bit design freedom is generally available with matrix body bits because they are cast in a moldlike natural diamond bits. Thus, matrix body bits typically have more complex profiles and incorporate cast nozzles and waterways. In addition to the advantages of bit face configuration and erosion resistance with matrix body bits, diamond compact matrix bits often utilize natural... 

Erosion resistance The mechanical properties of paints prevent their use in conditions where impingement or erosion by entrained solids is expected. 

Distributors Carbon steel, top distributor externally lined with 1 in. ( 2 cm) thick erosion-resistant refractory... 

Carbon steel, cold wall with 5 in. (12 cm) thick heavy w eight, erosion-resistant refractory lining... 

Material Shell carbon steel with 4-5 in. (10-12 cm) thick heavy weight, single-layer, cast-vibrated refractory with needles. Internals 304H stainless steel for temperature >1.200°F (650°C) and Grade H, % chrome for < ,200°F. Internal components exposed to catalyst should be refractory-lined for erosion resistance. Sliding surfaces should be hard-faced, minimum thickness in. (3 mm). 

Internally lined with 1 inch (2.5 cm) thick, erosion-resistant refractory attached by 304 stainless steel hexmetal anchors with every hex on every other row welded independently. The refractory should be cut out flush with the top of hex. The hexmetal should be discernible after the refractory installation. 

Primary diplegs internally lined with I inch (2.5 cm) thick, erosion-resistant lining. Secondary diplegs lined internally with I inch refractory on the top 5 feet (1.5 m) from the dust-bowl. Externally, diplegs should be lined where the spent catalyst returns and other known turbulent or wear areas. 

Type 4 Type D-4 Best corrosion resistance and erosion resistance of the austenitic irons Castings for industrial furnaces used in food industry for low contamination of product... 

Corrosion-Erosion Resistant High Chromium Alloy Iron ... 

Fig 8 78 Cavitation erosion resistance ranking of solid polymers... 

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