Steels, Chrome Molybdenum

Body bronze, cast iron, carbon steel, chrome molybdenum, stainless steel, exotic alloys. 

Jilloypiping comprises all piping that is stainless steel, carbon—molybdenum, or chrome alloys. 

Which Alloy to Use. Unalloyed mild steel parts have been known to corrode at rates as high as 800 mils per year. The low-chrome steels, through 9-Cr, are sometimes much more resistant than mild steel. No corrosion has been reported, with both 2%-Cr and 5-Cr furnace tubes, whereas carbon steel tubes in the same service suffered severe coiTosion. The 12-Cr stainless steels are scarcely, if any, better than the low-chromes. But the 18-8 Cr-Ni steels, without molybdenum, are often quite resistant under conditions of low velocity although they are sometimes subject to severe pitting. 

Rotor material in all cases is low alloy steel with an appropriate heat treatment to match the stresses imposed by the blades and rotor weight The rotor is generally manufactured from a forging with the material being a chrome-molybdenum alloy such as AISI 4140 or AISI 4340. 

Diborane is valued as a fuel for use in rocket propellants. Gallery Ghemical Co. developed equipment and procedures for the safe handling of diborane and by 1962 had produced about 5 million pounds of the material. It is offered for shipment in chrome-molybdenum steel cylinders at —80° (minimum order 100 g.), and technical bulletins present information on handling procedures and safety precautions. 

Carbon-molybdenum and chrome-molybdenum steels are listed in Table 4-15. There is no significant difference between the ASTM and the European steels except that in France and... 

Abrasive tool wear is also increased by the alloying elements chrome, molybdenum, and mngsten (Cr, Mo, W), which aU tend to form hard carbides in steels with greater carbon contents. These carbides plough into the surface of the cutting tool, which eventually results in shorter tool life. 

Common metals are suitable as materials of construction. These include the following metals and metal alloys chrome-molybdenum steel. Type 300 stainless steel, brass, lead, Monel, K-Monel, and nickel. Piping and appurtenances for undiluted diborane must be designed by experienced engineers and safety and fire pro-... 

The major fermentation method used to produce lactic acid on an industrial scale is the batch fermentation process. The factors affecting the batch process have been reviewed (Litchfield 1996 Vick Roy 1985). Because of the very corrosive properties of lactic acid, construction materials used for the fermenter and downstream processing equipment are a major cost item. Copper, copper alloys, steel, chrome steel, and high-nickel steels are all unsatisfactory. High-molybdenum stainless steel like SS316 is satisfactory. Plastic linings of fermentation tanks have been used successfiilly, and new developments in ceramics and plastics may provide future choices (Vick Roy 1985). 

Investigators determined that a carbon steel section of 6-inch (150 mm) line was installed in an area in which specifications required corrosion-resistant 5-percent chromium—1/2-percent molybdenum (generally called 5-chrome) alloy piping. In a process plant like a fluid coker, the materials used are a mixture of carbon steel and other steel alloys. Apparently, the welder and the maintenance crew, who previously repaired this piping some time ago, were not aware of the piping specifications. Apparently, they did not realize that if a material like carbon steel was installed in an area requiring 5-chrome alloy piping, erosion or corrosion could cause failure. 

Chrome-moly steels have % to 9% chromium and either % or 1% molybdenum. Chromium increases scaling resistance and molybdenum improves or provides elevated temperature strength. Carbon content is kept low to maintain weldability. Chrome-moly steels are widely used for piping and pressure vessels operating up to 1000°F in environments such as steam or hydrogen and are available in many product forms. The two most popular alloys are 1 chrome- moly and 2 chrome-1 moly. 

Samplers are instruments and devices enabling single or repeated samples to be taken either from a position which is not readily accessible (deep samplers) or without the attending personnel (automated samplers). Samplers and their components are made from corrosion-proof steels, usually chrome-nickel with addition of non-magnetic tungsten and molybdenum. 

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... 

Steel, particularly stainless steel, is the material most often used today for manufacturing fermentors. Two categories of stainless steel exist one contains molybdenum the other does not. Chrome-nickel-molybdenum steel is more resistant to corrosion and it is necessary for the long-term conservation of sulfited white wines, especially in partially filled tanks in the humid atmosphere above the wine, sulfur dioxide gas is concentrated and the condensation formed on the tank walls is corrosive. For red winemaking and storage in completely filled tanks, the less expensive chrome-nickel steel is sufficient. 

Stainless steels contain enough chromium to confer corrosion resistance by passivity. The passive layer is not as robust as in the case of titanium or the cobalt chrome alloys. Only the most corrosion resistant of the stainless steels are suitable for implants. These are the austenitic types — 316,316L, and 317, which contain molybdenum. Even these types of stainless steel are vulnerable to pitting and to crevice corrosion around screws. 

My experience indicates that stainless steels that have high chrome and nickel content are not very resistant to naphthenic acid attack. What is required is molybdenum. 304 stainless steel is unsuitable due to its low moly content. Even 316 stainless steel, which has about 2 percent moly, offers only marginal protection. I usually specify 317 stainless steel, which has about 3 percent moly, when designing for naphthenic acid services. 

Table 0-3. Extra Cost versus Extra Performance (Approximate) for Alloy Steels Used in Refinery Pipestills Applies primarily to chromium and chrome-nickel steels, some with molybdenum...

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