Graphite pipe

Impervious graphite centrifugal pumps, pipe fittings, and valves were developed because most chemical processes require the movement of Hquids. Graphite pipe and fittings in sizes ranging from 25 to 635 mm ID are used to convey corrosive fluids. 

TABLE 10-38 Standard Sizes of Impervious Graphite Pipe ... 

One company is modifying the final polysilicon deposition step in the Siemens process. The new method uses a graphite pipe heated to 1500°C, beyond... 

Graphite pipe technique is the next method used to atomize the sample. The graphite pipe filled with sample is used in this method. This pipe is electrically heated up such that the sample is atomized. The biggest advantage of this method is that the atoms of the sample can be held in the pipe much longer than in the flame. It makes the results of the analysis more accurate. 

Fio. 2.7. Chlorination furnace TC, thermocouple positions 1, chlorine gas preheater 2, charcoal diffuser bed 3, resistor carbon 4, charge of briquettes 5, graphite electrode 6, split graphite-pipe top heater 7, feed hopper 8, nichrome heater for cross-over pipe 9, nickel-lined condenser 10, water-cooled iron aftercondenser 11, exhaust to scrubbers 12, condenser heating air blower 13, nichrome air heater (Stephens, W. W. and Gilbert H. L. Ref. 62). 

Figure 6 Schematic diagram of the closed crucible designed by Ishii et al. A, graphite crucible B, charged powder of AIN C, space for crystal growth D, graphite pipe to transport nitrogen gas E, joint made of graphite F, outlet for nitrogen gas G, inlet for nitrogen gas H, holder (water cooled).

Carbon—carbon composites are used in high temperature service for aerospace and aircraft appHcations as weU as for corrosion-resistant industrial pipes and housings. AppHcations include rocket nozzles and cases, aircraft brakes, and sateUite stmctures. Carbonized phenoHc resin with graphite fiber functioned effectively as the ablative shield in orbital re-entry vehicles for many years (92). 

Because carbon is difficult to machine, very tittle impervious carbon equipment is made. However, impervious graphite has been accepted as a standard material of constmction by the chemical process industry for the fabrication of process equipment, such as heat exchangers, pumps, valves, towers, pipe, and fittings (9,10). 

Bayonet Heaters A bayonet-tube element consists of an outer and an inner tube. These elements are inserted into tanks and process vessels for heating and cooling purposes. Often the outer tube is of expensive alloy or nonmetalhc (e.g., glass, impeivdous graphite), while the inner tube is of carbon steel. In glass construction, elements with 50.8- or 76.2-mm (2- or 3-in) glass pipe [with lengths to 2.7 m (9 ft)] are in contact with the external fluid, with an inner tube of metal. 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

The occurrence of graphitic corrosion is not location specific, other than that it may occur wherever gray or nodular cast iron is exposed to sufficiently aggressive aqueous environments. This includes, and is common to, subterranean cast iron pipe, especially in moist soil (Case History 17.1). Cast iron pump impellers and casings are also frequent targets of graphitic corrosion (Case Histories 17.2 through 17.5). 

On subterranean pipeline, look for graphitic corrosion on the very bottom of the line where it rests on the backfill. When graphitic corrosion occurs under these conditions, the affected region may be a narrow zone running along the pipe bottom over some distance (Case History 17.1). 

Figure 17.5 Brittle fracture through pipe. The gray material is graphitically corroded cast iron. Unaffected pipe wall metal is orange from normal rust.

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