High Temperature Service

Mild steel is a suitable material of constmction for storage and handling of DMAC at ambient temperatures. Aluminum or stainless steel is recommended for cases involving very stringent color or iron contamination requirements. Mild steel is not recommended for high temperature service or handling aqueous solutions of less than 50 mol % (82.86 wt %) DMAC. 

Standard commercial iastmmentation and control devices are used ia fluorine systems. Pressure is measured usiag Bourdon-type gauges or pressure transducers. Stainless steel or Monel constmction is recommended for parts ia contact with fluoriae. Standard thermocouples are used for all fluorine temperature-measuriag equipment, such as the stainless-steel shielded type, iaserted through a threaded compression fitting welded iato the line. For high temperature service, nickel-shielded thermocouples should be used. 

A simple, low cost steel for high temperature service in electric power generation (qv) is the C—0.5% Mo steel known as carbon—half moly, which was widely used for many years. The power industry and oil refineries have turned to 1.25% Cr—0.5% Mo and 2.25% Cr—1% Mo steels for high stress and high temperature service, because these steels have improved resistance to graphitization and oxidation, as weU as higher creep and mpture strength. 

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). 

Integral pipe attachments are welded directly to the pipe and are usually of special design. They are used in high temperature services, with moderate or severe loads, and in conjunction with supports, braces, and restraints where rigidity with the pipe shell is desired. Integral attachments may be grouped into five types ears, lugs, shoes, cylindrical tmnnions, and skirts (see Fig. 8). 

Lugs are an improvement of the ear type by the addition of an element to provide lateral stiffening which also serves to improve load-carrying capacity and lateral strength. In high temperature services, unless heavily insulated, lugs are susceptible to distortion. 

Cylindrical tmnnions are of more favorable contour for stress distribution and frequently are used in high temperature services. Their load-carrying capacity is high and their stmctural effect on the pipe shell can easily be deterrnined. 

Chemically Functional. Refractory coatings are used for corrosion-resistant high temperature service in gas turbine and diesel engines, components such as cmcibles, thermocouple protection tubing, valve parts, etc. 

Types 321 and 347 have additions of titanium and niobium, respectively, and are used in welding appHcations and high temperature service under corrosive conditions. Type 304L may be used as an alternative for Types 321 and 347 in welding (qv) and stress-reHeving appHcations below 426°C. 

A number of steels suitable for high temperature service are given in Table 5. 

Figure 3.4 Grain growth in a UO2 fuel rod during high-temperature service, showing the three zones of the original grain structure (I), the equi-axed central zone (II), and the mainly single crystal zone (III) surrounding the central void...

The reaction of metals with gas mixtures such as CO/CO2 and SO2/O2 can lead to products in which the reaction of the oxygen potential in the gas mixture to form tire metal oxides is accompanied by the formation of carbon solutions or carbides in tire hrst case, and sulphide or sulphates in the second mixture. Since the most importairt aspects of this subject relate to tire performairce of materials in high temperature service, tire reactions are refeiTed to as hot corrosion reactions. These reactions frequendy result in the formation of a liquid as an intermediate phase, but are included here because dre solid products are usually rate-determining in dre coiTosion reactions. 

Another vulnerable area of concern is the result of the design requirement for high temperature service. To accommodate the thermal growth potential, the various sections of the expander are quite compliant. As a result, piping and forces need to be kept to a minimum. 

Hydrocarbons, hot Single suction, often of the special type called refinery pumps, designed particularly for high temperature service. Closed with large inlets. 

There are many design features and styles of safety relief valves, such as flanged ends, screwed ends, valves fitted internally for corrosive service, high temperature service, cryogenic service/low temperatures, with bonnet or without, nozzle entrance or orifice entrance, and resistance to discharge piping strains on body. Yet most of these variations have little, if anything to do with the actual performance to relieve overpressure in a system/vessel. 

Removable tube bundle permits easy internal cleaning. Design allows free expansion of tubes in high-temperature service. Needs no expansion joint if shell is used. 

Singh, J., Selecting Heat-Transfer Huids for High-Temperature Service, Chem. Png , June 1 (1981) p. 53. 

Valves must be made of fatigue-resistant carbon or alloy steel or 18-8 stainless steel, depending upon the service. The 18-8 stainless and 12-14 chrome steel is often used for corrosive and/or high temperature service. Any springs, as in the plate-type valves, are either carbon or nickel steel. Valve passages must be smooth, streamlined, and as large as possi-... 

ASTM A 217/A 217M-04 Standard Specification for Steel Castings, Martensitic Stainless and Alloy, for Pressure-Containing Parts, Suitable for High-Temperature Service (contains CA15)... 

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