Hot works

Operating, maintaining, repairing, and modifying a typical process facility frequently involves activities that produce sparks or use flame. The portability of spark and flame producing equipment and its inappropriate or careless use in areas not specifically designed for its safe use can increase the likelihood of a fire. 

Temperatures sufficient to start fires or ignite explosive materials may come from a number of sources including  

Diesel engines are used extensively at most sites for welding, air compressors, etc. These engines need to be remotely sited or provided with flame arrestors, insulation on hot surfaces/exhausts, etc. 

The principal hazard associated with these and other flame-, heat-, or spark-producing work is the introduction of unauthorized ignition sources into areas of the facility. Control of hazards related to portable equipment and hot work requires developing and maintaining a comprehensive hot work procedure. 

Toensure that necessary hot work for maintenance, construction, or modifications is done safely to prevent ignition of fires and protect life and property, the hot work control procedure should include the following as a minimum  

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Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

P/M Tool Steels. In conventionally produced high alloy tool steels (slowly cooled cast ingots), carbide tends to segregate (48). Segregated clusters of carbide persist even after hot working, and cause undesirable effects on tool fabrication and tool performance. P/M tool steels, on the other hand, provide very fine and uniform carbides in the compact, the final bar stock, and the tools. Several tool steel suppHers consoHdate gas-atomized tool steel powder by HIP to intermediate shapes, which are then hot-worked to final mill shapes. Water-atomized tool steel powder is also available (see also T OOL materials). ... 

Fig. 11. Primary hot-working processes for ingot breakdown (a) forging (b) extmding and (c) rolling.

Hot Work. The objective of a hot work standard is to prevent fires, explosions, and other causes of injury which might result from workplace ignition sources such as welding (qv), cutting, grinding, and use of electrically powered tools. The OSHA standards have specific requirements (36,94) for fire prevention and protection and a permit system. 

Hot Work Fire Prevention and Protection, 29 CFR 1910.252, U.S. Department of Labor, Occupational Safety and Health Administration, Apr. 11, 1990. 

Zirconium is a hard, shiny, ductile metal, similar to stainless steel in appearance. It can be hot-worked to form slabs, rods, and rounds from arc-melted ingot. Further cold-working of zirconium with intermediate annealings produces sheet, foil, bar wire, and tubing. Physical properties are given in Table 3. 

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