Document N2xVdO6mxogn1gq24Ojvm3m38

522 CHAPTER 27 1948 Guide - for refrigeration use, thread fits and tolerances on thread gages must be maintained within close limits. Brass fittings with S.A.E. dimensions are not interchangeable with the American Standard fittings for water tubes. Ammonia pipe fittings made of cast-iron were formerly used extensively in handling refrigerants in large installations. Replacement of ammonia by other refrigerants operating at lower pressures has seriously, curtailed the market for these fittings. For this reason formulation of an American Standard for these fittings was abandoned by the A.S.A. in 1936. FLANGE FACINGS AND GASKETS A number of different flange facings in qommon use are plain face, raised face, tongue and groove, and male and female'. Cast-iron fittings for 125 psi and below are normally furnished with a plain face, while the 250 lb cast-iron fittings are supplied with a Jja-in. raised face. The standard facing for steel flanged fittings for 150 and 300 psi is a Hs-in. raised face although these fittings are obtainable with a variety of facings. The gasket*>surface of the raised face may be finished smooth or may be machined with concentric or spiral grooves often referred to as serrated face or phonograph finish, respectively. The dimensions of elbows, tees, and crosses for 125 lb cast-iron screwed fittings are given in Table 6, whereas the dimensions for 125 lb cast-iron flanged fittings are given in Table 7. For low temperature service not to exceed about 220 F, a number of paper or vegetable fiber gasket materials will prove satisfactory; for plain raised face flanges, rubber or rubber inserted gaskets are commonly employed. Asbestos composition gaskets are probably the most widely used, particularly where the temperature exceeds 250 F. Jacketed asbestos and metallic gaskets may be used for any pressure and tem perature conditions, but preferably only with a narrow recessed facing. WELDING Erection of piping in heating and ventilating installations by means of fusion welding has been commonly accepted in the past few years as an alternate method to the screwed and flanged joint. Since the question of economy of welding as against the use of screwed and flanged fittings is dependent on the individual job, the use of welding is generally recom mended on the basis of a greatly reduced cost of maintenance and repair, of less weight resulting from the use of a lighter-weight pipe, and of increased economy in pipe insulation, hangers, and supports rather than on the basis of any economy that might be effected in actual erection by welding on low to medium pressure heating jo'bs. Fusion welding, commonly used in erection of piping, is defined as the process of joining metal parts in the molten, or molten and vapor states, without the application of mechanical pressure or blows. Fusion welding embraces gas welding and electric arc welding, both of which are com monly used to produce acceptable welds. Welding processes and pro cedure are described in various publications. Welding application requires the same basic knowledge of design as do the other types of assembly, but, in addition, requires a generous know ledge of the sciences involved, particularly as to welding qualities of metal, their reaction to extremely high temperatures, and the ability to determine and use only the best quality welding rods. This requirement applies equally to employer and employee with the employer accepting Pipe, Fittings, Welding 523 all of the responsibility. Thus the employer should select his welding mechanics with good judgment, provide them with first-class equipment and tools, arrange for their training and use of acceptable workmanship standards, and at regular intervals subject their work to prescribed tests. Rules for fusion welding of pipe joints, the qualification of welding operators, welding procedures and the testing thereof, are contained in the Standard Manual, on Pipe Welding of the Heating, Piping & Air Conditioning Contractors National Association, and other nationally recognized groups3'4-6. In general, the wall thickness and chemical analysis of the pipe are the governing factors; not the working pressure. There are a number of safety codes which govern the installation of welded piping in many cities and states. Some of the more prominent are listed at the end of this chapter4- " 6. Table 8. American Standard Dimensions for Butt-Welding Elbows, Tees, Caps, and Lapped-Joint Stub Ends, A.S.A. B16.9-1940 Nominal Pot SlZB Ottbidb Diamsteb 1 !/? 2 2A 3 2A 4 5 6 8 10 12 1.315 1.660 1.900 2.375 2.875 3.500 .4.000 4.500 5.563 6.625 8.625 10.750 12.750 Cbnteb-to-End 90-Deg Elbows A m. VA 2H 3 3H *A 5H 6 7A 9 12 15 18 45-Deg Elbows B % i m m m 2 2X 2A m 3A 5 6H 7A Of Run Tee C 1A m 2A 3 3 Vs m. 4A 4A 5H 7 8A 10 Caps b- 1A \a 1A lA lA 2 2A 2A 3 3A 4 5 6 LAFPEnJontr Stub Ends Length 4 4 4 6 6 6 6 6 8 8 8 10 10 Radius of RFillet A He A He He H % He A A A A Diam. of `of 2 2A 2A 3% 4A 5~ 5A 6He 7He Ato8 il 12'% 15 ' All dimensions given in inches. "The dimensions of welding tees cover those which have side outlets from one size less than half the size of the run-way opening of the tees to full size. A J>AiStamiani^36dlW39aPI>!iCab1' 0nly t0 fittinBS in 8chedu!ea "P to and including Schedule 80, "The shape of these caps shall be ellipsoidal and shall conform to the requirements of the AS M R Boiler Construction Code. dThis dimension is for standard machined facings in accordance with American Standard for Steel Pine Flanges and Flanged Fittings {AS.A. BI6e-1039). The back face of the lap shall be machined to conform to the surface of the tange on which it seats. Where ring joint facings are to be applied, use dimension K as given in AA.A. Bloe-1939. A complete line of manufactured steel welding fittings is now available and a dimensional standard has been prepared under the procedure of the American Standards Association to unify heretofore divergent dimensions for the same type welding fittings as produced by different manufacturers. Standard dimensions for steel butt-welding elbows, tees, caps, and lappedjoint stub ends are given in Table 8. Dimensions for eccentric and con centric reducers, and 180-deg return bends are not shown in Table 8 but