Chapter 14. -PIPING, FITTINGS, AND VALVES 



of 2.375 inches. In the larger sizes (above 12 

 inches) the nominal pipe size and the actual 

 measured outside diameter are the same. For 

 example, a pipe with a nominal pipe size of 

 14 inches has an actual measured outside dia- 

 meter of 14 inches. Nominal dimensions are 

 used in order to simplify the standardization 

 of pipe fittings and pipe taps and threading dies. 



The wall thickness of pipe is identified by 

 reference to wall thickness schedules estab- 

 lished by the American Standards Association. 

 For example, a reference to schedule 40 for 

 a steel pipe with a nominal pipe size of 3 inches 

 indicates that the wall thickness of the pipe is 

 0.216 inch. A reference to schedule 80 for a 

 steel pipe of the same nominal pipe size in- 

 dicates that the wall thickness of this pipe is 

 0.300 inch. A reference to schedule 40 for 

 steel pipe of nominal pipe size 4 inches in- 

 dicates that the wall thickness of this pipe is 

 0.237 inch. As may be noted from these ex- 

 amples, a wall thickness schedule identification 

 does not identify any one particular wall thick- 

 ness unless the nominal pipe size is also speci- 

 fied. 



The examples used here are given merely 

 to illustrate the meaning of wall thickness 

 schedule designations. Many other values can 

 be found in pipe tables given in engineering 

 handbooks and piping handbooks. 



Pipe was formerly identified as standard 

 (Std), extra strong (XS), and double extra strong 

 (XXS). These designations, which are still used 

 to some extent, also refer to wall thickness. 

 However, pipe is manufactured in a number of 

 different wall thicknesses, and some pipe does 

 not fit into the standard, extra strong, and 

 double extra strong classifications. The wall 

 thickness schedules are being used increasingly 

 to identify the wall thickness of pipe because 

 they provide for the identification of a larger 

 number of wall thicknesses than can be identi- 

 fied under the standard, extra strong, and double 

 extra strong classifications. 



It should be noted that pipe and tubing is 

 occasionally identified in ways other than the 

 standard ways described here. For example, 

 some tubing is identified by inside diameter 

 (ID) rather than by outside diameter (OD), and 

 some pipe is identified by nominal pipe size, 

 OD, ID, and actual measured wall thickness. 



A great many different kinds of pipe and 

 tubing are used in shipboard piping systems. 

 A few shipboard applications that may be of 



particular interest are noted in the following 

 paragraphs. 



Seamless chromium-molybdenum alloy steel 

 pipe is used for some high pressure, high tem- 

 perature systems. The upper limit for the piping 

 is 1500 psig and 1050° F. 



Seamless carbon steel tubing is used in 

 oil, steam, and feed water lines operating at 

 775 ° F and below. Different types of this tubing 

 are available; the type used in any particular 

 system depends upon the working pressure of 

 the system. 



Seamless carbon- molybdenum alloy steel 

 tubing is used for feed water discharge piping, 

 boiler pressure superheated steam lines, and 

 boiler pressure saturated steam lines. Several 

 types of this tubing are available; the type 

 used in any particular case depends upon the 

 boiler operating pressure and the superheater 

 outlet temperature. The upper pressure and 

 temperature limits for any class of this tubing 

 are 1500 psig and 875° F. 



Seamless chromium-molybdenum alloy steel 

 tubing is used for high pressure, high tempera- 

 ture steam service on newer ships. This type 

 of alloy steel tubing is available with different 

 percentages of chromium and molybdenum, with 

 upper limits of 1500 psig and 1050° F. 



Welded carbon steel tubing is used in some 

 water, steam, and oil lines where the tempera- 

 ture does not exceed 450° F. There are several 

 types of this tubing; each type is specified for 

 certain services and certain service conditions. 

 Nonferrous pipe and nonferrous tubing are 

 used for many shipboard systems. Nonferrous 

 metals are used chiefly where their special 

 properties of corrosion resistance and high 

 heat conductivity are required. Various types 

 of seamless copper tubing are used for re- 

 frigeration lines, plumbing and heating systems, 

 lubrication systems, and other shipboard sys- 

 tems. Copper-nickel alloy tubing is widely used 

 aboard ship. Seamless brass tubing is used in 

 systems which must resist the corrosive action 

 of salt water and other fluids; it is available in 

 types and sizes suitable for operating pressures 

 up to 4000 psig. Seamless aluminum tubing is 

 used for dry lines in sprinkling systems and 

 for some bilge and sanitary drain systems. 

 Many other kinds of pipe and tubing besides 

 the kinds mentioned here are used in shipboard 

 piping systems. It is important to remember 

 that design considerations govern the selection 

 of any particular pipe or tubing for a particular 

 system. Although many kinds of pipe and tubing 



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