Principles of naval engineering - Historic Naval Ships Association

Chapter 14. -PIPING, FITTINGS, AND VALVESof 2.375 inches. In the larger sizes (above 12inches) the nominal pipe size and the actualmeasured outside diameter are the same. Forexample, a pipe with a nominal pipe size of14 inches has an actual measured outside diameterof 14 inches. Nominal dimensions areused in order to simplify the standardizationof pipe fittings and pipe taps and threading dies.The wall thickness of pipe is identified byreference to wall thickness schedules establishedby the American Standards Association.For example, a reference to schedule 40 fora steel pipe with a nominal pipe size of 3 inchesindicates that the wall thickness of the pipe is0.216 inch. A reference to schedule 80 for asteel pipe of the same nominal pipe size indicatesthat the wall thickness of this pipe is0.300 inch. A reference to schedule 40 forsteel pipe of nominal pipe size 4 inches indicatesthat the wall thickness of this pipe is0.237 inch. As may be noted from these examples,a wall thickness schedule identificationdoes not identify any one particular wall thicknessunless the nominal pipe size is also specified.The examples used here are given merelyto illustrate the meaning of wall thicknessschedule designations. Many other values canbe found in pipe tables given in engineeringhandbooks and piping handbooks.Pipe was formerly identified as standard(Std), extra strong (XS), and double extra strong(XXS). These designations, which are still usedto some extent, also refer to wall thickness.However, pipe is manufactured in a number ofdifferent wall thicknesses, and some pipe doesnot fit into the standard, extra strong, anddouble extra strong classifications. The wallthickness schedules are being used increasinglyto identify the wall thickness of pipe becausethey provide for the identification of a largernumber of wall thicknesses than can be identifiedunder the standard, extra strong, and doubleextra strong classifications.It should be noted that pipe and tubing isoccasionally identified in ways other than thestandard ways described here. For example,some tubing is identified by inside diameter(ID) rather than by outside diameter (OD), andsome pipe is identified by nominal pipe size,OD, ID, and actual measured wall thickness.A great many different kinds of pipe andtubing are used in shipboard piping systems.A few shipboard applications that may be ofparticular interest are noted in the followingparagraphs.Seamless chromium-molybdenum alloy steelpipe is used for some high pressure, high temperaturesystems. The upper limit for the pipingis 1500 psig and 1050° F.Seamless carbon steel tubing is used inoil, steam, and feed water lines operating at775 ° F and below. Different types of this tubingare available; the type used in any particularsystem depends upon the working pressure ofthe system.Seamless carbon- molybdenum alloy steeltubing is used for feed water discharge piping,boiler pressure superheated steam lines, andboiler pressure saturated steam lines. Severaltypes of this tubing are available; the typeused in any particular case depends upon theboiler operating pressure and the superheateroutlet temperature. The upper pressure andtemperature limits for any class of this tubingare 1500 psig and 875° F.Seamless chromium-molybdenum alloy steeltubing is used for high pressure, high temperaturesteam service on newer ships. This typeof alloy steel tubing is available with differentpercentages of chromium and molybdenum, withupper limits of 1500 psig and 1050° F.Welded carbon steel tubing is used in somewater, steam, and oil lines where the temperaturedoes not exceed 450° F. There are severaltypes of this tubing; each type is specified forcertain services and certain service conditions.Nonferrous pipe and nonferrous tubing areused for many shipboard systems. Nonferrousmetals are used chiefly where their specialproperties of corrosion resistance and highheat conductivity are required. Various typesof seamless copper tubing are used for refrigerationlines, plumbing and heating systems,lubrication systems, and other shipboard systems.Copper-nickel alloy tubing is widely usedaboard ship. Seamless brass tubing is used insystems which must resist the corrosive actionof salt water and other fluids; it is available intypes and sizes suitable for operating pressuresup to 4000 psig. Seamless aluminum tubing isused for dry lines in sprinkling systems andfor some bilge and sanitary drain systems.Many other kinds of pipe and tubing besidesthe kinds mentioned here are used in shipboardpiping systems. It is important to rememberthat design considerations govern the selectionof any particular pipe or tubing for a particularsystem. Although many kinds of pipe and tubing365