Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGlook almost exactly alike from the outside, theymay respond very differently to pressures,temperatures, and other service conditions.Therefore, each kind of pipe and tubing can beused only for the specified applications.PIPE FITTINGSPipe or tubing alone does not constitute apiping system. To make the pipe or tubing intoa system, it is necessary to have a variety offittings, connections, and accessories by whichthe sections of pipe or tubing can be properlyjoined and the flow of the transferred fluid maybe controlled. The following sections of thischapter deal with some of the pipe fittings mostcommonly used in shipboard piping systems;these fittings include unions, flanges, expansionjoints, flareless fluid connections, steam traps,strainers, and valves.UNIONSUnion fittings are provided in piping systemsto allow the piping to be taken down for repairsand alterations. Unions are available in manydifferent materials and designs to withstanda wide range of pressures and temperatures.Figure 14-1 shows some commonly used typesof unions.FLANGESFlanges are used in piping systems to alloweasy removal of piping and other equipment.The materials used and the design of the flangesare governed by the requirements of service.Flanges in steel piping systems are usuallywelded to the pipe or tubing. Flanges in nonferroussystems are usually brazed to the pipeor tubing.EXPANSION JOINTSExpansion joints are used in some pipingsystems to allow the piping to expand and contractwith temperature changes, without damageto the piping. Two basic types of expansionjoints are used in shipboard piping systems:sliding-type joints and flexing-type joints,Sliding-type expansion joints include sleevejoints, rotary joints, ball and socket joints,and joints made up of some combination of thesetypes. The amount of axial and rotary motionthat can be abosrbed by any particular typeof sliding expansion joint depends upon thespecific design of the joint.Flexing-type expansion joints are those inwhich motion is absorbed by the flexing actionof a bellows or some similar device. Thereare various kinds of flexing-type expansionjoints, each kind being designed to suit therequirements of the particular system in whichit is installed. Figure 14-2 illustrates the generalprinciple of a bellows-type expansion joint.Expansion joints are not always used inpiping systems, even when allowance must bemade for expansion and contraction of the piping.The same effect can be achieved by using directionalchanges and expansion bends or loops.FLARELESS FLUID CONNECTIONSA special flareless fluid connection has recentlybeen developed for connecting sectionsof tubing in some high pressure shipboard systems.This fitting, which is generally known asthe bite-type fitting , is very useful for certainapplications because it is smaller and lighterin weight than the conventional fittings previouslyused to join tubing. The bite-type fitting is usedon certain selected systems where the tubingis between 1/8 and 2 inches in outside diameter.The bite-type fitting, shown in figure 14-3,consists of a body, a ferrule or sleeve thatgrips the tubing, and a nut. The fitting is notused in places where there is insufficient spacefor proper tightening of the nut, in places wherepiping or equipment would have to be removedin order to gain access to the fitting, or inplaces where the tubing cannot be easily deflectedfor ready assembly or breakdown of thejoint. The fitting is sometimes used on gageboard or instrument panel tubing, provided thegage board or panel is designed to be removedas a unit when repairs are required.STEAM TRAPSSteam traps are installed in steam lines todrain condensate from the lines without allowingthe escape of steam. There are many differentdesigns of steam traps, some being suitablefor high pressure use and others beingsuitable for low pressure use. In general, asteam trap consists of a valve and some deviceor arrangement that will cause the valve toopen and close as necessary to drain the condensatefrom the lines without allowing theescape of steam. Steam traps are installed at366