PRINCIPLES OF NAVAL ENGINEERING 



functioning of the system and equipment served 

 by the system. 



Various joints are used in shipboard piping 

 systems. The joints used in any system depend 

 upon the piping service, the pipe size, and the 

 construction period of the ship. Older naval 

 ships have threaded flanges in low pressure 

 piping; rolled-in joints for steel piping that is 

 too large for the threaded flanges; and spelter- 

 brazed flanges for copper and brass piping. On 

 new construction, welded joints are used to the 

 maximum practicable extent in systems that 

 are fabricated of carbon steel, alloy steel, 

 or other weldable material. On both older and 

 newer ships, flanged joints made up with special 

 gaskets are in use. 



Components welded in a piping system must 

 be accessible for repair, reseating, and over- 

 haul while in place; they are so located that 

 they can be removed, preheated, rewelded, and 

 stress relieved when major repairs or replace- 

 ments are necessary. Complex assemblies— 

 for example, assemblies of valves, strainers, 

 and traps in high pressure drain systems— are 

 designed to be removable as a group if they 

 cannot be repaired while in place and if they 

 require frequent overhaul. 



Flanged and union joints are placed where 

 they will be least affected by piping system 

 stresses. In general, this means that joints are 

 not located at bends or offsets in the piping. 



Valves are designed so that they can be 

 operated with the minimum practicable amount 

 of force and with the maximum practicable con- 

 venience. If a man must stand on slippery deck 

 plates to turn a valve handwheel, or if he must 

 reach over his head or around a corner, he can- 

 not apply the same amount of torque that he could 

 apply to a more conveniently located handwheel. 

 Thus the location of the handwheels is an impor- 

 tant design consideration. Toggle mechanisms or 

 other mechanical advantage devices are used 

 where the amount of torque required to turn a 

 handwheel is more than could normally be ap- 

 plied by one man. If mechanical advantage de- 

 vices are not sufficient to produce easy operation 

 of the valve, power operation is used. 



If accidental opening or closing of a valve 

 could endanger personnel or jeopardize the 

 safety of the ship, locking devices are used. 

 Any locking device installed on a valve must be 

 designed so that it can be easily operated by 

 authorized personnel; but it must be complex 

 enough to discourage casual or indiscriminate 

 operation by other persons. 



Supports used in shipboard piping systems 

 must be strong enough to support the weight of 

 the piping, its contained fluid, and its insulation 

 and lagging. Supports must carry the loads im- 

 posed by expansion and contraction of the piping 

 and by the working of the ship, and they must 

 be able to support the piping with complete 

 safety. Supports are designed to permit the 

 movement of the piping necessary for flexibility 

 of the system. A sufficient number of supports 

 are used to prevent excessive vibration of the 

 system under all conditions of operation, but 

 the supports must not cause excessive con- 

 straint of the piping. Supports are used for 

 heavy valves and fittings so that the weight of 

 the valves and fittings will not be entirely sup- 

 ported by the pipe. 



PIPE AND TUBING 



Piping is defined as an assembly of pipe or 

 tubing, valves, fittings, and related components 

 forming a whole or a part of a system for trans- 

 ferring fluids. 



It is somewhat more difficult to define pipe 

 and tubing . In commercial usage, there is no 

 clear distinction between pipe and tubing, since 

 the correct designation for each tubular product 

 is established by the manufacturer. If the manu- 

 facturer calls a product pipe, it is pipe; if he 

 calls it tubing, it is tubing. In the Navy, however, 

 a distinction is made between pipe and tubing. 

 This distinction is based on the way the tubular 

 product is identified as to size. 



There are three important dimensions of any 

 tubular product: outside diameter (OD), inside 

 diameter (ID), and wall thickness. A tubular 

 product is called tubing if its size is identified 

 by actual measured outside diameter (OD) and 

 by actual measured wall thickness. A tubular 

 product is called pipe if its size is identified 

 by a nominal dimension called iron pipe size 

 (IPS) and by reference to a wall thickness 

 schedule of piping. 



The size identification of tubing is simple 

 enough, since it consists of actual measured 

 dimensions; but the terms used for identifying 

 pipe sizes may require some explanation. A 

 nominal dimension such as iron pipe size is 

 close to— but not necessarily identical with— an 

 actual measured dimension. For example, a 

 pipe with a nominal pipe size of 3 inches has 

 an actual measured outside diameter of 3.50 

 inches, and a pipe with a nominal pipe size of 

 2 inches has an actual measured outside diameter 



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