Chapter 9-MACHINERY ARRANGEMENT AND PLANT LAYOUT 



NO. 2 SHAFT 



RED. 

 GEARS 



NO. 2 



MAIN 



ENGINE 



2MS3 



2MS4B 

 2MS5B 



TURBO- 

 GEN. 

 2B 



NO. 2 ENGINEROOM 



2MS2B 



2MS2A^ 



NO. 2 PI RE ROOM 



FWD 



Figure 9-11.— Principle of valve identification in engineering piping systems. 



147,82 



MAIN STEAM SYSTEMS 



The main steam system is the shortest and 

 simplest of all the major engineering piping 

 systems aboard ship. This statement is true 

 regardless of the steam pressures involved. 

 With the recent advent of the 1200-psi main 

 steam system,! there is a tendency to regard 

 high pressure main steam Systems as basically 

 different from (and mysteriously more complex 

 than) the lower pressure systems. In reality, a 

 1200-psi main steam system serves the same 



Classification of main steam systems according to 

 pressure is based on the operating pressure of the 

 boilers. Boiler operating pressures are discussed in 

 chapter 10 of this text; at this point, it is merely nec- 

 essary to note that main steam systems are frequent- 

 ly referred to as 1200-psi systems, 600-psi systems, 

 or 400-psi systems, depending upon the operating pres- 

 sure of the boilers. It should be noted, also, that such 

 pressure classifications are approximate rather than 

 exact. 



basic purpose as a lower pressure system, and 

 differs only in minor details, as noted in subse- 

 quent discussion. The major difference between 

 high pressure main steam systems and lower 

 pressure systems is in the materials used for 

 piping and fittings; in general, the metals for 

 1200-psi systems must be designed to withstand 

 operating temperatures approximately 100° to 

 200° F higher than the operating temperatures 

 of the lower pressure systems. 2 



On most ships, any piping which carries su- 

 perheated steam is considered as part of the main 

 steam system. On many ships, the main steam 

 system includes only the piping that carries su- 

 perheated steam from the boilers to the propul- 

 sion turbines, the turbogenerators, and the boiler 



Although the main steam systems are approximately 

 the same for a 1200-psi system and for a lower pres- 

 sure system, it should not be inferred that the plant 

 as a whole is identical. Important differences between 

 1200-psi plants and lower pressure plants are noted 

 in appropriate places throughout this text. 



205 



