Chapter 10- PROPULSION BOILERS 



Figure 10-6 shows a Boiler Tube Renewal 

 Sheet for a double-furnace boiler and illustrates 

 the method used to identify tubes. 



The water wall tube row is not identified by 

 a letter in figure 10-6. The tubes in this row are 

 often identified by the letter W and a following 

 letter which indicates the type of tube or its 

 position in the row. Still another letter (an R or 

 an L) may be added to indicate that the tube is 

 studded or finned on the right-hand side or on 

 the left-hand side. 



The tubes which screenthe superheater from 

 direct radiant heat are identified in figure 10-6 

 as the LA, LB, and LC rows. Within each row, 

 the individual tubes are numbered: LA-1, LA-2, 

 LA-3, and so forth. 



Figure 10-6 identifies the superheater sup- 

 port and drum support tubes as the LD row. 

 Note that these are NOT superheater tubes. 

 The superheater tubes in this boiler, as inmost 

 boilers, are installed horizontally. The super- 

 heater support tubes and the drum support tubes 

 are installed vertically; they are identified as 

 LD-1, LD-2, LD-3, and so forth. 



The first row of division wall tubes is iden- 

 tified in figure 10-6 as the LE row. The second 

 row of division wall tubes may be identified as 

 the LF row or as the D row. Identification of 

 tubes in this row is usually made by using the 

 row identification (LF, D, or whatever row 

 identification is used for the particular boiler) 

 followed by a letter to indicate the type of tube 

 or its position in the row; still another letter 

 (an R or an L) may be added to indicate that the 

 tube is studded or finned on the right-hand side 

 or on the left-hand side. 



Tubes in the main generating bank are iden- 

 tified by lettering the rows and numbering the 

 individual tubes, as shown in figure 6-6. The 

 two rows nearest the saturated-side furnace are 

 slightly larger than the rest of the generating 

 tubes; they serve as water screen tubes. These 

 two rows are often called the RA and the RB 

 rows. Individual tubes in these rows are identi- 

 fied by number in the same way that the rest of 

 the generating tubes are identified. 



Note that the superheater tubes are also 

 identified in figure 10-6. Identification of super- 

 heater tubes is discussed in the section that 

 deals with superheaters. 



The discussion of boiler tube identification 

 given here is based on one particular type of 

 boiler— that is, a double-furnace boiler. The 

 same general principles of tube identification 

 apply to most other drum-type boilers now in 



naval use, but the details of tube identification 

 are necessarily different in different types of 

 boilers. 



Superheaters 



Most propulsion boilers now in naval service 

 have convection-type superheaters, with water 

 screen tubes installed between the superheater 

 and the furnace to absorb the intense radiant 

 heat and thus protect the superheater. 



Most convection-type superheaters have 

 U-shaped tupes which are installed horizonally 

 in the boiler and two headers which are in- 

 stalled more or less vertically at the rear of 

 the boiler. One end of each U-shaped tube enters 

 one superheater header, and the other end 

 enters the other header. The superheater head- 

 ers are divided internally by one or more divi- 

 sion plates which act as baffles to direct the 

 flow of steam. In some cases the superheater 

 headers are divided externally as well as in- 

 ternally. 



Figure 10-7 illustrates some convection- 

 type superheater arrangements that are used 

 on double-furnace boilers. Part A is apian view 

 of the superheater tubes, showing how the tubes 

 enter the headers. Part B shows a superheater 

 in which each header is divided into two sec- 

 tions, and illustrates the flow of steam through 

 the superheater. Part C illustrates the flow of 

 steam through a superheater in which one header 

 has one internal division and the other header 

 has two internal divisions. As may be seen from 

 figure 10-7, the steam makes several passes 

 through the furnaces. The number of passes is 

 determined by the number of header divisions 

 and by the relative locations of the steam inlet 

 and the steam outlet. 



The superheater tubes are installed so that 

 their U-shaped ends project forward toward the 

 front of the boiler. In a double-furnace boiler, 

 the superheater tubes project forward into a 

 space between the water screen tubes and some 

 tubes called furnace division wall tubes . The 

 superheater tubes and the surrounding water 

 screen and division wall tubes are thus together 

 the dividing line between the superheater-side 

 furnace and the saturated-side furnace. In a 

 single-furnace boiler, the superheater tubes 

 project forward into a space in the main bank 

 of generating tubes. The tubes between the 

 superheater tubes and the furnace serve as 

 water screen tubes. 



Some recent boilers have walk- in or cavity- 

 type superheaters. In this type of superheater, 



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