BOILERS AND GENERATION OF STEAM 307 



)A A 



>A A 



Q 



metal has been removed. Therefore an additional piece of 

 metal, known as a strap, must sometimes be placed around 

 such rivet holes to make up this deficiency to some extent. 

 At the present time, most fire-tube boilers made to generate 

 steam for engines have the 

 different portions of the shell 

 overlapping one another, as 

 shown in Fig. 160, and these 

 are held with a single row 

 of rivets. This arrangement 

 forms what is called a lap 

 joint. Lap joints are not 



^ Copyrighted by Millers Falls Co.) 



used to any great extent in FlG> i6L Butt Joint. 



joining the two ends of the 



same sheet. In this case the ends are brought together and 

 one strap is placed on the inside and another on the out- 

 side, as shown in Fig. 161. This method forms what is called 

 a butt joint. These straps and the plate are joined by 

 riveting, as shown. If a single row of rivets is used on 



each side of the joint through 

 the outer plate, as shown at 

 A A, it is called a single-riveted 

 butt joint. If a double row is 

 placed on each side of the 

 joint through the outer strap, 

 as shown in Fig. 162, it is called 

 a double-riveted butt joint; if 



(Copyrighted by Millers Palls Co.) ^^ rQWg 



FIG. 162. Double-Riveted 



Butt Joint. 



, . , . , , , . . , 



a triple-riveted butt joint. 



348. Thickness of Boiler Plate. The Boiler Inspection 

 Department of Massachusetts recommends the following 



