Riveted Joints for Construction of Boilers
rivets and double
The diameter of the rivet is usually nearly twice the thickness of the plate and should never be less than the thickness of the plate.
The riveted seam must contain a whole number of rivets. and similar seams should have the same pitch.
The distance between rows, for double riveting, is about twice the diameter of the rivets.
In double butt riveting the rivets in double shear have 14 times the single section instead of 2.
The thickness of double butt straps should not be less than 5/8 the thickness of the plate (each) ; single butt straps not less than 9/8.
No one set of rules can be laid down for the best pitch of rivets for all circumstances of pressure, quality of plates, etc. The following table of proportions of riveted joints gives results for average practice in boilers of up to about 150 pounds pressure.
As the stress on the transverse section is one-half that on a longitudinal section, a single or double lap joint is sufficient for any ring seam. For externally fired multitubular boilers with shell plates less than 1/2 inch thick, single riveted ring seams are used. For our boiler, the plates being 5/16 inch thick, we will use rivets 11/16 inch in diameter, as this agrees with good practice. From the table, the pitch for a 11/16inch rivet for single riveted lap joint is Then as our ring seam is 3.1416 X 54 = 169.65 inches and pitch 2-1/16 inches we will have 82 + rivets. But as we must have a whole number of rivets we will alter the pitch slightly and use 82 rivets with a pitch of 2.069 inches. The result depends, in each case, upon the kind of joint used in longitudinal seams. This merely shows the general method. The lap will be 11/16 X 3/9 = 1-1/32 inch.
For the longitudinal scams we will use double butt joints with single riveting. The thickness of the butt straps will be 5/16 x 5/8 =.20 (nearly). To be on the safe side we will make the butt straps inch thick. The pitch for double butt joints is usually about 4 times the diameter of rivets, so in this case it will be 4 x 11/16 = 2-3/4 inches. We will use the same amount of lap for this joint as for the lap joint, that is 1-1/32 inches.