Boiler Seam Technology


| July/August 1977



Boiler Seam

R. R. #4, Red Deer, Alberta, Canada

Lap Seam Versus Butt and Double Strap Seam I have read quite a few comments in the last year or so on the two types of boiler seams used on the barrel part of the boiler. I would like to try to throw a little light on the subject if I may.

Lap Seam This seam is made up where the barrel is rolled and lapped over itself to make the complete circle of the barrel, then it is riveted together with one, two, and three rows of rivets.

Most all professional engineers will tell you that by lapping the plates that you in fact do not make a true circle, and thus create a point where when under pressure the barrel of the boiler is trying to become a true circle, thus where the seam joins, it's supposed to be the working point, where possible cracking can occur, 'whether this is true or not, I do not know.' I never found a seam that was cracked.

Also, one other reason for engineers pointing out the weakness, if there is any in the lap seam is where two plates are just lapped over and riveted, you have a single shear force on the rivet and this is where your safety factor, catches heck from the engineers. If you do not understand single shear, and double shear, in a riveted joint, it almost explains itself.

We will come back to the rivets in the two types of seam further on in this article.