Behavior and response of lead-caulked bell–spigot joints in cast iron water mains

The annular space between bell and spigot joints for cast iron pipes installed between 1850 and the early 1960s in North America was typically caulked with lead. Lead was caulked unto place using hand-held or pneumatic hammers and special chisels. Historical anecdotal evidence suggests that some bells may have cracked during caulking, especially if the jointer was over zealous in hammering the lead in place or used pneumatic hammers with excessive pressure to produce a tight joint. This paper examines two mechanistic models, one linear and another non-linear, to estimate the levels of hoop stress induced in the bell as a consequence of lead caulking. Illustrative analyses of lead caulking joints in 16″ and 48″ diameter pipes show that the linear model tends to predict unrealistic high stresses while the non-linear model produced more realistic stresses. Tensile hoop stresses can reach as high as 25% of the tensile strength of cast iron if the joint caulker is over zealous in the hammering action. The non-linear model was also used to reproduce caulking-induced stresses in tests conducted on 20″ diameter pipes by Prior in 1935.