My dad who smoked all day and never had pipes to rotate (smoked one pipe at a time) used to crack his cobs after about six months from steady use. With a PAD-high pipe rotation, I've never had one crack, and some are years old. I consider them part of the permanent stable. fishnbanjo has a number that are decades old and going strong. Now and then there is a cob that cracks with heat, but not nearly so many as you would think from this thread. Most go on ... and on.