Final answer:
Nuts are designed to withstand higher loads than bolts of the same grade to prevent thread stripping when tightened to the bolt's proof load. A longer pipe on a wrench increases torque, easing removal of tight bolts, but poses a risk of bolt breakage.
Step-by-step explanation:
It is true that nuts are designed to withstand higher loads compared to bolts of the same grade. This design ensures that when tightened to the bolt's proof load, which is the maximum tensile force that it can withstand without being permanently deformed, the nuts won't experience thread stripping. By thread stripping, we mean the threads of either the bolt or the nut being pulled out of shape or sheared off, which can result in a loss of clamping force and the potential failure of the bolted joint.
Mechanics might put a length of pipe over the handle of a wrench when trying to remove a very tight bolt to increase the torque applied. This works because the longer lever arm (the pipe) applied to the wrench handle creates greater torque at the nut or bolt head for the same amount of force. While this can indeed make the removal easier, it is also true that the increased torque can exceed the proof load of the bolt, potentially leading to bolt breakage.