Thread Content
Under internal pressure, a thick-walled cylinder experiences uneven stress distribution within its wall, with the inner wall experiencing higher stress than the outer wall. To improve this uneven stress distribution within the cylinder, pre-overpressure treatment can be carried out before the thick-walled cylinder is put into use. Under strictly controlled overpressure, the inner layer of the cylinder undergoes plastic deformation to form a plastic zone, while the outer layer of material remains in an elastic state. After maintaining this pressure for a period of time and then releasing it, the portion of the inner layer of the cylinder that has undergone plastic deformation cannot return to its initial position due to residual deformation. The outer layer material, which is still in the elastic stage, tends to return to its original state, but it is prevented from doing so completely by the inner layer material that cannot revert to its original condition. Thus, a prestressed state is formed within the cylinder wall, with the inner layer under compression and the outer layer under tension. When the cylinder is put into operation and subjected to operating pressure, the tensile stress resulting from this pressure – which is greater on the inside than on the outside – combines with the prestress created during preprocessing, characterized by internal pressure and external tension. As a result, the stress level on the inner wall, which was originally high, decreases, while the stress level on the outer wall, which was originally low, increases slightly. The stress distribution along the wall thickness becomes more uniform, thereby enhancing the cylinder’s yield strength. This treatment method, which involves controlled overpressure to cause only the inner layer to yield while the outer layer remains elastic, and utilizes the elastic contraction of the outer layer to generate prestress thereby improving the load-bearing capacity of the cylinder, is known as self-reinforcement of thick-walled cylinders.