Autofrettage

Autofrettage is a metal fabrication technique in which a pressure vessel is subjected to enormous pressure, causing internal portions of the part to yield and resulting in internal compressive residual stresses. The goal of autofrettage is to increase the durability of the final product. The technique is commonly used in the manufacture of high pressure pump cylinders, battleship and tank cannon barrels and fuel injection systems for diesel engines. While some work hardening will occur, that is not the primary mechanism of strengthening.

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As used for strengthening cannon barrels, the barrel is prebored to a slightly undersized inside diameter, and then a slightly oversized die is pushed through the barrel. The amount of initial underbore and size of the die are calculated to strain the material past its elastic limit into plastic deformation, sufficiently far that the final strained diameter is the final desired bore.

The technique has been applied to the expansion of tubular components down hole in oil and gas wells. The method has been patented by Norwegian oil service company READ, which uses it to connect concentric tubular components with the sealing and strength properties outlined above.

See also

• Shot peening which also induces compressive residual stresses.