Autofrettage Service

Autofrettage is just one of the many specialty processes A&A performs. Autofrettage involves subjecting a pressure vessel to intense pressure to increase strength and durability of the pressure vessel.

This process was first used to pre-stress both cannon and gun barrels. Both cannon and gun barrels experience high pressure, stress, and temperature variations when operated. These stresses cause fatigue in the bore of the barrels, which leads to cracking, deformation and eventual failure. Manufacturers needed a way to prevent fatigue – so they invented Autofrettage.

A&A primarily uses it to improve High Pressure (HP) tubing or HP fittings (cylinders, blocks, and quills) which also see high pressure (sometimes 40,000 psi), stress, and temperature. HP tubing and fittings are used in making plastic. Autofrettage makes the bore (ID) of the tube or fitting act like plastic. As the pressure is increased it deforms the bore and as it deforms – this plastic boundary moves from the inside ID toward the outside OD. If you kept increasing the pressure – the deformation would continue until it reached the outside wall, causing “plastic collapse” or rupture. In Autofrettage the pressure is increased from the point that the material first begins to move (its yield point) to a pressure, which will place this plastic region at a desired distance or radius from the bore. The removal of the pressure then produces “residual stresses” in the bore and on the OD. This makes the tube stronger. The three main reasons why you Autofrettage a tube is to:

1) Prevent future deformation of the cylinder or tube wall when a working pressure is applied.

2) Increase the fatigue life – last a long time over many cycles or repetitions.

3) Retard growth of fatigue or stress cracks near the bore.