The presented an analytical autofretage procedure to predict

The wide applications of
pressurized cylinder in chemical, nuclear, armaments, fluid transmitting
plants,
power plants and military equipment, in addition to the increasing scarcity and
high cost of materials lead

the designers to
concentrate their attentions to the elastic – plastic approach which offers
more efficient use of materials 1, 2.The process of producing residual
stresses in the wall of thick-walled cylinder before it is put into usage is
called Autofretage, which it means; a suitable large enough
pressure to cause yielding within the wall, is applied to the inner surface of
the cylinder and then removed. So that a compressive residual
stresses are generated to a certain radial depth at the cylinder wall. Then,
during the subsequent application of an operating pressure, the residual
stresses will reduce the tensile stresses generated as a result of applying
operating pressure 1,3.

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The effect of
residual stresses on load-carry capacity of thick-walled cylinders have been
investigate by Amran Ayob and Kabashi Albasheer 4, using both analytical and
numerical techniques. The results of the study reveal three scenarios in the
design of thick-walled cylinders. Amran Ayob and M. Kabashi Elbasheer 5, used
von.mises and Tresca yield criteria to develop a procedure in which the autofretage
pressure determined analytically resulting in a reduced stress concentration.
Then they compared the analytical results with FEM results. They concluded
that, the autofretage process increase the maximum allowable internal pressure
but it cannot increase the maximum internal pressure to case whole thickness of
the cylinder to yield. Noraziah et al. 6 presented an analytical autofretage
procedure to predict the required autofretage pressure of different levels of
allowable pressure and they validate their results with FEM results. They found
three cases of autofretage in design of pressurized thick – walled cylinders.

Ruilin Zhu and
Jinlai Yang 7, using both yield criteria von.mises and Tresca, presented an
analytical equation for optimum radius of elastic-plastic junction in autofretage
cylinder, also they studied the influence of autofretage on stress distribution
and load bearing capacity. They concluded, to achieve optimum radius of elastic
– plastic junction, an autofretage pressure a bit larger than operating
pressure should be applied before a pressure vessel is put into use. Zhong Hu
and Sudhir Puttagunta 8 investigate the residual stresses in the thick-
walled cylinder induced by internal autofretage pressure, also they found the
optimum autofretage pressure and the maximum reduction percentage of the
von.mises stress under elastic-limit working pressure. Md. Tanjin Amin et al.
9 determined the optimum elasto – plastic radius and optimum autofretage
pressure using von.mises yield criterion , then they have been compared with
Zhu and Yang’s model 8. Also they observed that the percentage of maximum
von.mises stress reduction increases as value of radius ratio (K) and working
pressure increases. F. Trieb et al. 10 discussed practical application of autofretage
on components for waterjet cutting. They reported that the life time of high
pressure components is improved by increasing autofretage depth due to
reduction of tangential stress at inner diameter, on other hand too high
pressure on outside diameter should be avoided to prevent cracks generate. In
addition to determine the optimum autofretage pressure and the optimum radius
of elastic-plastic junction , Abu Rayhan Md. et al.11 evaluated the effect of
autofretage process in strain hardened thick – walled pressure vessels using
equivalent von.mises stress as yield criterion. They found, the number of autofretage
stages has no effect on maximum von.mises stress and pressure capacity. Also,
they concluded that, optimum autofretage pressure depends on the working
pressure and on the ratio of outer to inner radius.

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