Autofrettage of piping

The subject is more familiar to Stress engineers. Thought of sharing the basics with others.

The link below gives the basics behind the Autofrettage.
http://www.interlaken.com/legacysite/pdf/Autofrettage_ABCs.pdf

Though widely popular in other industries, in petrochemical field, the lines subject to high pressure piping such as LLDPE plants of Borestar technology of Borealis and LDPE of Lupotech technology of Basell have very high pressure piping which are in most cases licensor engineered items. General recommendation in such piping is to ensure that the piping does not fail under fatique loads. To arrive the pre compression stress equivalent autofrettage pressure limit, the pipe is analysed and plotted for various thickness percentage segments and how the stresses peak and drop, so that to arrive the optimum residual stress and the equivalent autofrettage pressure.

The pipe and fittings are subject to that resultant pressure and pre stressed before installation. Thus it is ensured that the piping can withstand higher fatigue loads and shock pressures of very high pressure services. Also observe the various stress curves on the attached snap of a sample analysis.

Stress engineers in the group are requested to share more of thier experience and views.

With regards,
Kannan.