Consideration of strength anisotropy when estimating long- term strength of real pipes under plane stressed state conditions

A method is suggested to process results of long-term strength test of thin-walled pipes in a plane stressed state with regard for the material strength anisotropy. A fictitious stress equal to maximum tensile stress which is decreased in proportion to the material strengthening in the same direction is taken as a long- term strength criterion. The method application is demonstrated through an example of processing results of a long-term strength test at 850 deg C for a lot of 69 specimens, made of as-delivered thin-walled pipes (material-Kh18N10T steel). Loading was made by uniaxial and biaxial tension as well as by axial tension in combination with torsion. It is shown that the suggested method of strength anisotropy consideration results in a 30% decrease in the experimental point variance relative to an approximation straight line in binary logarithmic stress-time-to-failure coordinates