Abstract

This paper compares and discusses the change to the residual stresses and strains on four tubes of SA-723 Gr 1 Cl 2 (Timken HS 220) tubing material that were autofrettaged at different Overstrain ratios (20% and 40%). The four tubes were autofrettaged with strain gages to obtain actual OD strain. The effect on the residual stress and strain of the material is reviewed after a single autofrettage and after a low temperature heat treat followed by a second autofrettage. The low temperature heat treat was performed on two of the four tubes to create comparable data. Any strain aging effect from the low temperature heat treat is examined on the measured residual stress and strains. The effect and possible benefits of strain aging and re-autofrettage on tubes with different Overstrain ratios is discussed. To obtain the residual stress values in the tube wall after the autofrettage cycles, the sample tube pieces were tested by X-ray diffraction. The actual residual stresses after autofrettage were then compared with the calculated theoretical residual stresses including Bauschinger effect correction factors from ASME Section VIII Div. 3 KD-5. The residual stress and strain data between one and two rounds of autofrettage is also studied to see if the Bauschinger effect is present.

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