Collapse tests were performed on one-in. dia steel tubes with flats milled on the exterior to simulate worn casing. External pressure and axial load were applied to the tubs having a range of wall thickness, yield strength, and degree of wear. Empirical correlation of the data and comparison with elastic collapse calculations indicate the percentage reduction in collapse pressure due to wear. This reduction is predictable within upper and lower bounds. While the milled external flat may not accurately simulate severe internal wear, the correlation is adequate for less than severe wear to give an indication of remaining strength.

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