Deep-Hole-Drilling of High Pressure Tubes: Process Stability and the Influence of Eccentricity on Autofrettage and Heat Transfer

In this work, the measured values of wall thicknesses over the length and the circumference of nearly 1800 tubes were statistically evaluated and analyzed. With these results, a precise statement about the process reliability can be made. This makes it possible to minimize the costs for high-pressure tubes in such a way that both the demand for raw material and the rejects on manufactured tubes are minimized. In the next step, the influence of eccentricity in a pipe on the desired operating properties was investigated. For this purpose, a sensitivity analysis was performed to quantify the influence on the residual stresses resulting from autofrettage, operating stresses and fatigue endurance over the circumference, as well as the heat conduction between the inner wall and the outer wall of the tube. The results of this sensitivity analysis are finally used to discuss the requirements of manufacturing tolerances of licensors. It was found that there is nearly no influence of eccentricity, in the investigated range, on heat transfer through the tube wall. The influence of eccentricity on autofrettage depth and fatigue behaviour strongly depends on the tube nominal wall thickness.