Stress problems in cylinder openings
Thread Content
I saw in the book that having oblong holes in the cylinder, with the long axis perpendicular to the cylinder’s axis, results in the best stress distribution. But I’ve looked at a lot of information and still don’t know how this conclusion was reached. Does that friend know how it was calculated? Could you give a detailed explanation? Thank you very much. The stress concentration should be greatest at the ends of the long axis
To address this issue, we need to analyze the forces acting on the equipment. But first, I still need to say that what the original poster mentioned – namely, that it is advantageous for the long axis of the oblong hole to be oriented perpendicular to the axis of force – also comes with certain limitations. From a stress perspective, the longitudinal stress on the equipment is twice that of the circumferential stress; this is why, in pressure vessels, the weld coefficient used is typically the one for longitudinal welds. In the situation described by the original poster, the length of the long axis is less than twice the length of the short axis – if it were more than twice, then the stress conditions would be different! This is why, when the openings in a device are not radial, it is necessary to consider the ratio of the long axis to the short axis of those openings in order to determine whether it is the long axis or the short axis that plays a dominant role. It will be easier to understand this concept by looking at stress analysis!
Since the calculated thickness of a cylinder is based on the circumferential membrane stress, the cross-sectional area of an opening is also considered as the section that bears this circumferential membrane stress, that is, the longitudinal section parallel to the cylinder’s axis. Therefore, the short axis of an oblong hole must be parallel to the axis, which means the long axis is perpendicular to the cylinder’s axis; in this case, the stress concentration factor is relatively low. By the same logic, the long axis of the oblong hole in the skirt should be parallel to the axis; since the skirt is under compressive stress, the cross-sectional area of the opening should be taken as the circumferential section, which means that the short axis lies in the circumferential direction.
The previous speakers have explained it very clearly; the key is to understand it oneself. Here is the reference book, the comprehensive guide to chemical equipment, \"High-Pressure Vessels\", page 20