Study on Collapse Characteristics and CSRF Method for 45 Deg Cylinder-to-Cylinder Intersections

Abstract

It is known that the collapse strength of complex three dimensional structures is hard to evaluate accurately with elastic analysis, and more accurate results require the use of inelastic analysis. A cylinder-to-cylinder acute lateral intersection is one of basic structures of process plants. It is known that a high stress concentration occurs at an acute lateral more than 90 deg-lateral. In general, the area replacement method and the elastic analysis are applied for the design of acute lateral. However, these results may provide overly-conservative designs. In the previous work, the authors proposed CSRF (Collapse Strength Reduction Factor) method. The CSRF was defined as a ratio of the simple cylinder collapse pressure to the cylinder-to-cylinder collapse pressure. The proposed CSRF method provided more reasonable design than the elastic analysis. In this paper, the concept of the CSRF was redefined by using the maximum allowable working pressure. The CSRF were evaluated on the 45 deg and 90 deg-laterals based on the area replacement method, the elastic analysis, the limit load analysis and the elastic plastic analysis to study the collapse characteristics of 45 deg-laterals. The 45 deg-laterals are weaker than 90 deg-laterals, and inelastic analysis provides greater strength of 45 deg-laterals than elastic analysis. The results of elastic plastic analysis showed that overly-large plastic strain occurs on 45 deg-laterals. This plastic strain should be evaluated in addition to the collapse pressure.