Analytical Approaches to Subsea Pipeline Stress Analysis: Energy Methods as an Alternative to Numerical Methods

The process of subsea pipeline stress analysis is inherently complex, often necessitating the use of finite element method (FEM) software, particularly in "large displacement" conditions. However, for scenarios in which the deflection angle remains below 10 degrees, this study explores fundamental analytical methods as an alternative to FEM. Through the application of energy methods, the research addresses the frequently encountered scenario of single-point lifting above the seabed. Upon determining the pipeline's profile, tension, and bending moments, subsequent analysis employs the mechanics of materials to compute bending, tensile, and equivalent stresses. The equivalent stress is then evaluated and compared to the allowable material yield strength, enabling engineers to make design decisions aligned with established codes and standards. This work integrates case studies to validate the proposed methods by comparing their outcomes with results obtained from commercial FEM software. Additionally, the study introduces a prototype software tool designed to deliver instantaneous results upon input modification. Unlike FEM, the proposed program's underlying equations demand significantly less computational effort, offering an efficient alternative for commercial software. The accuracy of the proposed method is demonstrated to be approximately 99%, which is highly safe, especially when the total stress remains way below allowable stress. However, accuracy diminishes notably when the rotation angle exceeds 10 degrees and becomes critically unreliable at angles greater than 15 degrees, necessitating caution in such cases. In conclusion, this study underscores the viability of basic analytical methods for pipeline stress analysis, providing a practical and cost-effective alternative to FEM when the pipeline rotation angle is low. By advocating for context-appropriate methodologies, the research aims to enhance the selection of analytical tools, fostering efficiency without compromising accuracy in engineering design.