Axial stress calculation of epoxy steel sleeve repaired pipelines under axial forces

Abstract

[Objective] This paper aims to present clarified axial stress solution formulas for epoxy steel sleeve repaired and reinforced pipelines subjected to axial forces. [Methods] A mechanical model was first established to express simplified stress characteristics of pipelines repaired with epoxy steel sleeves under axial forces. Based on this model, theoretical solution formulas were derived for determining axial stresses on the pipe and sleeve layers under axial forces, through utilizing the stress solution method and considering deformation coordination.To verify the proposed axial stress formulas, ANSYS software was employed to establish sleeve repaired pipeline models, both with and without a flange, for numerical simulations. The calculations were performed for pipelines with diameters of 219 mm, 660 mm, and 1 219 mm,respectively. A comparison between the theoretical solutions for axial stress and the numerical solutions was made to verify the proposed formulas. Additionally, the proposed calculation formulas were further verified by comparison with examples found in the available literature.[Results] The study results demonstrated the validity of the mechanically simplified models and their conservative nature in the obtained outcomes. When subject to axial forces, the discrepancies between the theoretical and numerical solutions for axial stress on the inner and outer walls of the pipe layer and sleeve layer, using both the sleeve repair models with and without a flange, remained within 5%. Similarly, in the three diameter scenarios, the differences between the theoretical and numerical solutions for axial stress did not exceed 5%. Furthermore,with an axial force of 1 500 kN, the errors between the theoretical axial stress bearing capacity proportions and the measured values from full-scale tensile experiments on epoxy steel sleeve repaired steel pipelines were all below 5%. [Conclusion] Through the comparison of the theoretical solutions with the numerical solutions and measured values, the rationality and applicability of the theoretical formulas for axial stress have been verified. These formulas can be used for safe integral structural checks. The research findings provide a reference for the design and evaluation of epoxy steel sleeve repaired and reinforced pipelines subjected to axial forces.

Keywords

• epoxy steel sleeve
• pipeline repair
• stress analysis
• girth weld defect
• axial bearing capacity