Simulation of damage under cyclic loading for API 5L X70 steel pipelines (fatigue test)

Abstract

The most efficient way to move large volumes of gas and oil is through pipelines, either from points of production to storage locations or from storage locations to distributed points of end use. One of the main materials of gas transportation pipes is X70 material. Base on the importance of in-service API 5L X70 pipelines, it is important for the safe operation of this system to know the lifespan of pipelines, and predict fatigue crack growth (FCG) of API 5L X70 steel pipeline. The objective of this theme is to study the lifespan of pipelines used for the transport of natural gas, oil and water, manufactured by the company ALFAPIPE in the wilaya of Ghardaïa. The judicious choice for manufacturing metal is a crucial factor to ensure prolonged life duration and improve resistance to fatigue, as materials respond to loading with elastic or plastic deformation. Stresses applied to materials can result in permanent deformation, rupture, cracking or progressive degradation. Understanding the effects of applied stresses is essential for the selection and implementation of materials in industrial applications. Fatigue tests were carried out on API 5L X70 steel using simulations using ANSYS software. The life of different samples was determined for different thicknesses after applying repeated stresses. The obtained results demonstrate the material API 5L X70's sensitivity to fatigue and emphasize the significance of designing pipelines with sufficient safety margins to prevent premature failures caused by fatigue.