FRACTURE MECHANICS APPROACH FOR THE MAINTENANCE OF OFFSHORE OIL AND GAS PIPELINE. A RESEARCH PROJECT TOPIC ON SCIENCE AND ENGINEERING
ABSTRACT
Failure of offshore oil and gas pipelines occurs under certain conditions due to some applied mechanical forces. These conditions constitute a potential threat to the integrity of in-service life span of the pipelines which can lead to loss of resources and environmental pollution. Several studies have shown that pipelines fail as a result of Welding, Fatigue Crack Growth, Corrosion Fatigue, Stress Corrosion Cracking, and Erosion due to fluid flow.
This paper presents a model by using fracture mechanics to analyze the allowable applied stresses an in service pipeline needs to withstand in minimizing crack growth. Furthermore, the crack size, crack shape and hole radius with pipe thickness will be modeled. The modeling results will be validated using experimental data. The implications of the results will be discussed for the design or development of a robust oil and gas pipelines.
CHAPTER ONE: Background and Introduction
1.1: Research Background
Oil and Gas Pipelines are used as a medium through which petroleum products are transported from the wells to the tanks. When it is under operation, it fails rarely; meanwhile, it causes extremely serious problems like loss of resources and lives if failure does occur. Over half of all in-service pipelines fail as a result of some externally applied mechanical forces which must be properly analyzed to prevent reoccurrence. Fractographic examination is to determine the causes of failures by studying the characteristics of a fracture surface.
Griffith proposed that cracks that already exist will propagate when the released elastic Strain Energy is at least equal to the energy that is required to create the new crack surface. Life prediction for Fatigue Crack by Paris has showed that range of Stress Intensity Factor, k, might characterize Sub-Critical Crack Growth under fatigue loading. He examined that Crack Growth Rate of Stress Intensity Factor gave straight line.
Also, Rice’s J-integral is a commonly used Elastic Plastic Fracture parameter for the description of the local field in the neighborhood of the Stress Concentration and for the study of crack initiation and propagation. His theory is also interpreted as the potential difference in energy between two specimens that are loaded identically having slightly different crack length. Meanwhile, Irwin proposed the Stress Intensity Factor as crack primary driving force.
