Fatigue Crack Monitoring of T-Type Joints in Steel Offshore Oil and Gas Jacket Platform.

Liaqat Ali,Salem Bashmal,Naveed Iqbal,Weishun Dai,Yong Bai,Sikandar Khan

doi:10.3390/s21093294

Abstract

Several approaches have been used in the past to predict fatigue crack growth rates in T-joints of the offshore structures, but there are relatively few cases of applying structural health monitoring during the non-destructive testing of jacket platforms. This paper presents an experimental method based on the sensing of the piezoelectric sensors and finite element analysis method for studying the fatigue cracks in the offshore steel jacket structure. Three types of joints are selected in the current research work: T-type plate, T-type tube-plate, and T-type tube joints. The finite element analysis model established in the current study computes and analyzes the high stress and high strain regions in the T-type joints. The fatigue damage in the T-type joints was successfully detected by utilizing both the finite element analysis and experimental methods. The results showed that fatigue cracks of the three types of joints are prone to appear at the weld toe and spread in the welding direction. The fatigue damage location of T-type plate and T-type tube-plate joints is more concentrated in the upper weld toe area, and the fatigue damage location of the T-type tube joint is closer to the lower weld toe area.

Highlights

To monitor the fatigue damage of structural joints, this paper studies the fatigue analysis method and fatigue crack development rules of typical joints of platforms through fatigue test and finite element analysis
Fatigue cracks were found in the lower weld toe and its vicinity in four specimens, and cracks were found in the upper weld toe area in three specimens
While most of the studies in the literature are focused on one or two types of joints, the current study is focused on the main three kinds of joints that are found in the jacket platforms, i.e., T-type plate joint, T-type tube-plate joint, and T-type tube joint

Summary

Introduction

In the last few decades, a number of jacket structures were built to mine subsea resources and many of them have already been operated for over 20 years. Technical assessments, such as environmental condition analysis and corrosion or fatigue analysis, are needed to continuously check the condition of these jacket structures. In 2016, more than 2000 metric tons of oil and gas leaked from these offshore facilities. The steel jackets structure has been extensively used in the offshore oil and gas facilities for the past two decades [7] in (Bohai Bay) China, Gulf of Mexico, and Brazil

Results

Discussion

Conclusion