Root cause analysis of the corrosion-related coiled tubing failure

Sanja Martinez,Fuad Khoshnaw,Sally Elkatatny,Talal Aljohani,Sara Fahmi,Vuokko Heino

doi:10.5599/jese.1280

Abstract

Coiled tubing (CT) is widely used in the oil and gas industry. However, corrosion-related failures are frequently reported. Research into the causes of failures leads to improvement in the design of components and processes. In this study, a new CT sample and a CT sample with perforated wall that had failed after a few acidizing operations were selected for analysis. Scanning electron microscope (SEM) images at the fracture site showed that CT damage was caused by the low cycle fatigue. In addition, light and scanning electron microscopy (SEM) showed that a corrosion pit acted as the initiator of the crack. Elemental analysis using energy dispersive X-ray spectroscopy (EDS) indicated the presence of an iron oxide layer and a layer associated with the Sb containing inhibitor. The corrosion damage investigation showed that the internal CT wall pits likely formed during storage due to the acidizing operations in the areas where the remaining liquid was still at the tube bottom.

Highlights

Coiled tubing technology (CT) is widely used in well operations [1,2]
Statistical analysis of the CT failure causes was conducted [7] showing that mechanical damage, corrosion, manufacturing flaws, and human error were the main diagnoses for CT failures from 1994 to 2005
Materials and methods The current study examined the new and the failed CT samples

Summary

Introduction

Coiled tubing technology (CT) is widely used in well operations [1,2]. CT application can be divided into two general categories, fluid pumping and mechanical applications. Statistical analysis of the CT failure causes was conducted [7] showing that mechanical damage, corrosion, manufacturing flaws, and human error were the main diagnoses for CT failures from 1994 to 2005. These four major causes represented 80 to 90 % of the failures from 2006 to 2017. The combination of mechanical and corrosive actions during operations eventually leads to the development of fatigue cracks. Unpredictable CT service life is a serious economical and safety issue for the industry It results from the inadequate in-service inhibition and lacking tubing maintenance programs that do not include storage corrosion prevention. Maximizing CT service life requires effective corrosion control on both sides of the CT wall, during storage and in service

Materials and methods

Results and discussion

Conclusions