Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

Thiago Rodrigues Carbos,Jorge Carlos Ferreira Jorge,Matheus Campolina Mendes,Luís Felipe Guimarães De Souza,Ivani De Souza Bott

doi:10.1590/1980-5373-mr-2020-0363

Abstract

API 5L X80 steels are widely used in welded pipes in the petroleum industry. However, microstructural changes in the heat affected zone are a concern when welding such pipes due to the potential formation of regions with low toughness. Despite all the research concerning mechanical properties of welded joints, the acceptance criteria for the qualification of welding procedures are still limited. Welded joints do not always guarantee the safe operation of industrial equipment, because the current Standards adopted are not able to evaluate the properties at some critical regions of the welded joint. This work studied the characteristics of a girth welded joint and showed evidences of low toughness at 0.5 mm from the fusion line due to the micro-phases necklacing the prior austenite grain boundaries. As this feature is not considered by the current Standards for approval of welding procedures, this work proposes an alternative approach to improve the safety of welded structures.

Highlights

Population growth and industrial development in any country gives rise to a greater demand for petroleum products[1]
The American Petroleum Institute (API) 5L3 specification describes the requirements for the chemical composition, tensile test characteristics and impact toughness behavior of these pipes
The tension tests show an ultimate tensile strength superior to the minimum required for API X80 steel[3] and the facture occurring at the base metal (Figure 4)

Summary

Introduction

Population growth and industrial development in any country gives rise to a greater demand for petroleum products[1]. The API 5L3 specification describes the requirements for the chemical composition, tensile test characteristics and impact toughness behavior of these pipes. These requirements vary depending on the particular application and operating conditions. CE helps to estimate the combined effect of all the important alloying elements on the microstructure that occurs when welding steel. This is because this change in the microstructure of the steel is what defines its properties and behavior after the welding[1]. CEIIW is used for carbon contents greater than 0.12% and CEPcm for carbon contents less than 0.12%3

Methods

Results

Conclusion