Improving the Surface Properties of an API 5L Grade B Pipeline Steel by Applying the Boriding Process—Part II: On the Changes in the Mechanical Properties

Abstract

The mechanical performance of API 5L grade B steel, after undergoing a thermochemical boriding process, was assessed. We quantified the boride layer microhardness over cross-section specimens, with the aim of characterizing the mechanical resistance under different conditions. The pipeline steel was analyzed because of the changes in yield strength, ultimate tensile strength, and ductility after treatment with boron. These oil and gas pipelines must work in aggressive environments, so borided pipeline steel specimens were tested to assess their erosion–corrosion resistance. Another important characteristic to evaluate was the wearing resistance, because the pipelines tend to suffer scratches when they are under construction. We also present a discussion of the results of the total research work (Part I and Part II), including the results of the boride layer characterization as well as the changes in the substrate, with the goal of selecting the best conditions under which to treat pipeline steel. More extreme treatment conditions can help to form more stable and resistant boride layers, but they can considerably modify some mechanical characteristics of the API 5L grade B steel. For this reason, the boriding treatment conditions must be chosen in a synergistic way.