Abstract
The API 5L X70 steel is used in high-pressure gas transmission pipelines. Because of this, knowledge of presence of residual stress and their magnitude is important to assess the material integrity in service. For the pipeline manufacturing, tubes need to be curved which is often made using the hot induction bending process. This process can introduce different residual stress depending of tube position. For this research, in order to evaluate the residual stress, was used an API 5L X70 tube that was previously curved by hot induction process. Samples were taken from the extrados, intrados, neutral line and straight section of the curved tube. Residual stresses were studied by two conventional methods: X-Ray Diffraction (XRD) and Hole-Drilling, which are destructive and non-destructive methods, respectively, in order to assess their qualitative responses. Each of these methods presents particular methodologies in sample preparation and material analysis, but also they differ in factors such time consumption and cost of the analysis. The qualitative responses obtained by the two different methods were comparable and satisfactory and pointed out the existence of a compressive residual stress state in steel pipe.
Highlights
High-strength low-alloy (HSLA) steels are widely found in the oil industry due to their high mechanical strength and toughness
The material surface should be in compression and its interior in tension as reported by Barker and Sutton[4]
The residual stress results obtained by the X-ray diffraction method and hole-drilling (Table 2) whose experimental errors were between 2.9 and 3.4%, and 5.3 and 11.9%, respectively, show the presence of a compressive stress state in all samples
Summary
High-strength low-alloy (HSLA) steels are widely found in the oil industry due to their high mechanical strength and toughness. The material goes through several deformations, welds and phase transformations that can lead to residual stresses. Residual stresses are those that remain in the material even when all external forces are withdrawn. For the pipeline construction is necessary bending the tube in order to follow the project instructions. They are often curved via the hot induction bending process. This is one thermomechanical process because it inputs simultaneously, in a narrow ring of the tube, the induction heating and its mechanical bending. Since the technique of hole-drilling is destructive and expensive, this work aims to compare it to the X-ray diffraction technique, which is non-destructive and simpler to use
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
