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Evaluation of weld zone hardness in the HAZ of modern pipeline steels

Conference Paper


Abstract


  • Over the past few years, the pipeline industry has faced a reported increase of pipeline girth weld incidents, predominantly in API grade X70 pipelines. A significant research effort has been invested to understand the root causes of the failures. Although there are many pipeline construction practices that increase strain during construction, there have been two main aspects spotlighted: weld strength matching and HAZ softening. In order to help the sector to predict performance of current steel alloy designs following welding, this research project aimed to establish and clarify weld thermal effects on HAZ hardness of different steels subjected to both real welding and weld thermal simulation. The first stage of the research program was to calibrate the influence of weld cooling rate of both thermal simulations and real welds in steels over a wide range of chemical composition, typical of commercial API pipe. The influence of Pcm, carbon content, microalloying addition and heat input in terms of minimum and maximum hardness were compiled. The comparison between simulated HAZ’s and real welds showed that the thermal simulation produces samples that adequately duplicate the real condition in terms of maximum and minimum hardness and can be used to assess the hardening & softening tendency. Unfortunately, the width of the specific HAZs may be enlarged because a larger volume of metal subjected to the overall thermal cycle and therefore cannot be used to assessing strain performance or strength capacity during tensile loading tests. Three regions with distinguish hardness were detected: 1) Coarse-grained hardening peak; 2) Softening zone; 3) Subcritical hardening peak. It is concluded that the hardness response in the HAZ is directly related to steel chemical composition but the relative percentage change in hardness is not only affected by the steel composition and welding cooling rate, but also the input steel hardness as defined by steel processing

Publication Date


  • 2021

Citation


  • Portella Garcia, M., & Barbaro, F. (2021, March 2). Evaluation of weld zone hardness in the HAZ of modern pipeline steels. In https://www.prci.org/NewsEvents/MeetingsEvents/REX2021.aspx.

Web Of Science Accession Number


Abstract


  • Over the past few years, the pipeline industry has faced a reported increase of pipeline girth weld incidents, predominantly in API grade X70 pipelines. A significant research effort has been invested to understand the root causes of the failures. Although there are many pipeline construction practices that increase strain during construction, there have been two main aspects spotlighted: weld strength matching and HAZ softening. In order to help the sector to predict performance of current steel alloy designs following welding, this research project aimed to establish and clarify weld thermal effects on HAZ hardness of different steels subjected to both real welding and weld thermal simulation. The first stage of the research program was to calibrate the influence of weld cooling rate of both thermal simulations and real welds in steels over a wide range of chemical composition, typical of commercial API pipe. The influence of Pcm, carbon content, microalloying addition and heat input in terms of minimum and maximum hardness were compiled. The comparison between simulated HAZ’s and real welds showed that the thermal simulation produces samples that adequately duplicate the real condition in terms of maximum and minimum hardness and can be used to assess the hardening & softening tendency. Unfortunately, the width of the specific HAZs may be enlarged because a larger volume of metal subjected to the overall thermal cycle and therefore cannot be used to assessing strain performance or strength capacity during tensile loading tests. Three regions with distinguish hardness were detected: 1) Coarse-grained hardening peak; 2) Softening zone; 3) Subcritical hardening peak. It is concluded that the hardness response in the HAZ is directly related to steel chemical composition but the relative percentage change in hardness is not only affected by the steel composition and welding cooling rate, but also the input steel hardness as defined by steel processing

Publication Date


  • 2021

Citation


  • Portella Garcia, M., & Barbaro, F. (2021, March 2). Evaluation of weld zone hardness in the HAZ of modern pipeline steels. In https://www.prci.org/NewsEvents/MeetingsEvents/REX2021.aspx.

Web Of Science Accession Number