Evaluation of HIC Resistance in Two X70 Pipeline Steels Using Ultrasonic Testing

• Author / Creator

  Gawor, Steffen

• An evaluation of the resistance of two different X70 pipeline steels to hydrogen-induced cracking in severe (pH 2.7 and 1 atm H2S) and intermediate (pH 5.5 and 1 atm H2S) sour service conditions was undertaken. The two steels used in this work, X70-X and X70-B, were selected based on their different calcium to sulfur ratios. X70-X and X70-B possess calcium to sulfur ratios of 2.5 and about 0.5, respectively.
  Using the NACE standard TM0284-2016 and solution C, samples were tested at pH levels of 2.7 and 5.5 for test periods of 1 to 64 days. Cracking was then evaluated using ultrasonic techniques. At a pH of 2.7, both steels showed cracking after one day in test solution and reached a crack equilibrium after 4 to 8 days. Samples tested at a pH of 5.5 showed cracking after 32 days for steel X70-B and after 64 days for X70-X. For X70-B, a crack equilibrium seemed to be reached after 32 days. In direct comparison with the low calcium to sulfur ratio in X70-B, X70-X showed an increased resistance to hydrogen-induced cracking.
  In this work, an ultrasonic procedure, using the crack to backwall signal ratio (CBR), was developed and is used to quantify the extent of cracking in X70-X and X70-B. CBR maps and histograms give information about the location, extent and distribution of cracks. To compare different steels and conditions, a global crack to backwall ratio (GCBR) is obtained by the numerical calculation of the normalized integral of the local CBR values. The GCBR for X70-X after 16 days in a pH 2.7 solution is about 0.3. For X70-B, under identical solutions, a worse GCBR of about 0.55 was recorded. X70-X generally shows a better resistance to hydrogen-induced cracking than X70-B in test solutions of pH 2.7 and 5.5 and for 1 atmospheric pressure of hydrogen sulfide.

• Subjects / Keywords

  • HIC
  • NACE TM0284-2016
  • X70
  • Ultrasonic
  • Hydrogen-Induced Cracking
  • Corrosion
  • Crack Evaluation

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-hywa-sh11

• License

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