51314-3893-Hydrogen Induced Cracking (HIC) Assessment of Low Alloy Steel Linepipe for Sour Service Applications

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Product Number: 51314-3893-SG

ISBN: 3893 2014 CP

Author: Christoph Bosch

Publication Date: 2014

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The European Pipeline Research Group (EPRG) has initiated a project to compare Full Scale Hydrogen Induced Cracking (HIC) test results (1-sided exposure) with laboratory HIC test results (6-sided exposure) of the same materials with a view to generating acceptance criteria for sweet service steels that could be applied to milder sour conditions.The Full Scale HIC test utilized in this EPRG program is characterized by testing a full circumferential section of pipe by filling with a H2S containing test solution and periodic ultrasonic monitoring for HIC crack initiation and growth over the period of exposure. In addition the hydrogen permeation through the pipe is monitored over the test period to determine when steady-state is achieved.Full Scale HIC tests have been performed on two recently manufactured pipes intended for sweet service; an X65 SAWL pipe with 20" (508 mm) OD and 25.4 mm wall thickness and on an X65 ERW pipe with 24" (609.6 mm) OD and 12.7 mm wall thickness. The experiments covered the range of H2S partial pressures from 0.1 bar to 1 bar and pH values of 3.5 and 4.5. As a reference a Full Scale HIC test in NACE TM0284 solution A at 1 bar H2S was also performed on both pipe materials to confirm that the selected sweet service steels were susceptible to HIC under severe sour service conditions.For both pipe materials the comparison of Full Scale and laboratory HIC tests revealed severe HIC cracking under NACE standard test conditions after exposure in NACE TM0284 solution A at 1 bar H2S in both Full Scale tests after 30 to 40 days and laboratory tests after 96 hours. Full Scale testing of both materials at 0.1 bar H2S partial pressure at pH 3.5 up to 9 months revealed little to no cracking whereas the related laboratory tests performed for 14 days showed some propensity to HIC with a CLR up to 41 %. These findings are backed up by further comparative Full Scale and laboratory HIC tests on the two pipe materials.The results are discussed with regard to the “no cracking” HIC criterion given in NACE MR0175/ISO 15156-2 for application specific conditions.