51314-4061-Cracking Resistance of Alloy 904 L in Brine under Highly Sour Conditions

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Product Number: 51314-4061-SG

ISBN: 4061 2014 CP

Author: Gerit Siegmund

Publication Date: 2014

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The applicability of alloy UNS N08904 (alloy 904 L 1.4539) in chloride containing sour environments is presently discussed controversially. According to ISO 15156 Part 3 this material shall be used in chloride-containing media only under H2S partial pressures up to 1 bar. However this material has been used in many highly sour oil and gas environments without any reported failure. The ongoing discussions about the application limits of austenitic alloys in ISO 15156 part 3 prompted new experimental work to evaluate the cracking and pitting susceptibility of this material in highly sour brines at room temperature and elevated temperature. Round tensile specimens were subjected in triplicate for each set of conditions under 90% of the actual yield stress for 720 h fully submerged in brine with 180 g/L chloride in equilibrium with a gas phase containing up to 25 bar H2S. None of the tensile bars showed any indication of cracking or pitting and the integral corrosion rates ranged between 1 and 7 µm/y depending on the system’s corrosion severity. The results indicate that the tested type of material is very resistant against cracking in presence of high H2S and chloride concentrations even under the influence of galvanic coupling.