Laboratory Testing Of Corrosion Resistant Alloys In Deep Geothermal Well Environment

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Product Number: 51321-16693-SG

Author: Bente Cecilie Krogh; Bård Nyhus; Hans Husby

Publication Date: 2021

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Harsh geothermal fluid demands corrosion resistant alloys (CRA's) instead of traditional carbon steel
as production casing in a geothermal well. Differenct CRA's were exposed in a batch autoclave of nickelbased
alloy N10276. The different samples and purposes were coupons for weight loss measurements,
rod samples for interphase reaction examinations and C-rings for environmentally assisted cracking
(EAC). The C-rings simulated the thermal stresses introduced in the casing under thermal contractions
that appear when the well is under cooling or during irregularity operation. Going from supercritical
conditions into the two-phase region with HCl present, the aqueous phase can become very acidic. After
some experience with pure deionized water as fluid, testing of samples in a fluid with low pH are
described. The tests were performed at 350 °C, at saturated pressure 165 bars for 300 hours. Corrosion
damage of several austenitic alloys including nickel-based alloys N10276 and N06625 in addition to
titanium alloys are reported. The samples were visually evaluated, and microstructures and corrosion
products were further studied using light microscope, SEM/EDS and XRD. There were low weight loss
corrosion rates, but all austenitic alloys showed intergranular corrosion and/or stress corrosion cracking
(SCC), while titanium alloys appeared more resistant to EAC.