Pitting corrosion resistance by critical pitting temperature (CPT) has been determined per ASTM G150 on the full-size control line & chemical line specimens of UNS N08029 and UNS N08825 in 1M NaCl solution. With outer- and inner tube surfaces in existing delivery conditions, the full-size tube sections of UNS N08029 showed similar CPT obtained from specimen coupons of cold worked UNS N08029 OCTG material. The CPT was 70°C for UNS N08029 and 30°C ~ 45°C for UNS N08825, which was mainly dependent on pitting resistant equivalent (PRE) of the materials.

Effect of chloride concentration and pH on the CPT has also been studied however no significant effects have been observed for UNS N08029 and UNS N08825 in the tested conditions. UNS N08029 of high PRE, showed higher CPT compared to UNS N08825 in 3~15 wt% chloride concentrations.

UNS N08029 and UNS N08825 belong to the same categories 4a and 4c type nickel-based alloys defined by ISO15156-3 for down-hole applications. Good resistance to stress corrosion cracking (SCC) has been found in literature for the OCTG grade of these alloys. Of similar Ni+2Mo+0.5Cr content and high CPT in chloride solutions observed in this study, UNS N08029 would be recommended as a cost-efficient material for control line and chemical injection line applications when the SCC resistance is confirmed for the annealed tube product.

Subject
External surfaces, Test methods, Tubular goods, Materials, Nickel based alloys, Tubes, Sodium chloride solution, Internal surfaces, Pitting, Corrosion resistance, Chlorides, Stress corrosion cracking, Chloride stress corrosion cracking
Keywords:
austenitic stainless steel, nickel-based alloy, critical pitting temperature (CPT), Pitting resistance equivalent (PRE) number, corrosion resistant alloy (CRA), annealed condition, cold worked condition
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2019
Association for Materials Protection and Performance (AMPP)
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