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Additively Manufactured Alloy UNS N07718 (AM 718) has been increasingly adopted for components in oilfield applications. AM 718 fabricated using laser powder bed fusion (LPBF) has demonstrated not only excellent mechanical performance, but also promising capabilities in critical services such as sour or hydrogen-generating conditions. In oilfield applications, it is generally felt that AM 718 should comply with API standard 20S4, and align with the requirements for wrought 718 in API 6ACRA.
Additively Manufactured (AM) Alloy UNS(1) N07718, specifically using Laser Powder Bed Fusion (LPBF), has been increasingly adopted for components in oilfield applications. However, there is uncertainty of the differences in properties between AM (interchangeable with LPBF herein) 718 and wrought oilfield API 6ACRA 718 material used in sour or hydrogen-generating conditions. Recent literature has shown promising results in mechanical properties and sour performance for AM 718, but certain technology gaps persist. This paper shows results of mechanical and corrosion testing of AM 718 after API 120K solution and age hardening heat treatment. Equivalence to wrought API 6ACRA 718 120K was achieved in mechanical properties and corrosion performance in sulfide stress cracking (SSC) and hydrogen induced stress cracking (HISC) tests.
AM brings significant benefits in better performance, inventory management, and lifecycle cost reduction to the Oil & Gas industry. Both manufacturers and users are working towards AM qualification and standardization in order to realize and sustain these benefits. Starting at the product level, the goal is to ensure the product is sound in its form, fit, and function, and free from macroscopic (surface, sub-surface, internal) anomalies deleterious to its performance. Product qualification is supported by a foundational metallurgical or AM material qualification.1
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Alloy UNS N07718 (hereafter abbreviated as 718) is one of the most versatile precipitation-hardened nickel-based corrosion-resistant alloys (CRAs) used for both surface and sub-sea components in oil and gas production service. API 6ACRA1 provides heat treatment windows and acceptance criteria for 718 in these oil and gas production environments, in which the heat treatment is intended to obtain high strength and to minimize the formation of δ-phase at grain boundaries. As pointed out in NACE MR0175 Part 32 (Table 1), field failures of 718 components in sour service are primarily related to stress corrosion cracking (SCC) at elevated temperatures and hydrogen embrittlement in the lower temperature range. The latter is specifically called galvanically induced hydrogen stress cracking (GHSC or GIHSC), which is typically caused by atomic hydrogen uptake from galvanic corrosion or cathodic protection (CP) when 718 is used with steel components in a seawater environment. CP is normally used to protect steel component from corrosion in subsea environments.
Oil and gas production from highly saline reservoirs can present challenges to the completion materials. The most saline fields often require downhole injection of (low chloride) wash water to dilute the produced water and mitigate the threat of halite precipitation on the production tubulars. The present paper investigates the threats associated with the co-mingled wash water and production fluids with respect to common completion materials.