The Alloy UNS(1) N07718 is among the most used alloys in the oil and gas industry. Due to the presence of the alloying elements niobium, aluminum and titanium, this alloy is precipitation hardenable by the formation of the phases Gamma’ and Gamma’’. Although presenting excellent strength properties and good resistance in sour gas applications, this material is known to be susceptible to hydrogen embrittlement and most field failures are related to this limiting property.
The use of Alloy 718 (UNS N07718) for oil & gas applications is regulated by the API(2) 6ACRA1 standard and it is available in three different grades, the 120K, with minimum 120 ksi yield strength, the 140K, with minimum 140 ksi yield strength, and the 150K, with minimum 150 ksi yield strength. Previous studies showed that, due to the different hardening heat treatment parameters, each of the available grades presents a different precipitation behavior in terms of distribution and amount of precipitates, and the obtained microstructure is directly related to the resistance of the material to hydrogen embrittlement.