Corrosion Performance of Some Metals and Alloys in Liquid Ammonia⁽¹⁾ Available to Purchase

General weight loss corrosion measurements have been conducted on a variety of metals and their alloys that have been used, or have potential use, in liquid ammonia including carbon and low alloy steels, stainless steels, aluminum alloys, Monel, titanium, zinc, and high nickel stainless alloys. Coupons were exposed for periods of 1 and 8 months in an autoclave filled with liquid ammonia at room temperature. Very low weight losses, and often weight gains, were experienced. It is concluded that most metals and their alloys are essentially inert in liquid ammonia with respect to general corrosion. A reference electrode has been developed to measure the electrochemical potential of alloy surfaces in liquid ammonia at room temperature and elevated pressure [125 psi (8.75 kg/cm²)]. The electrode consists of a pure cadmium rod in contact with a saturated solution of CdCl₂ in liquid ammonia. The electrode is stable, rugged, and reusable. It has been used to establish a galvanic series in liquid ammonia to aid in engineering decisions regarding alloy suitability for various applications. The results are similar to the galvanic series for the same metals and their alloys in sea water. The stainless steels and nickel base alloys are noble to carbon steels, whereas zinc and aluminum are active (anodic) with respect to carbon steel. Significantly, these tests showed that aluminum, when coupled to steel, acts as a sacrificial anode and cathodicaliy protects the steel against stress corrosion cracking (SCC) in air contaminated ammonia.