Susceptibility to hydrogen embrittlement for C72900 exposed to H_2S environment and under cathodic polarization in simulated seawater

摘要

C72900 is a copper alloy containing 15% Ni and 7% Sn that combines high strength with anti-galling properties, it is non-magnetic, is easy to machine and has acceptable corrosion resistance in selected environments. The alloy has been used in bushings and bearings for aircraft, industrial equipment and heavy equipment. It is also used for oil and gas environments. In the open literature limited information about corrosion properties and resistance against hydrogen embrittlement (HE) have been published. However, material suppliers have published test results concluding that i) corrosion rate in seawater < 20 μm/year, ii) the material is not exposed to HE under cathodic protection in seawater, iii) the material is approved according to NACE MR0175 for use at NACE Levels I, IV and V with uniform corrosion rate below 100 μm/year. This paper presents results from testing of resistance against HE for Toughmet 3 AT110 alloy. The material has been tested against; i) sulfide stress cracking (SSC) according to ISO 15156-3 Level V by use of the four point bend (4PB) method, and ii) cathodic polarization in simulated seawater with specimens under tensile load. The outcome from the test program can be summarized as; 1. The results from SSC testing according to ISO 15156 Level V contradict the information given in the suppler information. 1.1 Severe transgranular cracks observed 1.2 Severe uniform - in the order of 1.2 mm/year - and pitting corrosion observed 2. The alloy did not suffer from hydrogen stress cracking (HSC) during tensile load above yield stress and cathodic polarization in seawater.