No abstract

In this study, the effect of sigma phase precipitation in duplex stainless steel (grade 2205) pipe fittings collected from top-side process systems offshore was investigated under realistic loading conditions. This was done by conducting quasi-static and dynamic impact tests on 3" fittings with nominal outside diameter of 88.9 mm, nominal wall thickness of 3.05 mm and D/t-ratio of nearly 30. The fittings had a sigma phase level between 0 and 15 vol.%, and were loaded by a massive steel indenter with a hemispherical nose of 25 mm radius. In the quasi-static tests, the loading rate was 2 mm/min, while in the dynamic tests the impact velocity was varied between 5 and 10 m/s.A few dynamic impact tests on 2" fittings with an increased wall thickness and low sigma phase levels were carried out for comparison, while some 3" fittings were pre-charged with hydrogen before dynamic testing to examine the effect of sigma phase on cathodic protected subsea components. When the sigma phase level was low (i.e., 5 vol.%   ), no evidence of fracture was found in any of the pipe fittings, whereas at higher sigma phase levels