Burner-Rig Hot Corrosion Evaluation Of High-Temperature Alloys

ABSTRACT Hot corrosion found in a gas turbine engine environment is typically simulated using either a burner-rig or two-zone Dean-rig set up. In this paper, hot corrosion behavior of various wrought alloys was studied by the burner-rig test method, while examining in detail the effects of exposure duration (200h and 1000h) and variations in salt concentration (5 ppm and 50 ppm). It was found that the burner-rig testing is extremely sensitive to exposure duration and the salt concentration, specifically for the alloys that are susceptible to catastrophic hot corrosion. In the most aggressive 1000h burner-rig tests containing 50 ppm salt concentration, R30188, N06230, and N06617 alloys were resistant to hot corrosion, whereas N07214, N06625, N06002, N06635, R30605, R50556, R30155, N08810, N06601, S31000, and R80330 alloys were susceptible to catastrophic hot corrosion. An attempt was made to compare burner-rig and two-zone Dean-rig hot corrosion tests by studying selected alloys. A comparative hot corrosion evaluation from the two test methods revealed a discernable difference between the magnitudes of corrosion attack; however, the nature of hot corrosion attack and the alloy rankings were found to be quite similar. INTRODUCTION Alkali-sulfate induced hot corrosion (HC) is an accelerated degradation process induced by the presence of a thin layer of molten oxidant on the surface of alloys in high temperature environments, such as gas turbine engines. Hot corrosion along with oxidation is limiting factor for marine, land-base, and aero gas turbines. The molten alkali-sulfate base oxidant that causes hot corrosion in gas turbines is principally sodium sulfate (Na₂SO₄ – T_melt = 884oC ) and in some cases even lower melting temperature eutectics of sodium-magnesium-calcium based sulfates (T_melt = 650°C) [1-4]. The source of alkali sulfates is sea water which contains ~3900 ppm of Na₂SO₄ directly, and ~ 30,000 ppm of NaCl which reacts with sulfur in the fuel to produce additional Na₂SO₄ [5].