David A. Shifler

The effects of water on the passive behavior of 1018 carbon steel in organic solutions

The passivation and breakdown behavior of 1018 carbon steel in propylene carbonate (PC) or dimethoxyethane (DME) mixtures with water and containing 0.5M LiAsF[sub 6] were studied. The behavior of the steel in the organic solvent/water mixtures was highly dependent on the organic solvent. The anodic polarization of carbon steel displayed active-passive behavior in 10--90 mole percent (m/o) PC/H[sub 2]O mixtures and a tenuous degree of stability within the passive range. The anodic polarization of carbon steel displayed no active-passive behavior in 50--90 m/o DME/H[sub 2]O mixtures and displayed active-passive behavior in 10--30 m/o DME/H[sub 2]O mixtures. The steel was stable within the passive range of these DME/H[sub 2]O solutions. The breakdown potential of the steel in DME/H[sub 2]O mixtures is more electropositive than the oxidation potential of the DME solvent at all molar ratios.

The effects of sulfides on the passivity of carbon steel in organic solutions

Abstract Corrosion is known to initiate at sulfide inclusion in aqueous solutions. The effects of sulfides on the passivity and the breakdown of passivity of 99.999% iron and 1018 carbon steel was investigated in two aprotic nonaqueous solvents: 1. (1) propylene carbonate (PC) with LiClO4 or LiAsF6 as supporting electrolytes and 2. (2) dimethoxyethane (DME) with LiAsF6 electrolyte. Carbon steel was also examined in PC-DME/LiAsF6 mixtures. Sulfides do not appear to interfere with passivation when it is provided by solvent adsorption in either nonaqueous solvent. Sulfides may lower the solvent oxidation potential and decrease the anodic potential at which breakdown initially occurs in either pure solvent. Sulfides also influence the kinetics of repassivation above the solvent oxidation potential of either solvent when passivation is provided by salt film formation or electropolymerization. The bleeding of sulfur or sulfide from inclusion sites where electro-polymerization has occurred in PC/DME mixtures undermines attempts at passivation and promotes instability leading to anodic current increases with time and further corrosion of carbon steel.

Performance Evaluation of High Temperature Coatings for Hot Section Turbine Components

501-K34 marine gas turbine engines serve as auxiliary power sources for the U.S. Navy’s DDG-51 Class ships. It is desired that 501-K34 marine gas turbine engines have a mean time between removal of 20K hours. While some engines have approached this goal, others have fallen significantly short. A primary reason for this shortfall is hot corrosion (Type I and Type II) damage in the hot section turbine area due to both intrusion of salts from the marine air and from sulfur in the gas turbine combustion fuels. Previous metallographic examination of several unfailed blades removed from a marine gas turbine engine after 18000 operating hours showed that the coating thickness under the platform and in the curved area of transition between the platform to the blade stem was either very thin, porous, and in a few cases, non-existent on each unfailed blade. Type II hot corrosion was evident at these locations under the platform. Corrosion fatigue cracks initiated at several hot corrosion sites and had advanced through the blade stems to varying degrees. Cracking in a few blades had advanced to the point that blade failure was imminent. The objectives of this paper are to: (1) report the hot corrosion results of alternative high temperature coating systems on Alloy M247 and Alloy 792 for hot section components of the 501-K34 gas turbine engine using a low velocity, atmospheric-pressure burner-rig (LVBR), (2) compare and rank hot corrosion performance of these coatings systems to the baseline coating/substrate system (2) down select the best performing coating systems (in terms of LVBR hot corrosion and thermal cycling resistance) to implement on future hot section components in the 501-K34 engine for the Fleet.Copyright

Evaluation of Alternative High Temperature Coatings to Improve Hot Corrosion Resistance in a Shipboard Environment

501-K34 marine gas turbine engines serve as auxiliary power sources for the U.S. Navy’s DDG-51 Class. It is desired that 501-K34 marine gas turbine engines have a mean time between removal of 20K hours. While some engines have approached this goal, others have fallen significantly short. A primary reason for this shortfall is hot corrosion (Type I and Type II) damage in the turbine area (more specifically the first row turbine hardware) due to both intrusion of salts from the marine air and from sulfur in the gas turbine combustion fuel. The Navy’s technical community recognizes that engine corrosion problems are complex in nature and are often tied to the design of the overall system. For this reason, two working groups were formed. One group focuses on the overall ship system design and operation, including the inlet and fuel systems. The second, the corrosion issues working group, will review the design and performance of the turbine itself and develop sound, practical, economical, and executable changes to engine design that will make it more robust and durable in the shipboard operating environment. Metallographic examination of unfailed blades removed from a marine gas turbine engine with 18000 operating hours showed that the coating thickness under the platform and in the curved area of transition between the platform to the blade stem was either very thin, or in a few cases, non-existent on each unfailed blade. Type II hot corrosion was evident at these locations under the platform. It was also observed that this corrosion under the platform led to corrosion fatigue cracking of first stage turbine blades due to poor coating quality (high porosity and variable thickness). Corrosion fatigue cracks initiated at several hot corrosion sites and had advanced through the stems to varying degrees. Cracking in a few blades had advanced to the point that would have led to premature blade failure. Low velocity, atmospheric-pressure burner-rig (LVBR) tests were conducted for 1000 hours to evaluate several alternative high-temperature coatings in both Type I and Type II hot corrosion environments. The objectives of this paper are to: (1) report the results of the hot corrosion performance of alternative high temperature coating systems for under the platform of the 1st stage blade of 501-K34 gas turbine engine, (2) compare the performance of these alternative coating systems to the current baseline 1st stage blade coating, and (3) down select the best performing coating systems (in terms of their LVBR hot corrosion and thermal cycling resistance) to implement on future 501-K34 first stage blades for the Fleet.