Development of Burner Rig Corrosion Tests for Gas Turbine Alloys: Study of Protective Metallic Coatings and Inhibitors for Hot Salt Corrosion

摘要

The efficiency of all types of gas turbine engines (aircraft, terrestrial and marine) is proportional to firing or turbine inlet temperature. In most cases, the use of heavy or contaminated fuels (by Na, S, V) in such combustion equipment is the life-limiting factor for the metallic parts constituting the hot gas path. Since several years, a burner rig was developed in the laboratory to evaluate the corrosiveness of the ash deposit formed on the gas turbine alloys in dynamic conditions. It has been designed to easily adapt the ash deposit rate and the level of the contaminants. The first part of the present paper is devoted to the evaluation of the resistances of several types of metallic coatings against sodium-induced hot corrosion. These coatings were deposited on IN738 alloy and have been treated during 1000h of test. For this, a NaCl solution was injected in the hot gas flux to obtain a deposit rate of 1 mg/cm~2/100h at 850℃. Different types of aluminide coatings obtained by pack cementation were tested and compared to a NiCrAlY coating produced by LPPS process. Among all these coatings, the Pt-modified alumides show the best anti-corrosion behaviour against the Na-induced hot corrosion. In the second part, the burner rig has been used to test additives introduced into crude oil burned in gas turbines. Indeed, the usual and low-cost defence against (Na,V)-induced hot corrosion is the addition to the fuel of some metals as corrosion inhibitors. To simulate this corrosion and its inhibition in the burner rig, an aqueous solution containing adjusted concentrations of sodium, vanadium with or without inhibitor was injected into the combustion gas just after the burner. A Mg/V ratio equal to 3 was tested to evaluate the efficiencies of the inhibition and the deposition rate in the presence of magnesium.