A METHOD AND ELECTROCHEMICAL MEASUREMENT FOR SIMULATING AND EVALUATING THE HIGH TEMPERATURE CORROSION
Publication Date: 2017-Jan-10
The IP.com Prior Art Database
A technique to simulate pit corrosion from field alloys and electrochemical measurement for quantitative evaluation of a pit corrosion rate is disclosed. The technique enables to know more about corrosion mechanism by studying several factors, such as, gas environment, temperature and corrodent. A coating method, corrodent compositions and dust size in the corrodent are three key factors to simulate the pit corrosion. Corrodent compositions, such as, sulfate or dust ratio and dust size are delicately designed to produce pit corrosion rather than general corrosion. Further, Electrochemical Impedance Spectroscopy (EIS) is used to quantitatively evaluate pit corrosion rate. When pit corrosion occurs, some oxides caps forms on top of pits, while, some metal elements diffuses to corrodent. The formation of the caps and diffusion of metal elements are highly related to pits number and size, which are used to quantify the corrosion rate. During the corrosion test, EIS is able to capture the corrodent resistance change which mainly is caused by the caps and metal elements diffusion. As a result, the EIS can eventually evaluate the corrosion rate.
The present invention relates generally to a gas turbine engine, and more particularly to a technique for simulating and evaluating high temperature corrosion of alloy based components used in the gas turbine engine.
Advancement in material development and cooling technology in recent years eventually enables operation of new-generation gas turbine engines at increased temperatures. A combination of such high temperatures with more and more harsh environment that contains contaminants, such as, sodium, sulfur, vanadium, and various halides requires special attention to hot corrosion. Such type of corrosion is known as pit corrosion. Pit corrosion, unlike oxidation, forms crack in alloys, which eventually results in catastrophic failure. For example, several components of a gas turbine engine, such as, blade, shroud, disk and nozzle, among others are prone to damage due to high operating temperature condition.
A conventional technique includes a method and apparatus for inspecting a multi-layer coating on a substrate of a turbine element airfoil. The method identifies thickness and defect of the layers as well as remaining useful life of the airfoil. At each of a number of locations along the airfoil, a number of frequencies of alternating current are passed through the airfoil. At least one impedance parameter is measured. The measured impedance parameters are utilized to determine a condition of the coating. The current is passed between first and second electrodes and an ionically conductive liquid is applied at contact points of the first and second electrodes with the coating.
Another conventional technique relates to an electrode system for electrochemical impedance spectroscopy (EIS) evaluation on hot metal corrosion and forms a relation between corrosion rate and polarization resistance in EIS.
One other conventional technique relates to an electrode system for EIS evaluation on corrosion of an oxide film on a surface of a steel product for a boiler.
The above mentioned conventional techniques include monitoring system or electrode design for several applications. However, the above mentioned conventional techniques do not provide a simple process for screening different alloys and coatings based on anti-corrosion performance.
Therefore, it would be desirable to have a technique to mitigate solution for corrosion problem in different alloys and coatings.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 depicts corrosion, pitting and crack formation in a blade, shroud, disk and nozzle of a gas turbine engine due to high temperature conditions along with presence of dust and other corrodents.
Figure 2 depicts a speed-mixer used for preparation of the slurry.
Figure 3 depicts coating of platinum paste and insertion of Platinum mesh in the reactor cell assembly.
Figure 4 depicts a reactor assembly used for EIS test.