Description
[0001] The present disclosure, in general, relates to heat insulation coating material of gas turbine. In particular the present invention relates to finding thickness of thermal barrier coating applied over Nickel base superalloy material for a gas turbine bucket manufacturing through non-contact method.
BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Coatings are widely used for protection of base material from the impact of high heat and corrosive gases produced during combustion of fuels to create pressure for movement of buckets to produce power for driving land based and air-based engines of gas turbine. Coating is applied over the buckets to extend the life of gas turbine buckets and maintain profile of bucket for long hours of operation. Coatings are normally applied with bond coat which acts as an intermediate phase to help in proper contact with metal substrate. The combined effect of bond coat and top is termed as coating thickness. Thickness of bond coat and top coat determines the strength of bond.
[0004] Technical Problem: Gas turbine buckets are exposed to corrosive gases and experience high temperature. The bare metal cannot withstand to such high temperature and maintain geometry profile of bucket intact during severe service conditions. Hence, it requires coating of high temperature resistance material over it such as Zirconia. Direct adhesion of Zirconia on a metal substrate is difficult due to difference in wetting characteristic of powder. Hence, a bond coat is applied which acts as interface between metal substrate and coating material. The uniform coating thickness over the bucket gets damaged during usage, like de-bonding, component cracking, oxidation and corrosion, etc. The intermixing of both top coat and bond coat deteriorates the coating properties and has direct impact on the profile of bucket. Direct measurement technique like manual scanning of complete profile is cumbersome and will reveal only thickness of particular area. However, it cannot be used to understand coating behaviour like insulation, formation of porosities, etc. and predicting life. Hence, a reference/calibration block is required to correlate the properties of service exposed components.
[0005] Gas turbine buckets manufactured through casting route has intricate profile that has to be coated with thermal barrier coating to protect the bucket material from high heat and corrosive gases during power generation. Due to complex geometry of buckets, coating may not be uniform at some portions of profile resulting voids, micro porosity, etc. When this extends to the whole profile in horizontal or vertical direction over the profile cannot be achieved. Stimulation of coating area with flash lamps radiates infrared signals containing the information of metal substrate, bond coat and top coat.
[0006] Technical solution: Accordingly, there is a need to prepare a metal substrate with varying thickness to inspect the coating using non-contact thermography with heating mechanism called as active thermography.
OBJECTS OF THE DISCLOSURE
[0007] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0008] It is a general object of the present disclosure to develop a method for estimating residual life of coating by inducing thermal cycles over coating applied on metal substrate.
[0009] It is another object of the present disclosure to study decay for every 50Hz of operation on calibration block for estimating the life of coating using non-contact thermography.
[0010] It is another object of the present disclosure to measure thermal stresses, porosities, etc., developed over coating to predict the residual life of coating for determining usability of GT bucket materials.
[0011] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY
[0012] This summary is provided to introduce concepts related to estimating residual life of coating of a gas turbine. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0013] In an embodiment, the present disclosure relates to a method for estimating residual life of ceramic coating applied on a gas turbine, comprising of preparing a metal substrate with desired thickness, dividing the metal substrate in multiple square blocks, applying a top coat and bond coat of coating on each of the provided multiple square blocks, testing each square block using a thermography mid-range camera and a plurality of flash lamps. The time lag in receiving an infrared signal from the flash lamp is calculated to find the thickness of the bond coat and top coat separately.
[0014] In an aspect, the metal substrate is preferably made of Nickel base superalloy material.
[0015] In an aspect, the multiple square blocks are preferably sixteen square blocks in number.
[0016] In an aspect, each of the sixteen square blocks have varying thickness
[0017] In an aspect, a numbering scheme is provided on the back of the metal substrate to identify each of the sixteen square blocks.
[0018] In an aspect, calculated energy is flashed upon metal side and infrared signals are picked up from coating side using the thermography mid-range camera.
[0019] In an aspect, the flash lamps and the camera is placed at a particular direction to pick up infrared signals in Reflection mode.
[0020] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0021] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0022] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:
[0024] FIG. 1 illustrates a schematic arrangement of the metal substrate thermography camera and flash lamp.
[0025] FIG. 2 illustrates an isometric view of Bond coat and Top coat with varying thickness sectioned image in.
[0026] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter.
DETAILED DESCRIPTION
[0027] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0028] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0030] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0031] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0032] Referring to Fig. 1 and Fig. 2, the present invention relates to a method for estimating residual life of ceramic coating applied on a gas turbine. The present invention discloses of preparing metal substrate (101) to measure thickness of service exposed gas turbine buckets with coating for inspection of gas turbine components, such as gas turbine buckets by non-contact thermography. The metal substrate (101) is coated with various thicknesses of top coat (102) and bond coat (103). The metal substrate used (101) here is made of Nickel base superalloy material. The metal substrate (101) is then serrated at 0.5mm and 1 mm deep having 0.5mm and 1 mm width.
[0033] A sheet of 200mmX200mmX5mm is taken as a metal substrate (101) or base metal and divided into multiple square blocks of equal sizes. A total of 16 square blocks of area of 50mmX 50mm is marked in a sheet of above mentioned dimensions. The Surface preparation of metal substrate (101) is done by maintaining a standard surface roughness. A numbering Scheme is provided on the back of the metal substrate (101) to help in identifying the thickness of coating applied on front side of metal substrate (101).
[0034] The first row of 50mm x 50mm blocks are applied with coating by masking all other blocks in other rows of the plate. The coating so produced over the block is used as reference block for measuring total thickness over material with non-contact thermography technique. On-contact infrared thermography technique is utilised to measure bond coat (103) and top coat (102) thickness independently by acquiring infrared signals emanated from the surface.
[0035] Table no. 1: A tabular presentation of top coat and bond coat thickness as shown below:
BOND COAT TOP COAT THICKNESS IN MICRON (SAMPLE NO)
0
0(1) 100(2) 200(3) 300(4)
50 0(5) 100(6) 200(7) 300(8)
100 0(9) 100(10) 200(11) 300(12)
150 0(13) 100(14) 200(15) 300(16)

[0036] Represented thickness of each block of dimension as provided above is 50mm X 50mm.
[0037] Transient and Reflection mode thermography techniques are applied to acquire the thermography signals. Calculated energy is then flashed upon metal side and infrared signals picked up from coating side using Thermography Mid-range camera (104). The Flash lamps (105) and camera is placed at a particular direction and picked up infrared signals in Reflection mode.
[0038] The camera (104) works on the principle of picking up infrared signals emanating from the sample to be tested and converts into pictorial form in 320X240 format. The technique of heating the sample is done with high power flash lamps (105) of the rating 2.5KW with provision of stepping down in terms of percentage power of the lamps. When lamps (105) are placed one side of sample to be tested and energy transferred measured with the camera (104) on other side it is termed as transient thermography. Whereas in Reflection thermography both the lamps (105) and the camera (104) is on same side and energy transmitted is measured.
[0039] Time lag in receiving the infrared signal from the flash lamps (105) is calculated to find the thickness of the bond coat and top coat separately. The metal substrate (101) helps in estimating the degradation of top coat (102) and bond coat (103) and its combined effect on the overall life of bond coat. Thermal cycle furnace is used to study thermal behaviour of coatings till coating peels off.
[0040] With the provided method, the following technical advantages are obtained.
[0041] The metal substrate (101) is be utilised as reference metal substrate for finding the degradation of coating for service exposed materials.
[0042] The residual life of coating is determined to study decay for every 50Hz of operation on metal substrate (101) for estimating the life of coating using non-contact thermography.
[0043] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

Claims:We claim:
1. A method for estimating residual life of ceramic coating applied on a gas turbine, comprising of:
preparing a metal substrate (101) with desired thickness;
dividing the metal substrate (101) in multiple square blocks;
applying a top coat (102) and bond coat (103) of coating on each of the provided multiple square blocks;
testing each square block using a thermography mid-range camera (104) and a plurality of flash lamps (105),
wherein the time lag in receiving an infrared signal from the flash lamps (105) is calculated to find the thickness of the bond coat (103) and top coat (102) separately.

2. The method as claimed in claim 1, wherein the metal substrate (101) is preferably made of Nickel base superalloy material.

3. The method as claimed in claim 1, wherein the multiple square blocks are preferably sixteen equal square blocks in number having equal dimensions.

4. The method as claimed in claim 1, wherein each of the sixteen square blocks have varying thickness.

5. The method as claimed in claim 2, wherein a numbering sscheme is provided on the back of the metal substrate (101) to identify each of the sixteen square blocks.

6. The method as claimed in claim 1, wherein calculated energy is flashed upon metal side of the metal substrate (101) and infrared signals are picked up from coating side of the metal substrate (101) using the thermography mid-range camera (104).

7. The method as claimed in claim 1, wherein the flash lamps (105) and the camera (104) are placed at a particular direction to pick up infrared signals in Reflection mode.