METHOD FOR PROTECTING VARIOUS HYDRO-TURBINE UNDERWATER COMPONENTS FROM ACIDIC WATER CORROSION

TECHNICAL FIELD

[0001] The present disclosure relates, in general, a method of protecting various hydro-turbine underwater components from acidic water corrosion due to presence of sulphuric acid in river water especially hydro power stations, for example, situated in north-eastern region of India.
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BACKGROUND
[0002] Background description includes information that may be useful in understanding the present subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior 15 art.
[0003] Hydro-turbine power stations situated in North-East region of India primarily in Meghalaya and Assam states face acidic water corrosion (pH of river water is 3.3) problem. Kopili, Khandong, and the like are some of the affected sites. Total installed capacity of 275 MW is affected due to this acid water 20 corrosion problem. The reason of acidic water with high pH was analysed and based on the analysis, it was found that there are many coal mines (as shown in FIG. 1A) around North East region of India from where the river passes through. During passage along the coal mines, the river water reacts with Sulphur present in coal (XRD pattern of coal, shown in FIG. 1B, confirms the present of Sulphur 25 in the form of Pyrites FeS2). After such reaction, Sulphur gets converted into sulfuric acid which reacts with metallic components of the hydro-turbine underwater components and corrodes them with time.
[0004] One solution to the acid water corrosion problem is provide a corrosion resistant coating. As such coating was not visualized during the design 30 of the hydro power stations as the acidic water issue was not present during the
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installation of the hydro power stations. With time, the acidity of the water has gone up and corrosion problem has become severe. As a result of such increase in the corrosion problem, the underwater components started to fail, which leads to shut down of hydro power station, which in turn resulted in huge revenue loss. The components were built up with welding and machine was put into operation. 5 But this approach was not appropriate as the failure of the component still continued due to heavy corrosion and high pH of the water (2.8). Some of the components like Hydro runner was coated with HVOF (High Velocity Oxy Fuel) coating. Some components were coated with brushable ceramic paints. Brushable ceramic paints was somewhat better in performance in comparison to HVOF 10 coating. So, basically no perfect coating was identified for the above acidic water corrosion in underwater components of hydro turbines.
[0005] Therefore, there is a need for a method or treatment protecting various hydro-turbine underwater components from acidic water corrosion.
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OBJECTS OF THE DISCLOSURE
[0006] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0007] An object of the present disclosure is to provide a method of protecting various hydro-turbine underwater components from acidic water corrosion. 20
SUMMARY
[0008] This summary is provided to introduce concepts related to a method for protecting various hydro-turbine underwater components from acidic water corrosion. The concepts are further described below in the detailed description. 25 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.
[0009] The present disclosure relates to a method for protecting various hydro-turbine underwater components from acidic water corrosion. The method 30
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includes applying epoxy-based polymer coating on hydro-turbine underwater components affected due to the acidic water corrosion.
[0010] In an aspect, before applying the epoxy-based polymer coating, the method includes preparing the epoxy-based polymer coating by mixing appropriate ratio of resin and hardener to obtain desired properties. 5
[0011] In an aspect, before applying the epoxy-based polymer coating, the method includes preparing surface of the water hydro-turbine underwater components using alumina grit of size 12-16 mesh for better bonding.
[0012] In an aspect, the epoxy-based polymer coating has a thickness ranging from 1.0 mm to 2.0 mm. 10
[0013] In an aspect, the epoxy-based polymer coating is an epoxy without flakes for vertical surfaces of the hydro-turbine underwater components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The illustrated embodiments of the subject matter will be best 15 understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein: 20
[0015] FIG. 1A illustrates location of coal mines in Meghalaya state;
[0016] FIG. 1B illustrates an XRD pattern of coal;
[0017] FIG. 2A illustrates samples before corrosion test; and
[0018] FIG. 2B illustrates samples after six months from the corrosion test.
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DETAILED DESCRIPTION
[0019] 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
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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 spirit and scope of the present disclosure as defined by the appended claims. 5
[0020] 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. 10
[0021] 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 15 “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.
[0022] It should also be noted that in some alternative implementations, the 20 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.
[0023] Unless otherwise defined, all terms (including technical and scientific 25 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 30 formal sense unless expressly so defined herein.
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[0024] Hydropower stations situated in north eastern region (Meghalaya and Assam states) are affected due to acid water corrosion. Corrosion is continuous phenomenon that eats the metal day and night and finally leads to catastrophic failure of the components. In order to continue the power generation, coating has to be applied to resist the corrosion. In Bharat Heavy Electricals LIMITED 5 (BHEL), such problem has not been experienced and hence no proper solution exits in BHEL. Accordingly, it is essential to identify a suitable corrosion resistant coating for preventing acid water corrosion.
[0025] To this, four different types of polymer coatings (vinyl ester with glass flake, epoxy with and without glass flake, polyurethane) along with aluminium 10 coating samples were prepared on MS rod sample after thorough grit blasting. For comparison SS 410 and Mild steel rods were also put. These samples were exposed to sulphuric acid spray atmosphere with a pH 2.0 for a duration of six months. Post acid spray testing, the various coatings were evaluated visually for corrosion resistance as well as under optical microscope. It was observed that 15 epoxy without flake and vinyl ester with glass flake were intact after the test. These coatings were also evaluated for bond strength (adhesion) and the strengths are 2200psi and 2800psi. The pot life of epoxy without flake is 40 min and that of vinyl ester is 90 min. Keeping in mind the site application, lesser the pot life better the application at least for vertical walls. Accordingly, epoxy based 20 polymer was selected to resist acid water corrosion.
[0026] Polymers are well known for their high corrosion resistance as well as its low cost. Accordingly, various polymers like vinyl ester with glass flake, epoxy with and without glass flake, polyurethane coatings were studied. For comparison wire arc spray coated aluminium, SS410 and MS samples were also 25 made. Polymers were coated on round rod samples after thorough grit blasting to a thickness of 1.0 – 2.0 mm. These samples were exposed to acid spray condition like salt spray testing using sulphuric acid as a corrodant with a pH of 2.0 which is more than the actual condition of pH 3.3. Testing was continued for a duration of six months. Post testing, samples were tested visually as well as under optical 30 microscope cum image analyser to see the extent of corrosion. Some of the
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photographs of coating before and after corrosion test are shown in FIGS. 2A and 2B.
[0027] Based on the corrosion test, bond strength and pot life of polymer coatings is analysed as shown in following Table 1:
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S No.
Polymer coating
Bond strength (PSI)
Pot Life (min)
1
Epoxy with glass flakes
2800
90
2
Vinyl ester
3000
40
3
Polyurethane
1200
90
4
Epoxy without flakes
2200
40
[0028] After the acid spray corrosion test, it can be seen from Fig-1 and Fig-2 that epoxy without flake and vinyl ester with glass flake were intact in comparison to polyurethane coating and epoxy coating with glass flake. But when it is compared with respect to pot life (Table 1) the epoxy with flake has long pot life. 10 Long pot life is not preferred as the coating may sag on the vertical wall (surface) leading to nonuniform coating thickness around the job which is not desirable for better performance. Whereas the epoxy without flakes has shorter pot life which is better suitable for vertical surface and hence preferred.
[0029] Further, it will be appreciated that those skilled in the art will be able 15 to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope.
[0030] Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to 20 furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Also, the various embodiments
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described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
[0031] The above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, 5 techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It 10 will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure 15 as encompassed by the following claims.
[0033] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for 20 example, may arise from applicants/patentees and others.
[0034] 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, 25 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.

We claim:

1. A method for protecting various hydro-turbine underwater components from acidic water corrosion, the method comprising:
applying epoxy-based polymer coating on hydro-turbine 5 underwater components affected due to the acidic water corrosion.
2. The method as claimed in claim 1, further comprising preparing the epoxy-based polymer coating by mixing appropriate ratio of resin and hardener to obtain desired properties. 10
3. The method as claimed in claim 1, further comprising preparing surface of the water hydro-turbine underwater components using alumina grit of size 12-16 mesh for better bonding.
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4. The method as claimed in claim 1, wherein the epoxy-based polymer coating has a thickness ranging from 1.0 mm to 2.0 mm.
5. The method as claimed of claim 1, wherein the epoxy-based polymer coating is an epoxy without flakes for vertical surfaces of the hydro-20 turbine underwater components. ,