TECHNICAL FIELD

[0001] The disclosure relates generally to turbine or turbomachine cast casing components. In particular, the disclosure relates to lifing enhancements for turbine or turbomachine cast casing components.

BACKGROUND

[0002] Nodular cast iron, such as ductile cast iron, is a common material used to manufacture casings of turbines used in power generation. Casings are usually large and cast in at least one of serial or mass production and non-serial or one-by-one production. This production may lead to areas that may be disposed to defects in casting, as the process is not fully optimized, a process can have drift or fluctuations in composition, process parameters, melt and solidification variations, and other process factors that can vary process outcomes. Furthermore, the casting may have complex configurations that may be inclined to damage during machining due to damaged cutting tools or incorrect process settings.

[0003] Turbine casings are exposed to high thermal, mechanical, and vibratory loads during operation and during each start and stop cycle of the turbine. These loading cycles create a series of alternating stress states, which can lead to material fatigue, the formation of cracks, and the propagation of fatigue induced cracks or pre-existing cracks from the manufacturing process. If the cracks exceed design limits, the casings may be scrapped and replacement casings would be required, which leads to high costs not only due to the manufacturing cost but also due to outage time and delays in turbine operation. If possible, defective castings are repaired rather than replaced. For castings made from cast iron, mechanical repairs have been preferred due to the difficulty of welding a material with such high carbon content. The welds often crack during the welding process, upon cooling, or shortly thereafter following further turbine operation.

[0004] Due to the relatively low fatigue strength of nodular cast iron, it is often hard or impossible to obtain access in all locations of a casing required fatigue life in terms of cycles to crack initiation. Such locations have geometrical stress concentrations that may not be avoided without compromising function of the part.

BRIEF DESCRIPTION [0005] All aspects, examples and features mentioned below can be combined in any technically possible way.

[0006] A particular aspect of the disclosure provides an article including a base portion including a cast iron with the cast iron having a first fatigue strength; at least one groove formed in the base portion: and a filler metal disposed in at least one of the at least one groove formed in the base portion with the filler metal having a second fatigue strength. The second fatigue strength is greater than the first fatigue strength.

[0007] A certain aspect of the disclosure includes any of the preceding aspects, wherein the cast iron includes a nodular cast iron.

[0008] Another aspect of the disclosure includes any of the preceding aspects, and the filler metal includes a low carbon steel.

[0009] A further aspect of the disclosure includes any of the preceding aspects, and wherein the filler metal includes a low carbon steel.

[0010] Certain aspects of the disclosure include any of the preceding aspects, and wherein the article is a cast turbine casing.

[0011] Another aspect of the disclosure includes any of the preceding aspects, wherein the at least one groove is located on the cast turbine casing at at least one of failure prone areas or trouble areas prone to cracking.

[0012] Certain aspects of the disclosure include any of the preceding aspects, wherein the at least one groove is formed during casting of the cast turbine casing.

[0013] Another aspect of the disclosure includes any of the preceding aspects, wherein the at least one groove is formed by machining at failure prone areas or trouble areas prone to cracking.

[0014] Yet another aspect of the disclosure includes any of the preceding aspects, wherein the at least one groove is machined after the article has been in service.

[0015] A further particular aspect of the disclosure provides a cast turbine casing including a base portion including a cast iron with the cast iron having a first fatigue strength; at least one groove formed in the base portion: and a filler metal disposed in at least one of the at least one groove formed in the base portion with the filler metal having a second fatigue strength. The second fatigue strength is greater than the first fatigue strength. [0016] Certain aspects of the disclosure include any of the preceding aspects, wherein the cast iron includes a nodular cast iron.

[0017] Another aspect of the disclosure includes any of the preceding aspects, wherein the filler metal includes a low carbon steel.

[0018] A further aspect of the disclosure includes any of the preceding aspects, wherein the filler metal includes a low carbon steel.

[0019] A still further aspect of the disclosure includes any of the preceding aspects, wherein the at least one groove is located on the cast turbine casing at at least one of failure prone areas or trouble areas prone to cracking.

[0020] A further certain aspect of the disclosure includes any of the preceding aspects,, wherein the at least one groove is formed by at least one of: casting with the cast turbine casing; or machining at failure prone areas or trouble areas prone to cracking.

[0021] Another particular aspect of the disclosure provides a method of forming a cast turbine casing. The method includes the steps of: forming at least one groove in a base portion of the cast turbine casing, where the cast turbine casing includes a cast iron, the cast iron having a first fatigue strength; and applying a filler metal in the at least one groove, the filler metal including a low carbon steel, the low carbon steel having a second fatigue strength, wherein the second fatigue strength is greater than the first fatigue strength.

[0022] Another aspect of the disclosure includes any of the preceding aspects, wherein forming the at least one groove in a base portion of the cast turbine casing includes forming the at least one groove in a base portion during casting of the cast turbine casing.

[0023] Another certain aspect of the disclosure includes any of the preceding aspects, wherein forming the at least one groove in a base portion of the cast turbine casing includes machining the at least one groove in a base portion after casting of the cast turbine casing.

[0024] Another aspect of the disclosure includes any of the preceding aspects, wherein forming the at least one groove in a base portion of the cast turbine casing includes forming the at least one groove at at least one of failure prone areas or trouble areas prone to cracking.

[0025] The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:

[0027] FIG. 1 illustrates an expanded view of a turbine section with a groove to be filled with a filler metal according to embodiments of the disclosure;

[0028] FIG. 2 illustrates a sectional view of a repaired region that includes one or more butter layers and a fill layer, according to embodiments of the disclosure; and

[0029] FIG. 3 illustrates a flowchart for a method for repairing a casing component that forms part of a flow path in a steam or gas turbine according to embodiments of the disclosure.

[0030] It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DET AIDED DESCRIPTION

[0031] As an initial matter, in order to clearly describe the subject matter of the current disclosure, it will become necessary to select certain terminology when referring to and describing relevant cast turbine casings and turbomachinery components. To the extent possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part.

[0032] In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow (i.e., the direction from which the flow originates). The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front or compressor end of the engine, and “aft” referring to the rearward section of the turbomachine.

[0033] It is often required to describe parts that are disposed at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. For example, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine.

[0034] In addition, several descriptive terms may be used regularly herein, as described below. The terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. 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” and/or “comprising,” when used in this specification, 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. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur or that the subsequently describe component or element may or may not be present, and that the description includes instances where the event occurs or the component is present and instances where it does not or is not present. [0036] Where an element or layer is referred to as being “on,” “engaged to,” “connected to” or “coupled to” another element or layer, it may be directly on, engaged to, connected to, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0037] As embodied by the disclosure, lifing enhancements can be made to cast materials and parts made therefrom. Cast materials and parts made therefore, as embodied by the disclosure can include turbomachinery components, such as but not limited to, gas turbine casings, steam turbine casings, turbine exhaust components, inlet casings, compressor casings, rotor casings, and other such cast turbomachinery components, now known or hereinafter developed. Lifing improvements, as embodied by the disclosure, are provided to meet strength, life, and functionality of needs of cast turbomachinery components.

[0038] As embodied by the disclosure and with respect to FIGs. 1 and 2, turbines, such as but not limited to gas turbines and steam turbines, have casings 10. In some turbines, casings 10 are formed from a cast iron. In accordance with certain cast iron casings 10, as embodied by the disclosure, the cast iron can include nodular cast iron. A substrate or base portion 12 of cast iron casings 10 can include nodular cast iron, which may also be referred to as ductile iron, ductile cast iron, spheroidal graphite iron, or spheroidal graphite cast iron.

[0039] Casings are exposed to thermal stresses during operation of the turbine. The thermal stresses can include, but are not limited to cyclic thermal stresses. These cyclic thermal stresses may be disadvantageous to casing 10 by causing stresses and limiting life.

[0040] The cyclic thermal stresses may cause cracking in locations of a casing. Additionally, cracking in a casing may be caused by vibration of the casing. In particular, there are certain failure prone areas or trouble areas prone to cracking on a casing. At these failure prone areas or trouble areas prone to cracking at least one of cyclic thermal stresses and vibration may form cracks at a higher frequency than at other casing locations during turbine operation. Failure prone areas or trouble areas prone to cracking may be compounded due to casting process considerations or limitations. For example and in no way limiting of the embodiments of the disclosure, casing thick sections may have at least one of weaker microstructures and/or degraded micros. Examples of such thick casting section include four way joints, where weaker structures are often formed and highly stressed in use.

[0041] Lifing improvements can be provided to cast iron casings, as per aspects of the embodiments. Of course, as embodied by the disclosure, aspects include other causes of cracking that may occur in a casting, including those causes now known or hereinafter discovered. An increase of material with a higher fatigue strength at failure prone areas or trouble areas prone to cracking where higher stress in the casing exists should increase the life of the casing.

[0042] As embodied by the disclosure, by joining a higher fatigue strength material, as a dissimilar metal addition to cast material such as but not limited to cast iron, lifing improvements may be realized. For example, and in no way limiting, failure prone areas or trouble areas prone to cracking in cast iron casings 10 for turbomachinery include joints, such as 4-way joints in the casing, anti-rotation configurations (not illustrated) formed during casting in the casing, complex intersections of casing segments, other casing areas where high stress or large scale temperature variations may occur.

[0043] Failure prone areas or trouble areas prone to cracking may be due to casting process related quality issues or service degradations. In other aspects of the disclosure, failure prone areas or trouble areas prone to cracking may occur through design driven stresses that occur during at least one of servicing or maintenance, and manufacturing.

[0044] As noted above, lifing improvements can be provided in certain aspects of the embodiments by joining metals having higher fatigue strength than cast iron to the casing. In one aspect of the embodiments, a material having higher fatigue strength than cast iron includes a low carbon steel material. Fow carbon steel having higher fatigue strength than cast iron, as embodied by the disclosure, includes carbon that does not exceed about 0.25% and a manganese content of which does not exceed about 1.65%. Fow carbon steel can have a substantially similar mean coefficient of thermal expansion as nodular cast iron of casing. This substantially similar mean coefficient of thermal expansion can ensure that low carbon steel will expand and contract at the approximately same rate as base cast iron of the casing during thermal cycling of the turbine casing. As discussed hereinafter, low carbon steel as the higher fatigue strength material, as embodied by the disclosure, can be provided as weld material, such as be not limited to, as a consumable welding electrode.

[0045] One non-limiting example of a low carbon steel as a more capable metal having higher fatigue strength than cast iron, as embodied by the disclosure, is disclosed in EP 3,725,457A filed April 17, 2018. Use of other capable metals with higher fatigue strength, in accordance with aspects of the embodiments, are envisioned by the disclosure when the fatigue strength of the filler metal is higher than the underlying cast iron.

[0046] As embodied by the disclosure, areas for providing a more capable metal having higher fatigue strength than cast iron may be formed into the cast material and structure by virtue of the design criteria of casing 10. For example, and in no way limiting of the embodiments, grooves, channels, troughs, or indentations (hereinafter “grooves”) may be designed into th casting. In other words, the mold used to form the cast article, can be designed with extensions or projections at areas where a more capable metal having higher fatigue strength will be applied to the cast article/material. As embodied by the disclosure, these mold extensions or projections can be located failure prone areas or trouble areas prone to cracking in cast iron casings for turbomachinery.

[0047] With reference to the figures, in an aspect of the embodiments, groove(s) 16 (FIGs. 1 and 2) may be formed in the casing 10. Groove(s) 16 is formed in a region where more capable metal having higher fatigue strength than cast iron can be filled or added to the cast article. Thus, the more capable metal having higher fatigue strength than cast iron is a “filler material” 34 in groove 16.

[0048] In one aspect of the embodiments, filler material 34 may be provided in groove(s) 16 by a process that includes, but is not limited to, welding. As embodied by the disclosure, welding of the more capable metal having higher fatigue strength than cast iron includes weld processing to avoid high stresses formed that are above life limits for casing 10. Moreover, according to another aspect of the embodiments, if welding forms any high stress locations that may be above life limits for the casing, the high stress locations are located, preferably completely located, in the welded filler material 34. Accordingly, the weld- formed heat affected zone (HAZ) and the casing base material should be free of high stress areas or fusion zones.

[0049] As embodied by the disclosure, welding processing for filler metal 34 into groove(s) 16 can include arc welding processing. For example, and in no way limiting of the embodiments, arc welding of filler metal 34 may include at least one of tungsten inert gas welding (TIG) or gas metal arc welding (GMAW), known also as metal inert gas welding (MIG) or metal active gas welding (MAG). Moreover, arc welding, as embodied by the disclosure, may include consumable or non-consumable electrodes, where if employing a consumable electrode, filler metal 34 is included in the consumable electrode. [0050] With further reference to FIG. 1, casing component (“casing”) 10 includes a (turbine) base portion (“portion”) 12 formed of nodular cast iron (or ductile iron). Region 14 is a failure prone area or trouble area prone to cracking on casing 10 that is located the turbine portion 12. Region 14 includes at least one groove 16 formed in portion 12. As embodied by the disclosure, each groove 16 can be designed into the cast casing 10 and cast therein. Alternately, at least one groove 16 can be machined into portion 12, for example before or after casing 10 has been in service. Additionally, even if a groove or grooves 16 are designed into the cast casing, 10, further groove(s) 16 be machined into portion 12, for example machined after casing 10 has been in service.

[0051] In an exemplary embodiment, region 14 is located in a region radially between blades (not illustrated for ease of understanding) of a turbine portion 12. However, as noted above, region 14 may be located anywhere in or on casing 10 in failure prone areas or trouble areas prone to cracking.

[0052] FIG. 2 illustrates a sectional view of a groove 16 in region 14 that has filler metal 34 disposed therein, as embodied by the disclosure. Groove 16 is illustrated in a generally “V” shape, however this configuration is merely illustrative and is not meant to limit groove 16 configuration in any manner. Groove 16 may be “V” shaped, “U” shaped, include a flat bottom with substantially perpendicular side and bottom walls, or any other groove configuration now known or hereinafter developed.

[0053] As per the welding process, according to one aspect of the disclosure, one or more butter layers 32 and a layer of filler metal 34 are disposed in groove 16. To provide the filler metal 34, groove 16 is initially provided with at least one butter layer 32. Thereafter, filler metal 34 is welded into groove 16 by a weld process. In accordance with an aspect of the disclosure, filler metal 34 can be applied by arc welding in one or multiple passes. Passes of arc welding are repeated until filler metal 34 “fills” groove 16.

[0054] FIG. 3 illustrates a flowchart for a method 40 for providing filler metal 34 as the low carbon steel as a more capable metal having higher fatigue strength than cast iron in a groove 16 of a cast article. As embodied by the disclosure, the cast article may include a casing 10 that forms part of a turbine. The turbine may be a gas turbine or a steam turbine.

[0055] The method 40, as embodied by the disclosure, includes a forming step 42 that defines the groove 16. As discussed above, groove 16 may be formed cast with the turbine casing 10 or machined in the casing 10 after casting, either before or after some turbine service. An applying step 44 applies at least one butter layer 32 in groove 16. Filler metal 34, as a low carbon steel for a more capable metal having higher fatigue strength than cast iron per the embodiments, is then welded in groove 16 on the at least one butter layer 32. Filler metal 34 is added at step 46 in one or more steps until the groove 16 is filled with low carbon steel as a more capable metal having higher fatigue strength than cast iron. If needed or desired, an optional finishing step 48 may be conducted.

[0056] In a still further aspect of the embodiments, in servicing casing 10 after some period of turbine service or use, groove 16 may be formed in casing 10 as per step 42. Thereafter, method steps 44, 46, and if desired step 48, may be provided to common trouble areas prone to cracking. In this aspect, one or more groove(s) 16 may be formed (step 42) in those common trouble areas, such as but not limited to at a crack or defect that has formed during use, to add the filler metal. Forming of the groove(s) 16 may include machining, CNC machining, manual drilling, laser forming, or any other machining process now known or hereinafter developed. Accordingly, once groove 16 is formed, the process 40 continues with step 44, the application of at least at least one butter layer 32 to groove 16.

[0057] The foregoing drawings show some of the processing associated according to several embodiments of this disclosure. In this regard, each drawing or block within a flow diagram of the drawings represents a process associated with embodiments of the method described. It should also be noted that in some alternative implementations, the acts noted in the drawings or blocks may occur out of the order noted in the figure or, for example, may in fact be executed substantially concurrently or in the reverse order, depending upon the act involved. Also, one of ordinary skill in the art will recognize that additional blocks that describe the processing may be added.

[0058] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. “Approximately,” as applied to a particular value of a range, applies to both end values and, unless otherwise dependent on the precision of the instrument measuring the value, may indicate +/- 10% of the stated value(s). [0059] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.