Patent Application
20180030991
This present disclosure relates generally to centrifugal compressors, and more particularly, to methods for repairing seal teeth on centrifugal compressor impellers.
In centrifugal compressors, labyrinth seals are commonly utilized to help minimize leakage in the gas flow path. The seals generally include teeth that rotate relative to a surrounding seal land, and are typically worn out by time in service during the relative rotation, or are damaged by foreign particles, both of which may result in increased leakage. As a result of the increased leakage, repairing or restoring the impeller is required, as it is more economical than replacement. During the repair process, certain impeller dimensions, e.g., the area of the discharge opening, the inner bore diameter, and the seal diameter, with close tolerances must be maintained during the repair process. Maintaining these impeller dimensions is critical for assembly and performance of the impeller during operation. Common repair methods with arc welding techniques include building weld overlays on an impeller eye of impeller, and later reshaping the weld overlays, via a machining process, into a shape of the impeller teeth. Unfortunately, these common repair methods causes a change in the impeller dimensions as heat is introduced into the impeller bore, which leads to a distortion of the impeller bore. Because of the distortion, the impeller bore requires welding, which leads to additional downtime of the compressor due to the additional welding procedure, and an increase in the amount of weld needed to complete the weld operation.
Therefore, there remains a need for an improved method which eliminates distortion, e.g., of the impeller bore when repairing the seal teeth, and reduces downtime of the compressor and decrease the amount of weld needed for the repair process.
In one exemplary embodiment, a method for repairing or restoring a tooth for an impeller seal is provided. The method includes the step of inspecting the impeller seal tooth and determining what portions of the impeller seal tooth to repair or restore.
The method also includes the step of removing the worn portions of the impeller seal tooth, i.e., the portions determined as requiring repair. After removing the worn portions, the method includes the step of forming a weld into a tapered shape that corresponds with a shape of a fully repaired/restored seal tooth. The weld is formed via a pulsed laser beam welding process (LBW), e.g., by introducing a minimal heat onto a weldable surface of a base of the seal tooth to be repaired. By introducing a minimal heat, via the LBW process, the impeller bore does not require further welding as a result of forming the weld in the tapered shape.
The method further includes the step of smoothing the tapered shape weld into a final repaired seal tooth shape, and subsequently, testing the repaired seal tooth via a balance and speed testing.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:
The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present invention.
Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the subject matter herein only and not for limiting the same,
With continued reference to
With continued reference to the figures and now
The repair restore process may proceed as follows: at least one or more teeth 32 of the impeller seal 31 may be inspected to determine if any portions 33 (
Upon determining what damaged/worn portions 33 require repair, the method 1000 includes the step of removing the worn portions 33 of the tooth 32 (1010). In one embodiment, a machining process (also called pre-machining) may be used to remove the worn portions 33 of the tooth 32 down to a weldable surface, shoulder, or reference point 34 of the tooth 32. It should be appreciated that pre-machining the worn portion 33 may continue until the weldable surface 34 of the tooth 32 is achieved.
With continued reference to the figures, in embodiments where a partial repair of the tooth 32 is desired (
Additionally or alternatively, where a full repair of the tooth 32 is desired (
With continue reference to the figures, the method 1000 may include forming a weld onto the weldable surface 34 into a shape corresponding to a shape of a restored seal tooth (1020). In this step, instead of applying general layers of a weld as taught by the common methods of repair, the weld is applied or built up, via a pulsed laser beam welding (LBW) process, into a tapered or substantially tapered shape, e.g., from the weld surface 34 to a peak point 36 as determined by a restored seal tooth 32.
In one embodiment, the peak point 36 may be the point at the height of the seal tooth 32 from the base or root, e.g., where the seal tooth 32 in operations engages the abradable insert ring 23. As used herein, a tapered shape tooth may be a tooth shape where the lower portion (i.e., base) is generally wider than its upper portion (i.e., tip). This tapered shape is exemplified in
It should be appreciated that less material (weld) may be used for forming the weld into the tapered shape as compared to traditional methods, which requires a plurality of weld overlays be performed onto or across the seal teeth base for later machining the seal teeth shape out of the weld overlays. Additionally, it should be further appreciated that forming the tapered shape, via the LBW process, applies less heat to the impeller than the traditional repair methods, which reduces the likelihood of distorting the impeller dimensions, e.g., the impeller bore.
With continued reference to
After machining the tapered shape weld into the restored seal tooth 32, the restored seal tooth 32 may be tested (1050). In this step, testing of the restored seal tooth 32 may include a balance and/or speed testing, e.g., a low-speed balance testing and an over-speed testing of the restored seal tooth 32. Upon completion of either testing or both, a further inspection (1055) may be conducted prior to returning the repaired impeller 30 to operation.
By using the above method(s), the need to weld the impeller bore in the prior-art methods to correct distortions is eliminated, as the amount of heat applied in the new method is reduced. Additionally, the amount of material for forming the repaired seal tooth in the new method is reduced by forming the weld into a shape that corresponds to a restored seal tooth.
The new method saves weld by eliminating the need to apply multiple weld overlays across the seal teeth as taught in the traditional arc welding process, and then reshaping the teeth only after solidification, as the new method forms the weld in the shape of a restored seal tooth, thus allowing an individual tooth to be restored.
While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. For example, elements described in association with different embodiments may be combined. Accordingly, the particular arrangements disclosed are meant to be illustrative only and should not be construed as limiting the scope of the claims or disclosure, which are to be given the full breadth of the appended claims, and any and all equivalents thereof. It should be noted that the terms “comprising”, “including”, and “having”, are open-ended and does not exclude other elements or steps and the use of articles “a” or “an” does not exclude a plurality. Additionally, the steps of various methods disclosed herein are not required to be performed in the particular order recited, unless otherwise expressly stated.
