490 Machinery Component Maintenance and Repair Figure 8-27. Another classical problem is erosion of steam turbine casings in the grooves that retain the diaphragms. These can be restored to original dimensions using a combina- tion of welding and mechanical techniques. Figure 8-28. Turbine diaphragm for the casing shown in Figure 8-27. Steam erosion, which is very evident on the outer diameter, is repaired by welding. Nozzles can also be repaired, although these are in good condition. Will a Repairer Manufacture Spare Parts? The supply of spare parts is a specialized function requiring the know- how of the original equipment manufacturer (OEM). Another OEM can indeed reconstruct spare parts manufactured by others. However, he has to spend engineering hours to create a drawing and to specify the processes and quality controls. This means that it is often more econom- ical to buy parts from the original manufacturer. An expert repairer who is also an OEM has the capability of designing and manufacturing a spare part required to complete a repair and will do so if needed. One should be wary of any repairer offering only spare parts since these will often not meet the original specifications and quality controls. Proof of Repairability An expert repairer keeps careful records of his activities. One of the quality records maintained is a job folder for each repair containing all the information pertaining to that repair. This includes dimensional checks, nondestructive examination, specifications, in-progress quality records, and a detailed list of the work carried out. Another set of records contains certified repair procedures carried out on certain classes of parts. This, in effect, is a repair manual containing all the necessary procedures, specifications, and quality checks to carry out a repair. This is also a record of repairs actually carried out, proved, and documented. By repeating the exact same process on a similar part, the repairability is 100 percent assured. In the rare case of an absolutely untested repair, the proposed proce- dure is first used on a model of the failed component. The parameters of the procedure are recorded. The model is then examined destructively to provide positive proof of the repair. Samples are provided to the owner of the part to make his own tests and reach the same results as those of the repairer (Figures 8-29 and 8-30). Ascertaining Integrity of the Repair Process A reputable repairer will take every precaution to determine the mate- rial, metallurgical, and physical state of the part prior to commencement of the repair. Only known and controlled processes are applied to the part prior to the repair. There should thus be no doubt as to the expected results of the process. Repair and Maintenance of Rotating Equipment Components 491 492 Machinery Component Maintenance and Repair Figure 8-29. Close-up view of a centrifugal compressor impeller. The damage to the impeller eye, cover, and disk outer diameter was repaired by welding. Even though the procedures were certified, a sample weld was made on similar material and given to the customer for his metallurgy department prior to commencement of work. The repair process is controlled through work instructions in which every step is detailed. Each step calls out the necessary tools and specifi- cations required to perform that step. Each step is inspected and verified before the next step is performed (Figure 8-31). Final inspection and tests confirm the quality that has been built into the repair process each step of the way. A final report must record the history of the repair as well as the verified results of tests and inspections. A formal and active quality system is mandatory for the repair facility. This means an all-encompassing system to control all the activities of an organization that ensures that what is shipped is exactly what was ordered. Included in such a system are the following as a minimum: • Formal organization and control • Control of documents • Calibration of instruments • Training and qualification of personnel • Product identification and traceability • Corrective action By the use of certified procedures carried out in a certified facility, it can be assured that no harm will come to an owner’s part during the repair. Furthermore, the part will perform exactly as predicted after the repair. Specifications Applied to the Process In general, the same specifications that were applied in originally making the part are applied to the repair. If the part is from a compressor or steam turbine of a petroleum refinery, for example, American Petro- leum Institute (API) standards are applied. In actual practice once a repair facility is capable of working to these high standards they will be applied to all parts whether they come from a refinery or not. Specifications are applied to individual processes as needed. For example, welders and weld procedures must be qualified to American Society of Mechanical Engineers (ASME) XIII and IX. Nondestruc- tive examinations are subject to Society for Non-Destructive Testing (SNT) standards. Material specifications are used in the selection and Repair and Maintenance of Rotating Equipment Components 493 Figure 8-30. The impeller shown in Figure 8-29 after weld repair and final machining. The impeller was heat treated prior to machining and overspeed tested at 115 percent of maximum continuous speed in accordance with API specifications. acceptance of materials as, for example, American Society for Testing Materials (ASTM), British Standards (BS), or Deutsche Industrie Normen (DIN). An overall specification must be applied to the repair facility and this is International Standards Organization (ISO) 9002 quality systems model for quality assurance in production and installation. This standard controls every facet of an operation. It includes control of calibration, order pro- cessing, documents, materials, personnel and procedures qualifications, and a method of eliminating root causes of problems. This international and demanding standard has as its objective that the customer should get exactly what he bought, precisely on time. Resolving Different Opinions: Scrap vs. Repair It could happen that the OEM recommends buying new while an expert repairer proposes a repair. It does not mean that the OEM is remiss or callous but only that he is not familiar with the repair technology. All OEMs are capable of designing and manufacturing new equipment. Only a very few have applied any research effort in developing repair 494 Machinery Component Maintenance and Repair Figure 8-31. ISO 9002 requires implementation of quality assurance system control pro- cedures, qualification of personnel, and calibration of instruments used. The aim is that the customer gets exactly what he ordered, precisely when promised. technology. Therefore, they simply are incapable of carrying out a repair, although they can manufacture a new part quite readily (Figure 8-32). With regard to the repair, the owner can assure himself of the security of the repair by asking to see references, certified procedures, and, if necessary, tests prior to committing to the repair. The savings in cost and delivery make it worthwhile to consider repair. Repair and Maintenance of Rotating Equipment Components 495 Figure 8-32. The foreign-object damage on these turbine blades was repaired by welding. The original manufacturers offered only new blades. The repair was made at a fraction of the cost of new blades and in a matter of weeks. Knowledge Base of Repairers Machines come in a wide variety of shapes, makes, models, and mate- rials. Nonetheless, they are all subject to the laws of nature as interpreted through the science and art of engineering. Any complex problem or machine can be broken down into its component elements and the laws of engineering applied to it. An expert repairer who is also an OEM is familiar with basic engineering principles and can apply them to any type of machine and problem. For example, rotor dynamic design for a pump, a compressor, and a turbine follow the same principles. Another example is seal clearance for an unfamiliar machine, which can be determined by knowledge of the fluid and its pressure, and the physical dimensions of the seal. Thus by knowing how to design a turbine or a compressor, an expert repairer can repair any type or make. Another means of repairing an unfamiliar machine is by technology transfer. The repair procedures can be transferred from one type of machine to an entirely different type. For example, a steam turbine and a mixer may seem two entirely dissimilar machines. However, the shafts perform the same basic function and can be made of the same type of material. Thus a journal or coupling repair developed for a steam turbine can be used with perfect assurance on a mixer shaft. Therefore, by having the experience of designing and manufacturing machinery, by the use of basic engineering, and by technology transfer, an expert repairer accumulates a wide reference list of repairs on all types of machines. This experience is greatly augmented if the repairer has a number of facilities around the world and these facilities freely exchange their information. Cost and Delivery Issues With few exceptions, the cost of repairing is a fraction of buying new. This cost is known prior to commencement of the work and indeed is quoted as a firm price to the owner. One of the big advantages of repair is that it can be done in a fraction of the time required to make a new component. This means that machines can be put back in operation within days or weeks instead of months. Even if the component is a spare, the owner has the security of having the repaired part close at hand sooner. By the foregoing discussion it is apparent that repairing is not a hit-or- miss proposition but a controlled science. By defining the work scope, the processes, and the specifications, a repairer can absolutely determine and 496 Machinery Component Maintenance and Repair guarantee the cost. Similarly, the time required to repair is calculated, and when combined with facility capacity and load, a delivery date is determined. Normal working hours are from 8 in the morning to 6 the following morning. In an emergency, around-the-clock working can be instituted. Repair Guarantees and Insurance Issues All repairs are guaranteed for material and workmanship as if they were new and this guarantee can be obtained in writing. This naturally follows from the discussion above, that repairing is scientific; consequently, the performance of the repaired component is generally predictable and guar- anteeable. Only in rare instances, damage may be just beyond the reach of guaranteed repairability. However, for operational reasons the owner may need to have the equipment running quickly. Under these circum- stances a repair may be effected on a best effort basis. Insurance companies that provide machinery breakdown coverage are intensely interested in repairs. Their interest is based on the ability to reduce the cost of a breakdown and to avoid the introduction of potential risks through the repair process. Consequently, they have become increas- ingly involved with owners, repairers, and researchers in qualifying repair methods. The principal focus has been in the weld repair of highly loaded rotors. Insurance companies are promoting the repair of components, provided (and it’s a very important proviso) that the risks of repair can be assessed and controlled. This control can be exercised through the specifications, qualified procedures, and facilities discussed above. Initiating the Repair Sequence The repair process can be initiated by simply telephoning an expert repairer, describing the problem, and asking for an opinion. If the repairer needs more information, he will conduct a visual inspection either at the owner’s site, if the part is large, or at the repair facility (Figure 8-33). This often results in a formal proposal to repair. Should a more detailed examination be required to assess the extent of the damage, it would be conducted at the repairer’s facility where the necessary equipment is avail- able. An owner can ask that the repairer formally quote the price and work scope of this examination. In any case, the cost is very small and usually worthwhile. Repair and Maintenance of Rotating Equipment Components 497 498 Machinery Component Maintenance and Repair Figure 8-33. The process of finding out the cost of repairing a component is easy. Most of the time a visual inspection can result in a price and delivery. The expert repairer will give an opinion free of charge. Figure 8-34. Detailed inspections result in a quotation and inspection report. These form a basis for discussion between the owner and the expert repairer. Only when the owner is fully satisfied about the security of the repair does the actual repair work commence. Following the tests, the repairer will present a report of the findings and a proposal for repairs (Figure 8-34). At this point a discussion can be held between repairer and owner so that the owner can be clearly informed of the proposed methods and select alternatives, if proposed. If the owner decides to proceed, the repairer creates work instructions detailing proce- dures and specifications to be used in doing the repair and the quality checks required. As the work is done, careful records are maintained. Ship- ment of the repaired component is followed by a report containing the quality records of the work. Installation vs. Reinstallation A part whose repair is guaranteed is indistinguishable from a new part. Where it is different than a new part is when additional work is carried out to make it better than a new part. Therefore, whether new or repaired, a part can be reinstalled. The owner should consider that the equipment has failed, and the failure mode must be examined to find and address the root cause of failure. It is possible to set up a monitoring system to make sure that the root cause has been eliminated. This monitoring should check the replaced part as well as any parts that are functionally related. This approach is valid regardless of whether the part is repaired or replaced with a new one. Shipments to Other Countries Components being temporarily exported are not subject to import duties, and shipping documents should be marked accordingly. Shipping documents should indicate that the component is being temporarily exported for repair and will be returned to the country of origin. The pro- cedure is simpler than for exporting new machinery. Transporting Damaged or Repaired Components The repairer can provide expert advice not only in export/import doc- umentation but in arranging quick methods of transportation. Low-cost air freight, good highways, and roll-on, roll-off vessels have made possi- ble extremely short transit times. Repair and Maintenance of Rotating Equipment Components 499 [...]... machining and assembly and never to disturb this balance by making indiscriminate 514 Machinery Component Maintenance and Repair corrections on the finished assembly To do all this properly is exceedingly difficult, and the methods and accuracies required border on (and often exceed) the limits of available technology of manufacturing and measuring These limits dictate how fast a rotor may run and how... run to mini- 506 Machinery Component Maintenance and Repair mize the windage loss of the spinning impeller Bursting speeds may range from 1 ,20 0 to 2, 000 ft/sec (tip speed) on fabricated and cast impellers, and may be even higher on forged and milled wheels Impellers of a ductile material will deform long before reaching burst speed If the operating tip speeds must be as high as 1 ,20 0–1,600 ft/sec,... authors 501 5 02 Machinery Component Maintenance and Repair Figure 9-1 Compressor repair and run-out verification at a major independent repair facility (Source: Hickham Industries, La Porte, Texas.) Built-Up Rotor This style is used for virtually all centrifugal compressors and some axial designs 1 Heavy-Shrink Style—The impellers are usually shrunk to the shaft with an interference fit of 3/4 to 11 /2 mils/in...500 Machinery Component Maintenance and Repair References 1 Nelson, W E., and Wright, R M., Amoco Oil Co., “Reengineering of Rotating Equipment through Maintenance, ” presented at the ASME Petroleum Division Conference and Workshop, Dallas, Texas, September 1 981 2 Wall Colmonoy Corporation, Detroit, Michigan Reprint in Welding Journal,... with basic knowledge and comparison standards (checklists and procedures, etc.), the user is in a good position to ask relevant questions of those responsible for turbomachinery repair Compressor Rotor Repairs* There are two basic types of compressor rotors: the drum type and the built-up type There are two variations of each style * Material contributed by W E (“Ed”) Nelson (†) and gratefully acknowledged... spacing and the roller configuration of the balancing machine 510 Machinery Component Maintenance and Repair Guidelines for designing the mandrel are: 1 The mandrel should preferably be made of low alloy steel, i.e., AISI 4140 or AISI 4340, which has been suitably stress-relieved 2 The journal surfaces should preferably be hardened and ground, with a finish not poorer than 16 rms 3 All diameters must... less) 5 12 Machinery Component Maintenance and Repair Rotor Bows in Compressors and Steam Turbines Rotors sometimes will operate very satisfactorily for years, then upon restarting after a shutdown, excessive vibration occurs at the first lateral critical speed This vibration problem may originate from the following: 1 The unit is tripped at rated speed and the rotative speed abruptly drops 2 The effective... Machining Company, Milwaukee, Wisconsin, 1990 Chapter 9 Centrifugal Compressor Rotor Repair Turbomachinery rotor repair is a complex business It involves knowledge of design concepts, good machinery practices, and above all, patience and keeping track of details Repair work on the rotating elements of compressors and turbines has traditionally been the field of the original equipment manufacturer, not... Rotor Repair 2 3 4 5 505 speeds—600 80 0 ft/sec With rivets milled integrally out of blade stock, and with alloy steel discs of 120 ,000 psi tensile stress or higher, tip speeds up to 1,000 ft/sec have been obtained operationally Fabricated shrouded impellers, assembled with the aid of welding This permits greater aerodynamic refinement in blade curvature design and, with newly developed alloy steels and. .. approximately 300°F for installation and removal 5 Keyways are not incorporated in the mandrel 6 The impeller balancing mandrel should be checked to assure that it is in dynamic balance Make corrections on the faces, if required 7 The impeller balancing mandrel should be free of burrs and gouges 8 Mount each individual impeller, together with its half-key, on the balancing mandrel A light coating of molybdenum . specifications are used in the selection and Repair and Maintenance of Rotating Equipment Components 493 Figure 8- 30. The impeller shown in Figure 8 -29 after weld repair and final machining. The impeller. the part prior to the repair. There should thus be no doubt as to the expected results of the process. Repair and Maintenance of Rotating Equipment Components 491 4 92 Machinery Component Maintenance. the repair. Samples are provided to the owner of the part to make his own tests and reach the same results as those of the repairer (Figures 8 -29 and 8- 30). Ascertaining Integrity of the Repair