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AMAZON multi-meters discounts AMAZON oscilloscope discounts High-Speed Shaft Repair In the foregoing we saw several successful pump shaft repair techniques described. Quite often the restoration of low speed shafts with less damage than we saw previously does not represent any problems. Flame spraying by conventional oxyacetylene methods most often will lead to satisfactory results. The market abounds in a variety of flame spray equipment, and most in-house process plant maintenance shops have their preferred makes and techniques. We would now like to deal with the question of how to repair damaged journals, seal areas, and general geometry of high speed turbomachinery shafts. We will mainly focus on centrifugal compressor and turbine rotor shafts in excess of 3,600 rpm. Four repair methods can generally be identified: Two, that result in the restoration of the original diameter, i.e.: 1. Flame spraying-hard surfacing. 2. Chemical plating. The other two methods result in a loss of original diameter. They are: 1. Polishing. 2. Turning down the diameter. Chemical Plating. Later, in Section 10, we will discuss the technique of industrial hard chrome plating of power engine cylinders. Worn bearing journals, shrink fit areas of impellers and turbine wheels, thrust collar areas and keyed coupling hub tapers have been successfully restored using industrial hard chrome. We don’t see much benefit in describing hard chrome specifications. We recommend, however, that our readers always consult a reputable industrial hard chrome company. Since chrome plating is too hard to be machined, grinding is the only suitable finishing process. Again, experience and skill of the repair organization is of the utmost importance: Soft or medium grinding wheels should be applied at the highest possible, but safe speeds. Coolant must be continuous and copious. Only light cuts not exceeding 0.0003 in. (7.5mm) should be taken, as heavy cuts can cause cracking and heat checks. As a rule of thumb, final ground size of a chrome plated shaft area should not exceed 0.007 to 0.010 in. Chrome plating for radial thickness in excess of these guidelines may require more than one chrome plating operation coupled with intermediate grinding operations. Knowing this, it would be well to always determine the required time for a shaft chrome plating project before a commitment is made. Flame Spray Coatings. The available flame spray methods will be described later. For practical reasons the detonation gun, jet gun, plasma arc, and other thermal spray processes may suit high speed machinery. There is, however, reason to believe that other attractive techniques will become available in the future. We believe that coatings applied by conventional oxyacetylene processes tend to have a weaker bond, lower density, and a poorer finish than other coatings. Further, there are too many things "that can go wrong," a risk to which we would not want to subject high speed machinery components. The authors know of an incident where a critical shaft had been allowed to be stored several hours before oxyacetylene metalizing. Dust and atmospheric humidity subsequently caused a problem with the coating well after the machine was up and running. In conclusion, we think that the occasional unavailability of D-gun or plasma coating facilities and the high cost of these methods far outweigh the risk that is inherent in applying oxyacetylene flame sprays. Shaft Repair by Diameter Reduction. In polishing up the shaft journal, minor nicks and scratches can be dressed up by light stoning or strapping. It goes without saying that depth of scratches, affected journal area, roundness and taper-or shaft geometry-are factors that should be considered when making the repair decision. Generally, scratch depths of 0.001 in. or less are acceptable for use. A good method is to lightly run the edge of a coin over the affected area in order to obtain a feel for scratch severity. Deeper scratches, from 0.001 in. to approximately 0.005 in. must be strapped or stoned. Usually scars deeper than 0.005 in. should call for a clean-up by machining of the shaft. Strapping. This is done with a long narrow strip of #200 grit emery cloth. The strap is first soaked in kerosene and abraded against a steel surface to remove sharper edges of the abrasive material. It’s then wrapped around the journal at least two times and pulled back and forth in order to achieve a circumferential polishing motion. This can best be accomplished by two persons-one on each end of the strap. The amount of material removed from the journal diameter must not exceed 0.002 in. Stoning. This consists of firm cutting strokes with a fine grit flat oil stone following the journal contour. The stone is rinsed frequently in diesel oil or cleaning solvent to prevent clogging. To avoid creating flat spots on the journal, stoning should be limited to removing any raised material surrounding the surface imperfection. If the journal diameter is 0.002 in. or more outside of the tolerance, then journal, packing ring, and seal surfaces can be refinished to a good surface by turning down and grinding to the original finish. This introduces the need for special or nonstandard bearings or shaft seals. Stocking and future spare parts availability become a problem. Machining of shaft diameters for nonstandard final dimensions can therefore only be an emergency measure. Generally, the diameters involved should be reduced by the minimum amount required to clean up and restore the shaft surface. For this the shaft must be carefully set up between centers and indicated to avoid eccentricity. "Standard" undersize dimensions are in 0.010 in. increments. The maximum reduction is naturally influenced by a number of factors. It would mainly depend on the original manufacturer's design assumptions. Nelson1 quotes the U.S. Navy cautioning against reducing journal diameters by more than 1/4 in., or beyond that diameter which will increase torsional shear stress 25 percent above the original design, whichever occurs first. TBL. 2 shows this guideline. Finally, the assembled rotor should be placed in "V" blocks and checked for eccentricity. TBL. 3 shows suggested guidelines for this check. TBL. 2 Limiting High Speed Shaft Journal Reductions1 Original Design Diameter Minimum Diameter to Which Shaft May Be Reduced Less than 3.6 inches 93 percent of original design diameter 3.6 inches or greater Original design diameter less 1/4 inch TBL. 3 Recommended Eccentricity Limits for High Speed Turbomachinery Rotors Surface Tolerance (in.) Impeller eye seal 0.002 Balance piston 0.002 Shaft labyrinth 0.002 Impeller spacer 0.002 All other 0.0005 Shaft Straightening Successful straightening of bent rotor shafts that are permanently warped has been practiced for the past 40 or more years, the success generally depending on the character of the stresses that caused the shaft to bend. In general, if the stresses causing the bend are caused from improper forging, rolling, heat treating, thermal stress relieving, and/or machining operations, then the straightening will usually be temporary in character and generally unsuccessful. If, however, a bent shaft results from stresses set up by a heavy rub in operation, by unequal surface stresses set up by heavy shrink fits on the shaft, by stresses set up by misalignment, or by stresses set up by improper handling, then the straightening will generally have a good chance of permanent success. Before attempting to straighten a shaft, try to determine how the bend was produced. If the bend was produced by an inherent stress, relieved during the machining operation, during heat proofing, on the first application of heat during the initial startup, or by vibration during shipment, then straightening should only be attempted as an emergency measure, with the chances of success doubtful. The first thing to do, therefore, is to carefully indicate the shaft and "map" the bend or bends to determine exactly where they occur and their magnitude. In transmitting this information, care should be taken to identify the readings as "actual" or "indicator" values. With this information, plus a knowledge of the shaft material available, the method for straightening can be selected. Straightening Carbon Steel Shafts Repair Techniques for Carbon Steel Shafts For medium carbon steel shafts (0.30 to 0.50 carbon), three general methods of straightening the shaft are available. Shafts made of high alloy or stainless steel should not be straightened except on special instructions that can only be given for individual cases. The Peening Method. This consists of peening the concave side of the bend, lightly hitting it at the bend. This method is generally most satisfactory where shafts of small diameters are concerned-say shaft diameters of 4 in. (100mm) or less. It’s also the preferred-in many cases, the only-method of straightening shafts that are bent at the point where the shaft section is abruptly changed at fillets, ends of keyways, etc. By using a round end tool ground to about the same radius as the fillet and a 2 1/2 lb machinist's hammer, shafts that are bent in fillets can be straightened with hardly any marking on the shaft. Peening results in cold working of the metal, elongating the fibers surrounding the spot peened and setting up compression stresses that balance stresses in the opposite side of the shaft, thereby straightening the shaft. The peening method is the preferred method of straightening shafts bent by heavy shrink stresses that some times occur when shrinking turbine wheels on the shaft. Peening the shaft with a light (1/2 lb) peening hammer near the wheel will often stress-relieve the shrink stresses causing the bend without setting up balance stresses. The Heating Method. This consists of applying heat to the convex side of the bend. This method is generally the most satisfactory with large diameter shafts-say 4 1/2 in. (~112.5mm) or more. It’s also the preferred method of straightening shafts where the bend occurs in a constant diameter portion of the shaft-say between wheels. This is generally not applicable for shafts of small diameter or if the bend occurs at a region of rapidly changing shaft section. Because this method partially utilizes the compressive stresses set up by the weight of the rotor, its application is limited and care must be taken to properly support the shaft. The shaft bend should be mapped and the shaft placed horizontally with the convex side of the bend placed on top. The shaft should be supported so that the convex side of the bend will have the maximum possible compression stress available from the weight of the rotor. For this reason, shafts having bends beyond the journals should be supported in lathe centers. Shafts with bends between the journals can usually be supported in the journals; however, if the end is close to the journal, it’s preferable to support the shaft in centers so as to get the maximum possible compression stress at the convex side of the bend. In no event should the shaft be supported horizontally with the high spot on top and the support directly under the bend, since this will put tension stresses at the point to be heated, and heating will generally permanently increase the bend. Shafts can be straightened by not utilizing the compressive stress due to the weight of the rotor, but this method will be described later. To straighten carbon steel shafts using the heating method, the shaft should be placed as just outlined and indicators placed on each side of the point to be heated. Heat should be quickly applied to a spot about two to three in. (~50-75mm) in diameter, using a welding tip of an oxyacetylene torch. Heat should be applied evenly and steadily. The indicators should be carefully watched until the bend in the shaft has about tripled its previous value. This may only require perhaps 3 to 30 seconds, so it really is very important to observe the indicators. The shaft should then be evenly cooled and indicated. If the bend has been reduced, repeat the procedure until the shaft has been straightened. If, however, no progress has been made, increase the heat bend as determined by the indicators in steps of about 0.010-0.020 in. (0.25-0.50mm) or until the heated spot approaches a cherry red. If, using heat, results are not obtained on the third or fourth try, a different method must be tried. The action of heat applied to straighten shafts is that the fibers surrounding the heated spot are placed in compression by the weight of the rotor, the compression due to expansion of the material diagonally opposite, and the resistance of the other fibers in the shaft. As the metal is heated, its compressive strength decreases so that ultimately the metal in the heated spot is given a permanent compression set. This makes the fibers on this side shorter and by tension they counterbalance tension stresses on the opposite side of the shaft, thereby straightening it. The Heating and Cooling Method. This method is especially applicable to large shafts that cannot be supported so as to get appreciable compressive stresses at the point of the bend. It consists of applying extreme cold- using dry ice-on the convex side of the bend and then quickly heating the concave side of the bend. This method is best used for straightening shaft ends beyond the journals or for large vertical shafts that are bent anywhere. Here, the shaft side having the long fibers is artificially contracted by the application of cold. Then this sets up a tensile stress in the fibers on the opposite side which, when heated, lose their strength and are elongated at the point heated. This now sets up compressive stresses in the concave side that balance the compressive stresses in the opposite side. Indicators should also be used for this method of shaft straightening-first bending the shaft in the opposite direction from the initial bend, about twice the amount of the initial bend-by using dry ice on the convex side-and then quickly applying heat with an oxyacetylene torch to a small spot on the concave side. Shafts of turbines and turbine-generator units have been success fully straightened by various methods. These include several 5,000-kw turbine-generator units, one 6,000-kw unit, and many smaller units. Manufacturers of turbines and other equipment have long used these straightening procedures, which have also been used by the U.S. Navy and others. With sufficient care, a shaft may be straightened to 0.0005 in. or less (0.001 in. or 0.025mm total indicator reading). This is generally satisfactory. Casting Salvaging Methods Repair of Castings. Quite often cast components of process machinery cannot be repaired by welding. We will now deal briefly with these salvaging methods: 1. Controlled-atmosphere furnace brazing. 2. Application of molecular metals. 3. Metal stitching of large castings. Braze repair of cavitation damaged pump impellers is an adaptation of a braze-repair method originally developed for jet engine components. The first step is rebuilding the eroded areas of the impeller blades with an iron-base alloy powder. The powder is mixed with an air-hardening plastic binder and used to fill the damaged areas. Through-holes are backed up with a temporary support and packed full of the powder/binder mixture. After hardening, the repaired areas are smoothed with a file to restore the original blade contour. A nickel-base brazing filler metal in paste form is then applied to the surface of the repaired areas and the impeller is heated in a controlled atmosphere furnace. In the furnace, the plastic binder vaporizes and the brazing filler metal melts, infiltrating the alloy powder. This bonds the powder particles to each other and to the cast iron of the blade, forming a strong, permanent repair. After the initial heating, the impeller is removed from the furnace and cooled. All nonmachined surfaces are then spray coated with a cavitation resistant nickel-base alloy and the impeller is returned to the furnace for another fusion cycle. After the treatment, the impeller will last up to twice as long as bare cast iron when subjected to cavitation. Because the heating is done in a controlled-atmosphere furnace, there is no localized heat build-up to cause distortion and no oxidation of exposed surfaces. Unless the machined surfaces are scored or otherwise, physically damaged, repaired impellers can be returned to service without further processing. An average impeller can be repaired for less than a third of the normal replacement cost. Molecular metals have been applied successfully to the rebuilding and resurfacing of a variety of process machinery components. Molecular metals 3 consist of a two-compound fluidized metal system that after mixing and application assumes the hardness of the work piece. The two compounds are a metal base and a solidifier. After a prescribed cure time the material can be machined, immersed in chemicals, and mechanically or thermally loaded. Molecular metals have been used to repair pump impellers, centrifugal compressor diaphragms, and engine and reciprocating compressor water jackets damaged by freeze-up. FIG. 23. Metal locking a machinery casting Metal stitching is the appropriate method to repair cracks in castings. One reputable repair shop describes the technique. 1. The area or areas of a casting suspected of being cracked are cleaned with a commercial solvent. Crack severity is then determined by dye penetrant inspection. Frequently, persons unfamiliar with this procedure will fail to clearly delineate the complete crack system. Further, due to the heterogeneous microstructure of most castings, it’s quite difficult to determine the paths the cracks have taken. This means that the tips of the cracks-where stress concentration is the highest-may often remain undiscovered. This also means that cracks stay undiscovered until the casting is returned to service, resulting in a potential catastrophe. It takes an experienced eye to make sure that the location of the tips is identified. 2. To complete the evaluation of the crack system, notice is taken of the variations in section thickness through which the crack or cracks have propagated. This step is critical because size, number, and strength of the locks and lacings--see FIG. 23--are primarily determined by section thickness. Where curvatures and/or angularity exist, the criticalness of this step is further increased. 3. Metallurgical samples are taken to determine the chemical composition, physical properties, and actual grade of casting. This enables the repair shop to select the proper repair material. And this, along with the cross-sectional area of the failure, determines how much strength has actually been lost in the casting. 4. After these decisions have been taken, the actual repair work is started. a. Repair material is selected. This material will be compatible with the parent material, but greater in strength. b. The patterns for the locks are designed onto the casting surface. c. These patterns are then "honey combed" using an air chisel. This provides a cavity in the parent metal that will accept the locks. Improper use of these tools produces a cavity which is not properly filled by the lock. The result is a joint that lacks strength and from which new cracks may emanate. d. Assuming the lock is properly fitted, a pinning procedure is now undertaken. This consists of mating the lock to the parent metal by drilling holes so that one half of the hole circles are in the parent metal and the remaining halves are in the locks. High alloy, high strength, slightly over-sized mating pins are driven into these holes with an air gun. This produces a favorable residual stress pattern: In the immediate area of the lock, tensile stresses exist which change to desired compressive stresses as one moves out into the parent metal. This is to prevent future crack propagation. Additionally, these pins prevent relative movement between the locks and the parent metal. e. The final repair step aside from dress-up is the insertion of high strength metallic screws into previously drilled and tapped holes along the cracks paths in between the locks. To clarify, it should be noted that the orientation of the locks is such that the longitudinal axis of the locks is perpendicular to the path of the crack. Thus, between locks, the lacing screws are used to "zipper-up" the crack. Care must be exercised to make sure each lock is properly oriented. Care must also be exercised so that, when the lacing screws are driven to their final positions, a harmonious blending with the parent metal is achieved. The entire repair sequence can be easily visualized by referring to FIG. 24. An amazing variety of machines have been successfully repaired using metal stitching techniques ( TBL. 4). TBL. 4 Typical Field and Shop Repair Services Offered by Process Machinery Repair Shops TBL. 4-cont'd Typical Field and Shop Repair Services Offered by Process Machinery Repair Shops FIG. 24. Metalstitch® process of casting repair (courtesy In-Place Machining Company, Milwaukee, Wisconsin) Contact with Service Shops The person or persons responsible and accountable for machinery repair and maintenance should establish contact with service shops. This is best done by visiting them and judging their facilities, "track record" and personnel. This could lead to a numerical rating on a scale of one to ten to help with the final decision. It goes without saying that quotations for new equipment prices should be obtained, so that the practicality of a rebuild or repair order can be ascertained. For instance, as a rule of thumb it would not be advisable to have an electric motor rewound if costs exceeded 70 percent of a new equivalent replacement, or if higher efficiency replacement motors are available. Also, if time is available, the purchase of surplus equipment may be considered. It would be advisable to maintain a subscription to at least one used or surplus equipment directory for that purpose. The machinery maintenance person, during his facility visit, should gather information as to what procedures the shop uses to comply with plant specifications. Obviously, a final sourcing decision should be made only after analyzing all available data and after the visit. The analysis can be made in form of a spreadsheet, using a marking pen to highlight pertinent facts and color-coding prices by relative position. In essence, this rigorous procedure is similar to a formal bid evaluation process and would rank the bidders by shop capacity, experience, reputation, recent performance, order backlog, or even labor union contract expiration date and the like. OEM vs. Non-OEM Machinery Repairs Equipment users are inundated with reams of technical information concerning machinery in the purchasing phase. Yet, seldom do operators/ users get an opportunity to ask some very basic questions that deserve to be answered to run their business, and even less information is available on repairing. The questions presented in this segment of our text were elicited by the Elliott Company* from a group of users, and answers to these questions are fundamental in helping to keep machinery running. Basic questions of what, why, when, and especially how to repair instead of buying new are considered. It’s a simple guide to what the buyer of repair services should ask. When to Consider Repairing a Worn or Damaged Component or Assembly Instead of Buying New FIG. 25. Gas expander blades of superalloy are typical examples of new parts deliveries that can exceed 10 months. These blades can be repaired with controlled welding, heat treatment, and coating processes in weeks. It’s always worthwhile to ask an expert repair company about the repairability of a worn or damaged component, and the advice is usually free. Fortunately, most turbomachinery components can be repaired at lower cost and shorter lead time than buying new. Only in the case of small, inexpensive, mass-produced components is repair not worthwhile. Usually repair is considered to reduce delivery time and costs while maintaining product integrity ( FIG. 25). The term expert repairer is meant to indicate a dedicated repair facility of an original equipment manufacturer. This type of facility provides rapid action required by an after-sales service organization while at the same time having available the experienced engineering department and know-how of an original equipment manufacturer. How to Find Out if the Component Is Repairable A phone call to an expert repairer with a description of the component and of the problem will often result in an answer ( FIG. 26). For bigger problems users can ask the repairer to conduct an inspection of the component at site. What Components Can Be Repaired Practically any part of a rotating machine can be repaired. Any list of parts that are repairable would be lengthy and still be incomplete. But just to give an idea, machinery that can be repaired includes pumps, compressors, steam turbines, gas turbines, mixers, and fans. Repairs can be effected for breakage, wear, erosion, corrosion, galling, fretting, cracking, bending, and over-temperature, to name but a few types of the many conceivable problems ( FIG. 27 and 8-28). Among the numerous components that have been successfully repaired we find rotors of all types, impellers, blades, disks, shafts, bearings, diaphragms, stators, seals, vanes, buckets, combustion chambers, casings, nozzles, valves, equipment casings, and gears. Knowing How to Manufacture a Component that Is Totally Destroyed The simplest way of reconstructing a destroyed component is to use a spare part from stores as a guide. In many instances the component is also contained in a spared machine, which can then be used as a model. As a last resort, a part can be redesigned from the space created by the surrounding parts. Great care must be used with this method. The repairer needs to be an original equipment manufacturer as well as a repair specialist. This means that he is fully familiar with the function of the part and the engineering principles and tools necessary to reconstruct it. FIG. 26. Classical repair problem on all types of rotating machinery is the scoring of shaft journals. Welding can be used to repair damage to any depth. Formerly journal repair was limited to allowable chrome plating thicknesses. Thrust collars can similarly be repaired. Quotations for this type of repair can be made quickly. FIG. 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 combination of welding and mechanical techniques. FIG. 28. Turbine diaphragm for the casing shown in FIG. 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’s often more economical 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 procedure 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 ( FIG. 29 and 8-30). Ascertaining Integrity of the Repair Process A reputable repairer will take every precaution to determine the material, 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. FIG. 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 specifications required to perform that step. Each step is inspected and verified before the next step is performed ( FIG. 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. FIG. 30. The impeller shown in FIG. 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. 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 Petroleum 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. FIG. 31. ISO 9002 requires implementation of quality assurance system control procedures, qualification of personnel, and calibration of instruments used. The aim is that the customer gets exactly what he ordered, precisely when promised. 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. Nondestructive examinations are subject to Society for Non-Destructive Testing (SNT) standards. Material specifications are used in the selection and acceptance of materials as, For example, American Society for Testing Materials (ASTM), British Standards (BS), or Deutsche Industrie Normen (DIN). FIG. 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. 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 processing, 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 technology. Therefore, they simply are incapable of carrying out a repair, although they can manufacture a new part quite readily ( FIG. 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. Knowledge Base of Repairers Machines come in a wide variety of shapes, makes, models, and materials. 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’s 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 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 guaranteeable. 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 increasingly 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 ( FIG. 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. FIG. 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. FIG. 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 ( FIG. 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 procedures and specifications to be used in doing the repair and the quality checks required. As the work is done, careful records are maintained. Shipment 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’s 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’s 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 procedure is simpler than for exporting new machinery. Transporting Damaged or Repaired Components The repairer can provide expert advice not only in export/import documentation but in arranging quick methods of transportation. Low-cost air freight, good highways, and roll-on, roll-off vessels have made possible extremely short transit times. 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 1981. 2. Wall Colmonoy Corporation, Detroit, Michigan. Reprint in Welding Journal, April 1971. 3. Technical Bulletin by Belzona Molecular Ltd., Harrogate, Yorkshire, U.K., publication No. 15673. 4. Harris, E. W., "Procedure for Repairing Large Castings or Forgings," Casting Repair Service, Inc., Center, Texas 75935, 1983, Pages 1-3. 5. Boak, J. D., "Selecting a Motor Repair Shop," Plant Services, June 1983, Pages 64-65. 6. Advertising Bulletin, Peacock Brothers Limited, Toronto, Ontario, Canada. 7. Byron Jackson Marketing/Sales Department, Los Angeles, California, "The Advisor," Volume 1, No. 4. 8. Technical Bulletin by In-Place Machining Company, Milwaukee, Wisconsin, 1990. |