Machinery Components Maintenance And Repair Episode 2 Part 8 pot

An expert repairer who is also an OEM has the capability of designingand manufacturing a spare part required to complete a repair and will do so if needed.. proce-Ascertaining Integrity

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 tion of welding and mechanical techniques.

combina-Figure 8-28 Turbine diaphragm for the casing shown in combina-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 how of the original equipment manufacturer (OEM) Another OEM canindeed reconstruct spare parts manufactured by others However, he has

know-to spend engineering hours know-to create a drawing and know-to specify theprocesses 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 designingand 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 partssince 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 thequality records maintained is a job folder for each repair containing allthe information pertaining to that repair This includes dimensionalchecks, nondestructive examination, specifications, in-progress qualityrecords, 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 containingall the necessary procedures, specifications, and quality checks to carryout 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 dure is first used on a model of the failed component The parameters ofthe procedure are recorded The model is then examined destructively toprovide positive proof of the repair Samples are provided to the owner ofthe part to make his own tests and reach the same results as those of therepairer (Figures 8-29 and 8-30)

proce-Ascertaining Integrity of the Repair Process

A reputable repairer will take every precaution to determine the rial, metallurgical, and physical state of the part prior to commencement

mate-of the repair Only known and controlled processes are applied to the partprior to the repair There should thus be no doubt as to the expected results

of the process

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 whichevery step is detailed Each step calls out the necessary tools and specifi-cations required to perform that step Each step is inspected and verifiedbefore the next step is performed (Figure 8-31) Final inspection and testsconfirm the quality that has been built into the repair process each step ofthe way A final report must record the history of the repair as well as theverified 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 anorganization 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, itcan 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 originallymaking the part are applied to the repair If the part is from a compressor

or steam turbine of a petroleum refinery, for example, American leum Institute (API) standards are applied In actual practice once a repairfacility is capable of working to these high standards they will be applied

Petro-to all parts whether they come from a refinery or not

Specifications are applied to individual processes as needed Forexample, welders and weld procedures must be qualified to AmericanSociety 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

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 TestingMaterials (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 modelfor quality assurance in production and installation This standard controlsevery 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 internationaland demanding standard has as its objective that the customer should getexactly what he bought, precisely on time

Resolving Different Opinions: Scrap vs Repair

It could happen that the OEM recommends buying new while an expertrepairer proposes a repair It does not mean that the OEM is remiss orcallous but only that he is not familiar with the repair technology AllOEMs are capable of designing and manufacturing new equipment Only a very few have applied any research effort in developing 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 anddelivery make it worthwhile to consider repair

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 rials Nonetheless, they are all subject to the laws of nature as interpretedthrough the science and art of engineering Any complex problem ormachine can be broken down into its component elements and the laws

mate-of engineering applied to it An expert repairer who is also an OEM isfamiliar 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 byknowledge of the fluid and its pressure, and the physical dimensions ofthe seal Thus by knowing how to design a turbine or a compressor, anexpert repairer can repair any type or make

Another means of repairing an unfamiliar machine is by technologytransfer The repair procedures can be transferred from one type ofmachine to an entirely different type For example, a steam turbine and amixer may seem two entirely dissimilar machines However, the shaftsperform the same basic function and can be made of the same type ofmaterial Thus a journal or coupling repair developed for a steam turbinecan be used with perfect assurance on a mixer shaft

Therefore, by having the experience of designing and manufacturingmachinery, 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 anumber of facilities around the world and these facilities freely exchangetheir 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 isquoted 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 machinescan 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 therepaired part close at hand sooner

By the foregoing discussion it is apparent that repairing is not a miss proposition but a controlled science By defining the work scope, theprocesses, and the specifications, a repairer can absolutely determine and

hit-or-guarantee the cost Similarly, the time required to repair is calculated, and when combined with facility capacity and load, a delivery date isdetermined Normal working hours are from 8 in the morning to 6 the following morning In an emergency, around-the-clock working can beinstituted.

Repair Guarantees and Insurance Issues

All repairs are guaranteed for material and workmanship as if they werenew and this guarantee can be obtained in writing This naturally followsfrom the discussion above, that repairing is scientific; consequently, theperformance 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 ownermay 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 areintensely interested in repairs Their interest is based on the ability toreduce the cost of a breakdown and to avoid the introduction of potentialrisks through the repair process Consequently, they have become increas-ingly involved with owners, repairers, and researchers in qualifying repairmethods The principal focus has been in the weld repair of highly loadedrotors

Insurance companies are promoting the repair of components, provided(and it’s a very important proviso) that the risks of repair can be assessedand 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 expertrepairer, describing the problem, and asking for an opinion If the repairerneeds more information, he will conduct a visual inspection either at theowner’s site, if the part is large, or at the repair facility (Figure 8-33) Thisoften 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 workscope of this examination In any case, the cost is very small and usuallyworthwhile

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 heldbetween repairer and owner so that the owner can be clearly informed ofthe proposed methods and select alternatives, if proposed If the ownerdecides to proceed, the repairer creates work instructions detailing proce-dures and specifications to be used in doing the repair and the qualitychecks required As the work is done, careful records are maintained Ship-ment of the repaired component is followed by a report containing thequality 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 carriedout to make it better than a new part Therefore, whether new or repaired,

a part can be reinstalled The owner should consider that the equipmenthas failed, and the failure mode must be examined to find and address theroot cause of failure It is possible to set up a monitoring system to makesure that the root cause has been eliminated This monitoring should checkthe replaced part as well as any parts that are functionally related Thisapproach is valid regardless of whether the part is repaired or replacedwith a new one

Shipments to Other Countries

Components being temporarily exported are not subject to importduties, and shipping documents should be marked accordingly Shippingdocuments should indicate that the component is being temporarilyexported 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 umentation but in arranging quick methods of transportation Low-costair freight, good highways, and roll-on, roll-off vessels have made possi-ble extremely short transit times

1 Nelson, W E., and Wright, R M., Amoco Oil Co., “Reengineering ofRotating Equipment through Maintenance,” presented at the ASMEPetroleum Division Conference and Workshop, Dallas, Texas, Septem-ber 1981

2 Wall Colmonoy Corporation, Detroit, Michigan Reprint in Welding

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

knowl-Repair work on the rotating elements of compressors and turbines hastraditionally been the field of the original equipment manufacturer, not theequipment owner However, a number of independently owned or originalequipment manufacturer (OEM)-owned dedicated repair facilities areavailable to users worldwide These should be considered for compressorrotor repair and reliability enhancements since their competence is often

as good as, or even better than, the OEM’s main factory

Figures 9-1 through 9-3 illustrate work in progress at one such OEM location

non-However, a reliability-focused user will seek involvement in the pressor repair process Equipped with basic knowledge and comparisonstandards (checklists and procedures, etc.), the user is in a good position

com-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 thebuilt-up type There are two variations of each style

501

* Material contributed by W E (“Ed”) Nelson (†) and gratefully acknowledged by the authors.