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y

Th m s H M C sk yM T m h y G t G p

l t P w R s h I st t t

P l lt C l f

Thomas H. (Tom) McClos ey, is the Manager, Turbomachine , in the GenerationGro at the Electric Power Research Institute (EP in Palo Alto, Cal ornia. B rejoining EPRI in 1980, Mr. McClos ey was a projec design engineer for steam turbinesat Westinghouse Electric in Philadelphia.Mr. McClos ey has over 25 years e periencein the design, operation, maintenance andtroubleshooting of steam turbines, umps,and related au iliaries, and hol si patents

in mechanical engineering and steam turbine design.Mr. McClos ey is a llow member of the ASME, past Chairmanof the AS Steam Turbine Committee, and Member of the AdvisoCommittee for the International Pump ers Symposium and acorre onding member of the Turbomachine Sy osiu . He isalso a Charter Member of the Technical Adviso Board for Pumpsand Systems M gazine.

Mr. McClos ey was th recipient the ASME George stinghouse Gold Medal in 1995, as well as the E ison Electric InstitutePrime Movers Award in 1984 H is an author of over 0 technical

papers on power plant equipment and, in particular, on steamturbine generator and pu p availabili y, l assessment, and thermal performance improvements.

BInfo mation and an app oach intended to help enginee ing and

othe plant pe sonnel t oubleshoot bea ng p oble s and diag-nose the mode of bea ing failu es a e p esented. ix leadingmodes of bea ing failu e (ab asion, co osion, elect ical pitting,fatigue, ove heating, and wiping) a e cove ed in some detailEach mode is defined and mechanisms of occu ence a e de-sc ibed. Also, fo each mode, the visual appea ance of fai edbea ings is discussed and possible causes of failu e a e e-viewed. An illust ative example is p ovided symptoms on abea ing su face a e desc ibed and the mode of failu e is identi-fied, as is the oot cause o failu e and possible emedial actions.Because lub ication system p oble s a e a leading cause ofbea ing failu es, effective means of monito ing oil condition a e

also discussed.

Tu bine gene ato bea ing failu es a e a leading cause ofpowe plant unavailability and can cause se ious damage notonly to bea ing systems but also to oto s, stato s, and nea byequipment. In addition to failu es in tu bine gene ato s, bea ingfailu es in othe otating equipment, including pumps, fans, andauxilia y gas tu bines and moto s, can also lead to plant outages.Given the se ious consequences of such b eakdow s, dete mina-tion of the causes of bea ing failu e and methods of effectiveepai a e of pa amount impo tance.

7

The elect ic utility indust y, in conjunction with use s, o iginalequipment manufactu e s and bea ing vendo s, has diagnosedva ious modes of th ust and jou nal bea ing failu es, linked thefailu e modes to potential causes and, fo each failu e inducingoot cause, developed a guideline manual fo emedial actionsand bea ing efu bishment [1]. The manual classi ied 16 sepa-ate modes of bea ing failu e that a e likely to occu in hyd ody-

namic bea ings on powe plant otating equipme t (Table 1).In the following six sections, symptoms, mechanisms andcha acte istics of six fai ly common modes of failu e ab asion,co osion, elect ical pitting, fatigue, ove heating, and wipinga e desc ibed and ways of visually identifying and diagnosingbea ing failu es in each of t e six modes a e t eated. Then theoot cause analysis and medy of an actual powe plant bea ingfailu e is outlined.

Table 1 Modes of Bearing Failure.

O r NAb asi n G in s in s at hiB n d ail e Spallinavitati n si n avitati n

si n hemi al atta kEle t i al pittin F stinE si n m t a ksti e

F ettin F ettin si nH h h mi m dama e i e-w l bla k s abN n-h m eneity Bliste in p osityOve heatin ttlin anis t opy at heting

sweatinSeiz eSt t al dama eS a e wea Bla k s aleTi ide dama e ea

p n Smea i polish n

Familia ity with and eco nition of visual and labo ato ysymptoms that may be conside ed ep esentative of a pa ticulamode of failu e can be inst umental in identifying the failu emode when a bea ing is damaged and a numbe of failu e modesa e possible. The e o e, the fol owing sections include seve alphotogra phs of damaged bearin g surfac es; the se and s imilarvisual aids can be impo tant tools fo pe sons attempting todiagno se the m ode of b earin f ailure in volved i n a part icularincident.

A numbe of possible unde lying causes a e listed fo each ofthe six modes of failu e unde conside ation. On should keep inmind the distinction between di ect and indi ect causes. Thus,while wiping is classified as a distinct mode, it is o ten aconsequence of othe mechanisms suc as fatigue o ove heat

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48 PROCEEDINGS OF THE TWENTY-FOURTH TURBOMACHINERY SYMPOSIUMing; the oot cause, the efo e, would not be a condition likely tocause wiping, but one leading to eithe fatigue o ove heating.The t oubleshoote ' s ultimate goal is to dete mine f om a num-be of possible mechanisms the one distinct cause of the p ob-lem. This is often specific to local situations and involves thepa ticula powe plant, its histo y, and p actices. Whenevepe tinent, the efo e, the t oubleshoote will conside these ele-ments too, to facilitate identification of the specific conditionthat led to a bea ing failu e.

Finally, because one thi d of tu bine bea ing failu es, includ-ing most failu es due to ab asion, involve contaminated lub i-cants o malfunctioning lub icant supply system components,some aspects of maintaining a tu bine lub ication system a ealso discussed.

BAb asion is a mode of bea ing failu e due to the e osive action

of a la ge numbe of solid pa ticles that a e ha de than thebea ing su ace. Unde ce tain conditions both the bea ing andthe sha t may be damaged by the ab asive action of the pa ticles.

M chanisms

When the lub icant ca ies few pa ticles, they eventually

become embedded ha mlessly in the bea ing su face. Whenthe e is a la ge numbe of pa ticles, they eci culate th ough theclea ance, causing wea and sco ing (Figu e The pa ticlesmay be metallic o nonmetallic, la ge o small. When they a ela ge they may become pa tial y embedded in the babbitt. Theywill then p ot ude against the jou nal and nction as a cuttingtool.

Figur 1 Abrasion of a 12 in 30 m) Turbin Journal B aring

Oc asionally, embedded pa ticles a e li ed out of thei seats

and deposited elsewhe e, leaving gouged out indentations, aswell as t acks in the bea ing su face. Because they a e deepethan the clea ance, such t acks become channels fo the d ainageof oil; likewise, any embedded la ge pa ticle o fe s a ba ie tothe flow of oil, fo ming a sta ved pocket nea by. The p esence ofa channel o sta ved pocket c eates a hot spot in the bea ing.When the bea ing st uctu e is penet ated by fo eign mate ial, thebabb tt is b ought past its the mal yield point and unde goesec ystallization accompanied by st ong local heating. Contam-inant pa icles too la ge to be d awn into the oil film will bebatte ed a ound in the oil g oove, gene ating many smallepieces which wi l then ente the clea ance.

Contaminants

Many diffe ent types of pa ticulate, va ying in size and p op-e ties and in potential fo causing damage, may ente the lub i-cation system. The most impo tant cha acte istics of thesepa ticles a e size, ha dness, and shape. Additional p ope ties ofimpo tance a e comp essive st ength and c ushability; a mate i-al that is ha d but b ittle may be less ha mful than a softemate ial. Pa ticles below mic omete s 4mil) in diametecan usually be conside ed too small to cause g ooving in bea -ings fo la ge powe plant otating machine y.

The mo e common pa ticulates found in lub ication systemsand thei possible o igins a e as follows

Quartz or Sand and is a ve y ha d mate ial that willsc atch the ha dest steel as wel as ch omium.

Grit Blasting Substanc s G it is not only damaging when itente s the clea ance space but it often lodges behind the bea ingshell causing high spots in the bea ing. This is pa ticula lyhaza dous in thin shell bea ings.

M tal Chips These a e usually le tove s f om manufactu -ing. Although they a e too soft to sc atch ha d sha ts, they o tenunde go undesi able changes. In the p esence of wate they willust and may fo m hematite (Fe ), which is a ve y st ong

ab asive.W ld Spatt r These, too, a e leftove s om the const uc-

tion pe iod and a e usually egg shaped.F Ash These a e elatively small combusted and noncom

busted coal pa ticles, anging f om 25 mic omete s mil)down to less than mic omete 4mil) in diamete .

Silicon Carbid These a e synthetic ab asives c ose to 25mic omete s mil) in si e with many sha p jagged edges.

Cast Iron Ch s These may come f om the bea ing housing,which on occasion is made of cast i on.

The appea ance of typical oil contaminants as seen unde amic oscope is shown in Figu e 2.

App aranc of Abrad d B arings

The main visual cha acte istic of ab asion is the p esence ofpa allel, ci cum e ential t acks unning ove most of the loadedpa t of the bea ing. mall pa ticles may bounce between shaftand bea ing, causing inte mittent sc atches F equently, the pitshave smooth bottoms; but o dina ily they do not have the meltedappea ance of elect ical pitting. Often a se ies of pits of identicalshape will be spaced at egula inte vals ci cumfe entially ovea po tion of the bea ing; this is unmistakable evidence of pit ingdue to fo eign pa ticles. Natu ally the most f equent location ofsco ing is nea the minimum film thic ess, h (Figu e 3). Asillust ated in Figu e 4,sco ing at low speed o ta tup p oducesa mo e i egula patte n than sco ing t high speed. The embed-ment of pa ticles is, of cou se, indicated by the te mination of apa ticula g oove, as documented in Figu e 5, fo the case of a tinbabbitt mat ix magnified

5times.

While sc atches nd t acks a e the most common featu es ofab asion, two additional cha acte istics a e often p esent withthis kind of damage

When the pa ticles a e small, the e a e g ooved t acks, butthe su face has a dull matte finish; this is easie to detect on thesteel shaft than on the g ay babbitt. Although individual g oovesa e not visible to the eye, the su face will be ough and g itty tothe touch.

When the pa ticles a e la ge and ha d, they may fo m"halos. The pa ticles gene ate ings of elevated babbitt that a ethen polished by contact wi th the shaft into shiny halos.

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TUTORIAL ON TROUBLESHOOTING BEARING ND LUBE OIL SYSTEM PROBLEMS 49

Figure 2 The Appearance under the Microscope of VariousForms of Conta inants. (a) Common sand, 20x (b) Siliconcarbide grinding compound, 70x (c) Garnet spark plug abrasive cleaner, 40 x (d Steel grit-blasting aterial, x (e) Steelgri ding chips from tool grinder, 20x Granulated nut shellsused for blast cleaning of engine arts, 1 x

c atch s an d g o oving a e ca used by pa ticles iding thesu face; pl owing is ca s d when pa tic les be come embe ddedunde the su face . Both g oov ing a nd plow in g a ise th e babbi ttedges on ei the si de of th e t ack . In an ab ad d su face theaspe ities a e an o de o f m ag nit d hig h than t he a ch in dsu face oughne ss. Du ing th e g oo ving, th babbitt i s p la stical-ly def o me , and the aise d edge s a e polish ed by the jou nal,givin g the m a a ttene d shin y app ea an ce. This, in co mbina tionwith the a ised banks of th e g oo ve, p oduc es ca nyons of thefo m sho wn i n Figu e 6; in th is f gu th e ve tical h as a agn i-fic ation 10 tim es th e ho izonta l. Both the flat oof on the ghtand the sh a p p ot usion s towa d th e jo na on the le ft a e

cl early vi sibl

on the s ides of the tr ack. The sha pe of the em bedm ent mo st ofte n evea s wh ethe t hepa ticl es a e ha d o sof t. If th m b d nt is due to a ha dpa ticle, the sha pe of the dep essio n co e spond s to tha t of th epa ti le; if due to a soft pa tic le, a wide s hallow indent ationesults and the pa ticle is often abs nt.

Appearance of the Journal

If the jou nal is damaged, that is usually the s lt of thep esence of la ge, ha d pa ticles o of embedded and wo k-ha dened soft pa ticles. Ab asions by ve y small pa ticles maybe mo e easily noticed on the jou nal than on the bea ing.

Hyd dynamiilm

e E ent i ity

L L ad an le

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150 PROCEEDIN GS OF THE TWENTY-FOURTH TURBOMACHINERY SYMPOSIUM

Figure 4 Abrasion of rust Bearing lting Pads (a) Concentric score mark at high speed (b) R agged score marks pro-duced at startup. (c) Magn cation of surface of part (b)

Figure 5 Scoring of a 3.0 in (7 6 m) Diameter Tin Base BabbittJournal Bearing with Embedment of Particle at the End of thePath.

Figure 6 Pro le Section of a Scratch n a Babbit t Surface,Showing Built up E es Adjac nt to the Scratch: horizont al,200x; vertical, 2000x.

6 ' 150'' ''5 ' 125''

: ' Tw samples 'dirty' 100

':4 Area m st sampleQ Q.!

3 \ 75 !( ' (Q \ Q2 50"

-. __ 25Cleanest il sampled_0 010 10 10 104 10

Numb ; ofParticles per 1 DOmlFigure 7 ica l Contamination Levels of Turbine Oils inElectric Utilities .

this dirt has been found to be of foreign origin; weld bead,machining chips, or other particles of considerable hardness. Awarning sign of scored journals has been found to be a spike inthe babbitt metal temperature occurring during coast down at aspeed somewhat below the rated rev/ in In other cases, thedamage is found onl during bearing inspection.

Polluted Environment

Another source of contaminants can be the en vironment of thepower plant. Fly ash, dusty air, desert conditions, proximity ofquarries, or other industrial pollutants will provide a steadysupply of contaminants that often fin their way into the lubri-cation system and directly into the bearing housing. Water isalso a likely contaminant, originating either from cooler leaks oratmospheric condensation

Inadequate Seals

In order for the environmental or locally generated contami-nants to be able to reach the bearings, it must penetrate the seals.Thus, inadequate sealing of the bearing drain areas are of enresponsible for the damage resulting from the presence of exter-nal (as opposed to oil carried) contaminants. For operation inharsh environme nts proper sealing is therefore particularlyim ortant.

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TUTORIAL ON TROUBLESHOOTING BEARING AND LUBE OIL SYSTEM PROBLEMS 5In-plant Formation of Contaminants

ometimes the facility itself gene ates fo eign pa ticles on asustained basis. These may come f om continuous wea ofmachine pa ts gea s, couplin s, o the bea ings themselves.Also, they may be gene ated by coking and chemical action inthe hot pa ts of the machine Thus, the fo mation of ca bonaceous deposits nea seals and baf les may p ovide a st eam ofla ge ha d pa ticles known to cause conside able damage bysco ing and cutting both bea ings and unne s.Too Thin a Minimum Film T ickness

While the p esence of contaminants is the p ima y cause,ope ating bea ings at too low an h may cause ab asions thatwould not have occu ed with a la ge film. The causes of a toosmall ilm thickness, fo a given bea ing geomet y, a e too higha load, too low a viscosity, misalignment, excessive shaft de ection, and vib ation. An inadequate ilm thickness may also becaused by the ope ation of bea ings with too low an pm attu ning gea and unde sta t stop conditions.

Rough Journal or Runner Surface

A common cause of bea ing ab asion is the installation of anew bea ing unning against a ough jou nal o unne su face.While this oughness may occasionally be due to poo machining, most of en it is a consequence of p evious ab asions. A newbea ing un against an ab aded jou nal su face wi soon itselfbecome ab aded.

As used he e, and as di fe entiated f om such p ocesses ase osion and cavitation, co osion damage is due to chemicalattack on metal su faces by eactiv agents. The damage can beto both the bea ings and the shaft. This damage esults omchemical attack on some bea ing constituent by a substanceo iginating in the lub icant o the envi onment. Co osion mayp oduce eithe e oval of bea ing mate ial o buildup of adeposit on the bea ing su face. The two main g oups of co osiveagents that affect bea ings a e elect olytes and o ganic acids.

Mechanisms

The p ocess of co osion conve ts metal to metallic compounds. In o de to cause p oblems, the p oducts of co osionmust be soluble o po ous, o must be continually emoved, so asto expose f esh metal to attack. Co osion is o en selective inthat it attacks some constituents mo e than othe s, as in the casewith the emoval of lead f om coppe lead bea ings. Co osionof lead based babbitts may be caused by acidic oi oxidationp oducts fo med in se vice, by decomposition of ce tain oiladditives, o by ing ess of wate o coolant into the oil. Theability of a tu bine oil to abso b wate unde equilib ium con itions is gi en in Figu e 8 as a function oftempe atu e. hould thewate p esent in the oil exceed the cu ve at some given tempeatu e, it would appea as f ee wate . The onset of co osion canbe sudden o g adual. A special set of conditions, pe haps acombination of p essu e, tempe atu e, and shea st ess in thebea ing is equi ed to p oduce co osion.

Corrosion by Electrolytes

Attack of metal su faces by elect olytes esults eithe in thepitting of the su face (Figu e 9) o in the oxidation of the alloy.ead co osion is the most common fo m of attack in lead base

babbitts and leaded b onze bea ing metals. Fuel sulfu is one ofthe agents likely to eact with lead babbitt, fo ming in thep ocess lead sul ides that a e likely to be deposited on bea ingsu faces. ulfu compounds a e added to many oils to p ovide

20

Q -

0 50 100 150 200Water Conce tration ppm

Figure 8 Equilibrium ter Content in a rbine Oil at 40Percent Humidi

ext eme p essu e p ope ties and as anti wea agents, dete gents,ust inhibito s and antioxidants. These p ope ties a e gene atedby an essential y co osive action o the sulfu compoundswhe eby a low shea st ength su face laye is fo med ove thebea ing mate ial to p event dest uctive contact with the jou nalmate ial Co osive contaminants in the su ounding atmosphe e,such as chlo ine and sulfu acids, ma also cause co osion,pa ticula ly when moistu e is p esent

When combined with soot, sul des an also clog oil passagesand bea ing g ooves, thus inte e ing ith adequate lub ication

Figure 9 Corrosion of a 5 0 in (1 7 ) Diameter Lead baseabbitt Journal earing

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TUTORIAL ON TROUBLESHOOTING BEARING AND LUBE OIL SYSTEM PROBLEMS 153

Figure 12 ad Surface Attacked by Environmental Su r.

Exter al corrosive substances which may flow i to thsystem

Operating practices may also contrib t to corrosion damageOp rating conditions that favor and accelerate corrosive attackare: high t p ratur s; high humidity; foa i g and a ration ofoi ; and prolonged sag of the same oil

Gl ctrical pitting consists of damage ca s d to bearings and

som tim s a so to ru n rs) by the i t rmitt nt arcing of electri-cal current as a r su t of voltage discharge across the oil lmThe source of the buildup in potential may be chro ic to theg rator or incid ntal such as an electrically charged lubricant

Mechanisms

The wear that occurs in electrical pitting is ca s d by the

n t rmitt n t passage of cu rr t betwe e the b aring and runn er.High v oltages are not necessar y for ar c i g, and dama g canoccu at potentials well below one volt The consequence ofarcing is the re oval o f metal fused in th arc, follow ed bym chanical wear All this is aggravated by the formation ofrough surfaces An additional penalty is contamination of the oiland the lubrication system by the r s lting debris The damagemay set in soon after startup or it may take months to becomeapparent

It is important to realize that a continuous flow of current isnot necessarily harmful; it is the int rmitt nt discharge du to abuildup of a potential which is relieved in the form of sparkingthat causes the damage Co s qu ntly when the lm thicknessis very small and there is near contact between the asperities ofrunner and bearing th r may be no wear because any potential

will produce a continuous c rr nt On the other hand if th filmthic ess is very large the resistance across the lm is too highto permit discharge and there will be no arcing In between thesetwo extremes there will be as shown in Figure 13, a point ofmaximum wear A three dimensional plot of the effect of vol -age and lm thic ess on wear rate Wear = f E h) will thenlook like the mountain of Figure 14, where a particular combi-nation of E and h yields aximum wear Thus in Figure 14,taking ABD along which E is constant notice that n ar D whereh is small there is no wear; at some h corresponding to point Bthere will be maximum wear; and when the film thickness hasincreased to an h corresponding to point A wear again will havedropped to zero

0.

0 4.E}I

0 3

*.l 0(5

0

F lm Th k es - h (m ls)Figure 13. Wear Rate Vs Film icknss for D rent Voltages.

L v ls j Damag

El ct ric arcing produc s four f c s The most damaging arepitti g and wear Often too a thin lay r of babbitt on the surfaceb com s overheated Finally metalli particles are set free inthe oil th s comm ncing an abrasive process

Although both are o t a f ct d i general the journal sur-face is less seriously damaged by pitti than is the babbitt Thisis as expected considering the gre ter area and the high rm lting poi t of the journal mat rial Amore serious effect is thero gh ning produced by built up debris which greatly increasesm chanical wear

Zero Wear Rate(Fi m In u ating)

F m/

T k ess

We r Rate

Zero e r Rate(F lm Abse t)

Figure 14 ct of Film- Thickness d Voltage on the WearRate Due to Electrical itting

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154 PROCEEDINGS OF THE TWENTY-FOURTH TURBOMACHINERY SYMPOSIUM

Visually Ident ing Electrical itting

In earl stages, damage caused b electrical pitting consists ofminute pits in the area of minimum ilm t ickness and gives thebearing a frosted surface These pits are characterized b acrater like appearance The backs of the bearing shells ma alsobe pitted where currents have passed through the pedestal Withrestricted lubricant circulation, electrical trouble often shows upas a gradual rise in bearing temperature and a darkening of theoil W en the oil is changed, temperatures return to normal fora while before starting to climb again Each electrical dischargereleases a cloud of ne babbitt particles and causes carbonization of the oil Both of these reactions serve to further lower oillm resistance, allow the passage of higher currents, and accel

erate the damage As the process continues, the pits begin tooverlap, masking much of the evidence of the origin of thedamage Still, if the surface appears osted, it is possible toidentif electrical pitting b scrutinizing the peripher of thefrosted area where isolated pits with a crater like appearance canbe found Also, with the proper beaming of a light source ontothe frosted area, electrical pits can usuall be detected b thereflection from their c aracteristic smooth, elted bottoms Aswith the c cling of the high temperatures in the oil exposed toelectrical arcing, there ma also occur a c cling in the formation

of an adequate fluid ilm When the bearing surface becomesincapable of accommodating an oi lm, the bearing ma wipeBut as this cleans awa the pits the bearing a recover an oililm and continue to operate, and pitting will again begin This

process ma occur several times until little babbitt is le t andfailure fol ows Even then i is possible to pinpoint the cause bthe telltale pits left on the shell and other adjacent parts of thebearing On the journal, which is generall hard, the pits areusuall smaller and not as easil homogenized as on the bearingIn Figure 15 the appearance of electrical pitting damage on alead babbitt bearing and its steel journal is shown

The severit of electrical pitting, expressed in extent ofdamaged area along with the size of the pits, depends on voltage,current, lm thickness, circuit resistance, and several otheractors Although individual pits var in size depending on these

factors, the pits all have the form of more or less hemisphericdepressions with smooth shin surfaces, giving the appearanceassociated with a melted metal, as shown in Figure 16 A slightridge of melted metal is usuall found around the peripher ofthe pit at the bearing surface, unless it has been worn awa b theoperation of the journal Higher levels of both voltage andcurrent aggravate the extent of damage arger pits are formedwith positive rather than with negative polarit

ossible Causes of Electrical itting

Electrical pitting is induced b two t pes of currents electrostatic and electromagnetic Although both t pes result inpitt ng damage, their nature and destructive capabilities aredifferent Electrostatic shaf current (or direct current) is t emilder of the two This is generated b either impinging particlesor condensed water droplets in the condensing stages of a steamturbine Pitting damage progresses slowl and alwa s occurs atthe location of lowest resistance to ground Thrust bearings areespeciall prone to electrostatic shaft currents

Electromagnetic sha t currents (alternating current) are stronger and more severe than electrostatic currents The are produced b the magnetization of rotating and/or stationarcomponents his t pe of current will not alwa s "jump the gapwith lowest electrical resistance Bearing damage is often accompanie b journal, collar, or runner da age

The principal sources of electromagnetic current are shown inFigure 17 The path of the current is indicated b the shortdashed line and is designated b the letter I

Figure 15 Electrical itting on a Lead Babbitt Bearing and ItsJournal (a) itting on lead-base babbitt, 5 x (b) itting onste l journal, 5x.

Figure 16. Typical Appearance of a Single Electrical it in aTin- Base Babbitt, 45 x.

F GFatigue failure is the cracking and fracture of metals due to an

excessive number of c cling stresses when the stress level isabove a threshold limit characteristic for a given material at agiven temperature

echanisms

Forces that tend to flex, reverse stress direction, or producethermal c cling in a bearing are conducive to fatigue However,

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/ Soure ofpotentiaO --5'_ ;Ai :B

B

: :_ Small G

Figure 17. rinc al Sources of Bearing Current. (a) otentialapplied to sha . (b) Dissymmetry e ect. (c) Shaft magnetizatione ect. (d-1) Electrostatic e ect-potential developed by impinging particles. (d-2) Electrostatic effect-potential developed bycha ged lubricant. ( d-3) Electrostatic ct-potential developed by charged belt.

o ini ia e da age e in ensi y of ese forces us exceed acer ain res o d The grea er he s ress, echanica or her a ,he sooner da age occurs In i s ear y s ages, fa igue fai ure isanifes ed in isola ed cracks A a ore advanced s age offa igue fai ure he cracks, aving reached he vicini y of ebond, rave para e o i , even ua y i ing ou s a pieces of

babbi This process wi u i a e y cause e bearing o seize orover ea as a resu of he drainage of oi fro ig pressureareas of he fi There is evidence ha he ra e of app ica ion ofoad is of so e i por ance in his process So e bearing a oysa wi hs and heavy oads see o fai w en subjec ed o si i aroads rapid y app ied

T ree exposures of fa igue caused by edge oading wi h ebu k of he da age caused o e end of e bearing are s ownin Figure 18 The se eri y of he cracks ha pene ra ed nearly oe bond are shown in e c ose up in igure 18 b ); oose chunks

of babbi pro ruding abo e he bearing surface are shown in aside iew of a fa igue crack in Figure 18 c)

A frequen cause of fa igue fai ure in hin wa ed s eevebearings is flexure, when par of he bearing is a erna e y forcedaway fro e shaf and re urned o he origina posi ion T is

f exing ove en is a par icu ar azard w ere con ac be weene bearing she and i s housing is fau y Bearings a are noin c ose con ac wi h he housing a so have poor hea dissipa ion,resu ing in f exing a co para ive y high e pera ures Fa iguefai ure a ways co ences in he vicini y of ese poor y fi ingareas

Factors in Fatigue Failure

Severa para e ers inf uence he ike i ood of fa igue fai ureT ese are:

Load and speed. T e onse of fa igue fai ure beco es oreike y as he difference be ween axi u and ini u s ress

Figure 18. Fatigue Caused by Edge Loading on a Steam Turbine4-7/8 x 1-7/8 in (12 x 4.76 cm)journal bearing. (a) Top view. (b)Close up of lower edge (c) Side view of (a).

es on e bearing increases and as e frequency of he s resscyc e rises

Temperature. Wi increasing surface e pera ure, e physica proper ies of babbi s de eriora e and fa igue fai ures erefore increase

Hardness and thickness. Suscep ibi i y o fa igue fai urevaries inverse y wi hardness, and direc y wi hickness of ebabbi

'Superimposed tensile stresses. W i e he ain s resses

ac ing on a bearing are co pressive, fa igue crac ing of bear

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ing i accelerated by the uperimpo ition of a ten ile tre ona pul ating compre ive tre Ten ile tre e et up by ca tinga bearing alloy on a bac ng material of different thermalexpan ion a well a tre e et up by the ani otropy of thermalexpan ion in the grain of an alloy can be ignificant

Thermal cycling Thermal tre e uch a tho e impo edduring repeated heating and cooling can in them elve lead tocrac ing of the bearing alloy Af er a relatively mall number ofcycle crack are formed in the babbitt in the vicinity of thebond and become more pronounced a the number of thermalcycle increa e Thi type of cracking depend on: relativevalue of the coe icient of thermal expan ion of bearing alloyand backing; operating temperature of the bearing; and thefrequency with which the bearing i heated and cooled

In addition to eld data a number of pecial tudie haveyielded information on the effect of mode of loading bendingtre e and geometry on fatigue failure in bearing In onetudy three kind of loading were impo ed on a bearing Figure19) The re ult in term of number of cycle and the fourdifferent mode of loading are given in Figure 20 A een therotating load wa the mo t damaging mode of loading followeby that of a tationary rever ing load The e loading mode areunfavorable becau e of the alternate impo ition of po itive andnegative tre e in the bearing that i of compre ive andten ile force A erie of fatigue te t conducted by the ameinve tigator [2] revealed that in the early tage axial cracktarted to form followed by a te ellat ed pattern with breakoutof piece of babbitt The theoretical tudie indicated that theaxial crack were due to the re ence of tangential tre e Thenature of fatigue cracking wa found to di er markedly depending on whether the load i unidirectional even if alternating) orrotating A unidirectional load produce crack normal to theurface wherea a rotating load produce crack at an angle of

about 60 degree It wa al o found that fatigue life under rotatingload i inferior to that under a unidirectional load

t4

G 8 a b (c) d

Un i nal Alte atingRota ing

Figure 19 Modes of Loading in Fatigue Tests (a) and (b)Unidirectional (c) Alternating (d) Rotating

Fatigue failure can al o occur at ite u ually a umed to beafe uch a for example the unloaded top pad of tilting padbearing In uch pad if not preloaded) there i u ually enoughradial play in the pivot to allow the ad radial motion withcyclic loading of the edge of the pad The re ult can be upperpad fatigue failure a illu trated in Figure 21 The mechani m ofthi failu e i a follow : when the radial play i the pivot ilarger than the conce tric clearance a elf excited ub ynchronou pad vibration i likely to occur The ba e frequency of thi

(78.4) 800

'(68.6) 700

" ( 8.8) 600

(49.0) 00!39.2) 400

< (29 4) 300

(19.6) 200

(9.8) 100

'. .-r 1 I

II III "

. ,II I rI II

. i-

. 1III I

N mbe Cy lesFigure 20 ailure Diagrams for the Four Modes of Loading

vibration will be le than half the rev/min The elf excitedmotion re ult f om the ab ence of a table tatic equilibriumpo ition for the pad which at each in tant eek an in tantaneou pre ure di tribution uch a to produce a zero force andzero moment

Babbittfati e- a kdama e

Figure 21 E ample of Damage to a Large Journal BearingTilting- ad Due to Se - cited Vibration under Statically Unloaded Conditions

Visually dent ing Fa tigue

Although the cycling loading that i required to producefatigue i not a very common condition f operation in electricutility rotating equipment uch failure do occur becau e of thepre ence of unbalance loa and becau e babbitt are particularly low in trength Fatigue u ually tart at the urf ce at thepoint of maxim m pre ure and i fir t vi ible a ine urfacecrack that penetrate the babbitt at an angle of about 45 to 90degree to the urface depending on the mode of loadingMicro copically fatigue appea on the urface in the form of acobbled pattern and the crack appear to grow or open up in the

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direction of rotation, as shown in Figure 2 In the case ofbonded babbitt, the cracks propagate from the surface toward thebond, turn and continue arallel to, but abo e, the bond, asshown in Figures 23 and 24 Continued stress extends the crackshori ontally, undermining wide areas until large segments ofbearing alloy are loosened and dislodged, thus reducing the areasupporting the load oose babbitt particles e entually worktheir way into the clearance space and cause additional damage

Tests with different layer thicknesses showed that the si e ofloosened babbitt pieces increases with i creasing layer thickness, pro ided the other parameters remain unchanged The lossof metal by fatigue breakout has the addi onal effect of disrupting the lubricating film, and causing loss of lubrica t from thepres uri ed ones, which requently leads to se ere damage

Figure Fi st Indication of tigue Failure-Fine SurfaceCracks

By comparing damaged bearings with photographs, inspec-tors may detect telltale traces of fatigue caused by load co cen-tration and i relati ely l ghtly loaded bearings, where fatigue

ma appear in the upper unloaded half in the presence of aunbalance load, and in t e loaded one, where fatigue may resultrom cutti g groo es, thereby raising the le els of maximum

pressures for a gi en load) and thus the proneness to fatigueFatigue ca also occur due to thermal cycling, part cularly in

tin based babbitts tha do not crystalli e u iformly Here thefissu e could penetrate the babbitt normal to the surface, usuallynot in the center but at the edges of the bearing

ossible Causes Fatigue

To summari e, fatigue ca be caused by a wide ariety ofoperating conditions and laws in bearing construction Them

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Bearing Su aceBabbBo d

Figure 9 Sketch Showing Babbitt Fatigue Initiating WipingDamage

the physical displacement of babbitt material The heaviest signsof this displacement are usually near h This displacementextends over a fairly wide angular region, and it is characterizedby irregular jagged edges at the end of the wiped area, where thedisplaced material has been deposited on top of the undamagedbearing surface If the temperatures during the wipe ar not high,the damaged area has a polished appearance; if high temperatures are generated in the process, parts of the wiped area maylook dark and burnished

Some speci c examples of wiped bearings together with theirunderlying causes as diagnosed in the field are given laterA typical case of light to moderate wiping of a journal

bearing is shown in Figure 30 A typical feature of such wiping,as already noted conce ing fatigue wiping, is the presence of alayer of babbitt that has been displaced from its original locationto a low pressure region where its deposition on the previoussurface can be noticed both by appearance and touch Such aperiphery is shown in enlarged scale in Figure 30b

A wiping concentrated is shown in Fig re 31 at one end ofthe bearing brought about by severe misalignment

B Y Q FG G B G FThere are, essentially, two generic approaches available foridenti ying the specific kind of damage incurred by a failed

bearing The first, already discussed, consists of a visual, andpossibly microscopic, inspection of the damaged surface andcomparison of its appearance with catalogued photographs ofclassified modes of failure The other consists of various laboratory techniques ranging from using a simple hand t ol tohighly sophisticated diagnostic procedures These la ter procedures include advanced physical and chemical techniques involving, for example, spectroscopy, lasers, and atomi scanningOne of these laboratory techniques for determining the nature ofbearing damage lube oil ferrography, a method o analyzingwear particles deposited in lubricants is discussed below

Ferrography

In use at dozens of utilities, ferrography is one of the morerecent methods of contaminant identification Its principle ofoperation Figure 32) consists of pumping a sample of oil at aslow, stead rate between the poles of a magnet The uid runsdown an inclined microscope slide and the net effect of theviscous and magnetic forces acting on the particles is to sortthem by size The larger particles are deposited first, and thes aller particles are carried farther downstream

Information on the morphology of the deposited particles iso tained with the aid of a bichromati microscope, which usessimultaneously re ected red light and transmitted green lightMetal particles as small as one micron re ect red light and block

Figure 30 A Wipe 3 0 in (7 6 m) Diameter Journal Bearinge Due to mpor Loss Lubricant (a) Loa e ha of

bearing (b) Section o wipe

Figure 31 Steam Turb ne Jou n l Bearing Wipe Due to Bearinglt

green light and thus appear red Particles composed of compounds allow much of the green light to pass and appear greenor, if they are relatively thick, yellow or green

Particles generated by different wear mechanisms have char-acteristics that can be identified with each specific mechanismubbing wear particles found in the lubricant of most machines

have the form of platelets and indicate normal permissible wearCutting or abrasive wear particles take the for of miniaturespirals, loops, and bent wires similar to swarf from a machining

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operation A concentrat on of such particles is indicative of asevere abrasive wear process Particles con isting of com-pounds can result from an oxidizing or corrosive environment

Various regimes are shown in Table 2 classified b the natureof the particles produced in sliding contact Six regimes ofrubbing wear that generate characteristic particles have beenidentified Regimes 1 and 2 represent normal wear conditionscorresponding to ydrodynamic and boundary lubrication Evi-dence of one or m re of the higher regimes (3 4 or 5) indicatesthat s me paramet r of the system has changed unfavorably Theoccurrence of regime 6 indicates impending failure Free metalparticles are produced in regimes 1, 2, 3 and 6, and these wearregimes may be identif ed by the particle size With steel wearparticles in regime 4 a mild form of oxidative wear dominatesand the majority of wear particles are hematite Regime 5generates black iron oxides which indicate a severe form ofoxidative wear

Table Wear Regimes

P r D r pj r D Su D r p

1 Free meta parti es Varies etwee po is edusua y ess t a a d very roug ; o e mi ro s su fa e a be po is ed

w i e t e opposi gsu a e remai sas ge erated

Free meta parti es St e, sm ot , s earusua y ess t a mixed ayer wit a few1 mi ro s grooves depe d i g o

t u er of parti esi t e oi

3 Free meta p rti es P oug ed wit evide eusua y ess t a of p asti f ow a d

1 0 mi ro s su a e ra ki g4 Re oxide part es P oug ed wit areas o

as usters or oxide t e su fa ei dividua y up to1 0 mi ro sB a k oxide parti es P oug ed wit areas ofas usters or oxide o t e surfa ei div dua y up to

0 mi ro s6 Free meta parti es S vere y p oug ed, gross

up to mm p asti f ow a d smeari g

F Y W Gn this section a diagnostic remedial sequence followi g thefailure of a utility's bearing is outlined Failure is traced to aspecific root cause and a brief description of repair proceduresis provided The particular case one of bearing wiping isincluded because wiping represents perhaps the most genericform of bearing failure n this particular case bearing failureoccurred in an old power plant and involved an overshot groovecircular bearing (Figure 33 The failure was instantaneous andmanifested tself as a near seizure of the rotor sha t accompa-nied by smok emanating from the bearing housing The plantwas immediately shut down and the housing opened for inspec

/ Ferrogram s ide

ag et

I- - - - - - - - - - - - - - 1 II I I1 Ope ati g 1 1- - - - - 1 tribo me a a syst m - - - -

I II I

Figure 3 Schematic Re resentation o Ferrogra h Analyzer

- - - - - Top PadFigure 33 Common Design of an Overshot Groove BearingT is e o bearing is a two-a ial groove bearing with orwithout reload i n which the unloaded (to ) ad is traversed bya dee circum erential channel e tendin across the entire arco the ad

tion A diagrammatic picture of the diagnostic remedial se-quence is given in Figure 34Mode o Failure

The bearing surface showed the follo ing symptoms:The loaded lower half showed no t ace of distressThe upper half having the overshot roove showed severe

displacement of babbitt over the downstream portions of thepad with lumps of recongealed babbitt deposited in the overshotgroove in the down tream oil groove and to a lesser extent atthe leading edge of the lower ha f of the bearing A diagram ofthe damaged upper half of the bearing is shown in Figure 35

No cracks were visible when the up er half of the beari gwas viewed rontally because the babbitt covered any possible

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Incident Near seizure Smoke

Bearing Symptoms Plant Operation Data Lower half undamaged Presence of unbalanced Displa cemen t of babbi loads

in upper half History of edestal shifts Transverse and longi ud-

inal cracks in babbitt onupper half

Mode of Failu re Root Cause of Fai lu re Wi i g second ary o Un bala ced load

fatigue in upper half combined with hift indi rection of static load

Remedial Action Rotate b aring in

Mode of Failu re housi g 80 E m inat ov r hot

roove fromu p r half

Figure 34 Illustrative Diagnostic Remedial Procedure for Caseof Secondary Wiping

evi e ce But whe the upper half was viewe si eways i si ethe overshot groove, the babbitt layer showe small cracks bothtra sversely across the layer a parallel to the bo li e Nosuch cracks were visible i the lower half

These symptoms suggest that failure was cause by seco -ary wipi g, triggere by a fatigue pper half of the beari g

Root Cause of Wiping

This case represe ts a compou mo e of failure, i volvi gboth fatigue a wipi g It is improbable that babbitt fatigue byitself woul have cause imme iate beari g failure ikewise,the severe hy ro y amic co itio s, while sig ifica t factors ithe failure, woul ot alo e have pro uce a wipi g failure ofthis mag it e A reaso able suppositio is that the fatiguestate of the babbitt aggravate the hy ro y amic co itio s,res lti g i a wipi g As such, fatigue co stitutes the primaryage t of failure

The ext iag ostic steps are to locate the root cause ofbeari g fatigui g, a the to etermi e the eleme t that favorea wipi g failure i the upper i stea of the lower loa e half ofthe beari g

About a oze isti ct processes ca cause a fatigue or wipi gfailure A eleme t commo to bot failure modes is vibratioof the rotor, cause by a oscillati g loa

A review of the history of the power pla t yielded someperti e t facts about two egative co itio s surrou i g thefailure:

Rotation

Babbitt \ _V ew BB (enla rge d)

Figure 35. Topography of Damaged Upper Ha of Bearing

The agi g pla t a a history of eteriorati g u bala celoa i gs

The pla t ha problems with rotor alig me t or mismatchue to shi s i the pe estals housi g the beari gs

The irst co itio supports the suppositio that a u bala celoa precipitate the fatigui g process However, the prese ceof a u bala ce loa oes ot resolve the questio of why theupper, a ot the loa e lower half suffere fatigue The secoco itio , rotor mismatch, suggests some possible expla a-tio s, amely:

The pe estal housi g the faile beari g ha shi e ow -war s, which u loa e the lower half a impose a u k owloa o the upper half

The u bala ce loa impose a rotati g force o both halvesof the beari g; but with the static loa iverte upwar s, theupper alf was loa e much more severely tha the lower half

The pper half with its overshot groove ha a much lower loacapacity tha the lower half oa capacity is proportio al to

/D) , where is le gth, D, iameter I this case the loacapacity of the upper half relative to the lower half is give iEquatio 1)

Ratio = /D) 2 = 1/3) 2 = 22% 1)

Thus, what has occ rre is the i tro uctio of a loa rotati gat a freque cy of 60 Hz acti g agai st the u per half of thebeari g, which ha o ly 22 perce t of the loa capacity origi al-ly esig e i to the beari g

It is evi e t that the root cause of failure lies i the impositioof both oscillati g a stea y loa s o the upper half of theovershot groove beari g

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R m dy

A ndamental remedy to this typ of problem consists ofeliminating the unbalance load and preventing the shift ofpedestals If feasible at all, this constitut s a major plant odi-cation However, om the standpoint of a b ar g remedy, twooptions are available:

Rotate the b ar ng 180 degrees so that the half with theunbroken surface is at the top This would work if no subsequentchanges in load dir ctio occur

Eliminate the overshot groove entir ly, yielding a d signthat ought to work sat sfactorily regardl ss of the directions ofthe load

G Y

The l bricatio syst of a turbine generator supplies oil tothe thrust and journal bearings und r all operating conditionsA er many years of tro bl r op ration, these systems cans ddenly fail b ca s of degradation of the br cant, alfunc-tio of chanical or electrical components, or deterioration ofthe e ergency power source Altho g lubr catio system fail-

res are rare, th y cause ajor damag to turbin bear ngs androtors Since th s can res lt in xt d d p ant outages regularnsp ct on and aintena ce of syste l ts are essentialGuidelines for aintaining steam turbine ubricat on systemswere developed for larg power pla t t rbines by the a thor'sorganization [3] In the following pages, disc ssion focus s onsome key aspects of mon tor ng oil condit on detailed in thoseg idel nes

T sting and Maintenance R quir m nts: St am Turbin Oils

Present day t rbine o s are for ulat d with a hig y r n dineral o l base a d a va ry ng nu ber of add t v s that e ha nce

or impart a spec ific o l p roperty . The f i ish d oil s require dto res st therm al or oxidati e br akdo n, inhi b t r sti g o rco rro sion, prov de satisfactory lubr cat on and cool n g of load-ca rryi g co pone ts, re sist fo a n g, a d poss ess go od w ater-separat ion pro pertie s Thro gh us , cer tain o f th s prope rtiesay dete riorat over xt d d peri ods of t . As a co n s -

q enc e, it is i p ortan t to es tabl s h a sampling and analys issched le tha t perm its th turb i op rato r to m on to r the oi condit ion. Inform atio obtain ed fr o o sa ple a nalys is no tonl y prov ides a basis for j dg t as to oil s itab il ty, but a lsoma y den tify s yste prob lems n ot ot h rw s det ectabl e, suc h ascoolant leak s, xce ssiv wear , overh at g , tc

Sp cifications

Sp cific at ons for n w l bric at ng o il are form lat d by q ip-m n t man ufactur rs, oi l s ppl iers, a nd c rta in tec hnical s ociet-ies active in th e field of turbin lubr c ation. A m ni umspecificatio n guide has be en issued by th A mer can So c ety forTesting and Materia ls (AS TM) a nd title d "S t an dard Spec fic a-tion for Mi ne ral Lubricati ng Oil Us d i Steam a nd Gas Tur-bines D 4304)

Additiv s

As a min u , steam turb ne oils contain an antioxidant toretard oxidative attack a d a rust inhibitor to protect iron basem tals In addition, an a t foa agent and a metal deactivatormay be pr s nt Depending o the prope ti s of the min ral oilbase, other functio al additives ay b sed to achieve therequired performance characteristics

Over extended periods of ti e, so e additives may be con-s med through adsorption onto syst aterials or contami

nants, d terioration by chemical reaction, thermal d gradation,etc This consumption may be wholly or partially offset by theroutine add tion of akeup oil It is not unusual for turbine oilsto r main in s rvice for p riods bet een 15 and 20 years Inturbine lubrication systems r quir ng relatively low makeup, oiproperties sho ld be monitored closely to make certain that anyp rforma c loss is id ntified While i t is poss bl to reinhibit anoil by mixing n an additive, this approach should be carefullyconsidered and should only be tak n after close consult tionwith th turbine o l supplier

Contamination

Contaminants within the turbine oil system may be generatedinternally or drawn into the system from the surrounding envi-ronment thro gh entry at seals or vents Ext rnal contaminationmay include airborn dust, sa d, coal particulates, moisture, etcInternally generated conta inants may consist of wear metalparticulates, which are constantly being produced in some de-gree; l aked coolant; oil degradation products such as sludge;and rust particles Typica plots of the state of turbine oils int r s of quantity and size of solid contaminants were shown inFigure .

Excessive or ncontrolled bui dup of contaminants shouldalert the turbine operator to identify the so rce, take correctiveact on, and d ter ine wh th r o l purif cation equipment orsystem i ters are properly function ng

Analys s

In service monitoring of the condition of a t rbine oil shouldfoc s on the following propert es:

Antirust protectioRe a ning oil lif (ox d tion stabil ty)ViscosityTotal acid n mberCleanlinessFoa ing tende cyColor/app ara c

Water cont ntFlash point

In th following paragraphs, the significance of the first twoproperties is discussed, a ong with reco mended test proc -dures that have been dev loped, approved, and published byASTM

Within the turbine oil system, numero s ferro s metals re-quire rusting protect on This protection s afforded in larg partby the anti rust addit ve present in the oil New and used oilssuitable for contin ed s rvice m st pass ASTM Method D 66583 Procedure A, or D 3603 8 2 Th s is a dynamic test designedto evaluate the ability of steam turbine oils to pr v nt the rustingof ferrous components should water become ixed with the oilin service

In this method, a cyl ndric l ste l specimen is immersed in aglass beaker containing 300 ml of th test oil and 30 ml ofdistilled water at a temperature of 14 F 60C) The mixtur isstirred throughout th test, which normally lasts 24 o rsRusting of the steel specimen is determin d by visual examina-tion after the test

Remaining oil life is a measu e of t e remaining capability ofoil to resist severe thermal/oxidative breakdown Remaininguseful oil l fe i s strongly related to the remaining concentrationof the antioxidant in th oil The oxidation stability of n w oilsis generally measured by ASTM Method D 43 81 Howev r,

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PROCEEDINGS OF THE TWENTY FOURTH TURBOMACHIN RY SYMPOSIUM

hi procedure can take a rela ively long time over ix week )and a a con quence i not employed for moni ori g thecondi ion of oil in ervice. For hi purpo e ASTM Me hod D

7 8 he ro a ing bomb oxidation e t RBOT) i preferred.A 50 g ample of the te oil and 5.0 ml of water are placed in

a mall gla container containing a copper cataly t coil. Thecon ainer i pu in o a metal oxida ion bomb that i pre urizedwi h oxygen o 90 p i 6 0 kPa) and then placed in a con tant

empera ure ba h a 30 F 50C). The bomb i rota ed a 100rpm a an angle within he ba h of 30 degree from horizontal.xygen pre ure i moni ored con inuou ly during a run and thee i erminated when he pre ure drop more than 25 p i 172kPa) below he maximum pre ure. Thi event generally re ecaccelera ed oxida ion of the te t oil and the te t time elap edbefore accelera ed oxidation i a mea ure of the remainingoxida ion life of the oil in ervice when compared with theBOT da a for he new oil.

bine Seve it Level

Each urbine generator lubrication y tem i unique due toexclu ive condi ion hat ari e during con truction and opera-ion of he y em. The e condi ion et the rate at which a newcharge of fre h oil will lo e it oxidation re i tance. A propertycalled urbine everi y B) level ha been e tabli hed which canbe u ed o take the e condition into con ideration when moni-oring he remaining oxidation re i tance of the oil during itervice life Den erder and Vienna). "B i de ned thepercen age of e h oil oxidation re i tance lo t per year due tooil reaction in he urbine genera or lubrication y em. "Bake into con ideration the following three factor :

Amount of make up oil added to the y tem to repleni h theoil oxida ion re i ance

Time ha he oil ha been in u e Oxidation re i ance that remain a determined by a RBOT

ASTM D 27 8

Equation ) de ermine turbine everity B:

= M (1 - X/100)/ (1 - e Mt ioo) 2)whereM = Amoun of oil added a makeup into the y em per year

expre ed a a percen age of the o al amount of oil origi-nally placed in the y tem percentage per year)

X= moun of oxidation re i ance that remain in the oilexpre ed a a percen age of the original oxidation re i -ance o he oil percen age of fre h oil)

= Amoun of time the original oil ha been in ervice in year

he e fec f makeup rate M on oil degradation for a turbinewi h a everi y level of 5 percen per year i hown in Figure 36.

he everi y level for a particular lubrication y em houldbe de ermined over a period of time beginning wi h ini ialopera ion or in alla ion of a fre h oil charge. Keeping accuraterecord of he amoun of oil makeup i e ential and RBOThould be conduc ed at hree to ix mon h in erval for one towo year . By knowing he oil makeup and degrada ion of the oilwi h ime he urbine everity for he oil can be found fromFigure 37.

A lubrica ion y em with a high everity level requirefrequen makeup or completely new charge wherea one witha low e erity level may have no problem with outine makeup.Turbine generato uni of recent de ign have higher "B levelhan uni in alled before 9 5. ncrea e n lubrication y emempera ure are u pec ed a rea on for the higher "B level

g

Qa0(;0-Q28

19876

4

3

2

1

2 4 8 1 12 14 16 18 2Ye s Use

Fig e 36 ct of Make p Rate on Oil Deg adation ( bineseve it B 5 pe cent pe yea )

1

? 15 ;; 6; ;;;7 ;; x5 ; 40 .; 0Q ; 0CQ ; 3;c: 2

2 "; 17;1 5 Q;12 6

M = 3 % 1 E9 Q8 27 86

T meFig e 37 Eect of bine Seve ity (B) and Make p Rate (M)on Oil Deg adation he dotted lines show the p ocess foobtaining a val e fo t bine seve i B In the e ample thet bine oil has been in se vice fo ve yea s and the ann alake p ate is 15 pe cent he oil has deg aded fom a ota y

bomb test l e of 1700 min tes initially to only 350 min tes aloss of 79 5 pe cent Sta ting at ve yea s on the time a is a point on the 15 pe cent make p c ve i s dete mined and a lineis p ojected le to the ( 1 x) a is A st aight line between th is

point on the (100x) a is and a point at 79 5 pe cent on the pe cent oil deg adation a is inte sects the t bine seve it scaleat 22 pe cent pe yea

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TUTOR AL ON TROUBLESHOOT NG BEAR NG AND LUBE O L SYSTEM PROBLEMS

obtained in new t rbines Larger sha ts t rning gears andco plings and smaller oil reservoir vol mes have increased theamo nt of heat each gallon of oil m st transfer per ho r to the oilcooler Oil contamination by coal d st and ly ash from press rized f rnaces has also been a factor

G KThe a thor s organization has developed a man al and soft

ware designed to help plant engineering and maintenance personnel identify speci c modes of bearing damage as well asroot ca ses and to respond appropriately By identifying themode and ca se of bearing fail res and o en remedying associated problems on site power plant maintenance costs can bered ced whi e q ipment reliability is increased Also beca sel brication deterioration is a leading ca se of t rbine bearingfail res incl ding fail res in several of the modes trea edherein t rbine l bri ation systems m st be properly matained The a thor s organization has developed ind stry g idelines for maintaining and monitoring s ch systems

F1 Pink s . , Man al of Bearing Fail res and Repair in Power

Plant Rotating Eq ipment EPRI GS 73 ( 99 ) Lang H "S rface Fatig e of Plain Bearings Wear 3 pp

3 ( 977)3 Lamp ng G A et al G idelines for Mainta ning Steam

T rbine brication Systems EPRI P blication CS 4 55(198 )

B B G YAdams M L "Large Unbalance Vibration Analysis of Steam

T rbine Generators EPRI CS 3716 (1984)Adams M L and Payandeh S "Self E cited Vibrat on of

Statically Unloaded Pads in Tilting Pad o rnal BearingsASME Paper 8 LUB 3 ( 98 )

A SLE Standard Handbook o f Lubrication Engine ring

O Con or J J and Boyd J editors New York New York:McGraw Hill ( 9 8)Bar ell F T and Scott D "The Investigation of Un s al

Bearing Fail res Proceedings IME 180 (pt 3K) pp 7797 ( 9 )

"Bearing Tro bleshooting Advisor an EPRI M&D CenterTechnology Review EPR AP 1 8 4 V P ( 993)

"Bearing Tro bleshooting Advisor (Version 2 ) A Complete Bearing Maintenance System EPRI AP 3 ( 994 )

Ha dbook of Lubrication o ume T eo and Design Booser E R editor CRC Press (198 4)

Boyd J and Ka fman H N "The Ca ses of Control ofElectrical C rrent in Bearings L brication Engineering 15( ) pp 8 3 (19 9)

Crankshaw E and Riss G Jr "Lead Based Babbitt BearingsA Symposi m ASME ( 95 )

DenHerder M J and Vienna P C "Control of T rbine OilDegradation D ring Use L brication Engineering 3 (2)pp 67 71 ( 98 )

Glacier Metal Co Ltd Bearing Damage CG 84 8 (198 )Johnson E T "Life Testing of Plain Bearings for A tomotive

Engines Symposi m on Testing of Bearings 49th Ann alMeeting of ASTM B falo New ork (194 )

Ka fman H N "Damage Analysis Chapter Tribo ogdited by A Szeri Bristol Penns lvania: Hemisphere P b

lishing Corp ( 98 )Ka fman H N and Boyd J "The ond tion of C rrent in

Bearings ASLE Transactions ( ) pp 7 77 ( 9 9)K re Jensen J "Cleanliness of Large Steam T rbine L be Oil

Systems L bri ation Engineering pp 7 8 ( 97 )"Abrasives and Wear L brication 3 ( ) pp 13 4 (Texaco)

( 9 7)"Plain Bearing Fail res L brication L (7) p 77 92 (Texa

co) ( 9 4)Scott D Seifert W W and Westcott V C "Ferrography

A Advanced Design Aid for the 8 s Wear 3 pp ( 97 )

K W GThe technical contr b tions of the following individ als and

organizations for specific data and b ckgro nd information forthis man script is grate lly a knowle ged and sincerely appreciated: Pinc s Mechanical Technology Inc M Adams CaseWestern Reserve University Glac er Bearings Inc Kingsb ryBearings Inc H N Ka fman J Boyd A Raimondi Westingho se Electric Corp E R Booser J K re Jensen GeneralElectric Company and G Lamping So thwest ResearchInstit te

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