Adding a New Dimension to Predictive Maintenance

8/17/2019 Adding a New Dimension to Predictive Maintenance

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Adding a New Dimension to PredictiveMaintenance Written by Johan Van Puyenbroeck and Kris Deckers

Pumps & Systems , November 2 !

"he bene#its o# $redictive maintenance are becoming readi%y acce$ted throughout industryin &uro$e as we%% as North America' (uy Mertens, who is res$onsib%e #or $redictivemaintenance at the )e%gian *e#inery +or$oration )*+-, added an e.tra dimension to his

$redictive maintenance $rogram by using it to identi#y common machine #au%ts #or themaintenance sta## to watch #or'

/ince the ear%y 011 s, )*+ has em$%oyed $redictive maintenance to get %onger %i#e out o#re#inery machinery whi%e avoiding une.$ected downtime' Mertens now monitors 0machines motors, $um$s, gearbo.es, com$ressors, turbines, #ans, etc'- as a $art o# this

$redictive maintenance $rogram' With su$$ort #rom )e%gian distributor +oservices, Mertensre%ies on vibration data #rom the #ie%d and $eriodic ana%ysis o# machine oi% sam$%es to

determine i# and when a machine shou%d be removed #rom service #or re$airs'

A#ter any $iece o# rotating e3ui$ment is removed to re$air a $rob%em identi#ied as a resu%t o# vibration monitoring, a root cause ana%ysis is a%ways $er#ormed' When certain issues occurtoo #re3uent%y, Mertens issues advisories to he%$ re#inery $ersonne% avoid them in the #utureto $revent breakdowns and im$rove machine %i#e' *esu%ts achieved through these root causestudies are o#ten cited in Mertens4 annua% $redictive maintenance re$ort to u$$ermanagement'

Anyone res$onsib%e #or the u$kee$ and %ongevity o# rotating machinery may want toim$%ement a simi%ar root cause ana%ysis $rogram' An awareness o# #re3uent%y occurring

conditions, a%ong with suggested corrective actions, can be a use#u% addition to any $redictive maintenance $rogram'

Brinelling (Damage Occurring When a Machine is Not Running)

Most $rocesses in re#ineries have s$are machines insta%%ed #or redundancy' 5# an o$eratingmachine breaks down or needs to be taken o##6%ine #or any reason, the s$are can be activatedto take over the %oad so no $roduction time is %ost' "his means many machines are ke$t onstandby, sitting id%e #or e.tended $eriods' 5# these machines are in an environment where a%ot o# vibration is common, a $henomenon known as brine%%ing may occur'

When a bearing is id%e, the grease at the bottom o# the bearing between the outer race andthe ro%%ing e%ements a%so between the ro%%ing e%ements and the inner race- wi%% be s%ow%y $ushed away due to the gravity and whatever vibration may be $resent' At some $oint, a%% o# the grease between the %ower ro%%ing e%ement and the outer race wi%% disa$$ear, resu%ting inmeta%6to6meta% contact'

(enera% vibration occurring in an industria% setting can cause the ro%%ing e%ement to hammer

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at the same s$ot on the outer race unti% it is damaged see 7igure 0-'

Figure 1, left. Brinelling of bearing outer race.

&ven i# the machine is brand new but has not been run #or two years, severe vibration soona#ter start6u$ may indicate that bearing damage has occurred' "o avoid this condition withe3ui$ment that sits unused #or e.tended $eriods8

7i%% ho%es under the #undation $%ates grounding-'*e$%ace cy%inder bearings in motors with doub%e ba%% bearings' 5t a$$ears that these

cy%inder bearings are much more sensitive to brine%%ing then ba%% bearings'

Brinelling Due To orrosion

+orrosion is much more %ike%y to occur when machines are not running' "his too can %ead to brine%%ing see 7igure 2-'


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Figure !. Bearing corrosion "ue to moisture ingress

"o $revent corrosion in bearings due to the entry o# moisture as we%% as condensation8

7re3uent%y a%ternate the use o# one motor and then the other' &stab%ish an o$eratingschedu%e so that no machine is %e#t id%e #or e.tended $eriods'

5# this $rob%em reoccurs on a number o# machines, an im$rovement can be made byadding an e.tra sea% s$ecia%%y designed to kee$ water out o# the bearings see 7igure 9-'

Figure #. $ffecti%e sealing arrangement for grease lubrication. &'ring seals are suitable for both grease an" oil'lubricate" a lications. Forsealing grease'lubricate" bearing arrangements against "ust or ater s ra*, the &'ring shoul" be arrange" outsi"e the housing co%er orhousing all. Dust, ater s ra* an" other im urities can be e+clu"e" in this osition. The &'ring ill also act as a grease %al%e. se" greaseor e+cess ne grease can esca e bet een the counterface an" the sealing li .


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Ball Bearings &ersus *lin"er Bearings

A survey on 02 motors in the re#inery revea%ed that the vibration im$act %eve% on N:6 bearings on the cou$%ing side is much greater than with ba%% bearings see 7igures ;a, ;b-'

Figure -a , abo%e


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Figure -b, abo%e

"his can occur when the bearings are not running under minimum %oad as s$eci#ied by the bearing su$$%ier 2 $ercent o# the nomina% %oad o# a bearing-' 5n this situation, ba%% bearings#it the a$$%ication very we%% and there is no need #or cy%inder bearings' We%%6a%ignedmachine trains, such as motor6$um$ grou$s, e.ert no ma


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Figure /

"he M")* ca%cu%ation has been done the same way very consistent%y over the years, $roviding a re%iab%e trend indicator' "he e3uation #or M")* e.$ressed in years- is sim$%y8M")* > ? machines @ ? re$airs during the year' A%% interventions re%ated to e%ectrica% andmechanica% $rob%ems initiated as the resu%t o# vibration monitoring and ana%ysis were takeninto account in the M")* ca%cu%ations, inc%uding8

• A%% bearing changes on motors, $um$s, #ans, gearbo.es, mi.ers, etc' because o# bearing damage or bearing c%earance

• Prob%ems with cou$%ings, inc%uding the re$%acement o# gear cou$%ings by diskcou$%ings

• *evisions o# gearbo.es due to gear wear

• &%ectrica% re$airs rotorbar de#ects and stator $rob%ems-

• )e%t re$%acement

Minor maintenance without re$%acing $arts is not considered to be a re$air' "hose are notinc%uded in M")* ca%cu%ations' 7or e.am$%e, re$%acing a sea% without re$%acing the bearingmay not constitute an intervention resu%ting #rom data deve%o$ed through condition


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monitoring' Bther e.am$%es inc%ude checking o# c%earances, be%t tension, e.tra %ubrication,oi% %eve%s, etc'

onclusion

7igure $rovides am$%e evidence that moving #rom $reventive maintenance to $redictivemaintenance, combined with the e.tra dimension o# root cause ana%ysis, had a $ositive andgrowing e##ect on the mean time between re$airs #or monitored machines in the )*+*e#inery' "he s%ight di$ in the M")*6$%ot in 2 0 was due to a %engthy re#inery shutdownduring which many $%anned $reventive revisions were im$%emented'

Without 3uestion, $eriodic vibration measurements in con

Adding a New Dimension to Predictive Maintenance

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