NON-DESTRUCTIVE INSPECTION OF WIRE ROPES IS WISE MEAN TO PROVIDE SAFETY AND COST SAVINGS
Alexander Mironenko & Vasanthpraveen Kumar Intron Plus, Ltd., Moscow, Russia !"# India $P% Limited, avi Mumai Ke'words( wire rope, inspection, stron) ma)neti*ation, residual rope li+e. Abstract
Lar)e numer o+ +errous steel wire ropes is in use in di++erent industries, carr'in) people and +rei)ht, supportin) rid)es and towers, li+tin) pipes and vessels o++shore and onshore, under)round and aove)round. "he i))er and the lon)er is the rope, the more expensive it is. Later or sooner ropes deteriorate +or di++erent reasons, their +urther use ma' e dan)erous, and important uestion arise( whether the rope should e discarded or still ma' remain in operation. Premature discard and replacement with the new rope involves in unreasonale costs, while operatin) the rope which alread' reached discard criteria is dan)erous. "he sensile answer is discardin) in time, i.e. +or reason. Reasonale discard is possile ased on proper inspection, otherwise technical condition o+ rope remains unknown. Visual inspection is ovious, ut onl' visual examination is not su++icient due to speci+ic rope desi)n. ondestructive ma)netic inspection inspection o+ ropes enales to )ather comprehensive data +or makin) reasoned decision. Ma)netic +lux leaka)e $M-L% euipment with stron) ma)neti*ation can inspect ropes relial', and smart so+tware +acilitates data interpretation. Reach experience with !" o+ ropes spilled over into development o+ relevant national and international norms and standards. Why must ro!s b! "#s!ct!$ a#$ !%am"#!$&
ire ropes are consumale items with limited li+e. !urin) service the ph'sical properties o+ the wire rope will chan)e. At the commencement o+ service, the individual wires and strands settle into position and the rope reakin) stren)th increases. A+ter reachin) a maximum it decreases rapidl'. $-i) /%
0ne o+ the o1ective o+ inspectin) or examinin) a wire ro pe is to supervise the normal process o+ deterioration so that rope can e removed +rom service e+ore ecomin) a ha*ard to sa+et'. Another ene+it o+ the inspection and examination procedures is to detect unexpected dama)e or corrosion. 1
Ro!s a#$ th!"r $!t!r"orat"o#
Ropes are widel' used +or li+tin) operations 2 winders, cranes, elevators, calewa's, as well as )u's +or rid)es, antennas, chimne's, roo+s, etc. Rope inte)rit' e++ects reliailit' and sa+et' o+ installation in which the' are in service. !ependin) on the installation, ropes ma' have di++erent construction, such as stranded, spiral or +ull locked, as well as ma' have rectan)ular cross3section $+lat ropes% and ruer coatin). Re)ardless o+ the construction, ropes deteriorate durin) their operation due to similar reasons, e.). +ati)ue, corrosion, arasion, mechanical dama)e, and overheatin). -ati)ue in wire rope is normall' caused ' repetitive endin) on sheaves, drums, and causes wire rakes. 4roken wires or +ractures, allocated on ver' short distance, are accepted to name as locali*ed +laws $L-%. "he' are one o+ indicator o+ rope de)radation. hen the numer o+ roken wires exceeds a++ordale limit, the rope must e discarded. 5orrosion ma' occur even in ver' dr' environment, especiall' on unprotected, non3 )alvani*ed wires. Arasion is ver' t'pical +or outer wires6 however internal wires also ma' e araded due to +riction, while the rope moves over sheaves. Moreover +or some rope constructions deterioration starts internall', and rope which looks )ood +rom outside ma' e dan)erous due to hi)h level o+ deterioration o+ internal wires. 5orrosion and arasion cause missin) some amount o+ metal +rom wires. "his is called as loss o+ metallic cross3section area $LMA%, and is normall' measured as relative amount in percenta)e to the cross section area o+ a new rope. Accordin) to relevant norms, the rope should e discarded when LMA value reaches limit, estalished +or particular rope construction and application. Sur'!y o( R!mo'a) *ro+!# W"r! A rope must e discarded i+ the permissile numer o+ wire reaks is reached or exceeded. It must also e replaced when local concentrations o+ wire reaks occurs. R!$uct"o# "# $"am!t!r Reduction in diameter can e caused ' arasion, corrosion or local +ai lure o+ the rope core. Accordin) to 4# 789:, ;wire should e discarded when the rope diameter is an'where reduced ' <:= o+ the nominal diameter in the case o+ six and ei)ht strand ropes>. Corros"o# 5orrosion can e external or internal, )eneral or locali*ed. Accordin) to 4# 789:, ;wire rope should e discarded when the sur+ace o+ the wire is completel' rou)hened or pitted, or i+ the wires are slack within the strands due to wasta)e. Ro! $!(ormat"o# a% aviness % 4asket de+ormation c% Loop +ormation d% Loose wires e% odes +% "hinnin) o+ the ropes )% Misplaced outer wires h% Kinks i% -lat areas Dama,! caus!$ by h!at
2
?eatin) rope wires to approximatel' @:: de)ree 5elsius and over will lead to considerale reduction in tensile stren)th o+ the wires. ire ropes which have een su1ected to excessive heat must e discarded. Ro!s $"scar$ o)"cy
"he +ollowin) policies can e considered +or discardin) wire ropes.
3 3
!iscard on timel' asis $automatic discard%, i.e. a+ter a set period, e.). / months.
!iscard +or reason, i.e. when technical condition o+ rope is ad, and continuin) its operation is dan)erous. Bsin) ;automatic discard> polic' one ma' e in risk to continue operatin) rope, which is much deteriorated, and is dan)erous. 0n the other hand discarded rope ma' have )ood condition and could e extended in operation. Premature replacement makes unreasonale costs. !iscard +or reason means that the rope ma' e in service until discard criteria not reached. !iscard criteria are re+erred in relevant standards and norms. "his approach reuires knowled)e aout rope condition, which can e otained resultin) proper rope inspection. ire ropes can e inspected destructivel' or nondestructivel'. !estructive inspection can e carried with relativel' short section o+ rope and )ives direct readin) o+ rope reakin) stren)th. Results o+ destructive testin) represent rope section which was destro'ed, ut the uestion is how to re+er these results to the rest len)th o+ rope.
Wh!r! "r! ro!s must b! "#s!ct!$&
!urin) an inspection or a periodic examination ' a competent person, +ull len)th o+ the ropes should e inspected. "he +ollowin) areas ma' reuire more detailed attention. a% Rope *ones with the hi)hest numer o+ c'cles. % Pick up points c% Cnd +ittin)s d% Cuali*in) sleeves e% Dones o+ maximum wear on drums +% #heaves )% Rope sections workin) in a hostile environment. .o ro!s ca# b! "#s!ct!$ #o#$!struct"'!)y V"sua) t!st"#,
Visual testin) $V"% enales to reveal outer de+ects such as corrosion, roken and missin) wires i+ rope sur+ace is accessile +or visual examination. V" ma' e accompanied with haptic testin), use o+ mirror, ma)ni+'in) )lass, and is carried at low speed. -or these reasons V" is tiresome, and reuires su++icient time ein) ver' su1ective. Most wires in the rope ma' not e visuall' inspected E/F. 0nl' outer wires are availale +or examination, ut these wires disappear inside the rope on hal+ o+ their len)th, and ma' e covered with heav' )rease, that reduces e++ectiveness o+ such inspection $-i). /%. Ropes with protectin) coatin) ma' not e inspected visuall'.
3
-i)ure /. 5ross section o+ multila'er rope $le+t% and heav' )reased crane rope $ri)ht%. ote, that low rotation multila'er rope, widel' used +or li+tin) operations, start deterioration +rom inside, however inner roken wires ma' not e revealed visuall'. evertheless visual inspection in comination with use o+ ma)netic instruments consideral' increase reliailit' o+ in+ormation otained +rom tested rope.
MF/ ro! "#s!ct"o#
owada's M-L principle is common +or nondestructive testin) o+ wire ropes. M-L instruments can precisel' and +ast measure LMA to assess level o+ arasion and corrosion, and detect outer and inner L-s even under the )rease or protectin) coatin). "o otain hi)h LMA accurac' and L- sensitivit' M-L euipment should contain stron) ma)nets to ma)neticall' saturate the rope under test, and inspect the rope at applied ma)netic +ield, i.e. while the rope is ma)neticall' saturated. "he operatin) principle is descried at -i). .
-i)ure . M-L instrument with stron) ma)neti*ation. Principle o+ operation. Ma)netic head o+ the instrument usuall' comprises ma)neti*in) s'stem with permanent ma)nets, surroundin) the rope under test and producin) the ma)netic +lux alon) the rope. hile rope is passin) throu)h the head, the section o+ rope inside the head is ma)neticall' saturated. #ensors $?all )enerators or coils%, which are located inside the head close to the rope sur+ace, catch ma)netic +lux leaka)e distortion, created ' L- orGand LMA. Permanent ma)nets must e stron) enou)h to ma)neticall' saturate the rope, i.e. to reach workin) point A at h'steresis curve $-i). @%. Most o+ euipment, desi)ned +or rope !", operate M-L principle, and +or this reason inspection o+ rope with such instruments o+ten called ma)netic rope testin) $MR"%.
4
-i)ure @. ?'steresis curve. Inspection with applied stron) $A% and residual weak ma)neti*ation. "he lar)er is rope diameter the stron)er ma)nets should e used, thus ma)netic s'stem ecomes heavier and i))er. #tate3o+3the art M-L rope tester I"R0# EF comprises ma)netic heads $M?% with stron) permanent ma)nets to inspect ropes o+ di++erent diameter. ei)ht and si*e o+ ma)netic heads are shown in the tale /. "ale /
Rope Ø, mm/
6-24/
20-40/
40-64/
MH type
MH 6-24
MH 20-40
MH40-64
Weight, kg
3
8
Size, mm
264x188 66
330x205x190
60-85/
MH
80-120/
100-150/
60-85
MH 80-120
MH 100-150
15
60
82
112
330x235x190
690x526288
895x520x440
950x550x490
evertheless there are two important reasons to uphold stron) ma)neti*ation( 3 Ma)netic properties o+ the rope ma' var' due to operational conditions, mechanical and thermal e++ect, etc. and variation in ma)netic condition ma' cause readin) errors. #tron) ma)neti*ation makes a ma)netic propert' uni+orm and so provides hi)her inspection reliailit' and increases measurin) accurac'6 - Bni+orm ma)netic +lux in the rope provides hi)her sensitivit' to oth outer and inner roken wires. eak ma)neti*ation instruments +or inspection o+ rope in residual ma)netic +ield, recentl' appeared on the market ma' seem as worth' alternative to M-L instruments mentioned aove due to relativel' small wei)ht. ?owever weak ma)neti*ation ma' not provide uni+orm steel ma)netic properties and so per+ormance o+ relevant instruments is worse( the' have lower sensitivit', especiall' to inner de+ects6 readin)s otained +rom consecutive runs var' $4 r, 4r/, 4r at -i). @% i.e. measurin) repeatailit' is poor. Cven use o+ sensors o+ hi)her sensitivit' and increase o+ )ain +actor ma' not improve their per+ormance. 4esides, the t estin) results +rom weak ma)neti*ation instrument depend on previous ma)netic condition o+ the rope. -or instance, ;ma)netic spots> on the rope, created ' heatin), mechanical impact, etc. ma' e interpreted as de+ects. "his was proved experimentall', ' comparative test o+ weak and stron) ma)neti*ation instruments availale on the market E@F.
5
Sur'!y o( sta#$ar$s a#$ ,u"$a#c! (or NDT o( "r! ro!s
A#"M C/89/ EHF is one o+ the asic documents, which descries relevant terminolo)', operatin) principles, application, euipment, procedures, standards +or caliratio n, etc. "his standard was recentl' accepted in 4ra*il in Portu)uese lan)ua)e ' chan)e o+ the cover. "he uidance +or ma)netic !" o+ steel wire ropes was issued ' Russian -ederal !epartment o+ Industrial #a+et' in :::, and accepted in Bkraine in ::@. It contains asic knowled)e re)ardin) inspection methods, procedures, reports, uali+ication, and other help+ul in+ormation. #tandards +or inspection o+ li+tin) euipment usuall' re+er to nondestructive inspection o+ ropes as a considerale mean +or increase sa+et'. C.). sa+et' codes +or under)round minin) industr' in man' countries descrie in details reuirements +or ropes !" E8F, and provide discard criteria. !ependin) o+ rope application 2 hoistin), alance, conductor, etc. rope discard criteria ma' var'. Bsuall' standards provide maximum LMA value and L- numer at certain len)th o+ rope as discard criteria. I#0 H@:< E7F re+ers to rope !" ' electroma)netic method as an aid to visual inspection and recommends initial MR" as soon as possile a+ter installation o+ rope, considerin) such inspection as re+erence point +or +urther examinations o+ rope. 5arr'in) and haulin) ropes o+ aerial calewa's also pla' important role in providin) sa+e operation. Relevant norms are accepted in B#A, 5anada E9, JF, Russia, other countries. Curopean norm C /<93J E
!urin) MR" the rope is passin) throu)h testin)Gma)netic head. Cuipment must e ru))edl' desi)ned to meet industrial reuirements. ?oldin) euipment in hands durin) inspection as well as hi)h rope speed is ha*ardous and ma' in1ure inspector and dama)e euipment. Cuipment is recommended to relial' +ix while rope moves throu)h, and keep speed not exceedin) /,83 mGs. In case o+ inspection o+ stale ropes $rid)e ropes, )u' ropes% ma)netic head moves alon) the rope with tu))in) slin)s or sel+3propeller device. !ata lo))er o+ rope tester I"R0# can e +ixed on the ma)netic head and moved alon) the rope to record data, thus no lon) cale is necessar' in this case $+i).H%.
-i)ure H. MR" o+ rid)e rope. !ata lo))er I"R0# $circled% is +ixed on ma)netic head 6
-or etter per+ormance it is recommended to ma)neti*e rope prior to inspection run, and make at list two runs +or comparison. Luricant and )rease do not a++ect readin) while protrudin) roken wires ma' dama)e the instrument, and it is recommended to cut o++ protrudin) wires prior to MR". Ma)netic heads ma' have wheels or sleeves which ali)n rope in the head, and the latter also protects +rom protrudin) wires. Cuipment must e euipped with encoder to +ix the position o+ de+ects. ire rope tester I"R0# measures LMA and reveals L-, and records all data into uilt3in memor' +or downloadin) and +urther anal'sis. "est data are arran)ed in traces +ormat as shown on +i). 8. -ollowin) traces are availale( LMA, L-, traces +rom individual sensors, rope speed. 0n3line re)istration o+ traces is also possile $+i). 7% that enales inspector to stop the rope +or visual examination in case o+ suspected de+ect. -eedack +rom customers operatin) I"R0# durin) lon) time showed that extendin) rope li+e ased on their !", and prompt plannin) o+ purchasin) new ropes and exchan)e ma' provide su++icient ene+its E/, /@F.
-i)ure 8. LMA $upper% and L- rope traces otained +rom I"R0#.
-i)ure 7. Real time LMA and L- traces shown on laptop screen.
Ass!ssm!#t o( ro! r!s"$ua) str!#,th
Providin) examination o+ rope, the pursued tar)et is assessment o+ residual stren)th o+ the rope in order to know residual li+e with consideration o+ its operational condition. Assessment result enales inspector to appoint the next inspection in reasonale manner. Intron Plus has created a mathematical model o+ rope deterioration that allows calculatin) rope sa+et' +actor, which, in turn, is used +or assessment o+ rope residual stren)th E/HF. Cxperiments with ropes carried in rope laoratories in -rance, -inland, and Bkraine, and +ollowin) comparison o+ experimental results with assessed residual stren)th 7
showed their )ood a)reement. "his makes possile to assess rope residual stren)th ased on the LMA and L- traces. As a result distriution o+ sa+et' +actor $#-% alon) the rope len)th can e otained. -i).J shows distriution o+ #- +or the rid)e sta' rope construction /99G9/HH@@*@H*H/*, diameter 9 mm containin) de+ects at the distance o+ 8, @8, 9: $out3o+3lock wires% and @/8 m $ outer roken wires%. "he minimum #- value is noted at the distance @/8 m, and it is eual to .H. 5onsiderin) relevant norms minimum permissile #- value is as much as , and it can e concluded, that the rope ma' still remain in service. Assessment o+ rope residual li+e time reuires accessile data +rom several consecutive inspections otained +rom the same rope.
-i)ure J. !istriution o+ rope sa+et' + actor o+ 9 mm rid)e rope. Co#c)us"o#
ondestructive inspection o+ wire ropes with stron) ma)neti*ation M-L instruments enales accurate assessment o+ technical condition o+ ropes, providin) reliale asis +or either timel' discard o+ rope or extension its li+e. In3time discard increase sa+et' o+ rope installation, while 1usti+ied extension provides economical ene+its. R!(!r!#c!s
/. R.Verreet. A new method +or detectin) wire rope de+ects. 0IPCC5 5on+erence Proceedin)s. Athens, reece. ::7, p.p. 8837/. . A.Mironenko. ondestructive inspection o+ steel wire ropes. Proceedin)s o+ MI5!" ://. @. V.#ukhorukov. Ma)netic -lux Leaka)e Method( #tron) or eak Ma)neti*ation Materials Cvaluation, vol. 8, :/@. H. A#"M C/89/3//. #tandard practice +or electroma)netic ex amination o+ +erroma)netic steel wire rope. 8. #outh A+rican #tandard #A4# :<@. 5ondition assessment o+ steel wire ropes on mine winders. /<<7. 7. I#0 H@:<3:/:. 5ranes 2 ire ropes 2 5are and maintenance, inspection and discard. 9. A#I 499./3::7. American ational #tandard +or passen)er ropewa's. J. D
/H. A.Vorontsov, V.Volokhovsk', !.#lesarev. 5omined approach to dama)ed wire ropes li+e3time assessment ased on !" results and rope mechanics 2
|
9
