Proceedings of the conference on marine engineering systems condition monitoring and preventive maintenance, ICMES'77

P 1 9 7 7 - 1 0

C O N F E R E N C E ON MARINE ENGINEERING SVSTEMS CONDITION MONITORING A N D PREVENTIVE M A I N T E N A N C E

PARIS, May 4 - 6,1977

0R6AN>ZIN6 COMMITTEE Chairman : Mr. F. Bureau Veritas Paris, France MONCEAUX GERMANY

(Federal Républic of) Or. J . RICHTER MAN

Augd)urg ITALY

Mr. R. GAUOiO Grandi Motori. Trieste Trieste

JAPAN

Mr. K;. KUROSU Ship Research Institute Tokyo

NETHERU^NDS Mr. H.F. STEENHOEK Technisch Physische Dienst Delft

NORWAY

Mr. M. RASMUSSEN

Norvsglan Institute of Technology Trondheim

SPAIN

Mr. R. CHORRO ONCINA Empresa Nacional Elcano Madrid SWEDEN Mr. N.E. WOLFF Brostroms Tekniska Göteborg UÄA^

Prof. A.R. KRAMER

State University of New York Maritime College New York INTERNArtONAL COMMITTEE DENMARK Mr. Ch. KNAK Ministry of Education Copenhegen FINLAND Prof. J £ . M N S S O N

Helsinki University of Technology ptanlemi FRAidCE Mr. J . COUNE Chantiers de TAtlantictue Saint-Naziaire GERMANY

(Federal Republic of) Prof.O. GiÈISLER technical University Hanover

JAPAN

Mr.S. OHASHI

Mitsui Shipbuildirig and Engineering Co. Tokyo

ITALY

Prof. E. V O L T A

Consiglio Nszionale delle Ricerche Genove

NETHERLANDS Mr. A . de MOOY

Institute of Mechanical Constructions fTNO) Oéift

NORWAY Mr.J.R. GETZ

Ship Research Institute of Norway Trondheim

POLAND

Prof. J . S T A L l N S k i Gdansk Pojytedinic Institute cidarak

SPAIN

Prof. L. D E MAZARREDO &euela T.S. Ingenierot Navales Madrid

SWEDEN

MR, B. WALLIN

Swedish Ship Researcfa Foundatton Göteborg

ÛNtTEb KINGDOM Mr. G.R. SNA(TH

British Ship Research Association Wallserxl

U;SA.

M r . H . a BRANDING American Bureau of Shipping New York

YUGOSLAVIA

Proi.W. M U U E V I C Zagreb University Zagreb

Spomoml by : The Danish Department of Ocean Engineering, the Finnish Committee on Marine Technplogy, Association Technique Maritime at Aéronautique (France). Institut de Recherche de la Cons-tructton Navale (France), Schlfftpaütechnische Gesellschaft (Germany). Verband der Deutschen Schiff-baüindustrie {Germany). the Marine Engineering Society in Japan, Associazionedi Tecnica Navale (Italy), Assoäazione Italisna per L'Automazicme, the Netherlands Maritime Insmuœ.technischPhysische Dienst (Netherlands), the Ship Research Instituta of Norway, the Association of Ship Technical Societies in Norway, Associacion de Ingenieros Navales (Spain), Aaocieclon de Investigacion de la Constrüccion Naval (Spain), the Swedish Ship Research Foundation, the Association of Swedish Mechanical Enjjineers, the Brijtish Ship Research A ô o d a t i o n , the Institute of Marine Engineers (United Kingdom), the Z^reb Electrotechnic Uriiveraity (Yugoslavia).

A M E S S A G E F R O M T H E C H A I R M A N O F I C M E S

F e l l o w D e l e g a t e s ,

I a m d e l i g h t e d tp j o i n y o u i n t h i s f i r s t i n t e r n a t i o n a l c o n f e r e n c e o r g a n i s e d u n d e r the a u s p i c e s o f the I n t e r n a t i o n a l C p o p e r a t i b n S c h e m e f o r M a r i n e E n g i n e e r i n g S y s t e m s . S i n c e y o u a r e r e a d i n g t h i s d o c u m e n t y o u a r e f a m i l i a r w i t h the name, h o w e v e r you m a y not b e quite s o a w a r e of the n a t u r e a n d p u r p o s e of the o r g a n i s a t i o n . L e t rne i n f o r n i you.

I C M E S was f o r m a l l y s e t up i n S e p t e m b e r 1973 a f t e r c o n s i d e r a b l e g r o u n d w o r k h a d b e e n c a r r i e d out b y a w o r k i n g g r o u p f o r m e d two y e a r s p r e v i o u s l y b y the A s s o c i a t i o n of S h i p T e c h n i c a l S o c i e t i e s i n N o r w a y . T h e p u r p o s e o f I C M E S i s to s t r e n g t h e n the t e c h n i c a l . s t a t u s of m a r i n e e n g i n e e r i n g b y p r o m o t i n g i n t e r n a t i o n a l c o o p e r a t i o n .

A t the a p e x of the o r g a n i s a t i o n i s a S t a n d i n g C o m m i t t e e o f s o m e 13 p e o p l e m a i n l y f r o m E u r o p e a n c o u n t r i e s , but i n c l u d i n g J a p a n a n d the U.S.A. T h e e s s e n t i a l w o r k of I C M E S i s c a r r i e d out b y T e c h n i c a l C o m m i t t e e s . A t the m o m e n t the l a t t e r n u m b e r s i x , c o v e r i n g C o n d i t i o n M o n i t o r i n g , R e l i a b i l i t y E n g i n e e r i n g , C o m p u t e r - a i d e d D e s i g n , M a t h f e m a t i c a l M o d e l l i n g and S i m u l a t i o n , C o m m i s s i o n i n g and T e s t i n g , and S h a f t i n g S y s t e m D y n a m i c s , bût s i n c e I C M E S c o v e r s a l l - a s p e c t s o f m a r i n e e n g i n e e r i n g s y s t e m s , i n c l u d i n g e n g i n e e r i n g a s p e c t s o f e x p l o r a t i o n o f f s h o r e , the n u m b e r and d i s c i p l i n e s o f t h e s e C o m m i t t e e s m a y c h a n g e f r o m t i m e to t i m e . M e m b e r s h i p o f the T e c h n i c a l C o m m i t t e e s c o m p r i s e p e o p l e w i t h s p e c i a l i s t k n o w l e d g e i n t h e i r i n d i v i d u a l f i e l d s . M e m b e r s a r e p r o p o s e d b y I C M E S N a t i o n a l C o m m i t t e e s , o r o r g a n i s a t i o n s r e p r e s e n t i n g i n d i v i d u a l i n t e r e s t s i n I C M E S . E a c h m e m b e r i s c h o s e n b e c a u s e he i s an e x p e r t c u r r e n t l y w o r k i n g p r o f e s s i o n a l l y i n a s u b j e c t ^ a n d f o r the p o t e n t i a l c o n t r i b u t i o n he i s l i k e l y to m a k e . A l t h o u g h T e c h n i c a l C o r i i m i t t e e s c a r r y out m u c h o f t h e i r l i a i s o n b y c o r r e s p o n d e n c e , they do m e e t p e r i o d i c a l l y s o that the e x p e r t s m a y d i s c u s s t h e i r s u b j e c t s i n t i m a t e l y and s h a r e t h e i r e x p e r i e n c e s . Out of t h e s e e x c h a n g e s i t i s i n t e n d e d t h a t d o c i i m e n t a t i o n of the s t a t e o f -t h e - a r -t o f -t e c h n o l o g i e s will b e k e p -t c o n -t i n u a l l y up -to da-te, and -tha-t a g r e e m e n -t s w i l l b e r e a c h e d on how w o r k m i g h t be s h a r e d , thus e n a b l i n g fro.ntiers to b e p u s h e d f o r w a r d s t e a d i l y and

e f f i c i e n t l y .

I C M E S i n t e n t i o n i s to publis.h the o u t c o m e o f the w o r k of the T e c h n i c a l C o m m i t t e e s , m a k i n g a v a i l a b l e the k n o w l e d g e a n d t e c h n i q u e s of the e x p e r t s to the p e o p l e who r e q u i r e to d e s i g n , b u i l d , p r o c u r e a n d o p e r a t e - s h i p s and the l i k e , thus f a c i l i t a t i n g t h e s e p r o c e s s e s .

P u b l i c a t i o n o f s o m e r e s u l t s w i l l b e d i r e c t t h r o u g h I C M E S S e c r e t a r i a t , büt i t i s h o p e d that m u c h o f the w o r k e m a n a t i n g f r o m I C M E S m a y b e o f f e r e d to l e a r n e d s o c i e t i e s a n d o t h e r o r g a n i s a t i o n s f o r p r e s e n t a t i o n at i n t e r n a t i c j n a l c o n f e r e n c e s o r g a n i s e d b y t h e m . It m a y b e n e c e s s a r y , of c o u r s e , to o r g a n i s e one o r two c o n f e r e n c e s s u c h as the p r e s e n t one, w h i c h h a s b e e n m a d e p o s s i b l e b y the e f f o r t s of M r . F., M o n c e a u x . C h a i r m a n of T e c h n i c a l C o m m i t t e e No. 1, d e a l i n g w i t h C o n d i t i o n M o n i t o r i n g , and u n d e r the a u s p i c e s of B u r e a u V e r i t a s . We a r e g r a t e f u l to M r , M o n c e a u x , h i s o r g a n i s i n g c o m m i t t e e . B u r e a u V e r i t a s , the m a n y I n t e m a t i o n a l s p o n s o r s of the c o n f e r e n c e , a n d a u t h o r s f o r t h e i r e f f o r t s and s u p p o r t .

I w i s h the c o n f e r e n c e s u c c e s s a n d I h o p e that y o u i n d i v i d u a l l y f i n d i t s t i m u l a t i n g a n d u s e f u l .

G e o r g e R. S n a i t h ,

A SHORT INTRODOCTION TO THE ICMES 7 7 CONFEREMCE ON CONDITION MOHITORINS ÄHD PREVENTIVE- MAHTOHAHCE

1 , ICMES T C 1 and the P a r i s 1 9 7 7 ICMES Conference.

The T e c h n i c a l Committee 1 of I C H B S has been e s t a b l i s h e d i n 1 9 7 4 v i t h the scope df s t u d y i n g "Condition M o n i t o r i n g " ( f a i l u r e mechanismst numitoring tecdiniques and methods, djata a n a l y s i s * p r e d i c t i o n methods) and with the aim of i

g i v i n g s p e c i a l i s t s i n d i f f e r e n t c c u n t r i e s engaged w i t h i n marine e n g i n e e r i n g an opportimity t o d i s c u s s questions o f connnon i n t e r e s t and t o exchange i n f o m i a t i o n on r e s u l t s obtained and work i n progressf o r contemplated* i n t h e i r r e s p e c t i v e c o u n t r i e s ;

- prcnioting c o c ^ e r a t i o n between s p e c i a l i s t s i n d i f f e r e n t c o u n t r i e s i n v o l v e d i n research and deve-l o ^ e n t i n order t o achieve a mare e f f i c i e n t iise o f the resources w i t h i n t h i s f i e deve-l d t

- recommending f u r t h e r r e s e a r c h and development, e s p e c i a l l y where cooperation between s p e c i a l i s t s i n différait c c u n t r i e s i s of s p e c i a l i n t e r e s t br when a standard procedure appears t o be s u i t a b l e *

The Members of l O f E S TC 1 met a few times and were soon convinrad that the f i e l d o f " C o n d i t i o n Monitoring*' weis v e r y l a r g e and extrôiely wideâpréadt t h a t a great amount o f work was going on i n v a r i o u s canuitxdest many of them rat represented w i t h i n TC 1 ; the TC 1 Heabers a c c o r d i n g l y thmight t h a t a " s t a t e o f the art" docuiaent, and a l s o f u r t h e r work w i t h i n the f i e l d * might be incomplete and expressed the i d e a that i t would be necessary and d e s i r a b l e t o have a s p e c i a l i n t e m a t i o n a l Conference arranged on t h i s p a r t i c u l a r s u b j e c t . The ICMES Standing Committee having given i t s approval and supp(n>t t o t h i s i d e a , the ^ e p a r a t o r y work f o r t h i s Conference began e a r l y 1 9 7 6 .

During tiieir meetings, the TC 1 Members e s t a b l i s h e d a s h o r t schone of the v a r i o n s probiens i n v o l ved i n the concept o f c o r u l i t i a n monituring and p r e v e n t i v e maintenance* T h i s scheme i s summarized h e r e -a f t e r -and some d e f i n i t i o n s -and thougSits -are gi'r-an ^icäi c o u l d be o f use f o r the d i s c u s s i o n s t o be h e l d d u r i n g the Conference ; i n particûleu: seme f i g u r e s are given ecinceming the economies b f c o a d i t i b n mo-n i t o r i mo-n g amo-nd p r e v e mo-n t i v e maimo-ntemo-namo-nce t i t i s hoped t h a t they w i l l g i v e r i s e t o c o mo-n t r o v e r s i a l argumemo-nta- argumenta-t i o n s h e l p i n g argumenta-t o reada moré accuraargumenta-te i h f o i m a argumenta-t i o n on argumenta-t h i s s u b j e c argumenta-t o f major imporargumenta-tance*

2* D e f i n i t i o n s .

2 . 1 . Bepair- aind Haintenauice

S e r v i c e keeping wox^s on board s h i p s i n c l u d e Repair and Mainteniance s

- R e y a i r i s any a c t i o n p e r f o r n e d on a system or e<jiûii»nent subsequent t o f a i l u r e , breakdqim o r ex-c e s s i v e dêtêH-oration and i s i n t e n d e l t o render tiie system or equipaeixt operable again« I n priiœiplei r e p a i r i s n e c e s s i t a t e d o n l y when maintenance procedure f a i l s or vhen the s y s t a n or equipment i s impro-p e r l y designed* b u i l t or oimpro-perated*

Maintenance i s an a c t i o n p e r f o m e d p r i o r t o any breakdown o r f a i l u r e £ar the puz^ese o f p r o l o n -ging the i z s e f u l l i f e of a systôn or equi^aiiöit and o f keeping t h i s system or equipmient i n r e l i a b l e con-d i t i o n s w i t h i n con-d e f i n e con-d l i m i t s . Maintenance i s p r e v e n t i w i n nature*

2.2. Various types of Maintenance

Maintenance may be ensixred on schedule or on c o n d i t i o n i

- .an schedule maintenance i s based on time or running hours* I t i s f i x e d a c c o r d i n g t o the e x p ^

r i e n c e gained eitiher by the Shipowner or by the Manufacturer of the equipment ( p i s t o n overhaul every 7000 hours, greasing of r o l l e r bearing every 1 0 000 h o u r s , e t c . . . ) .

_ on c o n d i t i o n maintenance i a b M e d em the s t a t e o f the system or equipment and i t r e s u l t s e i t h e r from the a c t u a l c o n d i t i o n s a t â determined t^me or on t r e n d c o n d i t i o n s which give an i n f o r m a t i o n on the probable behaviour o f the equipment w i t h i n a f o r e s e e a b l e p e r i o d of time i

• Maintenance based on a c t u a l c o n d i t i o n s depends u p ^ measurements (alarms) or up<m i n s p e c t i o n o p e r a t i o n s .

. Maintenance on t r e n d conditiorû ( p r e v e n t i v e maintenance)is based on the stirvey o f c o n d i t i o n p e u m e t e r s and e x t r a p o l a t i o n o f the informatiäi f u r n i s h e d on the o p e r a t i n g c o n d i t i o n s i n a f o r e s e e a b l e p e r i o d o f time.

2,3* Condition, monitoring and, preventive.maintenance

• Condition^ mimitoring i s t h e r e f o r e the a p p l i c a t i o n o f tecliniques, methods and procedures w h i d i a l -lows the o p e r a t o r t o olatain. i n due time, i n f o r m a t i o n (monitoring) about systems or equipment s t a t e or perfonnance ( c o n d i t i o n ) ? such infoxmation i s intended t o be used t o perform i n a s a t i s f a c t o r y mamner p r e v e n t i v e maintenance as d e f i n e d i n 2.2* above*

NOTE t From the t v o above mentioned d e f i n i t i o n s of Repctir and Medntenance i t r e s u l t s t h a t a same acrtion can be q u a l i f i e d e i t h e r as "Repair" or as "Maintenance" depexiding upon the l e v e l on which i t i s considered ; f o r example, i f we c o n s i d e r a system d e l i v e r i n g o i l under s p e c i f i e d c h a r a c t e r i s t i c s emd irtiicii i n c l u d e du-p l i c a t e du-pumdu-ps, the a c t i o n f o l l o v i n g the f a i l u r e of me o f these du-pumdu-ps w i l l be :

- r e p a i r of the system, i f the l o s s of the pump has l e d t o an e x c e s s i v e change i n the c h a r a c t e r i s t i c s o f the o i l s u p p l y , the system b e i n g then c o n s i d e r e d as o p e r a t i n g out o f the s p e c i f i e d l i m i t s ,

- maintenance o f the system, i f the f a i l u r e o f a pump has not l e d t o a change i n the c h a r a c t e r i s t i c s o f the o i l supply because of redundancy ; the a c t i o n performed on the pump i t s e l f w i l l be a r e p a i r .

Prom the same p o i n t of view, r e p a i r of a p r o p u l s i o n motor w i l l be understood as r e p a i r o f the s h i p i f the f a i l u r e o f t h i s p r o p u l s i o n motor leads t o unplanned s t o p p i n g of the s h i p . I f the s h i p r«nains opera-b l e d u r i n g r e p a i r of the f a i l e d p r o p u l s i o n motor t h i s w i l l opera-be termed maintenaiu:e o f the s h i p .

3. Shipowners' view on preventive maintenaice

3*1. The Shipowners' i n t e r e s t i n the a p p l i c a t i o n o f c o n d i t i o n monitoring t o preventive maintenance de-p ^ d s ude-pon the. o v e r a l l sayings t h a t can be obtained i n o de-p e r a t i o n exde-penses i such savings may be exde-pected as f o l l o w s :

- the permanent knowledge of the equipmsit c o n d i t i o n * monitoring of any d e v i a t i o n from foreseen valiœs, i s a h e l p f o r the crew, r e g a r d l e s s of the «ctent of t h e i r experiences* t o make a f a i l u r e d i a -gnosis and t o know the reason óf the p l a n t e f f i c i e n c y shortage j

- t h i s knowledge i s expected tp be o f a great help by c a l l i n g a t t e n t i o n to m a l f u n c t i o n s , thus p e r m i t t i n g e a r l y i n t e r v e n t i o n t o p r e v e n t ttoem developing i n t o dangerous o r c a t a s t r o ^ i c f a i l u r e s ;

- the d e v i a t i o n concept i s a vay of f o r e s e e i n g the most convenient time t o apply maintenance a c t i o n *

Saving may d e r i v e from the f o l l o w i n g sources :

a) Reduction o f o f f - h i r e time f o r t e c t o i i c a l reasons :

a l ) by c o l l i s i o n o r s t r a n d i n g ; t h i s r i s k may be reduced w i t h a b e t t e r knowledge of the opera-t i n g c o n d i opera-t i o n s o f p r o p u l s i o n maäiinery and s opera-t e e r i n g gear opera-t

a2) by e x p l o s i o n or f i r e ; c o n d i t i o n monitoring may c o n t r i b u t e t o reduce t h i s r i s k , c a l l i n g a t t e n t i o n t o the development o f components f a u l t s o r f a i l u r e s u ^ i c h would otherwise be unnoticed j f o r example e x t e n s i v e blow-by could l e a d t o f i r e i n the scavenging b e l t o f two s t r o k e engines ;

a3) by s t o p p i n g i n n a v i g a t i o n o r harbour j d i s c o v e r i n g minor f a i l u r e s and t h e i r causes allows the t i m e l y a p p l i c a t i o n o f c o r r e c t i v e maintenance a c t i o n before such defeats c o u l d degene-r a t e odegene-r pdegene-roduce majodegene-r f a i l u degene-r e s degene-reducing the s h i p t o i m m o b i l i z a t i o n ;

a4) by reducing the time r e q t i i r e d f o r maintenance work t o that %rtiich i s s t r i c t l y n e c ^ s a r y , a v o i d i n g unnecessary work, s h o r t e n i n g the t o t a l r e q u i r e d maintenance time.

E v a l u a t i o n o f the t o t a l o f f h i r e time i ^ i c h can be expected i s questionable and i s v e r y d i f f i -c u l t t o -che-ck. To begin w i t h , i t i s estimated ttat on a l e n g term b a s i s 3 - 4 days/year s a v i n g i n o f f - h i r e time can be expected.

b) Maintenance expenses

Maintenance has t o be planned* f o r ob\dous s a f e t y reasons w i t h a c e r t a i n l a t i t u d e * i n tfae s h o r t e s t time p e r i o d . Reduction of the maintenance work can be obtained on the assuiB^tian that the v ^ k i s done o n l y yhen there i s r e a l l y a need f o r i t . A f t e r a p p l y i n g d i s m a n t l i n g planned medntehahce work i t can be o f t e n found out t h a t the vork veis not yët necesseury and i n some t Other cases i t can appear t h a t a maintenance vork c a r r i e d out i n due time v o u l d have c u t the n e c e s s i t y o f more expensive maintenance a c t i o n s . The p a s i b i l i t i e s o f perfcmning a t r e n d ana-l y s i s v h i c h i n d i c a t e s v h a t i s tfae maintenance vork vhi<ät w i l l g i v e the best r e s u l t s , and ^ e n t h i s work has t o be done, gives a good p l a t f o r m f o r b e t t e r u t i l i z a t i o n o f the maintenance r e s u l t s . An e s t i m a t i o n o f the savings c o u l d be e i t h e r 20 % o f the t o t a l maintenance expenses i n -c l u d i n g the shore shop v o r k s , the vorks made by the -c r e v and spares and s t o r e -c<st8, or of 30 t o 50 X o f tiie machinery maintenance vorks o n l y .

c) F u e l o i l s a v i n g

c l ) Savings of f u e l , due t o the f a c t that the propulsicm w i i t s are maintained i n the best con-d i t i o n ancon-d ;Ln c o r r e c t adjustment should l e a d t o an economy v/tiidh appears t o be q u e s t i o n a -b l e î the f i g u r e Of 1 % g i v e s anyhov an o r d e r o f magnitude of suäi s a v i n g s , i f «œy.

c2) A more r e g u l a r operaticni o f the iship, due t o tiie p r e v e n t i o n o f undue stoppings, v i l l l e a d t o an a d d i t i o n a l s a v i n g Of f u e l y no p e r i o d of f a s t speed being i ^ c e s s a r y f o r compensating stoppages or reduced speed periods | no estinüiticm has y e t been r e t a i n e d f o r such s a y i n g s , but the f i g u r e o f 1 % can a l s o be r e t a i n e d as a IMSÎS foor d i s c u s s i o n .

3.2. O f f s e t t i n g the above mentioned advantages of preventive maintenance, the Shipowner sees sane d i f -f i c u l t i e s such as 1

- l o v motivatiffli i n the s t a f f a t the necessary t e d m i c a l l e v e l î

- l o v accuracy and r e p e a t a b i l i t y i n the measuring equipment ;

- s h o r t l i f e o f sane sensors, e s p e c i a l l y those t o be f i t t e d i n high tenperature and v i b r a t i o n l e v e l l o c a t i o n s ;

- furtlœr a t t e n t i o n t o tiœ preventive maintenance equipnent t seme engineerii cónsider that t ^ i s represents a d d i t i o n a l equipment v i t h i t s own f a i l u r e s and a d d i t i o n a l maintenance l o a d ; - l a s t t u t not l e a s t , the p r o f i t has t o be proved.

3.3. To get the best p o s s i b l e p r o f i t from the investment i n preventive maintenance i t i s a t f i r s t e s -sœitial t o monitor equipment vhich i s sutanitted t o high s t r e s s e s and h i g h l y exposed t o f a i l u r e s o r which l e a d t o high c o s t s of r e p a i r .

An i n i t i a l l i s t o f such cmqtonents i s as f o l l o w s i

- Ûain engines (about 20 % o f t o t a l machinery maintenarôe c b s t s ) i

. Turbochargers, c y l i n d e r l i n e r s , pistcms aiid p i s t o n r i n g s , exhaust v a l v e s . ~ Turbines j

. Deposit and wear dovna of blades, wear o f bearings, v e a r of a e a l i n g s . - B o i l e r I

. C o r r o s i o n of économiser,.aiz4ieater and tubes. Leakage of gas, d e p o s i t s on.tubes. - Ptimps t

. Vear o f bearings, i m p e l l e r and c o u p l i n g s * C o r r o s i o n o f h o u s i i ^ . - Separators

- Heat exehangera ï

. F o u l i n g and d e p o s i t s .

, C o n d i t i o n m o n i t o r i n g , t r e n d a n a l y s i s a j ^ maintenance p r e d i c t i o n 4.1. G e n e r a l i t i e s

Tbe b a s i c i d e a of c o n d i t i o n monitoring i s the d e v i a t i o n concept i n whiäi t^e c r i t e r i a t o a s

-sess the t e c h n i c a l c o n d i t i o n of a system or equipmttit i s the d e v i a t i o n between a s e r v i c e peo^ameter and a r e f e r e n c e parameter. T h i s d e v i a t i o n i s c a l l e d d e v i a t i o n parameter.

The s e r v i c e parameter i s e i t h e r measured d i r e c t l y i n the system or obtained, f o r example, by c a l c u l a t i o n from measured v a l u e s . The s e r v i c e parameter may be b e a r i n g v e a r o r temperature, v i i a r a t i o n l e v e l , e f f i c i e n c y o f a b o i l e r , thermal l o ^ i n a D i e s e l engine ^ l i n d e r * heat t r a n s f e r c o e f f i c i e n t s i n heat exchanging equipment, e t c •«.

However, the s e r v i c e parameter may not only be dependent on the c o n d i t i o n o f the conq?onent i t s e l f , i t mj^ a l s o be a f u n c t i o n o f the load c o n d i t i o n , of the c c m d i t i o n o f otiier o p p o n e n t s i n thé same system and/or o f envirenmental c o n d i t i o n s ; i n t h i s l a t t e r case and i n o r d ^ t o o b t a i n unique r e -l a t i o n s betyecin p h y s i c a -l c o n d i t i o n and the c o n d i t i o n parameter, i t i s necessary to compensate f o r the e x t e r n a l e f f e c t . TharaSore', a m a t h e n a t i c a l model i s g e n e r a l l y used t o c a l c u l a t e a parameter f o r tfae "as nev" c o n d i t i o n o f the compianent o p e r a t i n g tmder the same extexîial cóiditions. T h i s c a l c u l a t e d v a l u e i s the r e f e r e n c e parameter.

For p r e v s i t i v e maintenance, the f u t u r e c o n d i t i o n parameters are e v a l u a t e d through a t r e n d anar-l y s i s ; tfais i s a d i i e v e d by s t o r i n g the c o n d i t i o n deviatioU'.parameters from consecutive c o n d i t i o n ana-l y s i s ahd c a ana-l c u ana-l a t i n g a t r e n d c u r v e . By e x t r a p o ana-l a t i o n , the f u t u r e c o n d i t i o n i s ^ t i m a t e d . The a c t u a ana-l time f o r maintenance i s tfae time podnt vhere the t r e n d i n t e r s e c t s v i t ^ t h e p r e f i x e d t r e n d l i n i t . The e l a -b o r a t i o n o f the c o n d i t i o n parameters and t h e i r t r e n d üialysis can -be a d i i e v e d through "on l i n e " computer ( d i g i t a l or analog) o r t i n ^ g A t o t h e r methods such- as use o f faomograms, asfaore data p r o c e s s i n g or a com-b i n a t i o n o f these.

4.2, A p p l i c a t i c M

The choice of the parameter(s) t o be analyzed depeids e s s e n t i a l l y upon the v e r y nature of the equipment to' be p r o t e c t e d £^d can be determined s a t i s f a c t o r i l y but by the Manufacturers due to t h e i r knowledge of the c h a r a c t e r i s t i c s of the product and the experience they have gained i n o p e r a t i o n ; t h i s supposes e v i d e n t l y t h a t they are v e i l infoxmed of the o p ^ a t i o n a l r e s u l t s •••

The parameter(s) t o be analyzed being thus d i o s e n a s e l e c t i o n has t o be made between tfae pos-s i b l e methodpos-s of mbnitpz*ing v h i c h caii e v e n t u a l l y be a p p l i e d * B a pos-s i c a l l y thepos-se methodpos-s may i n v o l v e :

. Thermodynamic monitoring (which i m p l i e s monitoring of temperatiures, pressures, e f f i c i e n c i e s , . , . ) . • V i b r a t i o n m o n i t o r i n g .

. Mechanical monitoring (vear measurement, discharge o i l t e n p e r a t u r e i displacement o f p a r t s , con-t e n con-t o f mecon-tal p a r con-t s i n discharge o i l , * * • ) • .

The c o n d i t i o n monitoring systems may i n c l u d e a n a l o g i c a l Or numerical components such as com-p u t e r s , but tfae designer o f such systems must keecom-p i n mind t h a t t h e i r r e l i a b l X i t y and a v a i l a b i l i t y i s a must and t h a t a s a t i s f a c t o r y compromise miist be reached betveen s i m p l i c i t y and s o p h i s t i c a t i o n so t h a t the t o t a l c o s t e f f e c t i v e n e s s i s a t t r a c t i v e fcnr the shipowners.

5. CoTOlusion

P r e v e n t i w maintenance through o o n d i t i w i monitoring i s a concept \riiich p r o m i s ^ t o the marine i n d u s t r y sigid.jM.cant saîvings by reduced s h i p operating costs and i n c r e a s e d earnings bjr b e t t e r e f f i c i e n - ^

and reduced o f f r h i r e . The purpose o f the ICMES 1 9 7 7 P a r i s Conference i s t o e s t a b l i s h the s t a t e o f the a r t i n t h i s f i e l d and j:o promote an exchange o f i n f o r m a t i o n axid experience amongst s p e c i a l i s t s of the v a r i o u s t e d m i q u o s i n v o l v e d i through t h i s i t i s hoped that nev developments v i l l be f a c i l i t a t e d and t h a t t h e ' i ^ x t years v i l l see a wide use o f CTndition m o n i t o r i n g f o r p r e v e n t i v e maintenance and t h i s f o r the b e n e f i t o f a l l the i n t e r e s t e d p a r t i e s i shipowners, crews, s h i p b u i l d e r s , equipment manufacturers and f i n a l l y o f the cons:umers of the g o o ^ shipped a l l Over the s e a s .

F r a n c i s Monceaux Chairman, IQfES T.C. 1

C O N T E N T S

C O N D I T I O N M Ö N I T O R i r i l G A N D P R E V E N T I V E M A I N T E N A N C E C O N C E P T

" A B R I T I S H V I E W O F T H E C O N D I T I O N M O N I T O R I N G A S P E C T S O F P R E V E N T I V E M A I N T E N A N C E "

A . D . F . Venton and D. Parkes 1 " D E V E L O P M E N T IN M A I N T E N A N C E P H I L O S O P H I E S "

W. M. J.Geraerds 9 " A S P E C T S A N D C O N S I D E R A T I O N S O N O C G U R I N G A N D D E T E C T I N G O F M A I N T E N A N C E W O R K S B E L O N G E D

T O M A R I N E E N G I N E D E P A R T M E N T "

T . Hashimoto, K. Murayama and K. Hiejima 15 " SHIP'S M U L T I P U R P O S E I N F O R M A T I O N S Y S T E M " J . Soldek 25 " M E T H O D S Ô F P L A N N E D M A I N T E N A N C E A N D R E L I A B I L I T Y A N A L Y S I S T O O P T I M I Z E A V A I L A B I L I T Y O F S E A G O I N G V E S S E L S " K. Gtoth 31 " A Q U A N T I T A T I V E A N A L Y S I S A N D E V A L U A T I O N O F T H E M O N I T O R E D M A I N T E N A N C E A P P L I E D T O A SHIP-B O A R D S Y S T É M " Y . Kawasaki 3 9 " D I G I T A L S I M U L A T I O N O F SHIP'S E N G I N E P R E V E N T I V E M A I N T E N A N C E S T R A T E G I E S "

W. Adamkiewicz, P. Jedrzejowicz and J . Zolkiewicz 4 9 V I B R A T I O N M O N I T O R I N G

" A S I M P L E T O R S I O N A L V I B R A T I O N M O N I T O R I N G S Y S T E M "

R . G a u d i o 5 9 " V I B R A T I O N A N A L Y S I S U S E D F O R D E T E C T I O N O F R O L L E R B E A R I N G F A I L U R E S "

H. Engja, M . Rasmussen and J . Lippe 69 " C O N D I T I O N M O N I T O R I N G O F B A L L A N D R O L L E R B E A R I N G S W I T H T H E S P M - M E T H O D L. Ericsson " M O N I T O R I N G O F T H E H U L L P R O T E C T I O N A G A I N S T C O R R O S I O N IN C A T H O D I C P R O T E C T I Ö N . S Y S T E M S B Y I M P R E S S E D C U R R E N T " C. Quiniou " C O N D I T I O N M O N I T O R I N G : L O N G T E R M O R S H O R T T E R M ? " R. MoIlP S I " V I B R A T I O N C H A R A C T E R I S T I C S O F A T U R B O G E N E R A T O R " C . A J . T r o m p a n d A . C . Pijcke 87 M I S C E L L A N E O U S A P P L I C A T I O N S " A N E W L U B R I C A T I O N C O N T R O L S Y S T E M F O R S T E R N T U B E B E A R I N G "

5. Asanabe, T . M a t s u n o b ü , R. Asaj and J . Hyakutake 101 " T H E R M O D Y N A M I C M E A S U R E M E N T S O N H Y D R O S T A T I C C O M P O N E N T S "

K. Witt and W . M J . Schlosser 109

117 " Ç p N S I D E R A T l Ô N S O N T H E C O N D I T I O N M O N I T O R I N G O F R E L I Q U E F A C T I O N P L A N T S O N G A S C A R R I E R S "

É. Skramstad and L. Foyen 121 D I E S £ L E N G I N E S , G E N E R A L A N D 2 - S T R O K E E N G I N E S

" E C O N O M I C A L A N D S A F E SHIPPING C A L L S F O R C O R R E C T P R E V E N T I V E M A I N T E N A N C E O F M A R I N E D I E S E L E N G I N E S "

H . Dziewanowski 131 " S E R V I C E E X P E R I E N C E W I T H T H E S U L Z E R E N G I N E D I A G N O S T I C S Y S T E M "

P. Schneider and R. Le Mellec 135 " C O N D I T I O N C H E C K S Y S T E M , C C 1 0 F O R 2 - S T R O K E D I E S E L E N G I N E S " A . Ostergaard 145 " E X P E R I E N C E W I T H C O N D I T I O N M O N I T O R I N G O F SHIP P R O P U L S I O N D I E S E L E N G I N E S " Ë. Haaland 155 163 " N O N I N V A S I V E P I S T O N R I N G M O N I T O R I N G " R. Dubois 1 g7 " C Y L I N D E R C O N D I T I O N M O N I T O R I N G B Y D I R E C T M E A S U R E M E N T " N. Hammarstrand 17^ " S O N I C S I G N A T U R E M O N I T O R F O R I N T E R N A L C O M B U S T I O N ENiSINES " R. Hatschek 177

M E D I U M S P E E D D I E S E L E N G I N E S

" T H E M A I N B E A R I N G S L O A D A S A D I A G N O S T I C F A C T O R IN D I E S E L E N G I N E C O N D I T I O N M O N I T O R I N G "

S. Grzywacz, J . Gulbinski and J . Listevynik 183 " D E V E L O P M E N T O F E N G I N E C O N D I T I O N M O N I T O R I N G F O R M E D I U M - S P E E D D I E S E L E N G I N E "

H. lida 193 " C O N D I T I O N M O N I T O R I N G O F M E D I U M S P E E D E N G I N E S "

H. Fagerland 203 " S U R V E Y A N D D I A G N O S T I C S Y S T E M F O R 4 - S T R O K E M A R I N E E N G I N E S "

J . Gallois and A . Genot 209 O I L A N A L Y S I S

" P R E V E N T I V E D E H Y D R A T A T I O N A N D M O N I T O R I N G O F L U B R I C A T I N G O I L S F O R M E D I U M S P E E D E N G I N E S "

R, Nagel and L.W. Williams 219 " W E A R M O D E I D E N T I F I C A T I O N A N D P A R T I C L E R E M O V A L IN O I L W E T T E D S Y S T E M S "

R.S. Miller and'W.K. Petrovic 225 " F E R R O G R A P H Y , A NEW T O O L F O R A N A L Y Z I N G W E A R C O N D I T I O N S "

V . Westcott, E. Bowen and D. Scott 22? " E V A L U A T I O N O F 2 Y E A R S E X P E R I E N C E W I T H S P E C T R O M E T R I C A N A L Y S I S O N A I R C R A F T G A S T U R B I N E E N G I N E S IN T H E R O Y A L N E T H E R L A N D S A I R F O R C E " K . S m i t 233 T U R B I N E P L A N T S I " T H E R M O D Y N A M I C C O N D I T I O N M O N I T O R I N G O F S T E A M T U R B I N E P L A N T S "

O . Martens, J . C . Örertibo and K. Berge 239 " C O N D I T I O N M O N I T O R I N G S Y S T E M F O R S T E A M T U R B I N E SHIPS " G . Grossmann 249 " O P E R A T I O N S W I T H T H E L I T T O N M A R I N E T R E N D A N A L Y S I S S Y S T E M " H. H. Halperinand M.Sma.llberg 257 " T H E R M O D Y N A M I C C O N D I T I O N M O N I T O R I N G R E Q U I R E M E N T S A N D P R A C T I C E F O R M A R I N E S T E A M T U R B I N E P L A N t " M.D. Bürghardt 267 " E X P E R I E N C E W I T H C O N D I T I O N M O N I T O R I N G A N D P R E V E N T I V E M A I N T E N A N C E O F H I G H S P E E D / H I G H T O R Q U E S T E A M T U R B I N E S IN C H E M I C A L P L A N T S " A . f l r o e k m a t e 271 " A U T O M A T I C D E T E C T I O N O F O I L IN B O I L E R C O N D E N S A T E S " M J . C h a p p e l l 283 " T H E R M O D Y N A M I C A L P E R F O R M A N C E A N D M E C H A N I C A L B E H A V I O U R M O N I T O R I N G O F A I R C R A F T G A S T U R B I N E S " A . Mihaii 287 C O N D I T I O N M O N I T O R I N G I N S T R U M E N T A T I O N " P R E V E N T I V E M A I N T E N A N C E W I T H A D I S T R I B U T E D M I C R O - C O M P U T E R S Y S T E M " G . Soncin a n d G . Carlevaro 293 " R E V I E W O F M A R I N E M O N I T O R I N G T E C H N I Q U E S A N D C O M P U T E R A N A L Y S I S " T . C . Cottam 301 " A S T A N D A R D I Z E D M A I N T E N A N C E E N G I N E D I A G N O S T I C S Y S T E M "

F, Hasse tba cher , 309 " S H A R E D D I S P L A Y C O M P U T E R I Z E D A L A R M A N A L Y S I S I M P R O V E S P E R F O R M A N C E M O N I T O R I N G "

B. W, Edgerton arid R.S. Silva 317 " R E S E A R C H O N SHIP E L E C T R I C A L M E A S U R I N G I N S T R U M E N T S W I T H P A R T I C U L A R R E F E R E N C E T O

R E L I A B I L I T Y "

G . S. Raikov 323 " D I S P L A Y M E T H O D U S I N G T R E E P A T T E R N "

A B R I T I S H V I E W O F T H E C O N D I T I O N M O N I T O R I N G A S P E C T S O F P R E V E i y r i V E M A I N T E N A N C E A . O . F . V E N T O N Principal Consultant Y - A R D L t d , Consulting Engineers Glasgow, England D. P A R K E S Director

National Terotedinology Centre Leatherhéad, England

SÜMMARï, The paper d e s c f i h a a the p a r t t h a t p r e v e n t i v e maintenance aad c o n d i t i o n monitoring have to p l a y i n Terotecfanology. I t discusses Üie reasons f o r supposing that c o n d i t i o n monitoring should l e a d to a r e d u c t i o n i n maintënance c o s t s , d e s c r i b e s b r i e f l y a survey o f c o n d i t i o n m o n i t o r i n g c a r r i e d out i n

B r i t i s h i n d u s t r y , and uses the r e s u l t s and arguments t o make a f i r s t approximation t o b e n e f i t s and costs f o r a tanker,

A niunber of condition-monitoring approaches and t h e i r r e l a t i v e merits are d i s c u s s e d , together w i t h the problems o f lead time, s e t t i n g . a c t i o n - l i m i t s , e x t r a p o l a t i o n of trends, and c o l l e c t i o n and a n a l y s i s of data, a l l of whit±i a r i s e when a maintenance system i n c o r p o r a t i n g c o n d i t i o n monitoring i s devised. Some

suggestions are a l s o maide about the s e l e c t i o n of condition-monitoring methods.

F i n a l l y i t i s concltuted that condition-baaed maintenance protölses f i n a n c i a l saving;s; that methods p r o v i d i n g adequate lead time are needed; that o r d e r l y data, c o l l e c t i o n and a n a l y s i s are neces&ary f o r s e t t i n g a c t i o n l i m i t s and as a b a s i s f o r i f a i l u r e p r e d i c t i o n ; and t h a t , irtien s e l e c t i n g methods f o r use, the aim should be t o minimise the d i r e c t and i n d i r e c t costs f o r the whole s e t of p o t e n t i a l f a i l u r e s . 1 INTRODUCTION

C o n d i t i o n M o n i t o r i n g i s c l o s e l y r e l a t e d to maintenance; maintenance i s c l o s e l y r e l a t e d t o t e r e -technblOgy. Terotecfanology i s a word created i n the ÜK i n 1970 from a Greek root msaning *to care f o r ' or 'to look a f t e r * , I t i s d e f i n e d as a com-b i n a t i o n o f management, f i n a n c i a l , e n g i n e e r i n g and other p r a c t i c e s a p p l i e d to p h y s i c a l assets i n p u r s u i t of economical l i f e - c y c l e c o s t s . I t s p r a c t i c e i s concerned w i t h the s p e c i f i c a t i o n and design f o r r e l i a b i l i t y and m a i n t a i n a b i l i t y of p l a n t , machinery, equipment, b u i l d i n g s and s t r u c t t u r e s , w i t h t h e i r i n s t a l l a t i o n , commissioning, maintenance, m o d i f i c a t i o n and replacetoent, and with

feedback o f i n f o r m a t i o n on design, performance and cos t s .

f a s h i o n s . The s i g j i i f i c a n c e of p r e v e n t i v e a c t i o n has long been recognised both i n the marine engineering f i e l d and elsewhere, but the l o g i c a l p o l i c y of cohditionr-based maintenance has only been developed i n a s c i e n t i f i c way d u r i n g Üie p a s t decade or so. I t i s true t h a t maintenance engineers have f o r generations employed the human senses o f touch, s i g h t , smell and h e a r i n g i n a s s e s s i n g the onset of mechanical f a u l t s ; i t I s , however, tfae more recent development of a wide range of c o n d i t i o n n o n i t o r l n g equipment vhicfa, by s i g n i f i -c a n t l y supplementing the human senses, has taken c o n d i t i o n m o n i t o r i n g t o the p o i n t where i t i s now w i d e l y accepted as an inçïortant pa^t of preventive maintenance.

MAINTENANCE The concept of terotecfanology encourages more

c a r e f u l c o n s i d e r a t i o n of a l l aspects o f the c o s t * o f ownership of p h y s i c a l assets (the v e s s e l s , i n t h e present context) rathax than an undue concern

s o l e l y w i t h f i r s t c o s t . Maintenance costs are a large consonant of the cost of ownership and, a c c o r d i n g l y , maintenance i s recognised as a very inçortant p a r t of terotecfanology.

W i t h i n the 'costs of ownership' i n c u r r e d subsequent t o the f i r s t c o s t , or i n i t i a l / c a p i t a l c o s t s , the d i r e c t costs of c a r r y i n g out maintenance are i n e v i t a b l y l i n k e d w i t h ' l o s s of a v a i l a b i l i t y ' c o s t s . I f , because of. maintanance, the v e s s e l o r i t s machinery are not a v a i l a b l e f o r use when r e q u i r e d , then tfae costs of i t s n o o - a v a i l a b i l i t y may be thought of as the ' i n d i r e c t maintenance

c o s t s * . C l e a r l y such costs are i n c u r r e d when an item i s out o f s e r v i c e as a r e s u l t of f a i l u r e , but i t i s in^iortanc t o rewavbex that tiiere may be i n d i r e c t maintenance costs when p r e v e n t i v e maintenance i s u n d e r t ^ e n , unless t h i s c o i n c i d e s w i t h periods wfaen the item i s not r e q u i r e d f o r use. Maintenance p o l i c i e s have v a r i e d widely throughout i n d u s t r y and dhere have c e r t a i n l y been cfaanging

PREVENTIVE MAINTENANCE CORRECTIVE MAINTENANCE SCHEDULED MAINTENANCE CONDI T I O N ^ A S E D MAINTENANCE EXAMINATION CONDITION CHECKING TREND ANALVSIS PREVENTIVE ACTION (REPLACEMENT) (RECTIFICATION) CORRECTIVE ACTION (REPLACEMENT) (RECTIFICATION) F i g u r e 1 Maintenance T e r m i n o l o ^

F o r the purposes of t h i s paper a s e t 6f terms has been adopted which d i v i d e s maintenance up i n t o a ounfcer of c l a s s e s at d i f f e r e n t l e v e l s . The s t r u c t u r e of the s e t i s shown i n Figure 1, from

which i t w i l l be seen tfaat tfae assumption has been made tfaat a l l maintenance may be c a t e g o r -i z e d as e -i t h e r p r e v e n t -i v e or c o r r e c t -i v e , that -i s c a r r i e d out before or a f t e r f a i l u r e .

To conqilete tfae i n t r o d u c t i o n , two general p o i n t s sfaould be made.

(1) The s i g n i f i c a n c e of c o n d i t i o n monitoring w i t h i n terotecfanology i s not c o n f i n e d to the more e f f e c t i v e c a r r y i n g out of maintenance, althpugh that w i l l homàll'y be i t s primary r o l e . I t should a l s o r e s u l t i n an improvement i n the a v a i l a b i l i t y of data, and hence i n a b e t t e r b a s i s f o r future s p e c i f i c a t i o n and d e s i g n .

C2) Because of space l i m i t a t i o n s the paper con-centrates on the use of c o n d i t i o n monitoring on mechanical machinery and equipment. F u r t h e r , i t

concems i t s e l f w i t h the maintenance of e x i s t i n g or p r o j e c t e d p l a n t without examining the p o t e n t -i a l l y reward-ing f -i e l d s of us-ing knowledge ga-ined through c o n d i t i o n monitoring to improve f u t u r e d e s i s t .

2 THE PHILOSOPHY

P r e v e n t i v e maintenance nay be described as "tointenœice c a r r i e d out at predetermined i n t e r v a l s , , or to other p r e s c r i b e d c r i t e r i a , and intended to reduce the r i s k o f f a i l u r e " . Frpm tfae mid 1940s f o r about 20 years i t was tfae 'pre-determined i n t e r v a l s ' which a t t r a c t e d most

a t t e n t i o n , bût i t i s now b e i n g recognised Chat, i f maintenance p e r i o d s are to be s u f f i c i e n t l y s h o r t to a v o i d most f a i l u r e s , tfaey w i l l be u n n e c e s s a r i l y frequent f o r most itäns and w i l l 'thus be w a s t e f u l of maintenance resources.

For tfae case wfaere the replacement of a p a r t i s c a l l e d f o r . F i g u r e 2 shows the e f f e c t of d i f f e r e n t i n t e r v a l s lipon the average t o t a l number of r e p l a c e -ments r e q u i r e d , the average number o f unscheduled replacements r e q u i r e d , and tfae r e l i a b i l i t y achieved f o r an o p e r a t i n g p e r i o d of 40,000 hours - i . e . four times tfae mean l i f e of the p a r t . The u n d e r l y i n g f a i l u r e d i s t r i b u t i o n i s Normal w i t h a standard d e v i a t i o n of 2000 hours. 15 10 MEAN LIFE = 10,000 HRS! 0 = 2^000 HRS. "\ \ _ i ABrirr Y TO LPIACE fAL \ MENTS

\

V

T4

F i g u r e 2

Number of p a r t replacements vs scheduled raplacement i n t e r v a l I f we are to achieve very h i g h r e l i a b i l i t y - say

97% -. a replacement i n t e r v a l of 4,000 faours would

be necessary, and the t o t a l number of replacements r e q u i r e d would be 10. A t the other end of tfae s c a l e , i f we are t o t a l l y unconcerned about r e -l i a b i -l i t y and a -l -l o w f a i -l n r e t o occur i n a n a t u r a -l way, a replacement i n t e r v a l of 14,000 hours woiild

r e s u l t i n a n i l r e l i a b i l i t y , a l l replacements would

f o l l o w f a i l u r e s , and only four replacements would be necessary. A j u d i c i o u s c h o i c e of replacement i n t e r v a l can do something to improve the s i t u a t i o n . For example, a replacement i n t e r v a l o f about 7,000 faours would y i e l d a r e l i a b i l i t y of 76%, and s i x replacements - of iriiicfa, on average, only Ó>3 would be unscheduled.

thus i c can be seen t h a t , givcni the s t a t i s t i c a l data, planned maintenance can do much to achieve h i g h r e l i a b i l i t y , but t h a t the cost w i l l be r a t h e r more replacements than would be necessary i f tfae

f a i l u r e s were allowed to o c c u r . Top-frequent

maintenatuie may a i s p c o n t r i b u t e to unnecessary l o s s o f . a v a i l a b i l i t y , and may even make the maintenance s i t u a t i o n worse by i n t r o d u c i n g add:iCional f a u l t s . I f on Che other hand, tha wear on a component could be sumitored as i t develops,, and the time a t w h i d i

i t w i l l f a i l p r e d i c t e d w i t h s u f f i c i e n t confidence to enable i t to be changed s h o r t l y b e f o r e i t would otherwise f a i l , a h i g h x e i i a b i l i t y could be achieved w h i l e a t Che same time approacfaxng the minimum p o s s i b l e nuidter of replacements. Provided

t h a t the c o s t of the m o n i t o r i n g procedures does not exceed tfaa savings ( i n c l u d i n g those of reduced o f f h i r e time) r e a l i s e d by reducing the number of consonant changes * stich a procedure should l e a d to more economical achievement o f , h i g h r e l i a b i l i t y . T h i s , Cfaea, i s the o b j e c t i v e to be pursued by C o n d i t i o n M o n i t o r i n g .

C l e a r l y tfais i s a v e r y t a l l order i f one contem-p l a t e s monitoring a l l the wearing consonants i n

each equipment. But a t p l a n t l e v e l , p l a n t f u n c t i o n i s a f f e c t e d by l o s s of f u n c t i o n i n c r i t i c a l

equip-tieata. Is there tfaen a way of m o n i t o r i n g equipment

f u n c t i o n witfaout descending to con^onent l e v e l ? I n t h i s context one i s r e a l l y a s k i n g the q u e s t i o n : At \diat p o i n t should t h i s equipment be overhauled? The q u e s t i o n of wear, i n a d i r e c t sense, does not a r i s e .

I f we c o n s i d e r a s i n g l e equipment l i k e a sea-nrater pus^, one answer i s t h a t i t should be overhauled

•whan i t w i l l no Ipnger produce the output demanded

by the p l a n t under design i n l e t and power supply c o n d i t i o n s . But t h i s w i l l not n e c e s s a r i l y p r o y i d e a whole answer, f o r i t i s q u i t e p o s s i b l e Chat wear or e r o s i o n of a b e a r i n g , s e a l r i n g o r i m p e l l e r may reach such p r o p o r t i o n s chat a c a t a s t r o p h i c mechanical f a i l u r e occurs b e f o r e f u n c t i o n becomes loadequace. Hence, w h i l e cfae m o n i t o r i n g o f p e r f o r -mance parameters such as p r e s s u r e , temperature and flow w i l l p r o v i d e evidence of d e t e r i o r a t i n g p e r f o r -mance and impending l o s s of f u n c t i o n , the monitor-i n g of mechanmonitor-ical d e t e r monitor-i o r a t monitor-i o n monitor-i n c r monitor-i t monitor-i c a l com-ponencs i s ofCen a l s o necessary i f wear f a i l u r e s are Co be avoided.

3 ECONOMICS

In 1975 the Department of I n d u s t r y , on thé a d v i c e of i t s Terotecfanology and T r i b o l o g y Committee, commissioned a survey of c p n d i t i o n m o n i t o r i n g i n B r i t i s h indUscry and iCs p o t e n t i a l f o r wider a p p l i c a t i o n . The survey was undertaken by M i c h a e l Neale and A s s o c i a t e s , who are a l s o p r e p a r i n g ^ e subsequenC guide on the C o n d i t i o n H o h i t o r i n g o f Machinery ( r e f . 1 ) .

Among other aspects of the s u b j e c t , the survey and Che guide c o n s i d e r che quescion of the économe i c s of c o n d i t i o n m o n i t o r i n g from the p o i n t s o f view of b o t h b e n e f i t and c o s t . Across i n d u s t r y as a

whole, a poCenCial saving averaging 1.2% of the added value of output i s b e l i e v e d to be achievable. The u n d e r l y i n g arguments are of i n t e r e s t , f o r they faave some relevance to the s h i p case.

A sangle of B r i t i s h i n d u s t r y revealed chat the average production time l o s t because of

f a i l u r e s was 4 days i n a year; Che normal range was from 1 to 7 day's.- On average, about a c h i r d of t o t a l maintenance costs was devoted to c o r r e c t i v e maintenance and, again on average, ^ o u t a C h i r d o f CoCal maintenance costs was a c t r i b u c a b l e Co labour c o s t s .

The q u e s c i o n i s : How much of Chese costs could be saved, i n a sxiitable case, by the i n t r o d u c t i o n of c o n d i t i o n monitoring? In general, o p p o r t u h i t i e s Co r e p a i r machinery occur r a t h e r more frequencly i n most i n d u s t r i e s Chan chey do i n s h i p s . Given ChaC an i n d u s t r i a l p l a n t ' s c o n d i t i o n can be e s t a b l i s h e d , a r e l a t i v e l y short lead time w i l l do much to enable the maintenance to f o r e s t a l l f a i l u r e and avoid production l o s s . NP system i s p e r f e c t , however, ahd c o n d i t i o n - m o n i t o r i n g instruments, measurements and i n t e r p r e t a t i o n are a l l f a l l i b l e . To allow f o r t h i s , and f p r the u n p r e d i c t a b l e , t r u l y random f a i l u r e , i t i s assumed that only 75% of the un-scheduled p r o d u c t i o n downCitoe could be prevented by c o n d i t i o n monitoring.

One b e n e f i c i a l f e a t u r e of c o n d i t i o n m^niicoring i s that the element of p r e d i c t a b i l i t y i t introduces should isçrove p l a n n i n g and c o n t r o l of work, as w e l l as e n a b l i n g f a i l u r e s t o be f o r e s t a l l e d ; t h i s should l e a d t o higher working e f f i c i e n c y and hence some s a v i n g o f labour c o s t s . Since about one Chird of t o t a l maintenance expenditure i s devoced t o breakdown maintenance and about one t h i r d i s a t t r i b u t a b l e to labour c o s t s , i t i s deduced that about lOZ of maintenance éiqténdicure a r i s e s from breakdown labour c o s t s . I t i s assumed t h a t h a l f these costs can be saved because of the r e d u c t i o n i n f a i l u r e i n c i d e n c e and the i n c r e a s e i n e f f i c i e n c y r e s u l t i n g from improvements i n p r e d i c t a b i l i t y and i n the p l a n n i n g and c o n t r o l of work.

As f o r c o s t s , i t i s suggesCed ChaC, on Che b a s i s of Che experience of conqianies which have already engaged i n c p n d i c i o n monitoring, about 1% of the c a p i t a l value of the p l a n t to be monitored rep- . . r e s e n t s a reasonable inyestmenc. Where s a f e t y i s Oi; parcicülar inp'orcance, a g r e a t e r investment -of as much as 5% o f the p l a n t value - i s approp-r i a t e . In both cases the invescnent concemed covers the purchase of equipment and the costs of t r a i n i n g and l e a r n i n g ; on averagje, the

equipment element amounts to some 4031 of the t o t a l . For Che average B r i t i s h i n d u s t r i a l conçany t h i s means a p o t e n t i a l s a y i n g of about 1.2% of annual added value f o r s e t t i n g - u p costs of about 1% of the c a p i t a l cose of the p l a n t - o r . In the average case, 1% of added value f o r a year. Though Che ongoing coscs of o p e r a t i n g c o n d i t i o n m o n i t o r i n g may amount t o as much as a c h i r d of the p o t e n t i a l

s a v i n g s , the cumulative saving over a number of years can foe q u i t e s u b s t a n t i a l .

Needless t o say, the average case, l i k e 'the man i n the s t r e e t ' , i s an oversinçlificatipn, and con-s i d e r a b l e v a r i a t i o n occurcon-s between i n d u con-s t r i e con-s and between d i f f e r e n t escablishnencs w i c h i n an

i n d u s t r y . As an example o f the former, the gross b e n e f i t s estimated by Michael Neale range from 0.53% of average annual added value oùCpuC pér escablishmenc f o r paper, p r i n c i n g and p u b l i s h i n g compatiiea, t o 2.2% f o r gas, e l e c t r i c i t y and

water u t i l i t i e s . The d i f f e r e n c e s a r i s e from d i f -f e r i n g c a p i t a l i n t e n s i c i e s , d i -f -f e r e n c e s i n Che s u i C a b i l i t y pf the p l a n t f o r c o n d i t i o n monitoring, d i f f e r e n c e s i n working p r a c t i c e s , and d i f f e r e n c e s i n company s i z e . But the r u l e s of thumb a s s o c i a t e d with Che average casé provide a s t a r t i n g p o i n t f o r c o n s i d e r i n g the economics of c o n d i t i o n monitoring i n s h i p s .

Let Us consider the case of the machinery of a h y p o t h e t i c a l 250,000-ton dwt tanker. At end-1976 p r i c e s , che machinery, c o n s i s t i n g of main engines, generators, switchboard and e l e c t r i c s i n s i d e the engine room; pumps, p i p i n g and a u x i l i a r y b o i l e r s i n s i d e the engine room; and con^ressors, a l l as i n s t a l l e d , might have cost the shipowner about £7,500^000.

The annual added value might be C ^ e n , i t i s suggested, as the annual charter r a t e - around £4-,500j-000 at end 1976. For a w e l l - r u n s h i p , the annual o f f h i r e might average as l i t t l e as 5 days scheduled and 3 days unscheduled. The average annual d i r e c t mainCenaace cose might amount co about £400^000.

In i n d u s t r y some 32% of maintenance costs arc a c t r i b u t e d Co c o r r e c t i v e maintenance, and the q u e s t i o n a r i s e s whether t h i s i s a reasonable assun^tion f o r s h i p s . D u e l l ( r e f . 2) shows chat f o r a 19,000-ton dwt motor v e s s e l and a c l a s s of s i x 20p,00C>-ton dwt v e s s e l s , the reported c o r r e c t i v e maintenance undertaken by the crew amounts t o 50% of the r e p o r t e d work,, I t t h e r e f o r e seems reasonable to suppose that 50% would be more appropriate than 32% f o r the ship case, as f a r as crew work i s concemed. With 3 days downtime a t t r i b u t e d to c o r r e c c i v e maincenance and 5 to scheduled work (which w i l l i n e v i t a b l y i n c l u d e some c o r r e c t i v e maintensmce) i t seems l i k e l y t h a t sub-s t a n t i a l l y more Chan one t h i r d o f port maintenance cpsts stem from t h i s source, and i t i s t h e r e f o r e suggested chat i t i s reasonable to assûtnœ that 50% of machinery maintenance costs derive from

f a i l u r e s .

\Ihat p r o p o r t i o n of o f f h i r e costs could be saved by

i n t r o d u c i n g c o n d i t i o n monitoring? In the i n d u s t r i a l case i t i s assumed t h a t 75% of l o s t production c m i

be .saved. C o n d i t i o n mpnitoriftg cannoC eliminaCe Che mainCenance work - but, by f o r e t e l l i n g Che f a i l u r e s i t càa make i t p o s s i b l e to plan the p r e v e n t i v e work i n t o scheduled downtime such as voyage t u r n -round. U n l i k e most manufacturing i n d u s t r y , where periods of scheduled downtime occur f a i r l y o f t e n p o s s i b l y even weekly s h i p o p p o r t u n i t i e s are i n -frequent. The l e a d time necessary Co reduce the frequency of Che evencs which cause o f f h i r e time i s t h e r e f o r e s u b s t a n t i a l l y longer than t h a t which would be adequate i n i n d u s t r y . In these c i r -cumstances, h a l v i n g the frequency would appear to be a reasonable aim, and the corresponding

assimption t h a t 50% of the o f f h i r e time could be saved by c o n d i t i o n monitoring would a l s o appear reasonable.

What p r o p o r t i o n of c o r r e c t i v e maintenance costs could be saved by c o n d i t i o n moniCoring? In the s h i p case, two s o r t s of inaintéhahcè labour are i n v o l v e d - the crew and tfae ship r e p a i r e r .

Apart from the major maintenance or r e p a i r t a s k s , whose nature r e q u i r e s e x t e m a l a s s i s t a n c e , the maintenaice and r e p a i r load w i l l be undertaken by the crew, to the l i m i t o f t h e i r c a p a c i t y , before the overload i s c r a n s f e r r e d Co Che s h i p r e p a i r e r . Hence the b e n e f i t of c o n d i t i o n monitoring should be a r e d u c t i o n i n the ship r e p a i r e r ' s load.

I n d u s t r i a l users of c p n d i t i o n monitoring put the d i r e c t maintenance c o s t s a v i n g at h a l f the c o r r e c t -iye-maintendmce I d i o u r c o s t s . With c o r r e c c i v e

maintenance absorbing 50% o f che maintenance laboux, t h i s amounts to 25% o f Che labour c o s t . Tfae

i n d u s t r i a l assumption appears to n e g l e c t any r e d u c t i P n i n prevenCive maintenance e f f o r t which migfat be expected t o a r i s e from measuring, r a t h e r tfaan opening t o look,. The saving w i l l be o f f s e t to some extent by more extensive measurement and the need t o p l o t trends and so on, so that the g a i n w i l l probably not be l a r g e , say 5%: A l l o w i n g f o r t h i s i c might be reasonable to assume a saving of 30% o f the maintenance labour c o s t s .

Tfaere must a l s o be some r e d u c t i o n i n m a t e r i a l costs f o r l e s s frequent o v e i h a u l , and fewer f a i l u r e s wiäi consequent secondary damage must r e s u l t .in the use of fewer spares - i n f a c t Mucklow ( r e f . 3) and .Dayies ( r e f . 4) make i t c l e a r chac Che p r i n c i p a l

g a i n from c o n d i t i o n monitoring i n a i r c r a f t gas t u r b i n e s stems from the r e d u c t i o n i n secondary daioage. While sudti a dramatic r e s n l t cannot be envisaged i n sfaips, a r e d u c t i o n i n m a t e r i a l costs p r o p o r t i o n a l t o the r e d u c t i o n i n labour costs would not seem t o be unreasonable.

I f labour costs soount to ona tfaird of maintenance coats» tfae d i r e c t maincenance c o s t s a v i n g t o be expected from tfae i n t r o d u c t i o n of c o n d i t i o n monitoring would t f a e n f o r e be one t h i r d of the

t o t a l d i r e c t maintenance c o s t s .

For the 250,000 ton dwt t u i k e r exaiqile, tfae p o t e n t i a l ' sàvings are t h e r e f o r e :

3 X 4,500,000 + (400,000 x 0.3) 7 —

° £18,493 ( o f f h i r e ) + £120,000 ( d i r e c t maintenance) » £138,49^3

w i t h an annual added value of £4,500,000, these estimated saviiigs amount t o 3.1%, o r 2^ times tfae average of 1.2% f o r B r i c i s h i n d u s t r y . However, Che r e c u m o f c h a r t e r r a t e s Co p r o f i t a b l e l e v e l s would b r i n g Che savings/added-value r a t i o w i t h i n the i n d t i s t r i a l range of v a l u e s , and i f c h a r t e r r a t e s were Co reach cfaeir 1973 peak again, tfaat r a t i o would then be below the i n d u s t r i a l average. Hence the estimated s a v i n g of 3*1% of annual added v a l u e f o r a s e t of s h i p ' s machinery aëeas a reasonable f i r s t approximacion.

As f a r as s e t t i n g - u p c o s t s are concerned, the •consensus of aanbied i n d u s t r i a l users i s that 1%

of c a p i t a l value i s a reasonable estimate f o r equipment (0.4%) and t r a i n i n g and l e a r n i n g (0.6%); i n the Canker case t h i s amounts'to £75,000. " ^ o u ^ a higfaer investment migfat be j u s t i f i e d by s a f e t y c o n s i d e r a t i o n s d i r e c t e d , f o r exaiiq)le, at

pre-\renting major e x p l o s i o n s - the machinery p l a n t i t s e l f does not seem t o give r i s e Co risk.s not already covered by crankcase e x p l o s i d h doors, o i l m i s t d e t e c t o r s and so oh. Hence the 1% l e v e l seems a p p r o p r i a t e as a f i r s t approximation,

4 F0SSIBI£ APPROACHES

L e t us how consider the problem of d e v i s i n g a c o n d i t i o n - m o n i t o r i n g system f o r a s h i p . There are m a c h i h e r y ^ r o t e c t i o n and performance-monitoring systems wfaicfa need to be considered as w e l l as tfae p o s s i b l e c o n d i t i o n - m o n i t o r i n g systema

them-s e l v e them-s , Tfae them-sythem-stemthem-s are not mutually e x c l u them-s i v e and, because of t h e i r d i f f e r i n g c h a r a c t e r i s t i c s , a mixture of two or more i n a maintenance system i s i n e v i t a b l e .

4.1 P r o t e c t i o n System.

T h i s i s a machinery system whose f u n c t i o n i s t o c a r r y oUt a continuous dieck of the c o n d i t i o n of the equipmtent concerned, Co compare the measure of c o n d i t i o n witfa some predetermined l i m i t s , to warn the operator when a p r e s e t l i m i t i s reached and, i n d e f a u l t of a c t i o n by him, t o shut dawn tfae equipment b e f o r e a dangerous c o n d i t i o n occurs. Tfae ' d e c i s i o n response' time (tfae time C ^ e n t o decide upon and i n i c i a c e a c c i o n a f t e r Che l i m i c of

acceptiÀiîity has been readied) i s i n Che range nano-seconds t o seconds.

4.2 Perfoimance-mohitoring System

T h i s , too, i s a macfainery system. ICS main füncCion i s Co enable Che operator to make adjustments of .flows, p r e s s u r e , e t c , i n order t o maintain optimum

performance under v a r y i n g o p e r a t i o n a l c o n d i t i o n s . I t a l s o performs ah important s a f e t y f u n c t i o n i n p r o v i d i n g the operator w i t h the i n f o r m a t i o n fae needs to i n t e r v e n e b e f o r e performance d e v i a t i o n becomes dangerous. Tfae d e c i s i o n response t i n e i s

i n the range seconds to minutes.

4.3 Dedicated Condition-monitoring System Tfais i s a c o n d i t i o n - m o n i t o r i n g system wfaose f u n c t i o n i s t o provide freqiaent c o n d i t i o n cfaedking, Che frequetuqr b e i n g determined by the l i j c e l y d e t e r i o r a t i o n r a t e of the parameter concemed. Such a system w i l l probably c o n s i s t of c e n t r a l i s e d instruments, probably pf a r e l a t i v e l y sopfaistiaated k i n d , faard-wired Co permanenc Cransducers wfaose s o l e funcCidn i s t o sense some parameter i n d i i c a t i v e of a p r e c i s e form of d e t e r i o r a t i o n . The recording,- p l o t t i n g and cal-r c u l a t i o n may be done 'by hand' o r may be machine-aided Co cfae poinC where a l l Che f u n c c i o n s are eomplecely automatic. The d e c i s i o n response time i s i n the range minutes Co days,

4.4 P o r t a b l e P l u g - i n Equipment

The f u n c t i o n of sucfa équipment i s t o enable tfae crew to c a r r y out c o n d i t i o n checks. Any necessary c a l c u l a t i o n s , and the p l o t c i n s and r e c o r d i n g Of r e a d i n g s , would be done 'by hand'. The d e c i s i o n response time i s i n Che range hours t o days. 4.5 Sanple f o r A n a l y s i s

The f u n c t i o n of t h i s procedure £s to t ^ e samples of such things as d e b r i s , f l u i d s , or v i b r a t i o n , f o r a n a l y s i s elsewhere. The a n a l y s i s may be c a r r i e d out by the crew o r , c o n c e i v a b l y , by a shore laboraCory. Examples a r e : examinacion Pf cfae d e b r i s c o l l e c C e d from magnetic plugs (crew); speccromecric o i l a n a l y s i s ( l a b o r a C o r y ) ; r e a l - t i m e specCrmn a n a l y s i s of v i b r a t i o n ( l a b o r a t o r y , from a Cape r e c o r d ) . Tfae d e c i s i o n response Cime i s i n Che range hours Co weeks.

4.6 ConCribuCions Co C o n d i c i o n t t o n i t o r i n g From the c o n d i t i o n - m o n i t o r i n g p o i n t o f view, the extent, i n t i n e , to which f a i l u r e can be p r e d i c t e d - Che lead Cime - i s a l l - i n ^ o r t a n t , f o r t t must be