Bsi bs en 60609 2 1999 (2006)

4.1 Cav itation pit ing rep ir during the g uarante period 64.2 Measurement and calculation of the amou t of cav itation pit ing 7 Annex A normativ e Ex mples of amou ts of cav itation

Incor por a ting

Cor r igend um No 1 a nd

A mend ment No 1 to

This Brit ish Stan ard, hav ing

b en pre ared u der the

directon of the Engine ring

Sector Bo rd,was published

u der the authoriy of the

This British Stand rd reproduces v erb tim IEC 6 6 9-2:19 7 and implements

it as the UK national stand rd

The UK p rticip tion in its prep ration was entrusted to Tech ical Commit e

MCE/15, Hy draul c turbines, which has the responsibi ity to:

— aid enquirer to u der stand the tex t;

— present to the responsible international European commit e any

enquiries on the interpretation, or proposals for chang e, and ke p UK

interests informed;

— monitor related international and European dev elopments and

promulg ate them in the UK

A l st of org nizations represented on this commit e can be obtained on

request to its sec etary

Cros - referenc s

The British Stand rds which implement international or European

publ cations refer ed to in this document ma be fou d in the B SI Ca ta l ogue

u der the section entitled “ Inter national Stand rds Cor espondence Index”, or

b using the “ Sear h” faci ity of the B SI Electr onic Ca ta l ogue or of British

Stand rds Onlne

This publ cation do s not pur port to include al the neces ary prov isions of a

contract User are responsible for its cor ect a plcation

This publ cation do s not pur port to include al the neces ary prov isions of a

contract User are responsible for its cor ect a plcation

Com pl anc with a British Standard do s not of itself c nfer im m unity

f om leg al obl g ations

Sum m ary of pag es

This document comprises a font cov er,an inside f ont cov er, the EN title p g e,

the EN foreword p g e, p g es i and i, the IEC title p g e, p g es i to iv,

p g es 1 to 10, Annex ZA and a b ck cov er

This stand rd has be n up ated ( se copy rig ht d te) and ma ha e ha

amendments incorporated This wi be indicated in the amendment ta le on

the inside font cov er

Am endm ents is ued sinc publcation

9 6

Corig en um No.1

Mar h 19 8 Title on font cov er

15 3

Amen ment No.1

28 Apri 20 6 EN title p g e, EN foreword and Annex ZA

4.1 Cav itation pit ing rep ir during the g uarante period 6

4.2 Measurement and calculation of the amou t of cav itation pit ing 7

Annex A ( normativ e) Ex mples of amou ts of cav itation pit ing s 8

Annex ZA ( normative) Normativ e references to international publcations

Fig ure 2 — Location of d mag e due to cav itation pit ing 5

Fig ure A.1 — Ex mples of ma imum permis ible v alues

of cav itation pit ing on a Pelton ru ner

For word

1) The IE (nternational Electrotech ical Commis ion) is a worldwide org nization for

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b the subject of p tent rights The IE shal not b held resp nsible for identifying any or al such

p tent rights

International Stand rd IEC6 6 9-2 has be n prep red b IEC tech ical

commit e 4: Hy draul c turbines

The text of this stand rd is b sed on the fol owing documents:

Ful information on the v oting for the a prov al of this stand rd can be fou d in

the report of v oting indicated in the a ov e ta le

Annex A forms an integ ral p rt of this stand rd

Annex B is for information only

IEC 6 6 9 ( 19 8) treats cav itation pit ing in reaction machines but do s not refer to Pelton ( impulse)

turbines Appendix A of IEC6 6 9 states that Pelton turbines “ usual y are not subjected to cav itation

pit ing ”

Howev er, ex erience shows that with inc ease of specific spe d ( especial y of multijet turbines) and of

specific hy draul c energ y ( hea ) the prob bi ty of cav itation pit ing and drop erosion on Pelton turbines

inc eases Consequently weig ht los g uarante s on Pelton turbines ma be required

Various ty pes of d mag e are observ ed, each the result of diferent flow phenomena, such as pit ing due to:

— profi e er or ;

— u fav oura le inflow conditions;

— erosion due to trav el ng droplets ( drop erosion, also caled jet imping ement);

and in some instances

— set ing conditions ( e.g set ing of the ru ner refer ed to the tai water lev el, or tai water depres ion)

The causes of d mag e are often complex and hav e to be carefuly inv estig ated, taking into ac ou t also

conditions which are excluded in the cav itation g uarante ( se 1.2) Howev er it is not the objectiv e of this

p rt of IEC6 6 9 to des ribe the requirements and measures ne ded for av oiding cav itation pit ing due to

— hy draul c sha e and sur ace roug hnes of turbine p rts ( buckets, no zles, etc.), or

— instalation requirements ( set ing , inflow conditions)

Those requirements are p rt of the k ow-how of the turbine contractor

The d mag e ( i.e.pit ing respectiv e weig ht los ) due to these v arious causes ( cav itation pit ing and drop

erosion) is combined in the folowing clauses as the term “ cav itation pit ing ”

1.1 Scope and object

This p rt of IEC 6 6 9 serv es as a b sis for the formulation of g uarante s on cav itation pit ing on Pelton

turbine ru ner and also for the measurement and ev aluation of the amou t of cav itation pit ing on Pelton

turbine ru ner of a g iv en turbine, which is defined in the contract b power, specific hy draulc energ y of

machine ( hea ), rotational spe d, material, operation, etc

The sequence of clauses in this p rt of IEC 6 6 9 is the same as in IEC 6 6 9 ( 19 8) The clauses on

measurements and ev aluation of the amou t of cav itation pit ing are practicaly identical to those of

IEC6 6 9 Ev aluation has to be b sed on the los of material during a g iv en time and u der ac urately

defined operating conditions

Guarante s which restrict the extent of cav itation pit ing and drop erosion on Pelton turbines at the end

of an operating period specified in the contract are neces ary when cav itation pit ing is ex ected in al or

in some operating rang es Such g uarante s should include lmits for operation which are consistent with

specified operating conditions

1.2 Excluded topics

It is as umed in this p rt of IEC 6 6 9 that the water is not chemical y ag g res iv e to a sig nificant deg re

and that it is es ential y f e f om a rasiv e sol ds

The cav itation g uarante shal, howev er, be g iv en on the b sis of an ag re d water analy sis I it becomes

a p rent in the cour e of later analy sis that the water is in fact more ag g res iv e than the ag re d analy sis

indicated, this shal be taken into consideration when judg ing whether the g iv en g uarante s hav e be n

met

In case of a distorted inflow condition at the inlet of the turbine due to ir eg ularities upstream of the

turbine, hy draul c efects ma be raised, which bey ond the influence on hy draul c per ormance also ma

cause cav itation pit ing Therefore it is claimed for the b sis of cav itation pit ing g uarante s that a

satis actori y u iform and v ortex-fe flow condition shal be prov ided In case of d mag e, the influence of

improper inflow condition shal be taken into ac ou t

Abrasion due to water contaminated with solds ( e.g sand) can ot be considered as cav itation pit ing The

sol ds content of the water and also — if relev ant — the ty pe of minerals and siz and form of sold ( sand)

p rticles shal be stated in the water analy sis and, if it reaches sig nificant proportion, shal be the subject

of a special ag re ment Aspects of a rasiv e wear b sand erosion are dealt with in IEC613 6 ( Annex H)

Abrasion ma cause a chang e of the g eometry of the ne dle and/ or the bucket and subsequently cav itation

pit ing as second ry d mag e Such d mag e shal be excluded f om the ev aluation of cav itation

I cav itation pit ing oc ur in z nes where d mag e can be sep rately at ributa le to a normal chemical or

electrochemical cor osion, a rasion or mechanical imp ct, such d mag e shal be excluded fom the

ev aluation of cav itation

I cav itation pit ing oc ur in z nes where d mag e can be shown to ha e be n inc eased b chemical or

electrochemical efects a ditional to those normal to cav itation in water of the ag re d analy sis, then such

z nes shal be excluded f om the ev aluation of cav itation

In this context, at ention should be p id to the material selection in reference to a rasion b sand erosion

and/or chemical or electrochemical cor osion

Material defects rev ealed b wear on the machine suraces during operation are not taken into ac ou t to

v erify a g uarante ag ainst cav itation pit ing

Special operating conditions such as dis harg ing b means of deflector or cut- n deflector shal be excluded

f om cav itation pit ing g uarante s

1.3 Norm ative r f r nce

The fol owing normativ e document contains prov isions which, throug h reference in this text, constitute

prov isions of this p rt of IEC 6 6 9 At the time of publ cation, the edition indicated was v ald All

normativ e documents are subject to rev ision, and p rties to ag re ments b sed on this p rt of IEC 6 6 9

are encourag ed to inv estig ate the pos ibi ity of a ply ing the most recent edition of the normativ e document

indicated below Member of IEC and ISO maintain reg ister of cur ently v al d International Stand rds

IEC 6 6 9:19 8, Ca vi a tion pit ng eva lua tion in hyd r a ul ic tur bine , stor a ge pumps a nd

The are also b sed, where rele ent, on IE 6 3 4

2.2.1 cav itation V apour bub les which form when the lev el of local pres ure drops to

a proximately that of v apour pres ure and which cola se when the lev el

of local pres ure rises a ov e that of v apour pres ure

2.2.2 cav itation pit ing Los of material caused b cav itation

2.2.3 drop erosion Los of material caused b imp ct of trav el ing droplets ( liquid imp ct

erosion, jet imping ement)

2.2.4 a rasion Los of material caused b suspended sol ds ( e.g sand) eroding the

material sur ace ( abrasiv e wear, sand erosion)

2.2.5 cav itation g uarante Number of months or y ear of serv ice of a machine during which the

period cav itation pit ing g uarante is v ald

2.2.6 cav itation g uarante

duration of operation

Number of machine operating hour during which the cav itation pit ing

g uarante is v ald

2.2.7 reference duration of

operation t

R( h)

Number of machine operating hour used as a reference v alue for

esta l shing cav itation pit ing g uarante s

2.2.8 actual duration of

operation t

A( h)

The actual n mber of machine operating hour at the time of cav itation

pit ing ex mination

Up er power l mit for normal contin ous operation specified for each

specific hy draul c energ y ( se Fig ure 1)

2.2.14 P

TU

Up er power l mit for temporary a normal operation specified for each

specific hy draul c energ y ( se Fig ure 1)

2.2.15 P

C

Lower power lmit for normal continuous operation specified for each

specific hy draul c energ y

C( se Fig ure 1)

2.2.17 Hig h turbine loa

temporary a normal

operating rang e

Limited b P

CUand P

TU( se Fig ure 1)

2.2.18 S ( cm) The a solute ma imum depth of any pit ed area measured fom the

orig inal surace; for further ex lanation se also2.3; ( g uarante d

ma imum depth=S

ma)

orig inal surace

2.2.2

A ( cm

2

)

Total area of the whole run er d mag ed b cav itation pit ing :

— inside of bucket ( location3, 4, 5 and 6 of Fig ure 2),

— outside of bucket in the rang e of b ck of splt er and cut-out

( location1, 1a and 2 of Fig ure 2),

defined, either:

a) as al areas d mag ed b cav itation pit ing which require rep ir

( including those which only require g rinding ), or

b) only such areas where a stipulated mutualy ag re d depth has be n

exce ded, or

c) only such areas which require rep ir b welding ( g uarante d

ma imum total area = A

2

)Indiv idual areas d mag ed b cav itation pit ing as defined in 2.2.2

Total d mag ed area of an indiv idual bucket “ I”

2.2.2 a Co ficient defining the ma imum al owed dev iation f om g uarante d

ma imum bucket area ( =A

ma/z

2); it wi

Volume of material of the whole run er remov ed b cav itation pit ing

( g uarante d ma imum total v olume=V

ma

2.2.2 k, k

1

,k

2, k

3etc Co ficients used in a proximate calculation of v olume as indicated

Ex mples of ma imum p rmis ible v lues of ca itation piting to b guarante d for the reference d ration( 80 0h):

se Figure A.1 with v lues as a fu ction of in er bucket width B;se also 2

2.3 Location and type ofdam ag e to Pelton buckets

Various locations of d mag e due to cav itation pit ing ( i.e cav itation pit ing and/or drop erosion,

se Introduction) to Pelton buckets ma be observ ed, most of them at the inside of the bucket sur ace They

can be clas ified b the location which can be defined refer ing to Fig ure 2

The ev aluation of the amou t of cav itation pit ing ex res ed in depth S, area A or v olume V( se 3.2 to4.2)

is to be ma e independent of the question of the sour e of cav itation d mag e if caused b cav itation imp ct

or b jet lquid imp ct

Refer ing to the depth S, it is to be stated:

a) Ofthe thre p rameter defining the amount of cav itation pit ing ( depth S, area A and v olume V) the

a solute v alue of ma imum depth S is important, as far as the structural streng th is concerned

depending on the location

b) The depth S of pit ing is defined in a cav itated area of at least0,2 cm

2

, excluding indiv idual smal

holes which ma be orig inated also b phenomena diferent f om cav itation

c) Pit ing near or at sensitiv e locations as for instance cut-out of the bucket at locations 1, 2 and 3 of

Fig ure 2 shal not hav e a g reater depth than the lowest v alue shown in F ig ure A.1

ma, V

ma)d

)

Guarante d lmit of the amou t ofcav itation pit ing at the time of

cav itation pit ing ex mination

2.2.2 B ( m) In er bucket width ( se Fig ure 2)

2.2.2 z

2

Number of buckets

d

Ex mples of ma imum p rmis ible v lues of ca itation piting to b guarante d for the reference d ration( 80 0h):

se Figure A.1 with v lues as a fu ction of in er bucket width B; se also3.2

Fig ure 1 — Operating rang es