Mil Std 889 Dissimilar Metals

8/16/2019 Mil Std 889 Dissimilar Metals

http://slidepdf.com/reader/full/mil-std-889-dissimilar-metals 1/28

MILITARY STANDARD

DISSIMILAR METALS

FSC MFFP

ded by IHS Licensee=Naval Air Warfare/5954187003, User=Patricelli, MarcNot for Resale, 05/23/2012 07:03:23 MDTproduction or networking permitted without license from IHS

--`

,` ` `

, ,`

,` ` ` ` `

,` `

,`

,`

,` ` `

, ,`

,` -` -`

, ,`

, ,`

,`

, ,` ---



M I L - S T D - B B q B CHG N O T I C E 3 m 9’799913 0434333 L99

TO ALL IIOLDERS OF

MILITARY STANDARD

DISSIMILAR METALS

MIL-STD-889B:

NOT MEASUREMENTSENSITIVE

MIL-STD-889BNOTICE 3 (USAF)17 May 1993

1. THE FOLLOWING PAGES OF MIL-STD-889B HAVE BEEN REVISED ND

SUPERSEDE THE PAGES LISTED:

NEWAGEATE SUPERSEDED PAGEATE

a 3 21ovember979 - REPRINTED ITHOUTHANGE4 17ay 1993 4 7 July976

2. RETAIN THIS NOTICE ND NSERT BEFORE TABLE OF CONTENTS.

3. Holders of MIL-STD-889B will verify that page changes and additions ndicated above havebeen entered. This notice page will be retained as a check sheet. T h s issuance, together withappended pages, is a separate publication. Each notice is o be retained by stocking points untilthe military standard is completely revised or cancelled.

Custodians:ir Force - 11

Review activities:ir

Force-

13, 17, 99

Preparing activity:Air Force - 11

O AMSC:

DISTRIBUTION STATEMENT A. Approved for public release; distribution s unlimited.

ded by IHS Licensee=NavalAirWarfare/5954187003 User=Patricelli Marc

--`,```,,`,`̀```,``,`,`,`̀`,,`,`-`-`,,`,,`,`,,`---



MIL-STD-889B N O T I C E I G D m 7779933 00 352 73 8 m

M L- STD- 889BNOTI CE 121 November 1979

M LI TARY STANDARD

DI SSI M LAR METALS

TO ALL HOLDERS OF M L- STD- 889B:

1. THE FOLLOW NG PAGES OF M L- STD- 889B HAVE BEEN REVI SED ANDSUPERSEDE THE PAGES LI STED:

NEWAGEATEUPERSEDEDAGEE

1 7 J ul y976REPRI NTW THOUTHANGE. ) 7 J ul y 19762 21 November 1979 2 7 J ul y 19763 21 November 1979 3 7 J ul y 19764 7 J ul y976REPRI NTW THOUTHANGE) 7 J ul y 19765 21 November 1979 5 7 J ul y 19766 21 November 1979 6 7 J ul y 1976

2. RETAI N THI S NOTI CE ANDI NSERT BEFORE TABLE OF CONTENTS.

3 Hol ders of M L- STD- 889B w l l ver i f y t hat page changes and addi t i onsi ndi cat ed above have been ent er ed. Thi s not i ce page wi l l be ret ai nedas a check sheet . Thi s i ssuance, t oget her wi t h appended pages, i s asepar at e publ i cat i on. Each not i ce i s t o be r et ai ned y st ocki ng poi nt sunt i l t he M l i t ary St andar d s compl et el y r evi sed or cancel ed.

. Cust odi ansNavy - A SAi r For ce- 11

Ar my - MX

Revi ew ac t i vi t i es :Ar my AR

Navy - EC, OSAi r Force - 13, 17, 99

Pr epar i ng ac t i vi t y:Ai r For ce - 11

FSC MFFP




DEPARTMENT OF DEFENSE

. ii




Par agr aph l .

1. 11. 1. 1

2.2. 1

3 .

4

5.5. 1

5.2

M L- STD- 889B7 J ul y 1976

CONTENTS

TABLES

Appendi x A. Recommended t r eat ment s n or der of pr ot ect i veef f ect i veness- - - - - - - - - - - - - - - 10

B. What i s i nvol ved i n gal vani c cor r osi on- - - - 17

i i i

--


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---



M L- STD- 889ASept ember 1969

M LI TARY STANDARD

DI SSI M LAR METALS1. SCOPE.

1.1 Pur pose. Thi s s t andar d def i nes and cl assi f i es di ss i m l ar met al s ,and est abl i shes r equi r ement s f or pr ot ect i ng coupl ed di ssi m l ar met al s,wi t h at t ent i on di r ect ed t o t he anodi c member of t he coupl e, agai nstcorr osi on.

1.1.1 Appl i cabi l i t y. Thi s st andard i s appl i cabl e t o al l m l i t aryequi pment par t s, component s and assembl i es.

2. mFERENCED DOCUMENTS.

2.1 I ssues of document s. The f ol l ow ng document s of t he i ssue neffect on dat e o f i nvi t at i on f or bi ds r r equest . f or pr oposal , f or ma par t of t hi s st andar d t o t he extent speci f i ed her ei n.

SPECI FI CATI ONS

M LI TARY

M L- S- 8802 Seal i ng Compound, Temper at ur e- Resi st ant ,I nt egr al Fuel Tanks and Fuel Cel lCavi t i es, Hi gh Adhesi on

( Copi es of speci f i cat i ons, st andar ds, dr awi ngs, and publ i cat i onsr equi r ed by cont r act or s i n connect i on w t h speci f i c pr ocur ementf unct i ons shoul d be obt ai ned f r om t he pr ocur i ng act i vi t yr asdi r ected by t he cont r act i ng of f i cer . )

FSC MFFP


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---



3 DEFI NI TI ONS.

3.1 Di ssi m l ar met al s. Thi s st andar d t er ms met al s di ssi m l ar when t womet al speci mens ar e i n cont act r ot her w se el ect r i cal l y connect ed t o

each ot her i n a conduct i ve sol ut i on and generat e n el ec t r i c cur r ent .3 2 Gal vani c cor r osi on. Gal vani c cor r osi on mani f est s i t sel f i n t heaccel er at ed corr osi on caused t o t he more act i ve met al ( anode) of adi ss i m l ar met al coupl e i n n el ectr ol yt e sol ut i on or medi um anddecreased cor r osi ve ef f ect s on t he l ess act i ve met al ( cat hode) , ascompared t o t he cor r osi on of t he i ndi vi dual met al s, when not connect ed,i n t he same el ect r ol yt e envi r onment .

3 3 Gal vani c ser i es . A gal vani c ser i es i s a l i s t i ng of met al s andal l oys based on t hei r order and t endency t o corr ode i ndependent l y, i n apar t i c ul ar el ec t r ol yt e sol ut i on r ot her envi r onment . Thi s t endencyf or di s sol ut i on o r cor ros i on i s rel at ed t o t he el ec t r i cal pot ent i al f

t he met al i n conduct i ve medi um Gal vani c cor r osi on i s i nher ent l yaf f ect ed by t he rel at i ve posi t i on of t he gal vani c ser i es of t he met al sconst i t ut i ng t he coupl e. Met al s cl osel y posi t i oned n t he ser i es wi l lhave el ectr i cal pot ent i al s near er ne anot her , whereas wi t h gr eat erdi ver gence i n pos i t i on, gr eat er di f f er ences i n pot ent i al wi l l pr evai l .Gal vani c ef f ects , i . e. , cor r osi on of t he anode w l l i n t he f or mercondi t i on be m ni mal , t he l at t er condi t i on wi l l exhi bi t mor e s i gni f i -cant cor r osi ve ef f ects . A gal vani c ser i es f or cor r osi on s t ruct ur almet al s , f or sea wat er , i s shown i n Tabl e I I . Tabl e shal l be used as

a gui de n det er m ni ng t he r el at i ve compat i bi l i t y of di ssi m l ar met alcombi nati ons. Compati bi l i t y does not i ndi cat e a compl et e f r eedom f r omgal vani c act i on.

4. GENERAL STATEMENTS. ( Not Appl i cabl e)

5. DETAI LED REQUI REMENTS.

5.1 M ni m z i ng di s si m l ar met al cor r os i on.

5.1.1 When di ssi m l ar met al s are used i n i nt i mat e cont act , sui t abl epr ot ect i on agai nst gal vani c cor r osi on shal l e appl i ed. I n someenvi r onment s par t i cul arl y wi t h met al s such as magnesi um st eel , zi nc,al um num i n cont act wi t h copper , s t ai nl ess st eel , ni ckel , gal vani ccorr osi on may be appr eci abl e. Consequent l y, care shoul d be t aken opr ot ect t he anodi c member by pr oper el ect r i cal i nsul at i on of t he j oi ntor by exc l udi ng t he el ec t r ol yt e i f t hi s i s f eas i bl e.

2

Super sedes page 2 o f 7 J ul y 1976






M I L - S T D - 8 8 7 B CHG N O T I C E 3

P

7- I

t,I

d d b IHS Li N lAi W f /5954187003 U P t i lli M

,

, ,

,

,

,

,

,

, ,

,

, ,

, ,

,

, ,



M L- STD- 889B

2 1 November 1 9 7 9TABLE I I . Gal vani c ser i es of sel ect ed met al s i n Seawat er. -

PER: Ar my M ssi l e Command Repor t KS- TR- 67- 11 Pr act i calGal vani c Ser i es .

Act i ve ( Anodi c)

Magnesi um ( Mg)Mg Al l oy ' AZ- 31BMGl l oyK- 31AZi nc ( hot - di p, di e cas t r pl at ed)Ber yl l i um ( hot pr essed)Al um num ( Al ) 7072 cl . on 7075Al al l oy 2014- T3Al al l oy 1160- Hl 4Al al l oy 7079- T6Cadm um ( pl at ed)Ur ani um

Al al l oy 218 ( di e c as t )Al al l oy 5052- 0Al al l oy 5052- H12Al al l oy 5456- 0, H353Al al l oy 5052- H32Al al l oy 1100- 0Al al l oy 3003- H25A l . al l oy 6061- T6Al a. l l oy A360 ( di ecastAl al l oy 7075- T6Al al l oy 1160- Hl 4Al al l oy 6061- 0I ndi um

Al al l oy 2014- 0Al al l oy 2024- T4Al al l oy 5052- Hl 6Ti n ( pl at ed)St ai nl ess st eel 430 ( ac t i ve)LeadSt eel 1010I r o n, cas tSt ai nl es s s t e el 410 ( ac t i ve)Copper ( pl ated, cast r wr ought )

Super sedes page 5 of 7 J ul y 1976

Ni ckel ( pl at ed)Chr om um ( pl at ed)Tant al umAM3 50 ( act i veSt ai nl ess s teel 310 ( ac t i ve)St ai nl ess st eel 301 ( act i ve)St ai nl ess st eel 304 ( ac t i ve)St ai nl es s st eel 430 ( passi ve)St ai nl ess s teel 410 ( passi ve)St ai nl es s st eel 17-7 PH ( act i ve)Tungst enNi obi um ( Col umbi um 1% Zr

Br ass , yel l ow, 268

Ur ani um 8 Mo.Br ass , Naval , 464Yel l ow br assIvl untz met al 280Br ass (pl at ed)Ni ckel - s i l ver ( 18% Ni )St ai nl ess s teel 316L (ac t i ve)Br onze 220Copper 110Red br assSt ai nl ess s teel 347 ( ac t i ve)Mol ybdenum Comm pur eCopper - Ni ckel 715

Adm r al t y br assSt ai nl es s st eel 202 ( act i ve)Br onze, Phosphor 534 ( B- 1)Monel 400St ai nl ess s teel 201 ( ac t i ve)Carpent er 20 ( ac t i ve)St ai nl ess s teel 321 ( ac t i ve)St ai nl ess s teel 316 ( ac t i ve)St ai nl ess s t eel 309 (pass i ve)St ai nl ess s t eel 17- 7 H ( passi ve)Si l i cone Br onze 655

5


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---



M L- STD- 889B21 November 1979

St ai nl ess s t eel 304 ( passSt ai nl ess st eel 301 ( passSt ai nl ess st eel 321 ( passSt ai nl ess st eel 201 ( pass

i vei vei vei ve

St ai nl ess s teel 286 ( &t i ve)St ai nl ess s t eel 316L ( passi ve)AM355 ( act i ve)St ai nl ess s teel 202 ( passi ve)Car pent er 20 ( passi ve)AM355 ( pass i ve)A286 ( passi ve)Ti t ani um 5A1, 2. 5 Sn.Ti t ani um 13V, l l Cr , 3A1. ( anneal ed)Ti t ani um 6A1, V ( sol ut i on t r eat ed and aged)Ti t ani um 6A1, 4V anneal ed)Ti t ani um 8 MnTi t ani um 13V, 11Cr 3A1 ( sol ut i on t r eat ed and agedTi t anum 75AAM350 ( passi ve)Si l verGol dGr aphi t e

Nobl e ( Less Act i ve- Cat hodi c) oU.S. G O V E R N M E N T P R I N T I N GO F F I C E 1980 - 03-1211304

Super sedes page 6 o f 7 J u l y 19766


- -

` ,

` ` `

, ,

` ,

` ` ` ` `

, ` `

, `

, `

, ` ` `

, ,

` ,

` -

` -

` , ,

` , ,

` ,

` , ,

` - - -



MIL-STD-889B7 J u l y 1 9 7 6

a c i d o r a l k a l i n e m a t e r i a l s ( n e u t r a l p H , and f r e e o f c a r b o n o r m e t a l l i cp a r t i c l e s , n o t s u b j e c t o b i o d e t e r i o r a t i o n o r w i l l n o t s u p p o r t f u n g a lg rowth , and do no t abso rb o r w i c k water, th en he se may be c o n s i d e r e dn o n - m e t a l l i c s s u i t a b l e o r o i n i n g t o meta l s . Many m a t e r i a l s c l a s s e dn o n - m e t a l l i c will i n i t i a t e c o r r o s i o n of metals t o w h ic h he y a r e j o i n e d ,e . g . , c e l l u l o s i c r e i n f o r c e d p l a s t i c s , c a r b o n o r m e t a l l o a d e d r e s i n

m a te r i a l s , asbes tos-cement omposi tes .

5.1. 7 Where magnesium i s o n e o f h e metals i n v o l v e d n h e d i s s i m i l a rmetal c o m b i n a t i o n o r w h e r e s t a i n l e s s s t e e l i s u se d i n c o n t a c t w i t hi t s e l f , i t i s r e q u i r e d h a t t h e edges of t h e o i n t b e a d e q u a t e l y s e a l e dt o p r e v e n t excess g a l v a n i c o r c r e v i c e a t t ack . Where i t i s n o t e q u i r e dt h a t t h e m a t e r i a l b e e l e c t r i c a l l y c o n t a c t e d , h e n a n o n - m e t a l l i c n -s u l a t i n g g a s k e t i n g m a t e r i a l may be us ed .

5.1.8 I f h e e n v i r o n m e n t o w h i c h h e c o u p l e i s t o b e e x p o s e d i s h i g h l ya g g r e s s i v e , i t i s a dv is a bl e o employ maximum pr ote c t ive m e a s u r e s , o t h e r -wise some compromise i n t h e p r o t e c t i v e s y s t e m c o u l d b e a l l o w e d . n a n yevent, n:aximum protective s y s t e m s a l w a y s s h o u l d b e em pl oy ed when mag-nes ium i s one o f t h e metals i n v o l v e d , w h e t h e r o r n o t h e c o m b i n a t i o ni s t o serve i n a n e l e c t r i c a l conducting system:.

5 . 2P r e c a u t i o n s n d met hod s or o in i ng . Where i t becomes necessaryt h a t r e l a t i v e l y n c o m p a t i b l e metals m u s t b e a s s e m b l e d , h e o l l o w i n gp r e c a u t i o n s a n d o i n i n g m e t h o d s a r e p r o v i d e d f o r a l l e v i a t i o n o f g a l v a n i cc o r r o s i o n .

a. S e l e c t m a t e r i a l s which a r e i n d i c a t e d o b e more c o m p a t i b l e n acc o r d a n c e w i t h h e g a l v a n i c s e r i e s ; d e s i g n metal c o u p l e s s o t h a t h ea r e a o f h e c a t h o d e i s smaller ( a p p r e c i a b l y ) h a n h e area o f h e a n o d i cmetal . F o r e x a m p l e , b o l t s o r screws of s t a i n l e s s s t e e l f o r a s t e n i n g

aluminum sheet , b u t n o t h e reverse . I n t e r p o s e a compa t ib l e m e t a l l i cg a s k e t o r w a s h e r b e t w e e n h e d i s s i m i l a r metals p r i o r o f a s t e n i n g ; o rp l a t e h e ca th od ic member w i th a metal c o m p a t i b l e o h e a n o d e . T h e s ea r e a p p l i c a b l e o c o u p l e s w h i c h a r e t o s e r v e as a n e l e c t r i c a l connec t ion .

b. I n t e r p o s e a n o n - a b s o r b i n g , ' i n e r t g a s k e t i n g m a t e r i a l orwashe r be-tween the d i s s i m i l a r m a t e r i a l s p r i o r o c o n n e c t i n g them . T h i s i sa p p l i c a b l e o c o u p l e s w h i c h a r e n o t t o se rve as e l e c t r i c a l c o n d u c t o r s .

7




f l I L - S T D - B B 7 BN O T I C E I GD W I I 0 0 3 5 3 0 0 5 W~~~ ~

MIL-STD-889B7 J ul y 1976

c. Seal al l f ayi ng edges t o pr ecl ude t he ent r ance of l i qui ds.

d. Appl y corr osi on- i nhi bi t i ng past es or compounds under headsof screws or bol t s i nser t ed i nt o di ssi m l ar met al sur f aces whet heror not t he f ast ener s had been pr evi ousl y pl at ed or ot her w se t r eat ed.I n some i nst ances, i t may be f easi bl e t o appl y an organi c coat i ng t o

t he f ayi ng sur f aces pri or t o assembl y. Thi s woul d be appl i cabl e oj oi nt s whi ch ar e not r equi r ed t o be el ectr i cal l y conduct i ve.

e. Wher e pr act i cabl e or wher e i t wi l l not i nt er f er e wi t hhepr oposed use of t he assembl y, t he ext ernal j oi nt shoul d be coatedext er nal l y w t h an ef f ect i ve pai nt syst em

f . Wel ded or br azed di ssi m l ar met al assembl i es shoul d be coat edwi t h a pai nt syst em or ot her sui t abl e pr ot ect i ve coat i ngs o at l east1/ 3 i nch beyond t he heat af f ect ed zone.

g I n so cal l ed pr ot ect i ve envi r onment s ( usual l y r ef er r ed o ashum di t y- cont r ol l ed) caut l on shoul d be appl i ed t o di ssi m l ar met alcombi nat i on t r eat ment s. I f t he assumpt i on i s made t hat no cor r osi onwi l l occur because hum di t y cont r ol wi l l be mai nt ai ned, t he st r i ngentr equi r ement s woul d be unnecessar y. I t must be r ecogni zed t hat hum di t yand moi st ur e cont r ol l ed envi r onment s can be assur ed onl y by hermet i cal l yseal ed compar t ment s or cont ai ner s i n whi ch t he moi st ur e vapor cont enthas been adequat el y r educed, o as t o pr ecl ude condensat i on of wat erat t he - l owest t emperat ur e expect ed t o be encount ered i n t he act ual sur f aceof t he i t em I f hum di t y and condensat e cont r ol cannot be mai nt ai ned ri s uncer t ai n ( f requent l y thi s i s o t hen di ss i m l ar met al cont actsshoul d be t r eat ed as i f pr ot ect i on were r equi r ed agai nst t he worst en-vi r onment ,

6. APPENDICES.

6. 1 Appendi x A. Li st s pr i or i t y pr ot ect i ve t r eat ment s and syst ems f oreach met al or al l oy. Thi s l i st i ng shoul d be consul t ed f or t he sel ect i onof syst ems t o be appl i ed i n t he j oi ni ng of di ssi m l ar met al s. The sur -f ace f i ni shes provi ded i n the subl i st i ngs under each met al gi ve t heopt i mum f i r st , and other s i n descendi ng order f pr ef er ence. Envi r on-ment al condi t i ons t o whi ch. t he coupl e is expect ed t o be subj ect ed i nser vi ce must be t aken i nt o account . Assur ance shoul d be est abl i shed t hatl esser pro tec t i ve sys tems i f sel ec ted, w l l f ul f i l l t he need. Cons i der-at i ons must be gi ven o t hese f actors : ser vi ce condi t i ons, el ectr i cal




PROJECT NUMBER: MFFP-0113


--`

,` ` `

, ,`

,` ` ` ` `

,` `

,`

,`

,̀ ` `

, ,`

,` -` -`

, ,`

, ,`

,`

, ,` ---



MI L- STD- 889B7 J ul y 1976

APPENDI X A

RECOMMENDED TREATMENTS I N ORDER OF PROTECTI VE EFFECTI VENESS

10. GENERAL

10. 1 Scope. Thi s appendi x l i st s pr ot ect i ve syst ems f or each met al oral l oy w t h opt i mum t r eat ment s l i st ed f i r st , and ot her s i n descendi ngor der of pr ef er ence.

10. 2 Appl i cat i on. Each l i st i ng i s pr esent ed as a gui de onl y eachappl i cat i on must be r evi ewed consi deri ng servi ce condi t i ons, desi gnr equi r ement s and mai nt enance cost s,

20, REFERENCE DOCUMENTS

SPECI FI CATI ONS

FEDERAL

QQ- P- 416TT- C- 490

Pl at i ng Cadm um {El ect r odeposi t ed)Cl eani ng Met hod And Pret r eat ment ofFer r ous Sur f aces For Or gani c Coat i ngs

M LI TARY

M L- 3171agnesi uml l o y,nodi cr eat mentfM L- C- 5541hem calonver si onoat i ngsnl um num

And- Al um num Al l oys

Resi n- aci d {Asg)

Al um num Al l oys

M L- C- 8514oat i ngompound,et alr et r eat ment ,

M L- A- 8625nodi coat i ngs,orl um numnd

M L- C- 8837oat i ng,adm umVacuumeposi t ed)






+ pai nt or r esi n coat i ng syst em

b. Chr omat e conver si on coat i ng w t hout organi c syst em For use i nnon- per si st ent wet or mar i ne at mospher e. For el ect r i cal , t her mal con-duct i ng pur poses i n m l d at mospheres i n absence of wet , al i ne. or ac i di ccondi t i ons. Recommended f or beryl l i um i n hi gh t emperat ur e appl i cat i onst o f or est al l cat ast r ophi c oxi dat i on i n oxygen cont ai ni ng at mospher e.

3 0 4 Treat ment f or Al um num and Al um num Al l oys

a. Anodi c coat i ng ( M L- A- 8625) + pai nt or r esi n coat i ng syst em

b. Chr omate conver si on coat i ng ( M L- C- 5541) + pai nt or r es i ncoat i ng system or anodi c coat i ng, seal ed, w t h r esi n seal ( when por ouscast i ngs ar e used, i mpr egnat ed wi t h r esi n pr i or t o sur f ace t r eat i ng andf i ni shi ng) .

c. Chr omat e conver si on coat i ng w t hout pai nt or r esi n coat i ng, f orel ect r i cal , t hermal conduct i ng pur poses i n m l d at mospheres i n absenceof sal i ne, al kal i ne or ac i di c condi t i ons .

12


--`

,` ` `

, ,`

,` ` ` ` `

,` `

,`

,`

,` ` `

, ,`

,` -` -`

, ,`

, ,`

,`

, ,` ---



pl at i ng.

b. Net al l i c coat i ng, e. g. , s acr i f i ci al Zn or Cd, wi t h suppl ement alsur f ace t r eat ment , or non- sacr i f i c i al , e. g. , Cu or Ni , wi t hout pai ntcoat i ng syst em f or di r ect met al l i c cont act or f or achi evi ng l east pot en-t i al di f f er ence bet ween j oi ned met al s. For met al s of st r engt hs gr eat ert han 220 ksi , met al l i c coat i ng, i f r equi r ed, t o be appl i ed by non- el ect -r ol yt i c met hods; z i nc or cadm um pr ohi bi t ed.

c. Zi nc phosphat e conver si on coat i ng ( TT- C- 490) + pai nt coat i ngsystem Caut i on, i f phosphat e coat i ng used on steel s f st r engt hs be-t ween 150 t o 20 ksi hydr ogen r el i ef r equi r ed; s t r ess r el i ef r equi r edpr i or t o phosphat i ng and hydr ogen embr i t t l ement ewi r ed af t er phos-phat i ng.

d. Pr et r eat ment pr i mer ( M L- P- 15328, M L- C- 8514) + pai nt coat i ngsystem

e. Heavy phosphat e conver si on coat i ng ( M L- P- 16232) + suppl ement alt r eat ment . Not f or st eel s of st r engt hs gr eat er t han 220 ksi .

Not e: Bar e st eel not r ecommended.

30. 6 Tr eat ment . f or Lead, Ti n, Sol der s, and I ndi um

Coat i ngs of t hese mat er i al s appl i ed t o ot her met al s by hot - di ppi ng,f usi ng, or el ectr opl at i ng pr ocesses .

a. Coat w t h pai nt or r esi n coat i ng syst em El ect r opl at ed coat i ngsshoul d be f l owed pri or o appl yi ng coat i ng system

13


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---



b. El ect r opl at e wi t h ot her met al t o r educe t he el ect r opot ent i aldi f f er ence of met al s bei ng j oi ned, wher e di r ect cont act of met al s r e-qui r ed f or el ectr i cal pur poses.

30.7 Treat ment f or St eel s- Carbon, Lo Al l oy, Mar t ensi t i c and Ferr i t i cSt ai nl ess

St eel s w t h chr om um cont ent s i n t he r egi on of 2 per centwi l l under go consi der abl e sur f ace st ai ni ng and l i m t ed r ust i ngi n cor r osi ve envi r onment s, but on t he whol e ar e appr eci abl yl ess cor r oded t han car bon st eel s.

a. Pai nt or appl y r esi n coat i ng; zi nc phosphat e car bon st eel s pr i ort o appl i cat i on of pai nt or r esi n coat i ng.

b. May be el ect r opl at ed, or used bare f or use i n non- persi st ent wetor mari ne at mosphere, and f or el ect r i cal or t hermal conduct i ng pur poses.Fayi ng edges t o be seal ed t o pr event cr evi ce cor r osi on.

30.8 Treat ment f or Chr om um ( pl at e) , Mol ybdenum Tungst en

a. Pai nt or appl y r esi n coat i ng o r educe cor r osi on at voi ds i n. chr om um pl at i ng, or s t ai ni ng f mol ybdenum or t ungst en surf aces.

conduct i ng pur poses, Seal f ayi ng edges to m t i gat e crevi ce at t ack fmet al t o whi ch j oi ned.

30 9 Tr eat ment f or St eel s St ai nl ess- Aust eni t i c, PH, Super St r engt h, HeatResi st ant , Br ass- Leaded, Br onze, Br ass Br onze- Lo Copper,and Copper Hi gh Ni ckel

a. Appl y met al l i c coat i ng as may be requi r ed t o m ni m ze el ect r i -cal potent i al di f f erence bet ween t he met al s t o e j oi ned and appl ypai nt or r esi n coat i ng syst em pr i mar i l y o di m ni sh i bn cont am nat i onf r om met al s of t hi s gr oup ont o more anodi c met al s t o whi ch t hey m ghtbe j oi ned, t hereby di m ni shi ng pot ent i al damage t o t he more anodi c metal .

b. Appl y met al l i c coat i ng ( as ar 1 bove) , use w t hout pai nt orr esi n coat i ng, f or el ect r i cal or t her mal conduct i ng pur poses. Nay beexpedi ent t o over coat compl et ed assembl y w t h pai nt or r esi n.

c. Appl y pai nt or r esi n coat i ng syst em and seal f ayi ng edges.

14


--`

,` ` `

, ,`

,` ` ` ` `

,` `

,`

,`

,` ` `

, ,`

,` -` -`

, ,`

, ,`

,`

, ,` ---



15




s e r v i c e i s e l e c t r i c a l , o r a p p l y c o n f o-

b . May be used b a r e n e l e c t rs e r v i c e , o n d i t io n s e r m i t t i n g . e a l

16


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---





MIL-STD-889B

7 J u l y 1 9 7 6

s o l u t i o n p a t h n - t h e g a l v a n i c c i r c u i t ( i n t e r n a l c i r c u i t ) ; a n d R t h er e s i s t a n c e o f h e e l e c t r o d e s ( e x t e r n a l c i r c u i t ) .

30.2 Cor ros ive nv i ro nmen t . n a l i qu id med ium o r e l e c t r o l y t e o l u t i o n ,of a g i v e n c o n c e n t r a t i o n o f h e e l e c t r o l y t e , a n d a s p e c i f i c e m p e r a t u r e o ft h e medium, eac h metal h a s a s p e c i f i c e l e c t r i c a l p o t e n t i a l , i . e . , a b i l i t y

t o u n d e r g o d i s s o l u t io n - t o f o r m metal i o n s w i t h h e r e l e a se o f e l e c t r o n s .I n a v e r y c o r r o s i v e s o l u t i o n , h a v i n g h i g h c o n d u c t i v i t y a n d p r o d u c i n gr e a d i l y s o l u b l e c o r r o s i o n p r o d u c t s of t h e metal , c o r r o s i o n will c o n t i n u e .I n a l i m i t e d v o l u m e of so lu t i on , w h e r e cond i t ions more proba bly w i l ld e v e l o p o ham per c o r r o s i o n , e . g . , n c r e a s e o f c o n c e n t r a t i o n o f metali o n s , h e c o r r o s i o n may d i m i n i s h w i t h time. On t h e o t h e r h a n d , h esame metal as t h e a n o d e o f a g a l v a n i c c o u p l e , w i l l t e n d o e x h i b i t ac-c e l e r a t e d c o r r o s i o n , w h i c h c a n b e r e l a te d o a f l o w o f c u r r e n t n h ec i r c u i t , f h e c a t h o d e i s u n a f f e ct e d by p o l a r i z a t i o n . f h e e l e c t r o d e sp o l a r i z e p r o g r e s s i v e l y , g a l v a n i c c u r r e n t f l o w a n d c o r r o s i o n w i l l s u b s i d eand may actually s t o p . G e n e r a l l y , h e r a t e o f c o r r o s i o n w i l l d e c r e a s ew i t h h i g h e r c o n c e n t r a t i o n s o f h e e l e c t r o l y t e , o r w i t h o w e r e m p e r a t u r e .

G a l v a n i c e f f e c t s may c h a n g e because o f d i f f e r e n t pH c o n d i t i o n s w i t h i na n e l e c t r o l y t e . A metal which i s t h e a n o d e n a n e u t r a l o r a c i d i c s o l u -t i o n may become t h e c a t h o d e i f t h e s o l u t i o n i s made bas i c .

Oxygen d i s s o l v e d n h e e l e c t r o l y t e c a n d e p o l a r i z e h e c a t h o d e byox id i z ing abso rbed hydr ogen. n some cases, oxygen'may be n e c e s s a r y op romote oxidat ion o f he anode . Avai lable oxygen and he r a t e o f i t sd i f f u s i o n h e r e f o r e c a n n c r e a s e g a l v a n i c a t t a c k .

Ions wh ich a r e g e n e r a t e d a t t h e e l e c t r o d e as c o r r o s i o n proceeds con-c e n t r a t e a t o r n e a r h e e l e c t r o d e s u r f a c e s p o l a r i z a t i o n ) and impedec u r r e n t l o w. F o r e a c h o f h e s e cases, i n s t a t i c s o l u t i o n s , h e c o r -r o s i o n a c t i o n i s diffus ion-dependent and i s u n d e r d i f f u s i o n - c o n t r o l .A g i t a t i o n o f t h e s o l u t i o n w i l l i n c r e a s e t h e r e a c t i o n r a t e .

3 0 . 3 C o n d u c t i v i t y o f h e g a l v a n i c c i r c u i t . ' C o r r o s i o n o f a s i n g l e metal i na n e l e c t r o l y t e n v o l v e s h e f l o w of c u r r e n t f r o m o c a l a n o d i c o o c a l ca t -h o d i c areas o n t h e metal s u r f a c e . T h i s i s t e rmed loca l c e l l c o r r o s i o n "and i s t h e s i t u a t i o n o f n o r m a l c o r r o s i o n , R e l a t i v e l y smal l d i f f e r e n c e si n p o t e n t i a l s of l o c a l c e l l s a r e t h e r e s u l t o f c o m p o s i t i o n a l d i s s i r p i l a r i - .t i e s o n t h e metal s u r f a c e b e c a u s e o f d i f f e r e n t metal p h a s e s o r c r y s t a lo r i e n t a t i o n , c r y s t a l m p e r f e c t i o n s s e g r e g a t i o n s , g r a i n b o u n d a r i e s , a n do t h e r c o n d i t i o n s . T h e more nhomogeneous the s u r f a c e , h e m o re u sc ep -t i b l e i t i s t o g e n e r a l a t t a c k . D i s s o l u t i o n o f h e a n o d e r e l a t e s t o h eg a l v a n i c c u r r e n t a c c o r d i n g o F a r a d a y ' s law,

18


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---




--`

,` ` `

, ,`

,` ` ` ` `

,` `

,`

,`

,` ` `

, ,`

,` -` -`

, ,`

, ,`

,`

, ,` ---



MIL-STD-889B7 July 1 9 7 6

s h o u l d b e s p e c i f i e d a n d m a i n t a i n e d as c l o s e l y as p o s s i b l e .

TABLE I A

STANDARD ELECTRODE POTENTIALS - AQUEOUS SOLUTION,

IM-RESPECTIVE METAL I O N , 25OC, AT EQUILIBRIUM

Metal ( H i g h p u r i t y )

'Magnesium2+~Aluminum3+:Z inc 2+i Chr omium3+i ron'+Cadmium2+

Lead2+Hydrogen'Copper2+S i l v e r +

/Mercury 2+Platinum'+

IGold'

;Tin2+

I

S t a n d a r d E l e c t r o d e P o t e n t i a l (v)

'2.37-1.67

O. 76O. 7 4

O. 44

O. 4 0

O. 1 4O. 13

0.00+O. 34+O. 800. 8

l. 9l.

30.5 P o l a r i z a t i o n , The p o l a r i z a t i o n o fe l e c t r o d e s n a n e l e c t r o l y t es o l u t i o n o c c u r s b e c a u s e o f a f i l m o f o x i d e o r o t h e r compound o r g a s on t h ee l e c t r o d e u r f a c e s . T h e s e c h a n g e s e d u c e h e p o t e n t i a l d i f f e r e n c e

r e l a t i v e t o t h e ope n c i r c u i t p o t e n t i a l s * 2 a n d e s s e n h e c o r r o s i o n r a t e .S u c h c h a n g e s n c r e a s e h e r e s i s t a n c e o f h e e x t e r n a l c i r c u i t a n d d i m i n i s hc u r r e n t f l o w ; a n d n t e n s i f y o r d i m i n i s h with g a l v a n i c c u r r e n t , o r w i t ha p p l i e d c u r r e n t . E l e c t r o d e p o l a r i z a t i o n b e h a v i o r i s a means bywhicht h e c o m p a t i b i l f t y o f c o u p l e d d i s s i m i l a r metals i n s o l u t i o n c a n b ee s t a b l i s h e d . P o l a r i z a t i o n m e a s u r e m e n t s c a n p r o v i d e n f o r m a t i o n as t o h ee f f e c t s of r e l a t i v e a r e a s o f a n o d e a n d c a t h o d e a n d e f f e c t s o f c h a n g e si n p o t e n t i a l on t h e c o r r os i o n.

P o l a r i z a t i o n o f g a l v a n i c e l e c t r o d e s i s i l l u s t r a t e d i n F i g u r e 1A.When th e a n o d e , c a t h o d e , o r b o t h p o l a r i z e , h e c o n t r o l i s a n o d i c ,

20


--̀ ,̀ `̀ ,,̀ ,̀ `̀ `̀ ,̀ ,̀̀ ,̀ ,̀ `̀ ,,̀ ,̀ -̀ -̀ ,,̀ ,,̀ ,̀ ,,̀ ---



f l I L - S T D - B A 7 B O T I C E L G D m 7 7 7 7 7 3 3 0 0 3 5 3 3 3 m

MIL-STD-889B7 J u l y 1 9 7 6

c a t h o d i c , o rm i x e d , e s p e c t i v e l y. G a l v a n i c o r r o s i o n n d u r r e n t l o wa r e p o l a r i z a t i o n and r e s i s t a n c e co n t ro l l ed . When th e e l e c t r o d e s do n o tp o l a r i z e , e s i s t a n c e o f h e c i r c u i t , h e s o l u t i o n p a t h (R,) and t h em e t a l l i c p o r t i o n (Rm) c o n t r o l h e r e a c t i o n .

ALOl4TKOLAY 3 D I C

W

c - -ALOl4TKOLAY 3 D I C

W

c - -I

WIOp.

MrXED R E S l S T l H C E

FIGURE 1A. Types of p o l a r i z a t i o n a n d c o n t r o l n g a l v a n i c c o r r o s i o n .

30.6 E l e c t r o d e areas . Under c a t h o d i c o n t r o l , o r r o s i o n o f h e n o d ei s p r o p o r t i o n a l o h e a r e a of t h e c a t h o d e . f h e c a t h o d e a r e a i s two tot h r e e t i m e s ' t h e area o f t h e a n o d e a n d i f t h e p o l a r i z a t i o n i s n e g l i g i b l e ,t h e c u r r e n t i s g e n e r a l l y n c r e a s e d by t h e same f a c t o r . T h e . s a m e r e l a -

t i o n s h i p p r e v a i l s f h e a n o d e area i s d e c r e a s e d r e l a t i v e t o t h e c a t h o d e .D e c r e a s i n g h e a r e a of t h e c a t h o d e , n e f f e c t n c r e a s i n g h e a r e a o f h ea n o d e , e d u c e d h e g a l v a n i c c u r r e n t d e n s i t y a n d d i m i n i s h e s c o r r o s i o n o ft h e a n o d e s o t h a t n o r m a l co r ros ion becomes d om in an t. The s i t u a t i o n i ssomewhat d i f f e r e n t n m ixed c o n t r o l . A n i n c r e a s e n h e c a t h o d e areacan h av e some a c c e l e r a t i n g c o r r o s i o n e f f e c t b u t h i s i s g e n e r a l l y l e s st h a n n h e case o f c a t h o d i c c o n t r o l , a n d h e e f f e c t d o e s n o t o c c u r na pr op or t i on al way. Normal co rr os io n becomes l e s s pronounced. In a n o d i cc o n t r o l , h e c o r r o s i o n o f h e a n o d e e s s e n t i a l l y i s u n a f f e c t e d by t h ec a t h o d e a r e a ; i n c r e a s i n g h e a r e a o f h e a n o d e d e c r e a s e s h e g a l v a n i cc u r r e n t .

2 1




MIL-STD-889B7 J u l y 1976

30.7 R e s i s t a n c e a n d g a l v a n i c c u r r e n t . n a p o l a r i z e d g a l v a n i c c i r c u i t ,r e s i s t a n c e i s c o n t r i b u t e d by t h e p o r t i o n o f h e e l e c t r o l y t e b e t w e e n h eanode and cathode Re, i n t e r n a l p a t h ) a n d by t h e i l m s o f e a c t i o n p r o -ducts formed on t h e e l e c t r o d e s u r f a c e s Rm, meta l l i c path) , which mpedei o n e x c h a n g e a n d e d u c e c u r r e n t l o w, T h e r e f o r e , h e o t a l e s i s t a n c e ,R , of t h e c i r c u i t i s ex p re s s ed a s R = 4- . I n h e p o l a r i z e d y s t e m ,a s t h e r e s i s t a n c e n c r e a s e s , h e p o t e n t i a l s o f h e a n o d e a n d c a t h o d ea p p r o a c h e a c h o t h e r u n t i l a s t e a d y s t a t e r e a c t i o n i s a t t a i n e d . T h e limi-

t i n g c u r r e n t c o r r e s p o n d s w i t h h e n t e r s e c t i o n of t h e p o l a r i z a t i o n c u r v e s .T h i s i s t h e maximum c u r r e n t o b t a i n a b l e n h e s y s t e m f c o n s t a n t c o n d i -t i o n s a r e main t a ined .

30.8 The e l ec t ro l y t e medium. In ea ch i q u i d medium o r s o l u t i o n f o r ag i v e n c o n c e n t r a t i o n o f h e e l e c t r o l y t e a n d e m p e r a t u r e of he medium), ametal has a s p e c i f i c e l e c t r i c a l p o t e n t i a l . I n a v e r y c o r r o s i v e s o l u t i o n ,o n e h a v i n g h i g h c o n d u c t i v i t y. a n d p r o d u c i n g r e a d i l y soluble compounds ofthe anode of a g a l v a n i c c o u p l e , h e a n o d e w i l l c o r r o d e u n i f o r m l y. f h ec a t h o d e d o e s n o t p o l a r i z e , h e c o r r o s i o n o f h e a n o d e w i l l b e a c c e l e r a t e d .However, with p o l a r i z a t i o n o f h e e l e c t r o d e s , g a l v a n i c c u r r e n t f l o w a n dc o r r o s i o n u b s i d e . G e n e r a l l y, o r a g i v e n e l e c t r o l y t e s o l u t i o n , h e r a t eof c o r ro s i o n d e c re a s es w i t h h i g h er c o n ce n t ra t i o n o f t h e e l e c t r o l y t e o rwi th o w er empe ra tu r e .

I n a s o l u t i o n c o n t a i n i n g o n s h a t c a n p o l a r i z e h e a n o d e , h e ca t -hode , or b o t h , g a l v a n i c e f f e c t s w i l l b e small.

C o u p l e d d i s s i m i l a r metals may e x h i b i t d i f f e r e n t r e s p o n s e s i n t h ee l e c t r o l y t e s o l u t i o n b e c a u s e o f pH cha nge s. A metal whic.h i s t h e anodei n a n e u t r a l o r a c i d i c s o l u t i o n may become t h e c a t h o d e f h e s o l u t i o ni s made basic. T h i s i s i l l u s t r a t e d w i t h magnesium-aluminum c ou pl es n.d i l u t e , n e u t r a l , o r s l i g h t l y a c i d i c s od iu m c h l o r i d e o l u t i o n . Wi t hd i s s o l u t i o n o f h e m a gn e si u m an ode , he solu t ion becomes a lk a l i ne , a n dth en he aluminum i s r e n d e r e d a n o d i c , a r e v e r s a l of p o l a r i t y . n n e u t r a lsodium chloride so l u t i on , he a nod e r on o f a n ron -c opp e r c oup l e be c omes -t h e c a t h o d e when t h e s o l u t i o n i s a l t e r e d by t h e a dd i t i on o f ammonia.

3 0 . 9 A e r a t i o n , d i f f u s i o n , n d g i t a t i o n of s o l u t i o n . Oxygen d i s s o l v e d i nt h e e l e c t r o l y t e s o l u t i o n c a n a c t o d e p o l a r i z e h e c a t h o d e by ox i d i zi n gadsorbed hydro gen. n some cases, oxy gen may b e n e c e s s a r y e r o x i d a t i o no f t he anode . Ava i l ab l e oxygen a nd he r a t e of i t s d i f f u s i o n h e r e f o r ec a n n c r e a s e g a l v a n i c c u r r e n t . o n s w h i c h are formed a t t h e e l e c t r o d e sd u r i n g g a l v a n i c c o r r o s i o n c o n c e n t r a t e a t o r n e a r h e e l e c t r o d e s u r f a c e s( p o l a r i z a t i o n ) a n d m p e d e c u r r en t l ow. F o r each o f h e s e cases i n

22


--`,```,,`,`````,``,`,`,```,,`,`-`-`,,`,,`,`,,`---



23

Mil Std 889 Dissimilar Metals

Documents