penthouse spring 1988

Upload: john-m-cavote

Post on 08-Apr-2018

243 views

Category:

Documents


0 download

TRANSCRIPT

  • 8/7/2019 Penthouse Spring 1988

    1/2

    DAVID N. FRENC H, INC. , METALLURGISTSONE LANCASTER ROAD

    NORTHBOROUGH. MASSACHUSETTS 01532(617) 393-3 635 VOL. V , NO .

    A VIEW FROM THE PENTHOUSE: USEFUL INFORMATION FOR THE WORLD OF BO~LERST-TREATMENT OF STAINLESS STEELS

    T he r e ha s be e n some c on f us i on i n t h er e m e n ts f o r s o l u t i o n a n n e a l i n g o f c o ld -

    rke d a u s t e n i t i c s t a i n l e s s s t e e l s . More an dre p u rc h a s e s p e c i f i c a t i o n s f o r r e p la c em e n t

    n d r e h e a t e r s f a b r i c a t e d w i t ha i n l e s s s t e e l ma nd at e a h i gh - te m p er a tu r e

    m e n t , u s u a l l y o f t h e w ho le e l em e n t .e n t h e r e q u e s t i s b a se d on i n a c c u r a t e o r

    I t h i n k it i s t i me t osome l i g h t i n t o t h e d ar k n e ss o f

    i n fo r ma t io n on t h e n e c e s s i t y t o s o l u t i o nn e al a l l c o ld work a u s t e n i t i c s t a i n l e s se e l p r e ss u re p a r t s .

    T u bi ng f o r b o i l e r c om po ne nt s i s pur c has e d t om a t e r i a l s s p e c i f i c a t i o n SA-213. Th e t h r e e

    mon g r a de s u s ed i n t h e f a b r i c a t i on o ft s a r e 304(H) , 321(H) , and 347(H) . Each

    e n te m p e r at u r e f o r s o l u t i o ne a li n g. The s p e c i f i c a t i o n r e q u i r e s t h a t

    e p ur ch as ed t u b i n g b e s u p p l i e d t o t h es u r e- p a rt f a b r i c a t o r i n t h e s o l u t i o n -

    led co nd i t i on . However, Sec t ion I o f t h e& Pre ssu re Vesse l Code has no

    i f i c a t i o n r eq u ir em en t t h a t t h e f a b r i c a t e dp a r t b e h e a t - t re a t e d a f t e r b en di ng .

    u s t h e he a t - t r e a t m e n t r e qu i r e m e n t i s l e f te r t o t h e d i s c r e t i o n o f t h e m a nu fa ct ur ers a c o n t r a c t a g re em e nt b e tw e en b u y e r a nd

    FECTS OF COLD WORKThe e f f e c t s o f c o l d w or ki n g on t h e

    r o s t r u c t u r e d ep en d, o f c o u r s e , on t h eunt o f c o l d w or k. Up t o a bou t 15% s t r a i n ,c ha ng es i n t h e g r a i n s t r u c t u r e a r e h a rd l y

    s i b l e , e v en a t 5 00 m a g n i f i c a t i o n s . By 20%, s l i p l i n e s a nd t h e e a r l y s t ag e s of

    t o r t i o n a r e v i s i b l e . Above 20% s t r a i n ,e g r a i n s t h e m s e lv e s become v i s i b l yD ur in g s o l u t i o n a n n e a l i n g two e f f e c t s o c c ur :y c a r b i d e s p r e s e n t d i s a p p e a r a nd t h e g r a i nr u c t u r e c ha nges . The c o l d w or ke d g r a i n s go

    h a s e r i e s o f c h an g e s. The f i n a l s t a g e ,

    o f c o u r s e , i s a l a r g e e q ui ax ed g r a i n s i z e t h ai s s t r a i n f r e e . The p r oc e ss i t s e l f i s known " r e - c r y s t a l l i z a t i o n . " The more s e v e r e l yd i s t o r t e d g r a i n s form s m a l l , e q u ia x ed , s t r a i nf r e e , a u s t e n i t e g r a i n s f i r s t . D ur i ng c on t i nuh e a t in g o r t im e a t t h e s o l u t i o n a n n e al i ngt e mp e ra t ur e , t h e s e s t r e s s - f r e e g r a i n s t r u c t u rgrow a t t h e e x p en se o f t h e d i s t o r t e d o n e s .T hu s, o n e o f t h e s t a g e s d u r i n gr e c r y s t a l l i z a t i o n i s a g r a i n s t r u c t u r e whichm o s t l y e q u ia x e d b u t s m a l l .

    The same s e que nc e o f t r a n s f o r m a t i o ns w i t h it h e g r a i n s t r u c t u r e o c c u r s d u r in g no rm alo p e r a t i o n o f p r e s s u r e p a r t s . Ther e c r y s t a l l i z a t i o n c an o c cu r ov e r a l o n g p e r ioo f t i m e a t t e m p e r a t ur e s a s low a s a b o ut1 1 0 0 ~ ~ . 1 0 0 ~ ~s t h e a p p ro x i ma t e t e m p e r a t u rf o r t h e o ns et o f c re ep i n s t a i n l e s s s t e e l .The problem i s t h a t a s t h e c o l d worked g r a i n sr e c r y s t a l l i z e , t h e s t a g e w i t h f i n e , e qu ia xe d,a u s t e n i t e g r a i n s h a s a l o we r cr ee p s t r e n g t ht h a n t h e c o a r se - g r ai n e d s i z e . T hu s, u n d e rsome c o n d i t i o n s , c o ld -w ork ed s t a i n l e s s s t e e ld u ri n g r e c r y s t a l l i z a t i o n i n s e n r i c e w i l l f a i lby a c r e e p o r s t r e s s - r u p t u r e m ec ha ni sm . Thef i n e r t h e g r a i n s i z e , t h e p o or e r t h e c r e eps t r e n g t h ; a nd t h e r e f o r e u n de r n or ma lc o n d i t i o n s c ol d-w or ke d s t a i n l e s s w i l l l e ad t os te am l e ak s d u r in g t h i s r e c r y s t a l l i z a t i o n .

    The pr ob le m h a s be en r e p o r t e d i n 3 2 1 ( ~ )s t a i n l e s s s t e e l . To my k no wl ed ge it h a s n o to c cu r re d i n e i t h e r 30 4 o r 347 s t a i n l e s ss t e e l s . Of t he s e t h r e e common g r a de s o fs t a i n l e s s s t e e l t h e c re ep s t r e n g t h o r s t r e s s -r u p t u r e s t r e n g t h o f 3 2 1 i s t h e most s e n s i t i v et o g r a in - s iz e v a r i a t i o n s . I n f a c t , r e f e re n c et o SA-213 s p e c i f i c a t i o n i n d i c a t e s t h a t 321(H)ha s a s p e c i f i e d g r a i n s i z e , ASTM 7 o r c o a rs e rNone o f t h e o t h e r g r a d e s h a s a s p e c i f i e d g r a is i z e f o r a s s u r i n g a de q ua t e cr e e p s t r e n g t h .The s t r e s s - r u p t u r e s t r e n g t h of t h e s e o t h e rg r a d e s i s n o t a s s u s c e p t ib l e t o g r a i n s i z ev a r i a t i o n s a s i s 321 (H) .RECOMMENDATIONSS i n c e i t i s i m p o s s i b l e t o f a b r i c a t e as u p e r h e a t e r o r r e h e a t e r e le m en t w i t h o ut c o l db e nd in g , t h e q u e s t i o n i s how t o b e s t a v o i d t h

  • 8/7/2019 Penthouse Spring 1988

    2/2

    n t i a l c re e p f a i l u r e s d u r in g s e r v ic e a sold-w orked s t a i n l e s s r e c r y s t a l l i z e s . The

    i ou s f i r s t s t e p , o f c o u rs e , i s t o u sei t h e r 3 04 (H ) o r 347 (H) r a t h e r t h a n t h e

    The second s t e p i s t o l i m i t t h eount of co ld work i n any bend t o

    ximat e ly 20%. By us in g a bending-wheela me te r of a t l e a s t f o ur t im e s t h e t u b e

    m e te r , t h e c o l d work o r s t r a i n i n t h et h e be nd w i l l be no more than 20%.

    us, f o r a 2" d i ame te r tube , a l l o f t h eb e d on e on a t l e a s t a n 8 "-

    t e r bend ing wheel . Th i s obv io us ly worksr m os t o f t h e b e n di n g r e q u i r e d i n a

    o r r e h e a t e r e le m en t, e x ce p t f o rse - rad ius re tu rn bends . However, t h e

    mount o f s t r a i n o n t h e e x t r a d o s of t h e s es can be kep t be low 20% by t h e use o f a

    r a t t a c h m e n t t o t h e b e n d i n g m ac hi ne a n dn t h e i n t r a d o s . By p u sh i n g t h e t u b et h e be n di n g o p e r a t i o n w i t h a h y d r a u l i c

    , t h e amount o f wa l l t h i n n i n g on t h erad os o f th e bend can be kep t below 20%.

    th t h e w a l l t h i n n i n g l e s s t h a n 2 02 , t h e n e ti s a l s o l e s s t h a n 20%.

    There w i l l b e a g r e a t e r amount o f s t r a i n oni n t r a d o s o f t h e b end a s t h e m a t e r i a l

    s d u r i n g b e n di n g. However, t h e s t r e s sw i l l b e l e s s a s t h e w al l

    A c o n v e n ie n t q u a l i t y - c o n t r o l c h ec k i s t oa su re t h e h a r d ne s s on t h e e x t r a d o s o f t h e

    The SA-213 s p ec i f ic a t i o n l i m i t s t h e a s -r ch as ed h a r dn e s s o f a u s t e n i t i c s t a i n l e s st e e l s t o R oc kw el l B 8 5. The i n e v i t a b l e

    e o f any co ld work i s t o i n c r e a sei s h a rd n e ss . The g r e a t e r t h e ha r dn e s s

    , t h e more c o l d work a nd s t r a i n t h e r es w i t h i n t h e m i c ro s t r u c t u r e . A s a r e a s o n a b l e

    promise , an in cr ea se of some 20 po in ts ,el l B, above t h e Code -spec ified 85

    i s a re aso nab le amount of co ld worki s n ot l i k e l y t o r e c r y s t a l l i z e du r i ng

    i c e . S i n c e 20 R oc kwel l B p o i n t s p u t s t h et 1 0 5, w h ic h i s o f f t h e R oc kwel l B

    e , a h a r d n e ss o n t h e e x t r a d o s o f t h e be ndC 25 i s a c c e p t a b l e . F o r

    comparison, Rockwell C 20 i s a p p r o x i m a t e l ye q u a l t o R o ck wel l B 100. Thus, Rockwell Ci s approx ima te ly 20 Rockwel l B ha rdn ess p o iabove 85. Tab le I p r e se n t s some d a t a ,c o u r t e s y o f L e ig h to n I n d u s t r i e s , I n c . , o n t hh a rd n e ss c ha ng es a s a f u n c t i o n o f s t r a i n f o3 04 s t a i n l e s s s t e e l . N ote t h e c l o s e- r a d i usbend, sample iI4, has t h e l e a s t amount o fs t r a i n . T h i s b en d was made b y h e a t i n g t h ei n t r a d o s o f t h e bend t o e f f e c t t h e c l o s e-ra d i us bend . The amount o f s t r a i n i sa p p r o x im a t e l y 7% on t h e e x t r a d o s o f t h e b en

    The f i n a l q u e s t i o n t o b e a d d r es s ed i sw h et he r i n d i v i d u a l be nd s o r t h e e n t i r e e le ms h o ul d be s o l u t i o n a n ne a le d a f t e r b en d in g .Ob v io u s ly on e o f t h e p ro b le m s a s s o c i a t e d w is o l u t i o n a n n e a li n g t h e e n t i r e e le me nt i s t h ed i s t o r t i o n t h a t i s l i k e l y , na y, c e r t a i n l y , to c c u r . The who le -e le me nt d i s t o r t i o n n e e ds tb e s t r a i g h t e n e d , wh ic h a d d s b o t h t i m e a nd i sl i k e l y t o l e a d t o l e s s -t h a n - pe r f e ct a li gn m ewhen complete.

    The se co n d p r ob le m , o f c o u r se , i s t h a td u r i n g a 2000F s o l u t i o n a n n e a l , a c e r t a i namount of s team-side s c a l e w i l l form on thet u b e . T h i s s t ea m -s id e s c a l e f u n c t i o n s a s at he rm al b a r r i e r t o t h e h e at t r a n s f e r ; t h e ne f f e c t i s t o r a i s e t u b e m et a l t e mp e ra t ur edu ri ng se rv ic e . See VOL. I , No. 1 o f t h i sn e w s l e t t e r . I n o r d e r t o remove t h e s te am - sis c a l e b e f o r e i n s t a l l a t i o n , i n d i v i d u a l e le mew i l l n ee d t o b e c h e m i c a l l y c l e a n e d , wh ic h i san added expense . Thus, whole e lem ent s shon o t be s o l u t i o n a nn ea le d i f a t a l l p os s i b l e.I n d i v i d u a l be nd s c o u l d b e s o l u t i o n an n e a l edt h e h a rd n e ss i n c r e a s e i s more than 20 RockwB h a r dn e s s p o i n t s , b u t t h i s i s somewhatawkward and l ea ds t o exce ss i ve ha nd l ing .A ga in , t h e c o s t i n c r e a s e t o p e rf o rm t h es o l u t i o n a n ne a l d oe s n o t s eem t o b e j u s t i f i eThe b e s t c o u r s e o f a c t i o n i s t o u s e 3 0 4 ( ~ )3 47 (H ) s t a i n l e s s s t e e l s a nd b en d i n s u ch af a s h i o n a s t o ke e p t h e amount o f s t r a i n be lo20%. W it h l e s s t h a n 20% s t r a i n , n e i t h e rr e c r y s t a l l i z a t i o n n o r p re ma tu re c r ee p f a i l uw i l l b e l i k e l y t o o c c u r d u r i n g no rm alo p e r a t o n .

    BEND CONDITIONSTUBE DIMENSIONSTABLE I

    % STRAINBEND DIAM.1. 1 7/8" OD x 0.280" MWT 8" 19

    HARDNESSBEND END INCREASE2. 2 1/8" OD x 0.3001' MWT 10" 17 1 / 2 95 75 203. 2" OD x 0.220" MWT 12" 15 92 70 224* 1 7/8"OD x 0 .280" MWT 1" 7 85 71 1 4* h ot bend, i n t ra do s h e a t e d t o ~ l 7 5 0 ~ ~ .