18241-62491-1-PB

Tp ch Khoa hc v Cng ngh 50 (6) (2012) 695-823

N MN V PH HY VT LIU KIM LOI TRONG MI TRNG KH QUYN NHIT I VIT NAM

L Th Hng Lin

Vin Khoa hc vt liu, Vin KHCNVN, 18 Hong Quc Vit, Cu Giy, H Ni

Email: [email protected]

n Ta son: 19/12/2012; Chp nhn ng: 27/12/2012

TM TT Bi bo trnh by tm tt cc khi nim c bn v qu trnh n mn kh quyn kim loi v

nh hng ca cc yu t kh hu, mi trng n qu trnh n mn kh quyn nh nhit , m khng kh, thi gian lu m b mt, cc tp cht v nhim bn kh quyn ( mui kh quyn - hm lng ion Cl-, hm lng kh SO2). Cc dng h hng thng gp do n mn trong mi trng kh quyn c gii thiu; Mt s khi nim v phng php phn loi mc n mn kh quyn (atmospheric corrosivity) theo tiu chun ISO c cp v ng dng nh gi mc n mn cho mt s vng kh hu Vit Nam; Cui cng bi bo trnh by vn tt mt s kt qu chnh v nghin cu n mn vt liu kim loi trong mi trng kh hu nhit i Vit Nam cng nh cc nghin cu ng dng trong lnh vc phn tch h hng vt liu cng nghip ang c thc hin ti Vin Khoa hc vt liu.

T kha: thi gian lu m b mt, tp cht/nhim bn kh quyn, mc n mn kh quyn.

1. GII THIU

Vt liu kim loi l loi vt liu d b ph hy bi hin tng n mn. n mn kim loi (AMKL) v s suy gim dn n ph hy vt liu l mt qu trnh t nhin, xy ra trong tt c cc mi trng. AMKL gy tn tht ln cho nn kinh t, c chng khong 15 % tng lng thp s dng trn th gii b ph hy do n mn. Vi hn 80 % lng kim loi, thit b, cng trnh c khai thc, s dng trong mi trng khng kh, thit hi kinh t do n mn v ph hy vt liu trong mi trng ny l mt con s khng l, c chng hng trm t USD/nm. V d tn tht n mn hng nm M l 300 t $ (1994), c 117 t DM (1994), Canada 10 t $ (1979), c 470 triu A$ (1973), Nht 3 triu $ (nhng nm 70), v.v [1, 2].

Qu trnh n mn khng ch gy tn tht v kinh t m cn cn gy nhim mi trng do cc sn phm n mn hoc cc vt liu bo v b ph hy v ra tri theo ma, b ha tan v ngm vo t, nc v.v, gy tc hi n mi trng sinh thi v sc khe con ngi. C th hnh dung nhng tn tht trn cc kha cnh khc nhau do qu trnh n mn gy nn qua s trn hnh 1.

Khng ch nh vy, s n mn hay suy gim vt liu cn dn n s hng hc, nt gy chi tit thit b, nh th lm cho sn xut phi ngng tr sa cha, thay th; trm trng th

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gy nn nhng s c/tai nn thm khc, gy tn hao v ngi v ca. Bng 1 thng k mt s s c/tai nn xy ra do qu trnh n mn.

Hnh 1. Tc hi ca qu trnh n mn

Bng 1. Mt s v d v cc tai nn do n mn v tc hi ca n i vi con ngi v mi trng

Nm Ni xy ra Tai nn Nguyn nhn Hu qu

1967 M Chm tu River Queen

n mn l y tu Chm tu

1970

Bin Bc Platform b sp Gy do n mn ng lc

Tn tht khng l v ngi v vt liu

Sng Ohio (M)

Sp cu Silver Bridge

Gy do n mn ng lc

46 sinh mng b cp i v tn tht nhiu t $

1985 Thy S Sp trn b tng 200 tn ca mt b bi trong nh

Gy n mn ng lc cc thanh thp khng g trn do ion clorua b r g

12 ngi cht v mt s b thng

1996 Mhic Chy v n Xng b d g t van ca tc cha 1300m3, bt la v gy n

4 ngi cht, 6 ngi b thng; 950 ngi phi chm sc v 10.000 ngi lin i phi thm vn. Phi mt 2 ngy mi khng ch c m chy

1997 Canada Trn 35.000 lit du trong mt

m

Mt ng dn du ca hng Mobil Oil b r g

Mi trng b nhim trn din rng

1997 Nga R g hn 1200 tn du

ng b v Hn 400 tn du trn xung sng Volga. Ngi ta phi xy dng mt ci p nhnh sng ngn chn s nhim tip tc.

Mt vt liu, nng lng

Tn tht kinh t

Tc ng n mi trng v

sc khe

Tn hao trc tip

Tn hao gin tip

Dng my Ht sn phm Gim nng sut Bn sn phm Qu ti

TN THT DO N MN V H HNG VT LIU

MT TIN

n mn v ph hu vt liu kim loi trong mi trng kh quyn nhit i Vit Nam

797

2. MT S KHI NIM C BN V N MN KIM LOI TRONG MI TRNG KH QUYN

2.1. nh ngha

n mn kim loi trong mi trng kh quyn (amospheric corrosion - sau y gi tt l n mn kh quyn - AMKQ) l s suy gim cc tnh nng hoc s ph hy vt liu kim loi di tc ng ca cc yu t mi trng kh quyn nh nhit , m, tp cht kh quyn, cc iu kin kh hu [3].

AMKQ l mt qu trnh t nhin, xy ra do s hnh thnh cc vi pin n mn trn b mt kim loi gia vng anot (c trng thi nng lng cao hn) v vng catot (c trng thi nng lng thp hn), v vy n mang bn cht in ha. Qu trnh AMKQ xy ra trn b mt kim loi di mt lp mng m hp ph hoc dung dch mng, khng ch c qu trnh chuyn khi trong phn ng ha hc m cn bao gm c qu trnh trao i ca cc ht mang in (electron v ion) b mt phn chia kim loi - dung dch in li.

Cn ch rng AMKQ c phn bit khc hn vi n mn kim loi xy ra trong mi trng nhit cao hon ton khng c hi m trn b mt kim loi (cn gi l n mn kh hoc n mn kh). V bn cht, n mn kh l n mn ha hc - khng c s trao i in tch.

Trong mi trng kh quyn sch, n mn xy ra ch yu do tc nhn oxy ha ca oxy khng kh. Tuy nhin, khi khng kh b nhim hoc trong kh quyn ven bin, tham gia vo qu trnh AMKQ khng ch c oxi m cn c cc yu t nhim bn hoc tp cht quyn, v d ion Cl- trong kh quyn bin/ven bin, cc kh nhim cng nghip nh SOx, NOx, bi, ma axit Cc tc nhn ny c tc dng gia tc qu trnh AMKQ v lm tng tc n mn ln n hng vi chc ln [3].

2.2. Cc giai on ca qu trnh n mn kim loi trong mi trng kh quyn

C th hnh dung qu trnh n mn trong mi trng kh quyn xy ra theo s trn hnh 2.

Hnh 2. S qu trnh n mn kim loi trong mi trng kh quyn

Giai on u: Hp ph m/nc v cc cht xm thc sa lng trn b mt kim loi, xy ra cc phn ng in ha vi cc tc nhn kh phn cc, s phn ng in hnh c biu din trn hnh 3 i vi trng hp n mn thp [1, 2].

Ti vng anot xy ra phn ng oxi ha - st b tan ra: 2Fe 2Fe2+ + 4e (1)

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Ti vng catot ch yu xy ra phn ng kh phn cc oxi: O2 + H2O + 4e 4OH - (2)

Trong cc vng cng nghip hoc thnh ph, khng kh b nhim, in hnh bi SOx, NOx.., cc tp kh ny sa lng trc tip xung b mt kim loi, hp ph/ha tan trong mng m, hoc to thnh ma axit, do b mt kim loi s b axit ha, to ra ion H+, v khi ti vng catot s xy ra c phn ng kh phn cc ca hydro:

2H+ + H2O + 2e H2 (kh) (3)

Hnh 3. S hp ph m v phn ng in ha c bn ca qu trnh n mn kim loi trong kh quyn

Giai on trung gian: trong giai on ny cc cht xm thc s b ha tan (nh SOx, NOx, H2S, CO2, NH3, NaCl, (NH4)2SO4, Na2SO4, NH4Cl), lm bin i tnh cht ha hc ca mng nc, gia tc s ha tan kim loi v hnh thnh cc mm ca sn phm n mn. V d trong mi trng kh quyn cng nghip, kh SO2 khi hp ph v ha tan trong mng m s to thnh mi trng axit, lm tng tc AMKL (hnh 4).

Giai on cui: tch t v pht trin sn phm n mn (hnh 5).

Hnh 4. Giai on trung gian - ha tan cc cht xm thc trong mng m

Hnh 5. Giai on tch t v pht trin sn phm n mn


799

3. CC YU T NH HNG N N MN KH QUYN KIM LOI TRONG MI TRNG KH HU NHIT I M

3.1. Ch nhit m [3 - 10]

3.1.1. Vai tr ca mng m

Nhiu nghin cu ch ra rng qu trnh AMKQ ch xy ra khi c mt lng m ti hn trn b mt kim loi to thnh mt mng m hp ph hoc mng m pha, trong khng kh sch, m ti hn ny tng ng vi m tng i ca khng kh l 80 %). di m ti hn, qu trnh n mn s khng xy ra (hoc vi tc khng ng k). Lp mng m trn b mt kim loi c th l mng m hp ph hoc mng nc nhn thy (ma, sng). Khi vt qua m ti hn, lp nc hp ph bt u tc dng nh mt lp in dch th tc n mn tng theo m. Mng m c vai tr dn in, ha tan cc cht xm thc t khng kh (mui bin, SOx, NOx, H2S), v vy s n mn thng xy ra vng b mt d b tch t m, cng l ni tp trung cc tc nhn gy n mn b ha tan.

3.1.2. Thi gian lu m b mt v m ca khng kh

Thi gian lu m (Time of Wetness - TOW) l mt khi nim c bn c s dng rt ph bin trong nghin cu AMKQ cc vt liu kim loi. TOW c tnh l thi gian m trn b mt kim loi tn ti mt mng dung dch in ly mng - t cho cc pin n mn hot ng v qu trnh AMKQ xy ra. Theo tiu chun ISO 9223, TOW c nh ngha l khong thi gian (tnh bng s gi) m khng kh c nhit > 0 oC v m tng i RH > 80 %, khi s ngng t bt u, chnh l iu kin qu trnh n mn xy ra ngay c trong kh quyn sch. Khi RH > 90 % v T < 25 oC c th quan st c m ngng t trn b mt kim loi. TOW c s dng nh mt thng s kh hu chnh gii thch cc nh hng n AMKL trong mi trng kh quyn. ng ch rng lp m hp ph (mng hn) to thnh bi nhng s ngng t m u tin s d dng bo ha oxi, do tc AMKL trong trng hp ny s ln hn (nguy him hn) so vi trng hp trn b mt kim loi to thnh mt mng nc mng RH cao hn.

Trn thc t, khi khng kh b nhim hoc trong khng kh bin th do s sa lng cc tp cht ht m trn b mt kim loi (v d SOx, NOx, NaCl, MgCl2, NH4(SO4)2, MgSO4 ) gi tr m ti hn ny s gim xung, khi n mn kim loi xy ra thm ch c khi m tng i ca khng kh ch khong 40 50 % [4].

Thi gian lu m c quan h cht ch vi nhit v m tng i ca khng kh, TOW tng t l thun vi RH, tuy nhin n ph thuc vo nhit theo hai chiu khc nhau, TOW tng theo nhit n khong 9 oC 10 oC, nhit cao hn, gi tr ca TOW gim do m tng i gim cng vi s tng nhit (hnh 6) [6].

So vi nhit th nh hng ca m tng i ca khng kh n TOW n gin hn, nhit > 0 oC s tng RH lm tng TOW, vng nhit m, RH khng nh hng n TOW (nh ch ra trn hnh 6c).

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Hnh 6. Quan h T- RH TOW. Cc vng kh hu nhit i m trong Vit Nam c c trng bi nhit cao (trung

bnh 20 30 0C), thay i nhit theo ma khng ln v m tng i ca khng kh 80 % chim 12 gi/ngy ko di lin tc khong 2 - 12 thng/nm [11], lng ma ln (trung bnh trn 1000 mm/nm) [12], cc yu t trn lm tng TOW v gia tc qu trnh n mn.

3.1.3. Nhit (T)

nh hng ca nhit n qu trnh n mn kim loi phc tp hn v khng n gin theo mt chiu. S tng nhit lm tng tc ca cc phn ng in ho v qu trnh khuch tn. Ngc li, nhit tng lm tng tc bay hi ca mng dung dch b mt, do lm gim TOW. S tng nhit cng lm gim s ho tan ca xy v cc loi kh n mn khc.

Khi nghin cu nh hng ca nhit n qu trnh AMKQ ca hu ht cc kim loi, Tidblad v cc ng nghip [9] thy rng tc n mn tng theo nhit vng nhit thp v gim theo nhit vng nhit cao (hnh 7). Theo , cc vng kh hu nhit i c thang nhit cao, nn nhit c tc dng gim tc n mn. Cc kt qu th nghim Cu Ba v Vit Nam cng chng t iu ny [13, 14]. Tuy nhin, khi th nghim di hn th nhit khng cn l yu t quyt nh i vi qu trnh AMKL trong kh quyn ngoi tri.

Hnh 7. S ph thuc ca tc n mn kim loi vo nhit khng kh.

3.2. nh hng ca ch ma [3, 4]

Ma gp phn to nn mng dung dch trn b mt kim loi, tuy nhin, s nh hng ca ma n AMKQ rt phc tp. Mt mt, nc ma ra tri cc cht xm thc l tc nhn gy n

a/

b/ c/


801

mn sa lng trn b mt kim loi di dng kh (dry deposition), do c tc dng lm gim ng k tc n mn, k c khi TOW tr nn di hn. Mt khc, ma axit li mang n b mt kim loi cc cc ion gy n mn di dng t (wet deposition) nh H+, SO42-, Cl-, ng thi, nc ma ra tri hoc ha tan sn phm n mn, lm gim tnh nng bo v ca lp sn phm trn b mt, do cc tc nhn n mn t mi trng d dng tip xc vi kim loi v tc n mn tng ln.

Ch ma c lin quan n nhng tc ng ni trn i vi AMKL trong kh quyn, v d, tng lng ma v tn sut ma nh hng n vic ra tri cc nhim bn, trong khi tc ma, cng ma c tc dng lm bong trc, ha tan cc sn phm n mn. Trong cc vng kh hu nhit i m c tn sut ma ln, thi gian ca mt trn ma ngn nhng tc v tng lng ma rt ln nn tc ng ra tri c th chim u th. iu ny c chng minh bi cc s liu nghin cu n mn thp cacbon Cu Ba, Digha (n ) v Vit Nam tc n mn t cc i trc khi c ma v gim ng k khi ma bt u [14, 15, 16].

Tc ng thc s (net effect) ca ma i vi AMKL hon ton ty thuc vo cc iu kin ca mi trng cng nh bn cht kim loi v tnh nng bo v ca lp sn phm n mn to thnh trn b mt kim loi . Nhiu kt qu nghin cu cho thy rng trong nhng vng khng kh b nhim bn nng th tc AMKL trong kh quyn di mi che (sheltered) thng ln hn so vi tc AMKL trong kh quyn khng c mi che (un-sheltered). Ngc li, trong cc iu kin kh quyn t nhim hn, tc AMKL trong iu kin ngoi tri lun ln hn so vi iu kin di mi che [3]. Khi hnh thnh mt lp sn phm dy, c chc, bm dnh tt vo nn (th nghim di hn), nh hng ca ma s khng chim u th nh i vi kim loi mi b n mn c lp sn phm to thnh cn kh mng.

3.3. nh hng ca nhim bn kh quyn [3, 4]

C rt nhiu loi tp cht kh quyn (hn 2000 cht) c tn ti di dng kh hoc di dng cc ht rn/lng nh li ti, l lng trong khng kh (son kh - air-borne), tuy nhin ch c tm cht/cp cht ch yu c nh hng ng k n qu trnh AMKL (bng 2), trong s , NOx, SOx v ion Cl- c bit n l nhng tp cht ph bin nht gia tc AMKQ cc kim loi. C th gii thch tm tt cc nh hng ca chng nh di y.

Bng 2. nhy ca cc kim loi i vi cc tp cht gy n mn [3]

Cc cht gy n mn Ag Al

ng thau

ng thic Cu Fe Ni Pb Sn Thp Km

CO2/CO32- L L M L M M M NH3/NH4+ M L L L M L L L L L L

NO2/NO3 - N L M M M M M M L M M L

H2S H L M M H L L L L L L SO2/SO42- L M H H H H H M L H H H HCl/Cl- M H M M M H M M M H M L

RCOOH/COOH L L M M M M M H L M M

O3 M N M M M M M M L M M M

Ghi ch: H: rt nhy, M: trung bnh, L: yu, N: khng tc dng.

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3.3.1. Kh NOx, SOx [3, 4]

Cc kh SOx v NOx l nhng kh thi cng nghip ch yu gy AMKQ. Kh SO2 c hnh thnh khi t chy cc nhin liu c cha lu hunh, hoc do qu trnh luyn kim t cc qung cha lu hunh, SO2 ho tan trong mng m, b oxi ha, to nn mi trng axit (pH < 4,5) v gia tc qu trnh AMKL:

SO2(k) SO2(ngm nc) SO42- (4) SO2(k) + OH- HSO3- H2SO4. (5)

Trn thc t, mt s kim loi nh nhm/hp kim nhm v km kh bn trong mi trng trung tnh (pH = 6 - 7,5) nhng chng b n mn rt nhanh trong mi trng axit [4].

ioxit nit (NO2) c sinh ra ch yu l do s chy nhit cao, khi xit nit (NO) nhanh chng b xy ho bi zn v to thnh NO2. Nit ioxit hon ton khng tan trong nc, ch c mt phn nh phn ng trong pha kh vi gc hyrxyl v to thnh axit nitric (HNO3), axit ny tan rt tt trong nc v l tc nhn gy n mn.

3.3.2. nh hng ca ion clorua Cl- - n mn v ph hy vt liu trong mi trng bin [3, 4]

Ion Cl- tn ti di dng cc ht rn hoc lng nh li ti, l lng trong khng kh, thng gp trong kh quyn bin/ven bin hoc vng cng nghip xung quanh cc nh my sn xut axit clohydric hoc natri hypoclorua.

Trong kh quyn bin/ven bin, ion Cl- l tc nhn ch yu gy n mn, v vy nguy c h hng cc chi tit thit b v cng trnh cao hn nhiu ln so vi trong t lin v d xy ra cc tai nn ri ro. Ion Cl- l mt tc nhn nguy him i vi cc vt liu kim loi, n gia tc AMKL v l tc nhn gy n mn l. Hn na, cc ion Cl- c kh nng ht m tt, gp phn hnh thnh dung dch in ly trn b mt kim loi v ko di TOW ngay c khi khng kh c nhit cao. Ion Cl- cng lm tng dn in ca lp m/dung dch trn b mt kim loi, ph hu lp mng bo v, do lm tng tc n mn. Bn cnh , s c mt ca ion Cl- s lm tng nguy c v tc n mn ng lc ca cc chi tit, kt cu kim loi, c bit l cc kt cu lm bng thp khng g.

S sa lng ca ion Cl- c quyt nh bi v tr a l, iu kin a hnh v khong cch t b bin, cng nh tc v hng gi. Cc vng kh quyn bin nhit i thng c tc n mn cc i, tc n mn lun cao hn trong cc vng kh quyn bin n i v cc vng kh quyn thnh ph/cng nghip nhit i.

Mt s v d di y cc so snh tc n mn trong mi trng bin v t lin. Cc s liu iu tra n mn thp cacbon bi bin Kure Beach (M) cho thy tc n mn v tr cch mp nc 250 m l 0,143 mm/nm, nhng khi cch mp nc ch 25 m th tc n mn tng c 3,7 ln, t 0,53 mm/nm. Mt s liu khc cng cho thy tc n mn ca cc loi thp trong kh quyn bin gp t 1,3 n 1,5 thm ch 7,5 ln so vi tc n mn trong kh quyn t lin ca cng loi vt liu [17, 3]. Cc s liu nghin cu Vit Nam cng cho thy: tc n mn thp cacbon cc trm ven bin u ln gp 1,2 n 1,9 ln so vi cc trm trong t lin (bng 3) [17].


803

Bng 3. Tc n mn thp cacbon ti mt s a im ca Vit Nam [17]

Thi k Kh quyn ven bin Kh quyn trong t lin

Trm TN Tc n mn, g/m2.nm

Trm TN Tc n mn, g/m2.nm

1995-1996 Sn 280-290 H Ni 240

1995-1996 Nha Trang 254 TP. HCM 192

2010-2011 ng Hi 379 H ni 204

3.3.3. Cc tp cht khc [4, 5]

Mt s tp kh khc nh kh cacbonic (CO2), ozone (O3), amoniac (NH3), sunfua hydro (H2S) v clorua hydro (HCl) cng nh cc axit hu c nh axit formic (HCOOH) v axit axetic (CH3COOH), u c hot tnh n mn i vi hu ht cc vt liu kim loi. Sau khi sa lng xung b mt kim loi v b ha tan trong mng m chng s to thnh cc ion nh H+, Cl-, COOH-, CH3COO- lm tng dn in v gia tc qu trnh AMKL. Ngoi ra, hu ht cc ht xon kh hp th nc u lm tng gi tr TOW.

3.4. c im n mn v ph hy vt liu trong mi trng nhit i [3, 18]

Mi trng nhit i gy n mn v ph hy vt liu mnh hn nhiu ln so vi cc vng kh hu n i v nhng nguyn nhn sau y: - m cao, lng ma ln to nn thi gian lu m di, lm cho qu trnh n mn d dng xy

ra v xy ra vi tc ln. - Mt khc, cc vng nhit i quanh nm nhn c lng nhit mt tri rt ln, bnh qun

1 triu Kcal/m2nm, s gi nng trong nm t 1400 - 3000 gi. Cc yu t ny lm suy gim v ph hy nhanh chng cc loi vt liu polymer, cc lp sn hu c, cc loi vt liu xi mng, b tng, v.vT cc phn tch trn, c th thy rng cc vng kh hu nhit i gy n mn v ph hy vt liu mnh hn nhiu ln so vi cc vng kh hu n i.

- Theo cc s liu iu tra trn th gii, tc n mn trong cc vng nhit i ln hn nhiu so vi trong cc vng kh hu hai cc, tc n mn ca cc loi thp Panama (vng nhit i) ln hn tc n mn ca cng loi vt liu ti Kure Beach, M (vng n i) t 1,2 n 2,5 ln [3].

- So snh s liu nhn c t cc chng trnh th nghim n mn trn phm vi th gii Tidblad v cc ng nghip [18] nhn thy rng: so vi kh hu n i th cc vng kh hu bin nhit i c tc n mn thp v km ln gp 10 - 20 ln; cc vng kh hu xa bin c tc n mn thp ln gp 4 - 5 ln, tc n mn ng v km ln gp 2 - 3 ln.

4. MT S DNG H HNG VT LIU DO N MN THNG GP TRONG MI TRNG KH QUYN

C hai dng n mn ch yu xy ra trong mi trng kh quyn: n mn u (uniform corrosion) v n mn khng ng u (un-uniform corrosion) hay cn gi l n mn cc b (localized corrosion) [3, 4, 19 - 22].

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4.1. n mn u n mn u c tc tng t nhau trn khp b mt kim loi, y l dng n mn in

hnh i vi thp v ng trong kh quyn (hnh 8). Tc n mn u c xc nh bng phng php tn hao khi lng, tnh bng g/m2 hoc m.

Hnh 8. nh b mt v mt ct ngang ca kim loi b n mn u

4.2. n mn cc b

n mn cc b xy ra nhng v tr c bit trn mt din tch nh, ti qu trnh n mn c gia tc. n mn cc b thng hay gp i vi cc chi tit thit b, kt cu, cng trnh cng nghip v dn dng. C th k n nhng dng n mn cc b in hnh sau y. 4.2.1. n mn l (pitting corrosion)

n mn l l dng n mn cc b in hnh nht, thng gp i vi cc kim loi c kh nng th ng nh nhm/hp kim nhm, thp khng g, niken, Qu trnh n mn l xy ra khi mng th ng b ph hy v mt l do no (do mi trng xm thc hoc ph hy c hc, khi vng b mt kim loi ti mi (c in th m hn so vi vng kim loi b th ng xung quanh) s l anot v b n mn, do din tch vng anot rt nh so vi vng catot nn mt dng anot (tc ha tan kim loi) tr nn rt ln v kim loi b khot su nh trn hnh 9). n mn l cng xy ra khi lp ph dng in hn nn (vng/ng) b khuyt tt (hnh 10).

Tc nhn gy n mn l thng gp nht l ion Cl-, do vai tr ph mng th ng ca n, v d trong mi trng kh quyn bin/ven bin. Dng n mn l rt nguy him v lng tn hao kim loi khng ng k nhng cc l n su trong lng vt liu s dn n nt gy chi tit mt cch t ngt, khng lng trc c.

Hnh 9. Phn ng n mn l v cc dng mt ct khc nhau


805

Hnh 10. n mn l trn b mt l hng do lp m khng hon thin (c nhiu l chm kim) to nn chnh lch in th gia lp m vng v nn ng

4.2.2. n mn la chn (selective corrosion)

Hai dng n mn la chn in hnh nht, lm suy gim v h hng vt liu l n mn kh km (dezincification) v n mn graphit (graphitization corrosion). n mn kh km thng gp vi ng thau hoc cc loi hp kim ng-km cha >15 % km, xy ra khi c mt hi m v oxi. Khi , c ng v km u tan vo dung dch nhng ng kt ta li, cn km li trong dung dch, vt liu cn li tr nn xp, giu ng, c tnh gim v chuyn mu t vng thau sang (hnh 11a). n mn graphit xy ra vi gang xm khi st b tit ra v cn li nguyn vn ht graphit (hnh 11b). H hng do n mn la chn rt nguy him v n lm gim c tnh ca vt liu, dn n nt gy chi tit, cu kin, cng trnh.

a/ b/

Hnh 11. n mn la chn hp kim Cu-Zn (a) v s tit graphit t gang xm (b)

4.2.3. n mn bin ht (intergranular corrosion)

Mt s kim loi v hp kim rt nhy vi s tn cng cc b trn bin ht dng ny c gi l n mn bin ht hay n mn tinh gii (hnh 12), xy ra do s ha tan la chn ca nhng pha khc nhau dc theo bin ht. Dng h hng ny thng gp trong cng nghip m in hnh l n mn tinh gii i vi thp khng g - n mn xy ra ti pha cacbit trn bin ht, v n mn tch lp (exforliation corrosion) i vi hp kim nhm (hnh 13). S trng n kim loi do n

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mn tch lp c th to ra ng sut, lm cong hoc b gy mi ni v dn n h hng kt cu. n mn tinh gii rt nguy him v rt kh pht hin sm do s tn hao vt liu cha ng k, nhng bin ht b yu dn, lm cho c tnh ca vt liu b suy gim, dn n sp, gy cng trnh t ngt.

Hnh 12. Hnh nh mt ct ngang ca n mn bin ht

Hnh 13. n mn tch lp ca hp kim nhm

4.2.4. n mn tip xc (galvanic corrosion)

Tc n mn cng tng ln v gy n mn cc b khi hai kim loi tip xc trc tip vi nhau, dng ny c gi l n mn tip xc, khi kim loi m in hn s b n mn. Mt v d v n mn tip xc thng gp trong thc t l s ph hy cc tm tn hnh ln sng khi nn thp b h, din tch ny s rng hn khi lp ph km b n mn do c in th m hn thp v nn thp bn di tip tc b ph hy.

Mt v d rt l th l khi bo dng nh k Tng N Thn T Do vo nm 1980 pht hin n mn tip xc xy ra gia lp da bng ng v ct bng st c (hnh 14).

Hnh 14. n mn tip xc trn Tng N Thn T do


807

4.2.5. n mn khe (crevice corrosion)

Mt dng n mn cc b xy ra rt mnh lit trong cc khe rt hp do cu to hnh hc ca kt cu hoc do lp rp, v d, cc mi ni bng inh tn riv hoc bulong, gia bulong v ming m, trong rnh ca cc inh vt, v.v (hnh 15a). n mn khe xy ra do s chnh lch nng cht kh phn cc catot /oxy b mt kim loi bn ngoi khe (nhiu hn) v bn trong khe (t hn). B mt kim loi bn trong khe l anot so vi xung quanh v b n mn (hinh 15b).

a/ b/

Hnh 15. n mn khe

4.2.6. n mn ng lc (stress corrosion cracking SCC)

Gy do n mn ng lc l mt dng h hng nguy him v tng i ph bin i vi cc chi tit thit b cng nghip, c bit l trong cng nghip ha cht, ch bin du kh, nhit in, nng lng ht nhn, v.v... Dng h hng ny rt nguy him, v n xy ra m bn trong v lm gim ng k bn c hc ca kim loi, mc d lng kim loi tn hao rt t. n mn ng lc xy ra do tc ng ng thi ca ng sut ko v mi trng n mn i vi vt liu nhy SCC. ng lc tn ti c th do chi tit phi chu ti, do ng sut d li trong qu trnh ch to hoc kt hp c hai dng ny. C ch n mn ng lc l nt theo bin ht hoc xuyn ht, vt nt lan truyn theo hnh nhnh cy (hnh 16), v vy vt liu b yu i rt nhanh, dn n gy, sp t ngt cc kt cu. Cc loi thp khng g austenite thng b n mn ng lc trong kh quyn bin di s tc ng ca ion Cl-.

Hnh 16. Mt ct ngang ca thp khng g 316 L b n mn ng lc, vt nt hnh nhnh cy v lan truyn theo bin ht

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5. PHN LOI MC N MN KH QUYN S phn loi mc n mn ca kh quyn (atmospheric corrosivity) rt cn thit cho vic

la chn vt liu v phng php chng n mn thch hp i vi tng vng kh hu, cng nh a ra mt ch bo dng thch hp, m bo tui th yu cu ca cc cng trnh khai thc trong mi trng kh quyn.

Bng 4. Phn loi cc thng s mi trng TOW, Cl- v SO2 theo ISO 9223

Thi gian lu m (TOW), h/nm Tc sa lng ca ion Cl-, mg/m2. ngy

Tc sa lng ca SO2, mg/m2. ngy

Gi tr Phn loi Gi tr Phn loi Gi tr Phn loi TOW 10 T1 Cl 3 S0 SO2 10 P0

10 < TOW 250 T2 4 < Cl 60 S1 11 < SO2 35 P1 250 < TOW 2500 T3 61 < Cl 300 S2 36 < SO2 80 P2 2500 < TOW 5500 T4 301 < Cl 1,500 S3 81 < SO2 200 P3

5500 < TOW T5

Bng 5. Phn loi mc AMKQ da trn cc thng s mi trng theo ISO 9223

TOW = T1 TOW = T2 TOW = T3 Cl- SO2 Thp ng/Km Nhm Cl- SO2 Thp ng/Km Nhm Cl- SO2 Thp ng/Km Nhm S0 S1

P1 C1 C1 C1 S0 S1

P1 C1 C1 C1 S0 S1

P1 C2-3 C3 C3

.. P2 C1 C1 C1 .. P2 C1-2 C1-2 C1-2 .. P2 C3-4 C3 C3

.. P3 C1-2 C1 C1 .. P3 C2 C2 C3-4 .. P3 C4 C3 C3-4 S2 P1 C1 C1 C2 S2 P1 C2 C1-2 C2-3 S2 P1 C3-4 C3 C3-4 .. P2 C1 C1 C2 .. P2 C2-3 C2 C3-4 .. P2 C3-4 C3-4 C4 .. P3 C1-2 C1-2 C2-3 .. P3 C3 C3 C4 .. P3 C4-5 C3-4 C4-5 S3 P1 C1-2 C1 C2 S3 P1 C3-4 C3 C4 S3 P1 C4 C3-4 C4 .. P2 C1-2 C1-2 C2-3 .. P2 C3-4 C3 C4 .. P2 C4-5 C4 C4-5 .. P3 C2 C2 C3 .. P3 C4 C3-4 C4 .. P3 C5 C4 C5

TOW = T4 TOW = T5

Cl- SO2 Thp ng/Km Nhm Cl- SO2 Thp ng/Km Nhm S0/S1 P1 C3 C3 C3 S0/S1 P1 C3-4 C3-4 C4

.. P2 C4 C3-4 C3-4 .. P2 C4-5 C4-5 C4-5

.. P3 C5 C4-5 C4-5 .. P3 C5 C5 C5 S2 P1 C4 C4 C3-4 S2 P1 C5 C5 C5 .. P2 C4 C4 C4 .. P2 C5 C5 C5 .. P3 C5 C5 C5 .. P3 C5 C5 C5 S3 P1 C5 C5 C5 S3 P1 C5 C5 C5 .. P2 C5 C5 C5 .. P2 C5 C5 C5 .. P3 C5 C5 C5 .. P3 C5 C5 C5


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Bng 6. Phn loi theo ISO 9223 mc n mn kh quyn i vi cc kim loi da trn tc n mn trong nm u tin, CR tc n mn, mg/m2

Phn loi Thep cacbon ng Nhm Km C1 CR 10 CR 0.9 negligible CR 0.7

C2 10 < CR 200 0.9 < CR 5 CR 0.6 0.7 < CR 5

C3 200 < CR 400 5 < CR 12 0.6 < CR 2 5 < CR 15

C4 400 < CR 650 12 < CR 25 2 < CR 5 15 < CR 30

C5 650 < CR 25 < CR 5 < CR 30 < CR

Da trn cc s liu ca mt chng trnh th nghim ln bao gm nhiu nc chu u v chu M tham gia, t chc ISO thit lp tiu chun v phn loi mc n mn ca tng vng kh quyn - ISO 9223. Theo , mc n mn ca mt vng kh quyn c th xc nh bng hai cch: (1) Phn loi cc cc gi tr ca TOW, tc sa lng ca ion Cl- v kh SO2 (bng 4), sau phn loi mc n mn theo bng 5 i vi tng kim loi; (2) Da trn gi tr thc ca tc n mn c xc nh bng cch th nghim mu tiu chun trong thi gian mt nm. Tc sa lng ca Cl- v SO2 c xc inh theo cc phng php trnh by trong tiu chun ISO 9225 [23], tc n mn thc t c xc nh bng phng php tn hao khi lng theo ISO 9226 [24], s dng cc phng php th nghim theo ISO 8565 [25] v ty sn phm n mn theo ISO 8407 [26].

Tiu chun ISO 9223 c s dng rng ri v rt hu ch nh gi mc n mn ca tng vng kh quyn i vi 4 loi vt liu kim loi k thut chnh. Tuy nhin s phn loi theo ISO 9223 cn c nhng im hn ch nh ch cp n hai yu t nhim bn chnh l SO2 v ion Cl- m khng c s tham gia ca cc yu t nhim bn khc (NOx, kh clo, ma axit, mui kh ng bng, v.v). c bit, do cn thiu cc s liu trong vng nhit i v chu , nn tiu chun ISO 9223 cha thc s ph hp khi s dng cho vng nhit i m, c trng bi nhit v m rt cao, c lng ma ln, cc yu t dn n s vt thang gi tr TOW cng nh tc n mn (theo quy nh ca ISO 9223). Trong khi , nhng vng kh hu lnh, trn thc t qu trnh n mn vn xy ra di 0 oC do c mt mui n dng lm tan bng, v.v Cn ch l ISO 9223 ch p dng cho trng hp n mn u m cha cp n nhng dng n mn cc b khc.

6. C IM KH HU NHIT I M VIT NAM TC NG N N MN VT LIU KIM LOI

Nc ta nm trong vng kh hu nhit i gi ma, c nhit v m tng i trung bnh ca khng kh quanh nm cao, tng lng ma ln, lm cho thi gian lu m b mt TOW c gi tr rt ln. Mt mt t nc hng ra bin vi mt b bin di hn 3000 km, v vy trong t lin cng nh cc vng ven bin, nguy c vt liu kim loi b ph hy lun tim n, mc d cng nghip Vit nam cha pht trin mnh nh chu u trong nhng thp nin by mi. Mt s c im kh hu Vit Nam c nh hng n AMKQ c trnh by di y.

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6.1. Nhit khng kh

Vit Nam c nn nhit cao quanh nm, nhit trung bnh tng dn khi i t Bc vo Nam. min Bc c ma ng lnh vi s khc nhau ng k v nhit trung bnh gia ma h v ma ng (17 30 oC). Trong khi min Nam ch c hai ma: ma kh v ma ma vi nhit trung bnh 25 30 oC. khu vc min Trung, nhit trung bnh l 22 30 oC. Khu vc ni cao c nhit thp hn vng ng bng v trung du. Nh vy nn nhit cao l mt yu t thun li gia tc qu trnh n mn, tuy nhin nhit cao cng s gp phn lm gim TOW trn b mt kim loi nh phn tch phn 3.1.2.

6.2. m tng i

L mt t nc hp, pha ng hng ra bin, pha Ty b chn bi vng cung Ngn Sn pha Bc v dy Trng Sn min Trung, nn nc ta c m tng i ca khng kh rt cao, trung bnh 78 87 %, m tng i gim dn t Bc vo Nam, cc vng ni cao m c khi t ti 85 87 %. m cao gp phn lm t b mt kim loi v lm cho n mn d dng xy ra.

6.3. Tng lng ma

Do nh hng ca kh hu gi ma nn tng lng ma nc ta rt ln, trung bnh 10003000 mm/nm; Tuy nhin c mt vi vng c lng ma ln hn nh cc nh Bc Quang, Bch M - c tng lng ma trung bnh nm ti 5000 mm), trong khi , Phan Rang v Phan Thit li rt kh, tng lng ma ch t 1000mm/nm. Mc d ma t th lng ma Phan Rang, Phan Thit vn cn cao hn lng ma Stockholm, Thy in (700 mm/nm). Lng ma ln l mt c trng kh hu nhit i gi ma khc hn vi vng n i, y cng l mt yu t gp phn tng m khng kh v gia tc n mn.

6.4. Thi gian lu m TOW

Cc c trng kh hu nhit i ni trn to nn thi gian lu m b mt rt di quanh nm nc ta vi gi tr TOW trung bnh l 4000 - 6000 h/nm, tng ng vi khong 45 75 % thi gian ca nm, iu ny c ngha l 45 75 % thi gian ca nm khng kh c RH > 80 % vi T > 0o, trong khong thi gian qu trnh AMKQ lun xy ra.

Da trn cc s liu thng k hn 100 trm kh tng trong chu k 10 nm, mi quan h gia TOW vi nhit v m tng i c thit lp cho cc vng kh hu Vit Nam. Do nn nhit trung bnh quanh nm cao, khng c nhit m nn TOW lun bin thin gim theo chiu tng ca nhit .

TOW = -14,09T + 228,6RH 13050 (6) Phng trnh (6) rt thun tin tnh TOW thng qua T v RH - l nhng thng s lun sn c t cc trm kh tng. Phng trnh ny cng c s dng tnh TOW cho cc a im khng xc nh gi tr TOW theo phng php thng k, t mt bn phn b TOW theo cc phn loi ca ISO 9223 c xy dng cho cc vng trn c nc (hnh 17a). ng ch l thi gian lu m ca tt c cc vng kh hu ca nc ta u rt cao, chim mc T4 v T5 (cao nht) theo phn loi ca ISO 9223.


811

Hnh 17. Phn loi TOW (a) v mc nhim kh quyn do SO2 v ion Cl- (b) theo ISO 9223

6.5. Cc tp cht kh quyn - tc sa lng ion Cl- v SO2

mui kh quyn (tc sa lng ion Cl-) c xc nh ti 13 a im bng phng php nn m, tc sa lng ca SO2 c xc dnh bng phng php giy kim theo ISO 9225. Cc kt qu c nu trong bng 7 v hnh 17b.

6.6. Phn loi mc n mn kh quyn

Bng 7. Cc thng s kh hu, mi trng v phn loi theo ISO

TT Trm th nghim TOW Cl- SO2

gi/nm Phn loi theo ISO mg/m2. ngy

Phn loi theo ISO

mg/m2 ngy

Phn loi theo ISO

1. in Bin 5873 T5 1,16 S0

2. Vit Tr 5967 T5 1,88 S0 6,67 P0

3. Sn Ty 6007 T5 1,50 S0 7,92 P0

4. Sn 6352 T5 17,51 S1 2,80 P0

5. Hi Dng 6226 T5 6,89 S1 6,01 P0

b) a)

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Da theo phng php ca ISO 9223, s phn loi mc n mn i vi mt s vng kh hu Vit nam c thc hin trn c s cc s liu TOW, tc sa lng ca ion Cl- v kh SO2 (bng 5). Do thi gian lu m ca tt c cc vng kh hu ca nc ta u rt cao, chim mc T4 v T5, khin cho mc n mn ca cc vng kh hu Vit Nam t mc kh cao - C3 v C4 i vi tt c cc vt liu kim loi (bng 8), mc d mui kh quyn v hm lng SO2 ch mi mc thp nht - S0-1v P1 (bng 7).

Bng 8. Phn loi theo ISO mc n mn cc kim loi i vi mt s vng kh quyn Vit Nam, s dng cc thng s kh hu v nhim bn khng kh

6. H Ni 4917 T4 2,24 S0 7,95 P0

7. Thanh Ha 6158 T5 3,48 S1 3,90 P0

8. ng Hi 1 5604 T5 10,28 S1 2,49 P0

9. ng Hi 2(*) 40,10 S1

10. Hu 6001 T5 1,33 S0 0,98 P0

11. Nng 5702 T5 4,99 S1 3,83 P0

12. Nha Trang 4878 T4 15,64 S1 1,34 P0

13. Tp. HCM 4612 T4 4,58 S1 12,63 P1

14. Vng Tu 4400 T4 12,16 S1 3,23 P0

15. My Tho 5543 T5

TT Trm th nghim

Phn loi theo ISO Phn loi mc AMKQ theo ISO TOW Cl- SO2 Thp Km ng Nhm

1. in Bin T5 S0 C3 C3-4 C3-4 C4

2. Vit Tr T5 S0 P0 C3 C3-4 C3-4 C4

3. Sn Ty T5 S0 P0 C3 C3-4 C3-4 C4

4. Sn T5 S1 P0 C3 C3-4 C3-4 C4

5. Hi Dng T5 S1 P0 C3 C3-4 C3-4 C4

6. H Ni T4 S0 P0 C3 C3 C3 C3

7. Thanh Ha T5 S1 P0 C3 C3-4 C3-4 C4

8. ng Hi 1 T5 S1 P0 C3 C3-4 C3-4 C4


813

7. MT S KT QU NGHIN CU N MN VT LIU KIM LOI TRONG MI TRNG NHIT I M VIT NAM T 1995 N NAY

T nm 1995 cng tc nghin cu n mn vt kim loi c thc hin v duy tr lin tc ti Vin Khoa hc vt liu, Vin KH&CN Vit Nam. Mt s kt qu tm tt c gii thiu di y.

7.1. n mn thp cacbon

Thp cacbon l vt liu kt cu c s dng ph bin nht trong mi trng kh quyn ngoi tri,v th vt liu ny c quan tm nghin cu v bn n mn ca n trong mi trng kh quyn. Trong giai on t 1995 n nay, thp cacbon c th nghim qua nhiu thi k ti 15 a im i din cho cc vng kh hu khc nhau trn khp c nc. T cc kt qu c trnh by trong bng 9 c th thy rng tc n mn thp cacbon khc nhau ph thuc vo c im kh hu v mi trng tng vng, tuy nhin xt v s phn loi theo ISO th tt c cc vng kh hu u c mc n mn ca kh quyn i vi thp cacbon l C3.

9. ng Hi 2(*) S1 C3 C3-4 C3-4 C4

10. Hu T5 S0 P0 C3 C3-4 C3-4 C4

11. Nng T5 S1 P0 C3 C3-4 C3-4 C4

12. Nha Trang T4 S1 P0 C3 C3 C3 C3

13. Tp. HCM T4 S1 P1 C3 C3 C3 C3

14. Vng Tu T4 S1 P0 C3 C3 C3 C3

15. My Tho T5

Hnh 18. V tr cc trm th nghim (*): ng Hi (1) cch xa bin, ng Hi (2)

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Bng 9. Tc n mn thp cacbon sau nm u th nghim v phn loi theo ISO

Trn c s x l hi quy tuyn tnh cc s liu v tc n mn v cc thng s kh hu/mi trng c lin quan, mt m hnh d bo tc n mn trong nm u v cc thng s mi trng c thit lp, b qua s nh hng ca hm lng SO2 v n rt nh (


815

Bng 10. Tn hao n mn cc lp ph km th nghim trong nm u v phn loi theo ISO.

Trm th nghim

Km nhng nng Km phun K Phn

loi ISO K Phn loi

ISO H Ni 10,858 C3 31,180 C4 Sn 18,387 C4 31,828 C4 Nng 22,300 C4 35,581 C4

Nha Trang 36,262 C4 39,468 C4 Tp. HCM 16,129 C4 38,730 C4 Vng Tu 20,97 C4 30,645 C4

7.3. n mn ng

Cc mu ng kim loi k thut c th nghim ti 6 trm ni trn, ngoi ra cc s liu cn c b sung thm bi chng trnh RAPIDC(*) cho trm H Ni, TP. HCM v M Tho (tnh Tin Giang). Cc kt qu v tc n mn ng sau nm u th nghim trnh by trong bng 11. i vi ng, mc n mn ca cc vng kh quyn th nghim l kh cao, tng ng vi C3 v C4 (bng 11).

Bng 11. Tn hao n mn ng trong nm u th nghim.

Trm th nghim

Tn hao n mn, g/m2

Phn loi ISO

Trm th nghim

Tn hao n mn, g/m2

Phn loi ISO

H Ni 6.950 C3 TP. HCM 7.000 C3 H Ni * 5.385 C3 TP. HCM * 8.000 C3 Sn 27.970 C4 Vng tau 33.850 C4 Nng 17.040 C4 Tin Giang* 12.065 C4

(*) S liu th nghim theo chng trnh RAPIDC (2002-2006): Region Air Pollution in Developping Countries Program

7.5. Cc nghin cu ang tip tc hin nay

Lng kim loi s dng trong na th k ti c d bo l tng khong gp ba ln so vi hin nay, cng vi s tng ca cc ngun nhim cng nghip th tc n mn v tn hao do vt liu kim loi b ph hy cng s tng gp bi. T.E. Graedel v C. Leygraf [28] tnh ton d bo n mn s dng cc m hnh cho 13 vng kh hu in hnh trn th gii, cc kt qu cho thy s n mn v ph hy vt liu kim loi s xy ra nghim trng, vi tc nhanh hn nhng vng km pht trin, c bit l khu vc chu , chu Phi, khu vc Trung ng. V vy vic nghin cu nm vng quy lut ca qu trnh AMKQ nhm d bo nguy c, kim sot v gim thiu h hng do n mn kim loi khng ch l mt lnh vc khoa hc nghin cu/iu tra c bn m cn mang tnh ng dng su sc. Cc nghin cu ng dng v n mn kim loi v ph hy vt liu trong mi trng kh quyn, c bit l trong mi trng cng nghip ang c ch trng thc hin ti Vin Khoa hc vt liu bao gm:

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- Cc nghin cu v n mn thp bn kh quyn (thp Corten) v kh nng hnh thnh lp sn phm c tnh nng km hm n mn c bt u t nm 2010 v hin ang tip tc. Cc mu c th nghim ti H Ni, ng Hi, Phan Rang v TP. HCM. Mt s kt qu bc u c cng b ti Hi ngh n mn th gii t chc ti Perth, Australia thng 11/2011[29].

- Mt chng trnh th nghim n mn i vi thp, thp bn kh quyn, lp km nhng nng v lp Zn-Al55 s c thc hin trong giai on 2013-2015 trn c s hp tc vi Nht Bn v Thi Lan Corrosion Mapping of some Structural Metals in atmosphere with Understanding Effects of Environmental Factors. Chng trnh c thc hin nhm xy dng bn n mn cho tng nc v khu vc chu , cc s liu th nghim cng c s dng iu chnh cc tiu chun ISO v phn loi mc n mn kh quyn ph hp vi khu vc chu .

8. PHN TCH H HNG VT LIU nh gi h hng vt liu kim loi, trn th gii pht trin mt chuyn ngnh k thut,

gi l Phn tch h hng chi tit thit b (sau y gi tt l phn tch h hng PTHH). Lnh vc ny c nghin cu v ng dng c bit ph bin nhng nc cng nghip pht trin. Tuy nhin, Vit Nam, PTHH l mt lnh vc cn kh mi m k c trong nghin cu v ng dng. T nm 2005, di s h tr ca d n k thut do CHLB c ti tr, Vin Khoa hc vt liu (Vin KHVL) xy dng Trung tm nh gi h hng vt liu (Center of Material and Failure Analysis COMFA/IMS) nhm h tr cc doanh nghip cng nghip Vit Nam nng cao hiu qu sn xut thng qua vic kim sot cht lng vt liu, tm nguyn nhn gy h hng/ph phm, ngn nga h hng lp li [30, 31].

8.1. Khi nim v h hng

Chi tit my c xem l b h hng khi khng cn kh nng hot ng tin cy v an ton theo cc chc nng c thit k. H hng khng nht thit l gy hay s c trm trng, nhiu h hng lin quan ti s suy gim tnh cht lm vic ca chi tit m bng mt thng khng thy c nh c tnh, cu trc tinh th, t chc t vi vt liu, khuyt tt bn trong chi tit

H hng lin quan n nhiu nguyn nhn, trong ch yu l: - Li vt liu (thnh phn, cu trc, s dng vt liu khng ng chng loi); - Li thit k (proifile, gc, mi ni); - Khng tun th quy trnh vn hnh, bo dng, kim tra; - Hot ng qu ti; - Tc ng ca mi trng lm vic, nht l mi trng kh quyn nng m

T l h hng theo cc nguyn nhn khc nhau c trnh by trong hnh 19. Cc dng h hng ch yu bao gm:

- Gy do ng lc, do mi, do khuyt tt, do n mn bn trong vt liu chi tit; - Bin dng chi tit thit b, khng cn kh nng hot ng vi cc thng s thit k, lu ngy

dn n s ph hy chi tit;


817

- n mn, mi mn do tc ng ca mi trng xm thc cng vi s chu ti ng dn n nt v gy chi tit thit b;

- Cc dng ny c th kt hp v tng tc vi nhau, gy nn s h hng ca mt chi tit thit b.

T l cc dng h hng khc nhau c trnh by trn hnh 20

Mc tiu v nhim v ca cng tc phn tch h hng l nhm: - Tm nguyn nhn gy h hng chi tit thit b, t vn gii php khc phc, loi b hoc

gim thiu ti a h hng lp li trong cc chu k vn hnh tip theo; - Tch cc hn: kim tra, theo di nh k bn v cc tnh nng hot ng ca cc chi tit

thit b, d bo (pht hin sm) cc nguy c h hng v thi gian phc v (life time) ca chng;

- Hon thin v nng cao cht lng sn phm ngay trong qu trnh sn xut nhm loi b sn phm sai hng;

- m bo an ton sn xut, gim thiu tai nn, nng cao hiu qu kinh t.

8.2. K thut phn tch h hng

Phn tch h hng l mt qu trnh tng hp, i hi phi kt hp nhiu k thut phn tch khc nhau nh: phn tch cc tnh nng c hc, cu trc v thnh phn ha hc ca vt liu, cng nh cc yu t tc ng ca mi trng v quy trnh vn hnh, v.v Mi quy trnh PTHH u hng ti mc tiu cui cng l xc nh c nguyn nhn gc r gy h hng v xut gii php thch hp ngn nga h hng lp li. Mt quy trnh PTHH c cc bc c bn nh trong bng 12.

28,8%

Thit k

4,1%

8,2% 9,6% 9,6%

10,9%

12,3%

16,4%

Lp rp

Ch to

Tc ng bn ngoi

Vn hnh

Bo dng

Sa cha

Vt liu

Hnh 19. Thng k cc nguyn nhn h hng Hnh 20. Thng k cc dng h hng

L Th Hng Lin

818

Bng 12. Quy trnh phn tch h hng

TT Cc bc phn tch K thut/Thit b

1 Thu thp s liu/ti liu lin quan, chn mu hng v cha hng kim tra/phn tch

Hi/p, ghi chp, chp nh, xem xt ti liu, vv

2 Kim tra s b: quan st bng mt, chp nh v s dng k thut NDT

My nh thng, knh hin vi soi ni. Thit b kim tra khng ph hy (PT, UT).

3 Phn tch c tnh Th ko, un, th dai vai p, o cng

4 Phn tch macro v micro: Chp nh kim tng cu trc th i v cu trc t vi, tm cc bng chng lin quan n h hng v cu trc, khuyt tt vt liu, im xut pht, hng lan truyn vt nt

Knh hin vi quang hc (kim tng) v cc thit b ph tr (my mi/nh bng), thit b Replica (ly mu cu trc ti hin trng)

5 Phn tch ha hc thnh phn kim loi v cc phn tch ha hc khc

Thit b phn tch quang ph pht x, SEM-EDX v cc thit b khc

6 Phn tch c hc mt gy: xc nh kiu (mode) gy, tm im xut pht ca vt nt, kiu lan truyn vt nt, pht hin tp cht, khuyt tt vt liu

Knh hin vi in t qut phn gii c micr v cn c bung cha mu ln

7 Tng hp bng chng v nh gi cc s liu phn tch.

Cc chuyn gia trong i

8 Th nghim m phng: gia tc ti v mi trng Cc thit b m phng (nhiu loi khc nhau ty thuc vo i tng v c im h hng)

9 Kt lun: c ch h hng, nguyn nhn ct li v xut gii php ngn nga lp li.

10 Vit bo co

8.3. Hot ng PTHH phc v cng nghip ti Vin Khoa hc vt liu

V nhng li ch PTHH mang li nn n tr thnh cng c khng th thiu cho mi ngnh cng nghip, v cng nghip Vit Nam cng khng ngoi l. Sau 7 nm hot ng, hin nay Trung tm COMFA c cng nghip Vit Nam nhn bit nh l mt n v cung cp cc dch v phn tch vt liu v nh gi h hng trong cc lnh vc sau y:


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Bng 13.Cc lnh vc sn xut cng nghip s dng dch v PTHH ca Vin KHVL

TT Lnh vc CN Yu cu PTHH Cc n v s dng dch v ca COMFA

1. Nhit in - nh gi hin trng (mc do) cc chi tit thit b, cu kin lm vic trong iu kin nhit cao, p sut ln (>550oC, 200bar). - PTHH chi tit thit b trong h thng ni hi, tua bin,

Cng ty CP nhit in Ph Li; Cng ty CP nhit in Ung B; Cng ty nhit in Sn ng; Cng ty CP nhit in Hi Phng D n nhit in Vng ng 1

2. Thy in nh gi hin trng v PTHH cc bnh xe cng tc (tua bin thy in)

Cng ty CP thy in a Nhim Hm Thun a Mi; Cng ty CP thy in min Trung; Nh my thy in Nm Kha; Nh my thy in Nm Chim.

3. Ma ng, sn xut giy

- PTHH chi tit thit b trong dy chuyn sn xut: trc cn ma, h thng ni hi, tua bin, h thng truyn nhit - T vn kim sot cht lng nc/hi cho h thng ni hi/tua bin - D bo tui th ca trc cn ma.

Cng ty CP Ma ng Lam Sn Cng ty CP giy Vn im Cng ty CP Giy Tissue Sng ung

4. Cng nghip ph tr (Cc sn phm c kh v ch to ph tng t/xe my)

- Phn tch nguyn nhn lm gim tui th ca chi tit (h hng trc thi hn d kin/gy li sn phm). - T vn gim thiu h hng. - T vn nng cao cht lng sn phm thng qua chun on qui trnh cng ngh.

Cng ty TNHH t Ford, VN; Cng ty sn phm thp Vit Nam (VSP); Cc doanh nghip c kh Cng ty Lisemco, Hi Phng Cng ty Phanh Nissin, Vit Nam

5. May mc, ch bin thc phm v thc n chn nui gia sc

T vn kim sot cht lng nc/hi cho h thng ni hi v h thng lm mt nhm tit kim nng lng, chng n mn, tng tui th hot ng ca ni hi v cc thit b khc.

Cng ty CP may Hng Yn Cng ty CP may Tin hng Mt s nh my, x nghip ch bin thc phm

6. Dch v gim nh v bo him

Phn tch nguyn nhn h hng cc chi tit thit b l i tng c bo him

Cc cng ty bo him/gim nh

7. Ch bin du kh nh gi hin trng v PTHH cc chi tit thit b, cu kin lm vic trong iu kin nhit cao, p sut ln

Nh my lc du Bnh Sn, Dung Qut

9. GII THIU MT S TRNG HP PHN TCH H HNG THC HIN TI COMFA/IMS

9.1. Phn tch nguyn nhn h hng trc khuu tu thy

Trc khuu ng c 4 k 8 xylanh model X8320ZC4B-L ca tu thy b nt gy sau 3700 gi (khong 5 thng) hot ng, c yu cu tm nguyn nhn gy h hng phc v cng

L Th Hng Lin

820

tc gim nh/bo him. Cc phn tch v thnh phn ha hc, thm thu (PT), t chc t vi, cng ca vt liu v phn tch mt gy s dng SEM-EDX c tin hnh.

Kt qu phn tch cho thy: Qu trnh nhit luyn b mt trc khng m bo, chiu dy lp thm ti qu thp (220-

250 m) so vi yu cu (3 mm), qu trnh gia cng c tinh sau nhit luyn to nn lp bin cng trn b mt, lp ny c cng cao, ng sut d ln, l nguyn nhn to ra cc vt nt nh trn b mt lm vic ca c trc (hnh 21).

Trc b mi, vt nt mi lan truyn dn t cc vt nt nh trn b mt, ng thi vt liu lm bc lt trn c trc b xc v, ri vo vt nt (hnh 22).

Hnh 21. Trc khuu ng c 4 k Hnh 22. Vt nt gy trn c trc

a/ b/

Hnh 21. Trc khuu ng c 4 k (a) v vt nt trn c trc (b).

Hnh 22. Cc vt nt xut hin trn b mt trc (a) v cu trc t vi mt ct ngang t b mt trc vo bn trong (b)

Kt lun: Qu trnh nhit luyn v s gia cng b mt sau nhit luyn khng tt, to thnh lp thm ti qu mng v lp bin cng c cng cao, gy nn cc vt nt b mt, dn n s gy mi sm ca trc khuu.

9.2. Phn tch nguyn nhn gy n ng qu nhit trong h thng ni hi ca phn xng cracking nh my lc du

Cc ng qu nhit trong h thng ni hi phn xng cracking nh my ha du b phng n sau ba nm a vo s dng, gy thit hi ln v kinh t v kh nng cung cp sn phm ca nh my. Cc nh gi phn tch ti hin trng v phng th nghim c tin hnh bao

Vt nt trn b mt lm vic ca chi tit b bin

cng


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gm: phn tch thnh phn ha hc (ca lp cn, ca vt liu ch to ng), phn tch cu trc t vi vt liu, phn tch mt gy v vi phn tch SEM/EDX, phn tch c tnh vt liu ( cng, dai va p). Cng vi nhng kt qu phn tch ti hin trng ngay sau khi h thng dng hot ng, nguyn nhn gy ra h hng ca cc ng c th c kt lun: cc ng b qu nhit cc b ngn hn v cng mt hng do chu tc ng ca dng nhit ln tp trung t h thng vi phun. H thng li chn chia nhit b thng l nguyn nhn gy ra s tp trung dng nhit vo mt khu vc ng v gy ra s phng, n ca cc ng (H.23 v H.24).

Hnh 23. V tr ng qu nhit b n.

Hnh 24 . ng b h hng (a) v nh chp cu trc ca ng b h hng (b).

9.3. Phn tch h hng cnh tuc bin thy in Bnh xe cng tc dng cnh go ca mt nh my thy in b h hng sau khong 35000 gi

lm vic. Cnh gu s 8 b nt 170mm ti v tr u mi, cnh gu s 18 b gy hon ton. Trung tm COMFA thc hin PTHH cho trng hp ny. Cc kt qu phn tch cho thy cc cnh gu b nt gy do ph hy mi. Cc vt nt lan truyn t pha mi cnh ni c cng qu cao, do qu trnh hn sa cha v x l nhit sau hn khng tt. Thm vo cu trc vt c c nhiu khuyt tt c lm gim c tnh ca vt liu, to cc vt nt t vi trong lng vt liu v lm tng nhanh qu trnh ph hy mi dn n gy cnh gu (H.25).

Hnh 25. Ton cnh bnh xe cng tc (a) v cnh gu s 18 b gy (b)

(a) (b)

Vt nt lan truyn

L Th Hng Lin

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TI LIU THAM KHO 1. Gerhardus H. Koch, Corrosion Costs and Preventive Strategies, www.nace.org. 2. Corrosion: Understanding the Basics, ASM International 2000,

www.asminternational.org.

3. Christofer Leygraf, Thomas Graedel - Atmospheric corrosion, A John Wiley and Sons, Inc., Publication, 2000.

4. ASM Corrosion Handbook, Vol.13A - Corrosion: Fundamentants, Testing, and Protection, Ed. Stephen D. Cramer and Bernard S. Covono, Jr, ASM International 2003.

5. Rez a Javaherdashti - How corrosion affects industry and life, Anti-Corrosion Methods and Materials 47 (1) (2000) 30 - 34.

6. Tidblad J., Mikhailov A. A., Kucera V. - Model for prediction of time of wetness on the basis of annual average dataon relative humidity and temperature, Zashchita Metallov 36 (6) (2000) 533-540.

7. Shreir L.L., Jarman R.A., Burstein G.T., Ed. - Corrosion, Vol.1, Metal/Environment Reactions, 3rd ed. Butterworth - Heinemann, 1994.

8. ISO 9223: Corrosion of metals and alloys - Corrosivity of atmospheres Classification. 9. Tidblad J., Mikhailov A. A., Kucera V. - Application of a model for Prediction of Atmospheric

Corrosion in Tropical Environments, Marine Corrosion in Tropical Environments, ASTM STP 1399, S.W. Dean, G, Hernandez - Duque Delgadillo and J. B. Bushman, Eds., American Society For Testing and Materials, West Conshohocken, PA , 2000, pp.18 - 31.

10. Tidblad J., Mikhailov A. A., Kucera V. - Unifield Dose-Respond Function after 8 years of exposure, Quantification of Effect of Air Pollutiants on Materials, UN ECE Workshop Proc., Berlin 1999.

11. GOST 24482-80: Macroclimatic regions of the world with tropic climate. Regionalizing and statistical parameters of climatic factors for technical purposes.

12. Wikipedia - Kh hu nhit i gi ma. 13. Le Thi Hong Lien - Corrosion mapping of cacbon steel in non-coastal areas of Vietnam,

Tp ch Khoa hc Cng ngh 48 (2010) 84-91. 14. Perez F.C. - Atmospheric corrosion of steel in a humid tropical climate; Corrosion 40

(1984) 170 -175. 15. Strekalov P.V., Vu Dinh Huy, Mikhailovski N. - Kinetics of atmospheric corrosion of

steel and zinc in tropical climates, Results of 5-year tests, Zaschita Metallov 18 (1983) 220 -230 (in Russian).

16. Rao, K.N., Lahiri A.K. (Eds.), Corrosion Map of India, 1972 17. S liu th nghim qua cc thi k ca Vin Khoa hc vt liu. 18. Tidblad J., Mikhailov A.A., Kucera V. - Acid deposition effect on materials in subtropical and

tropical climates, The Report C-2000-11 of Swedish Corrosion Institute, 2000. 19. http://corrosion.ksc.nasa.gov. 20. http://www.corrosion-club.com. 21. nuclearpowertraining.tpub.com. 22. http://en.wikipedia.org/wiki/Selective_leaching.


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23. ISO 9225: Metals and Alloys - Aggressivity of Atmospheres - Method of Measurement of pollution data.

24. ISO 9226: Corrosion of metals and alloys - Corrosivity of atmospheres - Method of determination of corrosivity using the corrosion loss standard specimens.

25. ISO 8565: Metals and Alloys - Atmospheric Corrosion Test - General Requirements for Field Test.

26. ISO 8407: Metals and alloys - Procedure for removal of corrosion products from corrosion test specimens.

27. Le Thi Hong Lien - Corrosion mapping of cacbon steel in non-coastal areas of Vietnam, Tp ch Khoa hc Cng ngh 48 (2010) 84-91.

28. Graedel T.E., Leygraf C. - Scenarior for atmospheric corrosion in the 21th century, The Electrochemical Interface, 2001, pp. 24-30.

29. Lien Le Thi Hong, Hong Hoang Lam, The Formation of Protectiveness Layer on Weathering Steel in Initial Stage of Exposure to Vietnam Tropical Climate, Proc. of the 18th ICC, 20-24 Nov. 2011, Perth, Australia, paper 455.00.

30. Failure Analysis and Prevention, Volume 11, ASM Handbook, 2005, 31. Failure Analysis for Materials and Components, training course for ASEAN trainees, 22/2

- 30/3/2010, KIMS Changwon, Korea.

ABSTRACT

CORROSION AND DAMAGE OF METALLIC MATERIALS IN TROPICAL ATMOSPHERE OF VIETNAM

Le Thi Hong Lien

Institute of Materials Science, VAST, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam

Email: [email protected]

Corrosion and damage of metal materials in atmosphere are interested by scientists aiming to control and minimize economic losses and unexpected accidents as well as protect sustainable environment. It is necessary to understand naturally the atmospheric corrosion of metals and the relevant factors that affect corrosion process as well as to learn the knowledge in this field in order to control corrosion and prevent the failures of components, devices and structures those are utilized in atmosphere.

The paper introduces briefly some fundaments of the metallic atmospheric corrosion and the corrosion effects of climatic and environmental parameters as air temperature, air humidity, time of wetness and pollutants (air salinity - Cl- content and SO2 deposition rate). The common types of failure in atmospheric environment are given, the concepts and methodology on classification of atmospheric corrosivity according to ISO standard are mentioned and applied to estimate the atmospheric corrosivity of some climatic regions in Vietnam. And finally, the paper summarizes the main results of atmospheric corrosion investigation and failure analysis those have been carried out at Institute of Materials Science.

Keywords: time of wetness, air pollutant, atmospheric corrosivity.

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