Hauv kev pabcuam dej hiav txwv kub (60-90 degree, 3-4% salinity), PFA cov cua sov tiv thaiv cov tub ntxhais hlau los ntawm cov tshuaj tua hluav taws. Txawm li cas los xij, microscopic defects lossis permeation txoj hauv kev nws thiaj li tso cai rau cov chloride ions mus txog qhov tseem ceeb. Thaum cov tshuaj chloride hu rau cov hlau, kev ntxhov siab corrosion tawg (SCC) dhau los ua qhov tseem ceeb tsis ua haujlwm. Ib tug titanium Qib 2 core resists chloride -induced SCC yuav luag tsis tas li ntawd, thaum Incoloy 825 core tawg nyob rau hauv lub hlis mus rau ob peb xyoos nyob rau hauv tensile stress. Qhov sib txawv no tshwm sim los ntawm kev ruaj ntseg zaj duab xis passive: titanium tsim ib txheej tenacious TiO₂ uas tus kheej - kho sai sai thaum muaj oxygen lossis dej. Incoloy tsim cov chromium oxide (Cr₂O₃) zaj duab xis uas yooj yim rau chloride ion nres, ua rau pitting thiab tom qab tawg pib. Rau PFA cov cua sov hauv dej hiav txwv kub lossis dej hiav txwv ib puag ncig, titanium core txuas ntxiv lub neej kev pab cuam los ntawm 5-10 × piv rau Incoloy.
Mechanism of Chloride-Induced Stress Cracking on Incoloy
Incoloy 825 (Ni-Cr-Mo-} Fe) tso siab rau ib qho passive chromium oxide zaj duab xis rau corrosion kuj. Hauv dej hiav txwv kub, chloride ions adsorb rau ntawm zaj duab xis nto, hauv zos cuam tshuam nws. Cov hlau raug yaj, tsim ib lub qhov. Ntawm lub qhov taub, cov kua qaub, chloride- nplua nuj ib puag ncig tiv thaiv re-passivation. Tensile stress (los ntawm thermal expansion lossis residual manufacturing stress) concentrates ntawm lub qhov, pib tawg. Thaum cov ntaub ntawv tawg, nws propagates transgranularly los ntawm Incoloy. Rau lub tshuab cua sov PFA nrog cov ntaub ntawv ua txhaum cai lossis cov tshuaj permeated chloride, cov tub ntxhais Incoloy feem ntau ua tsis tiav hauv 1,000-5,000 teev ntawm 80 degree, txawm tias PFA zoo li qub. Qhov tawg ua rau lub hauv paus poob hluav taws xob txuas ntxiv lossis qhov chaw rau PFA, ua rau lub rhaub tsis ua haujlwm.
Titanium Qib 2 (kev lag luam ntshiab) tsim cov yeeb yaj kiab TiO₂ uas ruaj khov heev hauv chloride ib puag ncig. Cov yeeb yaj kiab hloov kho yuav luag tam sim yog tias puas tsuaj, muab cov pa oxygen lossis dej tam sim no. Cov dej hiav txwv muaj ntau cov pa oxygen yaj. Chloride ions tsis cuam tshuam rau TiO₂ zaj duab xis; lawv yeej stabilize nws. Titanium tiv thaiv chloride SCC ntawm qhov kub thiab txias hauv qab 120 degree. Hauv dej hiav txwv kub, titanium cores qhia tsis muaj SCC tom qab 50, 000+ teev ntawm kev raug, txawm tias thaum muaj kev ntxhov siab.
Sib piv Kev Ua Haujlwm hauv Dej Hiav Txwv Kub (80 degree, 3.5% NaCl, 50 MPa thov kev ntxhov siab ntawm cov tub ntxhais)
| Hlau Core Khoom | Passive Zaj duab xis | Sijhawm rau Pitting (hour) | Lub Sijhawm Ua Haujlwm Ua Haujlwm (teev) | Lub Sijhawm Ua Tsis Taus (teev) | Dominant Failure Hom | Kwv tij neej tsa |
|---|---|---|---|---|---|---|
| Incoloy 825 (raws li - tau txais) | Cr₂O₃ | 500–1,000 | 1,000–2,000 | 2,000–5,000 | Transgranular SCC | 1.0× |
| Incoloy 825 (passivated) | Cr₂O₃ | 1,000–2,000 | 2,000–4,000 | 4,000–8,000 | SCC | 1.5–2.0× |
| Titanium Qib 2 (annealed) | TiO₂ | >50,000 (tsis muaj) | >50,000 | >50,000 | Tsis muaj (ductile failure possible) | >10× |
| Titanium Qib 7 (Pd-alloyed) | TiO₂ | >50,000 | >50,000 | >50,000 | Tsis muaj | >10× |
| Stainless hlau 316L | Cr₂O₃ | 200–500 | 500–1,000 | 1,000–2,000 | Pitting + SCC | 0.3–0.5× |
Cov ntaub ntawv pov thawj los ntawm Marine Heat Exchangers
Lub chaw tsim hluav taws xob ntug dej hiav txwv siv PFA cov cua sov nrog Incoloy 825 cores hauv dej hiav txwv -cooled heat exchanger (80℃). Cov cua sov ua tsis tau txhua txhua 12-18 lub hlis vim yog cov tub ntxhais tawg. Tom qab-kev soj ntsuam tsis ua tiav tau pom cov tshuaj chloride nkag mus los ntawm cov kab mob me me PFA voids thiab tom qab SCC ntawm Incoloy. Cov nroj tsuag hloov cov cua sov nrog PFA sheaths zoo tib yam tab sis titanium Qib 2 cores. Tom qab 5 xyoos ntawm kev ua haujlwm tas mus li, tsis muaj qhov ua tsis tiav. Cov titanium cores pom tsis muaj pitting lossis tawg. Cov nroj tsuag tam sim no qhia txog titanium cores rau tag nrho cov dej hiav txwv - tso tawm PFA tso cua sov.
Vim li cas Incoloy tseem muaj ntau thiab thaum nws txais tau
Incoloy tseem siv dav vim tias nws tsis tshua kim (kwv yees li 50% ntawm tus nqi titanium) thiab ua haujlwm txaus nyob rau hauv tsis yog -chloride ib puag ncig lossis qis dua (<50°C). For freshwater or deionized water service, Incoloy cores can last 10+ years. For hot seawater, brine, or any chloride-rich environment above 60°C, Incoloy is a liability. The additional cost of titanium (typically $200–500 per heater) is recovered after one prevented failure event.
Tsim Cov Lus Pom Zoo rau Kev Pabcuam Chloride
| Ib puag ncig | Chloride Concentration | Kub | Cov khoom siv tseem ceeb pom zoo | Kev xav |
|---|---|---|---|---|
| Dej qab zib (deionized) | <10 ppm | Ib qho | Incoloy (tus nqi -zoo) | Tsis muaj kev pheej hmoo SCC |
| Cov dej khov | 100-1,000 ppm | <50°C | Incoloy | Txais tau |
| Cov dej khov | 100-1,000 ppm | >60 degree | Titanium Qib 2 | SCC kev pheej hmoo siab dua 60 degree |
| Seawater (qhib voj) | 30,000-40,000 ppm | Ib qho | Titanium Qib 2 | Yuav tsum tau |
| Brine (evaporator) | >100,000 ppm | >70 degree | Titanium Qib 2 lossis Qib 7 | Yuav tsum tau |
| Kub seawater (heat exchanger) | 35,000 ppm | 80 degree | Titanium Qib 2 | Proven life >5 xyoo |
Xaus: Titanium Core tshem tawm chloride kev nyuaj siab tawg hauv dej hiav txwv kub
Hauv kev pabcuam dej hiav txwv kub (80℃, 3.5% NaCl), PFA rhaub nrog titanium Qib 2 hlau core nthuav tawm 10 × lub neej ntev dua li Incoloy 825 core vim titanium's TiO₂ passive zaj duab xis yog tiv thaiv chloride -induced stress corrosion cracking. Incoloy's chromium oxide zaj duab xis tawg hauv chlorides, ua rau pitting, tawg pib, thiab ua tsis tiav nyob rau hauv lub hlis mus rau ob peb xyoos. Rau txhua lub tshuab cua sov PFA ua haujlwm hauv chloride- thaj chaw nplua nuj tshaj 60 degree, qhia meej titanium core. Tus nqi pib them nqi rov qab los ntawm kev tshem tawm lub sijhawm poob thiab hloov cov nqi. Cov kws tsim qauv xaiv cov khoom siv rau kev ua dej hiav txwv, desalination, lossis cua sov brine yuav tsum tau ua ntej titanium. Incoloy belongs rau hauv dej tshiab; titanium tswj lub hiav txwv.
