Duplex stainless hlau, zoo li 2205, feem ntau xaiv rau lawv lub zog thiab corrosion kuj, tab sis lawv lub peev xwm txav tau kub yog feem ntau xav tias zoo ib yam li 316L. Zaj dab neeg tiag tiag yog qhov hloov maj mam thiab nthuav tawm vim li cas lub tshuab hluav taws xob duplex feem ntau tuaj yeem ua kom muaj zog dua thiab ua kom zoo dua thermal. Thaum ntsuasduplex stainless hlau thermal conductivity vs 316L aciddaim ntawv thov kev pabcuam, kev sib piv ncaj qha ntawm cov lej thermal conductivity qhia tsuas yog ib feem me me ntawm zaj dab neeg.
Raw Thermal conductivity: Qhov txawv me me
Nyob rau hauv chav tsev kub, lub thermal conductivity ntawm ob alloys yog tiag tiag nyob ze. Rau cov khoom siv hluav taws xob ua haujlwm kub (20-100 degree):
316L stainless hlau: kwv yees li 13 W/m·K.
TIAB SA 2205: kwv yees li 15 W/m·K.
Qhov sib txawv ntawm kwv yees li 2 W / m·K yog qhov tsis txaus ntseeg hauv kev tsim cov khoom siv hluav taws xob. Lub thermal tiv thaiv ntawm phab ntsa hlau tube twb yog ib qho me me heev rau tag nrho cov tshav kub hloov coefficient (U-tus nqi), tshwj xeeb tshaj yog thaum piv rau ciam teb txheej tiv thaiv ntawm lub raj thiab lub plhaub sab. Rau ib tug raug 1 hli raj phab ntsa, qhov conductive kuj (thickness muab faib los ntawm conductivity) yog hais txog 0.000077 m²·K/W rau 316L thiab 0.000067 m²·K/W rau duplex- ib tug sib txawv ntawm tsuas yog 0.00001 m²·K / W, uas yog poob nyob rau hauv cov margins. Yog li ntawd, ntawm conductivity ib leeg, duplex tsis muaj txiaj ntsig zoo.
Qhov txiaj ntsig ntawm Thermal tiag los ntawm lub zog
Nws tsis yog cov hlau conductivity, tab sis dab tsi cov hlau lub zog tso cai rau uas xa cov txiaj ntsig thermal. Duplex 2205 muaj qhov tsawg kawg nkaus tawm lub zog ntawm kwv yees li 450 MPa, thaum 316L muaj txog 170 MPa- ntau dua ob npaug. Lub zog siab dua no tso cai rau kev tsim cov khoom siv hluav taws xob sib txuas nrog cov phab ntsa nyias nyias thaum tseem tiv taus tib lub siab sab hauv. Standard raj phab ntsa thicknesses rau 316L nyob rau hauv dilute acid kev pab cuam ntawm nruab nrab pressures (xws li, 10 bar) tej zaum yuav 1.2-1.6 hli. Rau duplex 2205, tib qhov kev ntsuas siab tuaj yeem ua tiav nrog phab ntsa tuab ntawm 0.7-0.9 hli.
Lub phab ntsa nyias nyias ncaj qha txo cov thermal conductive. Rau cov kua-rau-kua kub exchanger, qhov twg cov zaj duab xis tshav kub hloov coefficients ntawm ob sab yog kuj siab (xws li, 2000-5000 W / m²·K), lub raj phab ntsa kuj yog ib feem tseem ceeb ntawm tag nrho. Txo cov phab ntsa thickness ntawm 1.2 hli mus rau 0.8 hli txiav cov hlau tsis kam los ntawm ib feem peb, uas yuav ua rau kom tag nrho U-tus nqi los ntawm 3-8%, nyob ntawm qhov kev pab cuam. Hauv cov ntawv thov hnyav- lossis qhov chaw tseem ceeb-xws li offshore platforms, cov khoom siv txawb, lossis cov txheej txheem kev sib tw yooj yim- qhov kev txhim kho no tuaj yeem ua kom pom tseeb cov khoom hloov kho.
Corrosion Resistance nyob rau hauv Dilute Acid Service
Ob leeg 316L thiab duplex 2205 yog siv nyob rau hauv dilute acid ib puag ncig (xws li, acetic acid, citric acid, dilute sulfuric los yog phosphoric acid). Txawm li cas los xij, duplex muaj kev tiv thaiv zoo rau chloride-induced stress corrosion cracking (SCC). Nyob rau hauv dilute acid kwj uas muaj cov kab chlorides (ntau tshaj hauv cov dej), 316L yog qhov raug rau SCC ntawm qhov kub siab tshaj li 50-60 degree. Duplex 2205 muaj kev tiv thaiv ntau dua rau cov tshuaj chloride SCC, tso cai rau kev ua haujlwm ntawm qhov kub thiab txias ntau dua yam tsis muaj kev pheej hmoo ntawm kev tawg sai.
Vim tias duplex tuaj yeem siv rau hauv cov xwm txheej uas 316L yuav ua tsis tiav, qhov kev sib piv ntawm kev ua haujlwm thermal yog qee zaum moot-yog tias 316L tsis tuaj yeem ua haujlwm zoo, kev xaiv raug yuam. Tab sis qhov twg ob qho tib si siv tau, duplex qhov sib xyaw ua ke ntawm cov phab ntsa nyias thiab SCC kuj muab ob qho tib si thermal thiab mechanical zoo.
Tswv yim cuam tshuam rau U-Value thiab Exchanger Size
Rau ib tug raug dilute acid heat exchanger (xws li, kua qaub - dej txias los yog cua sov), tag nrho U-value kev txhim kho los ntawm kev siv thinner duplex tubes tej zaum yuav me me -tej zaum 50–100 W / m²·K siab tshaj qhov sib npaug 316L tsim. Qhov no txhais tau hais tias txo qis hauv qhov xav tau hloov chaw sov ntawm 5-10%. Qhov ntawd yuav tsis txaus los txo qis qhov sib pauv los ntawm lub plhaub tag nrho, tab sis nws tuaj yeem txo cov raj lossis qhov ntev, txuag qhov hnyav thiab tus nqi.
Qhov twg duplex tiag tiag ci yog nyob rau hauv daim ntawv thov uas twb siab-los yog thickness-limited. Piv txwv li, lub tshuab hluav taws xob siab acid uas xav tau cov phab ntsa tuab 316L (piv txwv li, 2 hli) tuaj yeem muaj cov khoom siv hluav taws xob zoo li no uas thermal kev ua tau zoo. Duplex tuaj yeem muab tib lub siab ncaj ncees nrog phab ntsa tuab ntawm 1.2 hli, txhim kho U-tus nqi thiab ua kom muaj qhov sib txawv me me.
Mechanical Design Considerations
Thaum qhia cov raj duplex rau lub tshuab hluav taws xob, ntau yam tshaj li cov phab ntsa yooj yim yuav tsum tau xav txog:
Yam tsawg kawg nkaus fabrication thickness- Txawm hais tias lub siab tsim tso cai rau lub raj nyias nyias (piv txwv li, 0.5 hli), lub raj dov lossis vuam rau hauv cov ntawv yuav tsum muaj qhov tsawg kawg nkaus phab ntsa kom tsis txhob tawg lossis hlawv. Rau duplex, qhov ua tau yam tsawg kawg nkaus yog 0.7-0.9 mm rau feem ntau lub plhaub-thiab-tube exchangers.
Kev tso cai yaig- Yog tias cov kua qaub diluted muaj cov khib nyiab tshem tawm, lub zog siab dua ntawm duplex tsis txo qhov yaig. Ib qho nyiaj pub dawb (piv txwv li, +0.3 mm) tseem yuav tsum tau ntxiv.
Thermal expansion- Duplex muaj cov coefficient ntawm thermal expansion (kwv yees 13 µm / m·K) uas yog me ntsis qis dua 316L (li 17 µm / m·K). Qhov no tuaj yeem txo cov kev ntxhov siab hauv cov qauv tsim cov tubesheet ruaj khov, tso cai rau cov pob qij txha tsawg dua.
Fabrication nqi- Duplex yog me ntsis kim dua ib kilogram thiab yuav tsum tau ceev faj ntxiv cov txheej txheem vuam. Txawm li cas los xij, qhov txo qis hlau ntim (thinner phab ntsa) ib nrab offsets tus nqi.
Daim ntawv qhia txog Dilute Acid Corrosion
Nyob rau hauv cov kua qaub diluted, ob qho tib si 316L thiab duplex vam khom rau cov yeeb yaj kiab chromium oxide passive. Duplex cov ntsiab lus ntau dua molybdenum (3% vs 2% rau 316L) muab kev tiv thaiv zoo dua rau pitting thiab crevice corrosion, tshwj xeeb tshaj yog nyob rau hauv muaj cov chlorides. Txawm li cas los xij, nyob rau hauv nruj heev txo cov kua qaub (xws li, kub dilute hydrochloric acid), ob qho tib si tsis haum; yuav tsum muaj cov nickel alloy lossis PTFE hauv ob sab phlu. Rau cov organic acids lossis cov ntxhia ntxhia ntxhib ntxhib ntxhib ntxhib ntawm qhov kub nruab nrab, duplex ua tau zoo heev.
Xaus
Duplex khwv tau nws cov thermal kom zoo dua los ntawm nws lub zog, tsis yog nws cov conductivity. Thaum rawduplex stainless hlau thermal conductivity vs 316L acidKev sib piv qhia tau hais tias tsuas yog qhov sib txawv me me (15 W / m·K vs 13 W / m·K), qhov txiaj ntsig tiag tiag los ntawm duplex lub zog roughly ob npaug, uas tso cai rau cov phab ntsa nyias nyias rau tib qhov kev ntsuas siab. Ib phab ntsa nyias yuav txo tau cov thermal conductive, txhim kho tag nrho cov tshav kub hloov coefficient (U-tus nqi) los ntawm ob peb feem pua mus txog ze li kaum feem pua, nyob ntawm qhov kev pab cuam. Qhov no, ua ke nrog kev tiv thaiv zoo tshaj rau chloride kev nyuaj siab corrosion cracking, ua rau duplex ib qho kev xaiv zoo rau dilute acid heat exchangers qhov hnyav, qhov chaw, lossis kev cia siab ntev ntev yog qhov tseem ceeb. Qee lub sij hawm txoj hauv kev zoo tshaj plaws los txhim kho cov cua sov yog txhawm rau txhim kho kev tsim kho tshuab- thiab duplex stainless hlau ua pov thawj qhov taw qhia zoo kawg nkaus. Qhov tshwm sim yog qhov sib dua, ua haujlwm zoo dua, thiab muaj zog dua cov khoom siv hluav taws xob, tsis yog los ntawm tus neeg xyuas pib zoo dua, tab sis los ntawm cov qauv muaj zog.
