Dab tsi yog Qhov Kev Tshawb Fawb Cov Thickness rau 316 Stainless Steel Flow Heaters hauv 50% Propylene Glycol nrog 2000 ppm Chlorides ntawm 90℃thiab Tsawg Flow Conditions

Qhov Kev Lag Luam Yooj Yim - tawm hauv Glycol Inhibition nrog Chloride Contamination

Propylene glycol (PG) yog cov dej hloov pauv kub ntawm kev xaiv hauv kev ua zaub mov, kev tsim tshuaj thiab kev siv brewing qhov twg cov tshuaj lom ntawm ethylene glycol tsis tuaj yeem lees txais. Ib qho 50% PG tov hauv dej muab kev tiv thaiv zoo khov rau txog -35 C thiab tseem ua haujlwm raws li kev tiv thaiv corrosion thaum npaj kom raug. Txawm li cas los xij, nyob rau hauv kev lag luam PG circuits chlorides nyiam ua rau lawv txoj hauv kev los ntawm ntau qhov chaw xws li cov khoom siv tu cov khoom seem, kev nkag mus ntawm cov dej txias ntauwd los ntawm cov khoom siv hluav taws xob los yog siv cov dej pleev xim dawb (unsoftened). PG poob nws cov kev tiv thaiv corrosion ntawm 2000 ppm chloride theem, uas yog ib theem ib txwm pom nyob rau hauv cov kev tswj tsis zoo los yog cov tshuab nrog dej hiav txwv to. Nyob rau ntawm 90℃kev khiav hauj lwm kub thiab tsis tshua muaj txaus txaus nyiam ciam teb txheej stagnation, 316 stainless hlau yog qhov txaus ntshai rau pitting thiab crevice corrosion. Nyob rau hauv daim ntawv thov no, lub thickness ntawm sheath tsis yog ib tug yooj yim corrosion pub xam, tab sis ib tug pov thawj ce qhia tau hais tias cov xaiv phab ntsa tuaj yeem tiv thaiv kev sib xyaw ua ke ntawm cov tshuaj chlorides, siab kub thiab txo cov cua sov hloov vim tsis tshua muaj ntws.

Mechanism ntawm pitting induced los ntawm chloride hauv propylene glycol daws

Lub 2000 ppm ntawm chlorides nyob rau hauv 50% propylene glycol tov ntawm 90℃yog ib qho kev txhoj puab heev rau cov zaj duab xis passive ntawm 316 stainless hlau. Propylene glycol nws tus kheej tsis muaj zog inhibitory tab sis nws txoj kev inhibition mechanism nyob ntawm adsorption ntawm glycol molecule mus rau cov hlau nto. Nyob rau ntawm 90℃lub adsorbed txheej yog tsawg npaum li cas vim thermal zog. Chloride ions yog cov mobile thiab me me thiab sib tw rau qhov chaw saum npoo thiab ua rau pitting ntawm qhov chaw tsis muaj zog xws li sulfide inclusions lossis khawb ntawm qhov chaw tom qab ua txhaum cov txheej txheem passive. Qhov tseem ceeb pitting kub ntawm 316 stainless hlau hauv 2000 ppm chloride tov yog nyob ib ncig ntawm 50-60℃hauv dej ib leeg. Lub xub ntiag ntawm inhibitor glycol nce qhov tseem ceeb pitting kub nyob rau hauv 50% propylene glycol los ntawm ib ncig ntawm 10-15℃mus rau ib ncig ntawm 65-75 degree. Kev khiav hauj lwm kub yog 90℃thiab lub kaw lus yog li ua haujlwm siab tshaj qhov tseem ceeb pitting kub, yog li cov lus nug ntawm qhov pib tsis yog "yog" tab sis "thaum". Thaum ib lub qhov dej tsim, tus nqi ntawm nws txoj kev loj hlob tuaj yeem kwv yees los ntawm logarithmic lossis linear qauv nyob ntawm qhov muaj cov pa oxygen thiab cov tshuaj tiv thaiv. Tshaj tawm cov txiaj ntsig rau 316 stainless hlau hauv chloride contaminated glycol ntawm 90℃qhia qhov kev loj hlob ntawm 0.2 - 0.6 hli / xyoo rau aerated tej yam kev mob. Ib lub trench nthuav dav ntawm tus nqi ntawm 0.4 hli / xyoo yuav tho lub phab ntsa 1.5 hli hauv 3.75 xyoo rau lub rhaub nrog lub sijhawm ua haujlwm ntawm 5000 teev hauv ib xyoos (kwv yees li 60% dej num). Ib phab ntsa 2.0 hli yuav txuas ntxiv mus rau 5 xyoos. Txawm li cas los xij, cov kev suav no yog nyob ntawm ib lub qhov, thaum qhov tseeb ntau lub qhov tau pib thiab qhov tsis ua haujlwm yog tswj los ntawm qhov tob tshaj plaws.

Kev cuam tshuam ntawm cov dej ntws qis ntawm corrosion thiab nws cov amplification

Rau daim ntawv thov no, cov dej ntws tsis zoo yog qhov tshwj xeeb vim lawv tso cai rau cov ciam teb txheej ntawm cov ntaub npog los ua supersaturated nrog cov khoom siv corrosion thiab chloride ions. Convection ntawm chlorides deb ntawm qhov chaw yog txwv tsis pub rau kev khiav tawm tsawg dua 0.5 m / sec. Cov ntsiab lus chloride ntawm cov hlau saum npoo tej zaum yuav yog tsib los yog kaum zaug uas nyob rau hauv ntau thiab thiaj li txo tau lub peev xwm pitting. Tsawg txaus kuj nyiam ib nrab boiling los yog zaj duab xis boiling ntawm sheath nto thaum tshav kub flux muaj zog. Kev tsim thiab kev sib tsoo ntawm npuas mechanically degrade cov txheej txheem passive thiab tsim cov tshuaj chloride hauv zos hauv cov kua nplaum nyias hauv qab npuas. Cov txheej txheem no ua rau tus yam ntxwv "pitting nplhaib" qauv uas tau pom nyob ib ncig ntawm qhov chaw npuas nucleation ntawm cov cua sov ua tsis tiav. Piv txwv li, rau lub tshuab rhaub dej ua los ntawm 316 stainless hlau siv nyob rau hauv qhov kub ntawm 90℃thiab sheath watt ntom ntawm 7-8 W / cm2, ciam teb txheej txheej kub tuaj yeem siab dua 110-120℃txawm tias qhov qis qis. Nyob rau ntawm qhov kub thiab txias, qhov tseem ceeb pitting qhov pib yog siab heev thiab tus nqi ntawm qhov propagation yuav yog 1-2 hli / xyoo. Yog li ntawd, qhov tseeb thickness yuav tsum tau coj mus rau hauv kev txiav txim siab tsis yog tsuas yog cov chloride concentration thiab kub tab sis kuj lub zos amplification cuam tshuam ntawm tsawg txaus. Lub thickness uas zoo nkaus li txaus nyob rau hauv tej chaw yuav tawg nyob rau hauv lub hlis thaum lub ntws yog qis dua 0.3 m / s.

Thermal Hydraulic Interactions Limiting Maximum Thickness

Kev sib cuam tshuam ntawm phab ntsa thickness, kev xa hluav taws xob thiab cov dej ntws qis imposes ib qho kev txwv ntxiv ntawm qhov siab tshaj plaws ua tau zoo sheath thickness. Nrog rau kev nce ntawm phab ntsa thickness, thermal kuj nce ntxiv uas ua rau cov sheath nto kub rau tib lub zog hluav taws xob input. Thaum tsis tshua muaj ntws, lub convective heat transfer coefficient twb raug txo lawm - feem ntau 300–600 W / m²·K ntawm 0.3 m / s piv nrog 1500–2500 W / m²·K ntawm 2 m / s. Lub phab ntsa tuab ua rau muaj kev tiv thaiv hluav taws xob hauv qhov tsis zoo convective scenario. Ua kom cov phab ntsa tuab ntawm 12 hli txheej txoj kab uas hla lub raj hauv 50% PG, ntawm 90 degree, thiab nrog lub nrawm nrawm ntawm 0.3 m / s los ntawm 1.2 hli mus rau 2.0 hli ua rau qhov kub ntawm ∼ 125℃mus rau 155℃ntawm watt ntom ntawm 7 W / cm2. Qhov kub nce 30℃ua rau 3 mus rau 5 npaug ntawm cov tshuaj chloride pitting raws li tus cwj pwm Arrhenius. Lub phab ntsa tuab, uas yuav tsum tau muab kev tiv thaiv corrosion, es tsis txhob ua rau pitting nres sai heev uas lub net kev pab cuam lub neej tej zaum yuav tsawg dua nrog lub thinner, txias phab ntsa. Qhov no tus kheej-kev tawm tsam cov lus tawm tswv yim txhais tau hais tias nyob rau hauv qis- ntws, siab -chloride glycol systems muaj qhov zoo tshaj plaws ntawm cov tuab tshaj uas ntau cov hlau ua rau lub neej poob qis dua li txuas ntxiv mus. Cov ntaub ntawv pov thawj ntawm ob qho tib si brewery thiab zaub mov kev lag luam kev lag luam cov cua sov qhia qhov zoo tshaj plaws ntawm 1.4 thiab 1.8 hli rau feem ntau 50% PG systems nrog cov tshuaj chloride.

Kev pom zoo Thickness pom zoo rau ntau yam Flow Regimes

Qhov twg qhov khiav ceev tuaj yeem paub tseeb tias yuav tsum siab tshaj 1.0 m / s, lub thickness ntawm 1.5-1.7 hli muab kev pabcuam txhim khu kev qha rau tsib xyoos thaum muaj 2000 ppm chlorides. Moderate thickness keeps sheath temperature below 120℃at normal watt densities and turbulent flow prevents chloride concentration at the surface. Yam tsawg kawg uas tau txheeb xyuas qhov tuab dhau los ua 1.8-2.0 hli rau cov tshuab uas muaj qhov sib cuam tshuam los sis qhov twg ntws tuaj yeem ua tsawg dua 0.5 m / s hauv qee qhov kev ua haujlwm. Cov hlau ntxiv no tsis yog ntau heev rau kev tiv thaiv corrosion raws li kev tiv thaiv lub pitting ceev uas tshwm sim thaum cov xwm txheej tsis tshua muaj. Txawm li cas los xij, rau phab ntsa ntawm 2.0 hli, watt ceev yuav tsum raug txwv rau 5-6 W / cm2 kom cov sheath kub qis dua 135℃ntawm qhov qis qis. In case it is not possible to reduce the watt density owing to space or heating capacity limitations, the thickness must be limited to 1.5–1.6 mm to prevent the thermal acceleration of corrosion, and the system owner must accept a shortened service life of three to four years. 316 stainless is not suggested for systems where flow can be fully stagnant (zero velocity) during heating cycles, regardless of thickness. Nyob rau hauv cov xwm txheej nyob rau hauv qhov chaw tsis muaj zog boiling yog ib qho kev zam tsis tau thiab qhov kub thiab txias, cov ntsiab lus chloride thiab cov khoom ua npuas dej yuav ua rau lub qhov dej los ntawm qhov ua tau zoo hauv ib mus rau ob xyoos. Nyob rau hauv cov xwm txheej zoo li no, lub titanium sheath lossis Incoloy 825 rhaub yuav tsum tau teev tseg.

Kev txheeb xyuas los ntawm kev kuaj corrosion thiab cov ntaub ntawv teb

Peb qhov kev pov thawj txhawb nqa cov lus pom zoo saum toj no rau cov tuab yog: Pitting qhov tob ntawm 0.2-0.3 hli / xyoo tau pom hauv kev sim nplawm (siab ntws) thiab 0.5-0.8 hli / xyoo hauv kev ntsuas tsis muaj zog (tsis tshua muaj ntws) thaum lub sij hawm kuaj immersion ntawm 316 stainless hlau daim coupon nyob rau hauv 50% PG nrog 0.8 ° C ntawm 2000 degree. Thib ob, kev tshuaj xyuas cov khoom siv hluav taws xob tawm ntawm kev pabcuam tom qab peb mus rau tsib xyoos hauv cov zaub mov cog glycol loops uas cov tshuaj chloride tau tshaj tawm ntawm 1500-2500 ppm qhia tias chav nyob nrog 1.5-1.6 hli phab ntsa thiab turbulent flows muaj qhov siab tshaj plaws qhov tob ntawm 0.4-0.7 mm tawm ntawm phab ntsa txaus. Cov chav nyob nrog 2.0-2.2 hli phab ntsa thiab cov dej ntws tsis zoo muaj qhov tob ntawm 0.8-1.2 hli tsis yog vim cov khoom siv tsis tshua muaj zog tab sis vim tias cov phab ntsa tuab ntxiv tau txhim kho qhov kub thiab txias thiab nrawm nrawm. Qhov thib peb, electrochemical polarization scans ntawm 316 stainless hlau nyob rau hauv chloride paug PG ntawm 80-100℃qhia tau hais tias lub pitting tej zaum yuav poob sharply saum 100℃paub meej tias ua kom lub sheath kub hauv qab no qhov pib yog tseem ceeb tshaj qhov ntxiv thickness.

Xaus: Kev Tshawb Fawb Ntau Yam ntawm Thickness rau Kev Pabcuam Kev Ntseeg

Ib qho kev siv tau zoo rau kev txiav txim siab ntawm cov ntaub qhwv tuab rau 316 stainless hlau ntws cov cua sov hauv 50% propylene glycol nrog 2000 ppm chlorides ntawm 90℃ntawm qhov tsis tshua muaj dej yuav tsum sib npaug pitting tsis kam thiab thermal acceleration. Rau cov txheej txheem ntawm kev tsim qauv zoo, nrog kev khiav nrawm ntawm 1.0 m / s thiab watt ntom ntawm 6 -8 W / cm2, lub thickness ntawm 1.5-1.7 hli muab lub neej siv tau 5 xyoo. Rau cov tshuab uas muaj kev khiav hauj lwm ib txwm khiav qis dua 0.5 m / s, lub thickness yuav tsum tau nce mus rau 1.8-2.0 hli, tab sis tsuas yog yog hais tias lub watt ceev yog ib txhij txo mus rau 5-6 W / cm². Tsis muaj qhov system qhov twg stagnation ntawm ntws tuaj yeem ua tau rau 316 stainless hlau, tsis hais nws qhov tuab. Engineers specifying a heater for this difficult environment must specify not only the wall thickness, but also the lowest allowable flow velocity, the maximum watt density, and the verification method (coupon testing or electrochemical monitoring) to be followed during service. Qhov no hloov pauv qhov yuav tsum tau muaj nyob rau hauv cov txheej txheem tswj kev txhim kho corrosion ncaj qha uas cuam tshuam ncaj qha rau phab ntsa thickness rau pitting tsis kam thiab thermal kev ua tau zoo hauv chloride-contaminated glycol systems.