Ntawm Dab tsi tshwj xeeb kev sib xyaw ntawm Nitric Acid Concentration thiab Kub Puas Yog 1.2 millimeter 316 Stainless Steel Sheath Yuav Tsum Tau Derating hauv qab 10 Watts Ib Square Centimeter los tiv thaiv kev sib ntaus sib tua hauv Passivation Tank Service?

Nyob rau hauv cov hlau tiav thiab aerospace manufacturing, cov txheej txheem engineers feem ntau siv nitric acid li nruab nrab rau hluav taws xob immersion heaters nyob rau hauv stainless hlau passivation tso tsheb hlau luam. Passivation daws, feem ntau 20-40% nitric acid, feem ntau yog siv rau ntawm 40-60℃kom tshem tawm cov hlau dawb thiab tsim kom muaj ib hom chromium oxide txheej ntawm stainless hlau qhov chaw . 316 stainless hlau muaj corrosion kuj zoo nyob rau hauv cov xwm txheej no, vim nitric acid yog ib qho oxidising acid uas tswj cov zaj duab xis passive. Txawm li cas los xij, ntawm qhov kub siab lossis nyob rau hauv muaj cov tshuaj chlorides lossis txo cov tshuaj, kev tawm tsam intergranular tuaj yeem tshwm sim, tshwj xeeb tshaj yog nyob rau hauv qhov chaw welded lossis rhiab heev ntawm cov ntaub qhwv. Passivation tank tso cua sov feem ntau yog ua nrog phab ntsa tuab ntawm 1.2 hli kom haum rau qhov chaw yuav tsum tau thiab muab cov cua kub hloov ceev. Tsab ntawv qhia txog kev sib xyaw tshwj xeeb ntawm nitric acid concentration thiab kub ntawm 1.2 hli 316 sheath yuav tsum tau derated rau watt ntom <10 W / cm2 kom tsis txhob muaj kev sib tsoo intergranular.

Mechanism ntawm Intergranular Attack nyob rau hauv 316 Tawm rau Nitric Acid
The intergranular attack of 316 in nitric acid is caused by the loss of chromium at the grain boundaries due to sensitisation by welding or earlier heat exposure. Nitric acid preferentially attacks these chromium-depleted zones and causes grain boundary corrosion, which can lead to full disintegration of the metal. The vulnerability to intergranular attack in nitric acid is concentration and temperature dependent Significant intergranular assault is observed in 20% nitric acid only at 70°C. In 30% nitric acid the threshold falls to 60° C. attack at above 50°C in 40% nitric acid. Attack is performed in 50% nitric acid >40 degree. Qhov chaw tsis muaj zog ntawm 1.2 hli sheath nrog welded flange lossis txuas yog qhov vuam kub- thaj tsam cuam tshuam. Qhov kev siv watt ntom ntom ua rau qhov kub ntawm qhov chaw uas feem ntau yog 10-20℃siab dua qhov kub ntawm cov kua qaub. Nyob rau hauv 40% nitric acid, ntawm ib tug kub ntawm 55 degree, lub sheath nto tuaj yeem ncav cuag 70-75 degree, uas yog tshaj 50℃pib rau intergranular nres. Qhov qis watt ntom ntom txo qis qhov kub thiab txias tuaj yeem tswj xyuas thaj tsam weld hauv qab qhov pib nres.

Tseem ceeb Derating Thresholds rau 1.2 hli Jacket
Cov kev txwv watt ceev hauv qab no siv rau 1.2 hli phab ntsa sheath los tiv thaiv intergranular nres nyob rau hauv lub tshav kub cuam tshuam cheeb tsam raws li immersion kev ntsuam xyuas ntawm welded 316 qauv nyob rau hauv nitric acid ntawm kub thiab concentrations cuam tshuam rau passivation kev pab cuam. Tus nqi yog rau 15-20℃nce hauv qhov kub thiab txias ntawm 10 W / cm², scaling linearly nrog watt ntom.

Bulk Acid Temperature Maximum Sheath Surface Temperature kom tsis txhob cuam tshuam Intergranular Attack Nitric Acid ConcentrationMaximum Allowable Watt Density for 1.2 mm Sheath (15℃sawv ntawm 10 W/cm2) Pom Zoo Ua Haujlwm 20% 40℃70℃20 W/cm2 Safet 20%℃pracity 13 W / cm2 Derating pom zoo saum 13 W / cm2
20% 60°C 70°C 7 W/cm² Derating needed 20%>65℃70℃< 5 W / cm² Siv 316L lossis cov khoom siv annealed
30% 40℃60℃13 W / cm2 Muaj kev nyab xeeb ntawm me ntsis watt ceev
30% 45℃60℃10 W / cm2 Marginal ntawm 10 W / cm2
30% 50℃60℃7 W / cm² Derating xav tau 30% > 55℃60℃< 5 W / cm² Siv 316L los yog alloy upgrade
40% 30°C 50°C 13 W/cm² Acceptable 40% 35°C 50°C 10 W/cm² Marginal 40% 40°C 50°C 7 W/cm² Derating needed 40%>45 degree> 50℃< 5 W / cm² Siv 316L lossis alloy hloov kho
50% 25℃40℃10 W / cm2 Marginal 50% 30℃40℃7 W / cm2 Derating tsim nyog 50% Saum 35℃40℃Hauv qab 5 W / cm² 316 Tsis pom zoo
Rau ib tug raug 30% nitric acid passivation tank nrog ib tug 50℃tej kub, ib tug 1.2 hli 316 sheath yuav tsum tau derated mus rau ib ncig ntawm 7 W / cm2 kom lub sheath nto hauv qab no 60 degree. Lub plhaub saum npoo yog kwv yees li 65 ° C siv qhov kev lag luam ib txwm muaj watt ntom ntawm 10 W / cm 2 . Intergranular nres hauv vuam kub- thaj tsam cuam tshuam tuaj yeem tsim nyob rau hauv 3-12 lub hlis.

Safe Operating Envelope rau 1.2mm Sheath hauv Passivation Service
Qhov siab tshaj plaws uas tau txais nitric acid kub rau 1.2 hli 316 sheath rau ntau yam watt ntom yog muab nyob rau hauv cov lus hauv qab no piv txwv li qib 316L (tsawg carbon) los yog annealed weld cheeb tsam kom txo tau qhov kev pheej hmoo ntawm rhiab heev.

Nitric Acid Concentration Watt Density 5 W / cm2 (8℃sawv) Watt Ceev 8 W / cm2 (12℃sawv) Watt ceev 10 W / cm2 (15℃sawv) Watt ceev 12 W / cm2 (18℃sawv)
20% Safe mus txog 62℃Safe mus txog 58℃Safe mus txog 55℃Safe mus txog 52 degree
Safe rau 57℃25% Safe rau 53℃Safe rau 50℃Safe rau 47 degree
30% Kev nyab xeeb txog 52℃Kev nyab xeeb txog 48℃Kev nyab xeeb txog 45℃Kev nyab xeeb txog 42℃35% Kev nyab xeeb txog 47℃Kev nyab xeeb txog 43℃Kev nyab xeeb txog 40℃Kev nyab xeeb txog 37 degree
40% Txog 42 ° Txog 38 ° Txog 35 ° Txog 32 ° 45% Txog 37 ° Txog 33 ° Txog 30 ° Txog 27 °
50% Safe rau 32℃Safe rau 28℃Safe rau 25℃Tsis pom zoo
Rau lub tank passivation nrog 35% nitric acid thiab qhov kub ntawm 45 degree, 1.2-mm 316 sheath ntawm 10 W / cm² yuav muab qhov kub thiab txias ntawm li 60 degree, uas yog dhau qhov kev nyab xeeb txwv ntawm 47℃hais saum toj no. Lub tshuab cua sov yuav raug cuam tshuam rau kev quab yuam intergranular. Los ntawm kev txo qis watt ceev mus rau 5 W / cm2 qhov kub ntawm qhov chaw yog khaws cia ntawm 53 degree, uas yog qis dua qhov kev nyab xeeb txwv ntawm 57℃rau 25% acid tab sis dhau qhov txwv ntawm 47℃rau 35% acid-qhia tias yuav tsum muaj kev sib xyaw ntawm derating thiab concentration hloov kho.

Tsim cov kev hloov pauv kom tsis txhob cuam tshuam intergranular
Plaub qhov kev hloov kho tsim muaj los tiv thaiv kev tawm tsam intergranular yog tias cov txheej txheem passivation xav tau nitric acid ntau thiab qhov kub thiab txias uas yuav dhau qhov kev txwv rau 1.2 hli tuab 316 sheath. Thawj yog los qhia 316L (tsawg carbon), tsis zoo li 316. Cov ntsiab lus qis dua txwv cov chromium carbide nag lossis daus thaum lub sijhawm vuam, yog li cov cua sov- raug cuam tshuam rau qhov tsis hnov ​​tsw txawm tias qhov kub siab dua . 316L nce lub intergranular nres qhov pib 15{{9} thib ob ntawm qhov thib ob yog qhov thib ob. ncej-weld annealing ntawm flange txuas cheeb tsam. Localized induction annealing rau 1050℃thiab quenching dissolves cov chromium carbides thiab restores corrosion kuj. Qhov kev hloov tom ntej no yog kom txo qis cov kua qaub kub ntawm 5-10 degree. Qhov ntsuas kub me me tuaj yeem ua rau muaj kev pab cuam lub neej zoo heev yam tsis muaj kev cuam tshuam kev ua haujlwm passivation. Plaub, txhawm rau txhawm rau txhawm rau txhawm rau cov kua qaub hla cov cua sov. Turbulent flow txo cov sheath nto kub ntawm 15℃mus rau 8-10℃ntawm tib watt ceev. Lub turbulent flow ntse derates lub rhaub tsis muaj zog txo. Rau cov tso tsheb hlau luam passivation ua haujlwm ntawm qhov kub siab tshaj 45℃hauv 30-40% nitric acid, engineers tej zaum yuav xav txog kev kho dua tshiab rau cov hlau tsis muaj silicone zoo xws li Durimet 20 lossis titanium alloy. Cov ntaub ntawv no yuav luag impervious rau intergranular quab yuam nyob rau hauv nitric acid tsis hais txog ntawm vuam los yog thermal keeb kwm. Thaum qhia txog cov cua sov rau kev pabcuam passivation, nco ntsoov hais txog qhov tseeb nitric acid concentration, bulk kub thiab seb lub rhaub puas tau welded attachments. Yog tias cov chaw tsim khoom pom zoo 316 rau 40% nitric acid ntawm 50C yam tsis tau hais txog watt density derating lossis 316L qib, nws tsis tiav cov lus qhia. Nws yog maj mam thiab tshav kub cuam tshuam cheeb tsam ntawm ib tug welded 1.2 hli sheath thins tawm mus txog rau thaum lub flange detaches los yog lub sheath leaks nyob rau hauv nitric acid. Cov txheej txheem vuam kom raug yog ib qho kev tiv thaiv zoo dua li kev soj ntsuam, txij li qhov kev tawm tsam qee zaum tsis pom kom txog thaum muaj ntau cov khoom tau ploj ntawm qhov chaw vuam.