Nyob rau hauv Titanium Tube Bundle rhaub rau 20% Ammonium Nitrate tov ntawm 80 degree, PH (4.5 Vs . 6.5) Yuav Ua Li Cas Hloov Cov Passivation tam sim no ntom thiab pheej hmoo ntawm kev ntxhov siab Corrosion tawg?
Tso lus
Hauv 20% ammonium nitrate (NH₄NO₃) ntawm 80 degree, pH cuam tshuam rau tus cwj pwm passivation ntawm titanium. Nyob rau ntawm pH 6.5 (ze nruab nrab), cov zaj duab xis passive yog qhov ruaj khov, nrog rau qhov passivation tam sim no ntom ntawm 0.05-0.1 µA / cm² thiab muaj kev pheej hmoo tsawg ntawm kev ntxhov siab corrosion cracking (SCC). Ntawm pH 4.5 (acidic los ntawm hydrolysis), passivation tam sim no ceev nce mus rau 0.5-2 µA / cm², thiab qhov kev pheej hmoo ntawm SCC nce ntau. Cov nitrate ion (NO₃⁻) yog ib qho oxidizer, thiab nyob rau hauv qis pH, nws cov tshuaj tiv thaiv txo kom nrawm, nce qhov muaj peev xwm corrosion mus rau ntau qhov chaw hauv cheeb tsam tawg. SCC tawg pib ntawm cov ntsiab lus kev ntxhov siab xws li cov ntiv taw los yog khoov.
Mechanism ntawm pH-Dependent Passivation thiab SCC hauv Ammonium Nitrate
Thaum siab dua pH (6.5), cov tshuaj tiv thaiv cathodic feem ntau yog txo cov pa oxygen, uas tswj cov titanium nto ntawm qhov muaj peev xwm qis dua 0.5 V piv rau tus qauv hydrogen electrode. Cov zaj duab xis passive ruaj khov thiab kho sai sai. Thaum qis pH (4.5), qhov txo qis ntawm nitrate ions (NO₃⁻ + 2H⁺ + 2e⁻ → NO₂⁻ + H₂O) ua qhov tseem ceeb. Cov tshuaj tiv thaiv no muaj kev sib pauv ntau dua tam sim no, tsa cov peev txheej sib xyaw rau hauv qhov kev hloov pauv siab tshaj 1.0 V. Hauv qhov ntau, cov zaj duab xis passive tawg hauv zos. Yog tias muaj kev ntxhov siab tensile, SCC pib ntawm qhov chaw tawg.
Quantitative Passivation Current Density thiab SCC Risk raws li kev ua haujlwm ntawm pH
Kev tswj xyuas hauv 20% NH₄NO₃ ntawm 80℃tshaj 1,000 teev tau tsim cov kev coj cwj pwm hauv qab no rau Qib 2 titanium. Ntawm pH 6.5, passivation tam sim no ceev yog 0.05-0.10 µA / cm², SCC pib lub sij hawm tshaj 5,000 teev, thiab SCC kev pheej hmoo yog tsawg. Ntawm pH 6.0, passivation tam sim no yog 0.08-0.15 µA / cm², SCC pib lub sij hawm yog 3,000-5,000 teev, thiab qhov kev pheej hmoo yog tsawg rau nruab nrab. Ntawm pH 5.5, qhov passivation tam sim no yog 0.15–0.30 µA / cm², SCC pib ntawm 1,000–3,000 teev, thiab qhov kev pheej hmoo yog nruab nrab. Ntawm pH 5.0, passivation tam sim no yog 0.30–0.70 µA / cm², SCC pib ntawm 500–1,500 teev, thiab qhov kev pheej hmoo yog siab. Ntawm pH 4.5, passivation tam sim no yog 0.50–1.50 µA / cm², SCC pib ntawm 200–800 teev, thiab qhov kev pheej hmoo loj heev. Ntawm pH 4.0, qhov passivation tam sim no yog 1.0–3.0 µA / cm², SCC pib ntawm 100–400 teev, thiab qhov kev pheej hmoo loj heev.
Kev cuam tshuam ntawm Chloride thiab Nitrate Concentration ntawm SCC Risk
Kev muaj cov tshuaj chloride hauv cov tshuaj ammonium nitrate ua rau muaj kev pheej hmoo SCC ntawm txhua qhov pH. Ntawm pH 5.5 nrog 0 ppm chloride, SCC kev pheej hmoo yog nruab nrab. Ntawm pH 5.5 nrog 100 ppm chloride, SCC kev pheej hmoo ua siab, thiab Qib 7 titanium raug pom zoo. Ntawm pH 5.0 nrog 0 ppm chloride, SCC muaj kev pheej hmoo siab, thiab Qib 7 raug pom zoo. Ntawm pH 5.0 nrog 100 ppm chloride, SCC kev pheej hmoo loj heev, yuav tsum tau qib 7 ntxiv rau kev cais hluav taws xob. Ntawm pH 4.5 nrog 0 ppm chloride, Qib 7 muab kev ua tau zoo. Ntawm pH 4.5 nrog 100 ppm chloride, txawm Qib 7 tuaj yeem ua tsis tiav hauv 2,000 teev.
pH Tswj thiab SCC Mitigation Guide for Ammonium Nitrate Heaters
Cov lus hauv qab no muab cov lus pom zoo rau pH tswj thiab titanium qib xaiv rau 20% ammonium nitrate ntawm 80 degree, raws li qhov xav tau lub neej kev pab cuam thiab chloride paug.
| Ua haujlwm pH | Chloride (ppm) | Pom zoo Qib | Cia siab SCC-Lub Neej Dawb (teev) | Passivation tam sim no ceev (µA / cm²) |
|---|---|---|---|---|
| >6.0 | <100 | Qib 2 | >10,000 | 0.05–0.15 |
| 5.5–6.0 | <50 | Qib 2 | 5,000–10,000 | 0.15–0.30 |
| 5.5–6.0 | 50–100 | Qib 7 | 8,000–15,000 | 0.10–0.25 |
| 5.0–5.5 | <50 | Qib 7 | 5,000–10,000 | 0.20–0.40 |
| 5.0–5.5 | 50–100 | Qib 7 + cais | 3,000–6,000 | 0.30–0.60 |
| 4.5–5.0 | <50 | Qib 7 + cais | 3,000–5,000 | 0.50–1.00 |
| <4.5 | Ib qho | Rov tsim txheej txheem | <2,000 | >1.00 |
Engineering Tshaj pH Control
Phab ntsa thickness muab ib qho kev nthuav tawm tawg; ib phab ntsa 2.0 hli nrog SCC tawg ntawm 0.1 hli ib teev muaj sia nyob 20 teev tom qab tawg pib. Cov tshuaj ammonium nitrate yuav tsum tau nruab nrab nrog ammonium hydroxide kom tswj pH siab tshaj 6.0. Lub pH saib nrog lub tswb ntawm 5.8 thiab kev cuam tshuam ntawm 5.5 tiv thaiv kev ua haujlwm nyob rau hauv siab - ntau yam txaus ntshai. Lub tshuab cua sov yuav tsum muaj kev ntxhov siab-relied tom qab fabrication los txo qhov seem tensile kev nyuaj siab. Weld toes yuav tsum tau polished kom txo tau kev ntxhov siab concentration. Cov tshuaj yuav tsum tau lim kom tshem tawm cov khoom uas tuaj yeem ua raws li SCC qhov chaw pib.
Ua ib qho kev qhia tshwj xeeb
Rau lub titanium raj bundle rhaub nyob rau hauv 20% ammonium nitrate ntawm 80 degree, tuav lub pH saum toj no 6.0 rau Qib 2 los yog siab dua 5.5 rau Qib 7. Nruab ib tug nruam pH saib nrog lub tswb teem ntawm 5.8 thiab ib tug interlock uas kaw lub rhaub yog tias pH poob qis dua 5.5. Ntxiv ammonium hydroxide cia li tswj pH. Rau cov tshuaj chloride siab tshaj 50 ppm, qhia Qib 7 titanium. Thaum lub sijhawm ua haujlwm, tshuaj xyuas lub tshuab cua sov rau SCC txhua xyoo uas siv cov dye penetrant ntawm welds thiab khoov. Los ntawm kev tswj cov pH saum toj kawg nkaus qhov tseem ceeb, tus kws ua haujlwm txo qis qhov passivation tam sim no ceev thiab tiv thaiv kev ntxhov siab corrosion tawg.
