Rau Titanium Heater Tube Siv los Preheat 40% Sodium Hydroxide Solution ntawm 80 degree, Vim Li Cas Qib 7 Titanium nyiam tshaj Qib 2 Txawm tias tib lub phab ntsa tuab?

Kev Lag Luam Tseem Ceeb-Offs hauv Titanium Qib Xaiv rau Kev Pabcuam Caustic
Titanium tsis tsuas yog tiv taus corrosion nyob rau hauv feem ntau aqueous daws, nws kuj muaj zoo heev corrosion kuj nyob rau hauv kub, concentrated caustic tov xws li sodium hydroxide (NaOH). Qib 2 titanium (kev lag luam ntshiab) tsim cov yeeb yaj kiab tiv thaiv ntawm titanium dioxide hauv cov tshuaj nruab nrab thiab cov kua qaub, tab sis cov oxide zaj duab xis dissolves kom tsim cov sodium titanate soluble nyob rau hauv concentrated caustic ntawm kub. Qhov no ua rau kom nyias nyias thiab qhov tseem ceeb dua hydrogen absorption ua rau embrittlement. Titanium (Ti-0.15% Pd) ntawm qib 7 muaj palladium, cov hlau muaj txiaj ntsig, uas hloov cov peev txheej corrosion mus rau hauv cheeb tsam passive txawm tias nyob rau hauv qhov kev txo qis los yog caustic ib puag ncig. Kev suav nrog palladium ua rau Qib 7 los tsim cov yeeb yaj kiab tsis tu ncua hauv 40% NaOH ntawm 80℃thaum Qib 2 corrodes ntawm qhov tsis xav tau pace. Qhov kev tshuaj ntsuam no piv rau ob qib ntawm tib phab ntsa tuab, thiab vim li cas Qib 7 raug xaiv txawm tias cov khoom siv nqi siab dua.

"Mechanical Integrity Issues - Corrosion thiab Hydrogen Embrittlement hauv Caustic"
Qib 2 titanium muaj corrosion tus nqi ntawm 0.1-0.3 hli ib xyoo nyob rau hauv 40% NaOH ntawm 80 degree, raws li nyob rau hauv immersion kuaj ib ASTM G31 . Rau ib tug raug phab ntsa thickness ntawm 1.2 hli, qhov no sib raug mus rau lub perforation lub sij hawm ntawm 4-12 xyoo, uas yuav tsim nyog nws. Txawm li cas los xij, qhov teeb meem loj tshaj plaws tsis ua haujlwm yog hydrogen embrittlement . Nyob rau hauv caustic, cov tshuaj tiv thaiv corrosion tsim atomic hydrogen: Ti + 4OH⁻ → TiO₂ + 2H₂O + 4e⁻ (anodic) 2H₂O + 2e⁻ → H₂ + 2OH⁻ (cathodic) amicrogen rau hauv tanice. thiab tsim titanium hydride nkig (TiH 2) ntawm cov ciam teb nplej. Qib 2, hauv 40% NaOH ntawm 80 degree, tus nqi ntawm hydrogen uptake yog li 50-100 ppm / hli. Tshaj 200-300 ppm hydrogen concentration titanium ua nkig thiab yuav raug tawg nyob rau hauv thermal lossis residual stress. Qhov embrittlement tsis ua hauj lwm no tshwm sim ua ntej phab ntsa tau thinned ntau thiab feem ntau nrog me ntsis pom corrosion. Nyob rau hauv lub caustic preheaters, teb tsis ua hauj lwm ntawm Qib 2 titanium raj coj qhov chaw nyob rau hauv daim ntawv ntawm cov kab nrib pleb ntawm welds los yog khoov radii, nyob rau hauv 12-18 lub hlis. Txawm li cas los xij, phab ntsa thickness yog ze rau qhov qub.

Qib 7 titanium nrog 0.12 txog 0.25 feem pua ​​palladium ua txawv. Palladium yog cathodic catalyst rau recombination ntawm atomic hydrogen rau molecule H2 uas tsis nkag mus rau hauv titanium lattice. Lub peev xwm corrosion ntawm Qib 7 hauv 40% NaOH ntawm 80℃yog roughly +0.2 V vs. SHE, piv rau -0.3 V rau Qib 2-a 500 mV hloov mus rau hauv qhov passive ntau yam. Corrosion npaum li cas rau Qib 7 yog tsawg dua 0.01 mm / xyoo thiab hydrogen absorption yog undetectable (<1 ppm/mo). A similar Grade 7 tube with a wall thickness of 1.2 mm has a service life of more than 10 years limited by mechanical considerations only, not by corrosion or embrittlement.

Kev cuam tshuam rau Kev Ua Haujlwm Thermal: Tib Lub Sij Hawm Hloov
Lub thermal conductivity ntawm Qib 2 thiab Qib 7 titanium zoo sib xws (17 W / m·K ntawm 80 degree) vim tias qhov sib ntxiv ntawm palladium tsuas yog 0.15%. Qhov kub thiab txias ntawm qhov chaw sab nraud yog tib yam rau tib lub phab ntsa tuab thiab lub zog ntom ntom. Yog li tsis muaj thermal nqi rau kev xaiv Qib 7. Qhov loj downside yog qhov txawv ntawm cov khoom siv (Qib 7 yog li ntawm 50-70% kim dua Qib 2).

Caustic Service Qib Xaiv Matrix: Synthesis of the Trade-tawm
NaOH Concentration & Temperature Qib 2 Lub Neej (1.2 hli phab ntsa) Qib 7 Lub Neej (1.2mm phab ntsa) Pom zoo Qib Core Engineering Reasoning
20% NaOH, 60 degree> 10 xyoo> 15 xyoo Qib 2 Qib 2 txaus; Qib 7 dhau lawm - teev.
30% NaOH, 70℃3 - 5 xyoo (embrittlement) 10 xyoo Qib 7 Qib 2 ua tsis tiav los ntawm hydrogen tawg ua ntej perforation los ntawm corrosion.
40% NaOH, 80°C 1 to 2 years (embrittlement) >10 xyoo Qib 7 Qib 2 tsis haum. Palladium ntxiv yuav tsum tau.
50% NaOH, 90oC < 6 lub hlis 5 - 8 xyoo Qib 7 Txawm Qib 7 tau luv lub neej; tshawb nrhiav lwm yam ntaub ntawv.
40% NaOH, 80℃, nrog cov tshuaj chlorides (pab paug) < 6 lub hlis 3 - 5 xyoo Qib 7 + CP Chlorides nce pitting, CP tej zaum yuav tsim nyog.
Engineering Beyond the Grade: Surface Condition and Welding
Qib 7 titanium tsuas yog ua haujlwm raws li qhov xav tau hauv lub luag haujlwm caustic yog tias qhov chaw tsis muaj hlau paug. Cov galvanic hlwb tsim los ntawm embedded hlau hais hauv zos ua rau lub passive txheej, thiab ua rau pitting txawm nyob rau hauv qib 7. Fabrication yog ua raws li pickling nyob rau hauv 10% HNO₃ + 2% HF rau 5 feeb kom tshem tawm cov hlau nto. Vuam Qib 7 ua raws li cov kev ceev faj tib yam li Qib 2 (argon shielding, tsis muaj kab mob) thiab cov hlau weld khaws cov corrosion kuj zoo ib yam li lub hauv paus hlau vim palladium nyob rau hauv cov tshuaj. Post weld annealing tsis tsim nyog rau kev pabcuam caustic tab sis yuav siv tau rau kev ntxhov siab.

Xaus: Thicker Caustic Hu rau Qib 7 Txawm nyob ntawm Tib Phab Ntsa Thickness
Qib 7 titanium yog qhov zoo dua li Qib 2 titanium rau titanium rhaub tube cua sov 40% sodium hydroxide ntawm 80℃txawm tias ob qho tib si tau teev nyob rau tib phab ntsa tuab. Qib 2 ua tsis tiav los ntawm hydrogen embrittlement tom qab 1-2 xyoos vim qhov nqus ntawm hydrogen los ntawm cov tshuaj tiv thaiv corrosion. Qib 7 tseem ua tsis taus pa thiab tiv thaiv hydrogen uptake rau ntau tshaj 10 xyoo. Lub xub ntiag ntawm 0.15% palladium hloov lub peev xwm corrosion mus rau thaj tsam passive, txo tus nqi corrosion los ntawm qhov zoo ntawm 30 thiab tiv thaiv kev nqus ntawm hydrogen. Rau kev ua haujlwm thermal tsis muaj qhov sib txawv ntawm ob pawg. Cov khoom siv nce nqi ntawm Qib 7 yog qhov ncaj ncees los ntawm nws lub neej ua haujlwm ntev dua. Rau cov kev pabcuam ua kom muaj zog, siv Qib 7 titanium rhaub nrog cov ntaub ntawv palladium (0.12 txog 0.25%) concentration thiab tom qab kev tsim khoom los tsim kom muaj qhov huv si, tsis muaj zog. Rau daim ntawv thov no, Qib 2 yuav tsum raug tso tseg tsis hais txog ntawm phab ntsa tuab.