Qhov siab tshaj plaws tso cai rau cov organic acids (Acetic / Formic) ntawm 100℃Bulk Temperature Tiv Thaiv General Corrosion ntawm 316 Stainless Steel Heater Sheaths hauv cov khoom noj khoom haus

Organic Acid Corrosion Threshold rau Kev Siv Khoom Noj thiab Bioprocess

The maximum permissible concentration for the general corrosion resistance for 316 stainless steel sheathed electric heating tubes used in food processing, beverage production or bioprocess effluent heating – where organic acids such as acetic acid (CH 3 COOH) and formic acid (HCOOH) are present from fermentation, cleaning in place (CIP) solutions or food degradation products – is not a single value but depends strongly on temperature, pH and the presence of oxygen. 316 stainless steel is passive in concentrations of acetic acid up to around 10-15% at neutral pH and up to 20-25% at pH >5 at 100°C (boiling water temperature). However, formic acid is more aggressive. Active corrosion at rates of 0.1-0.5 mm/year is possible at 100°C at concentrations >1-2%. Rau cov organic acid sib xyaw ua ke (xws li fermentation broths uas muaj ob lub acids), tus nqi corrosion yuav yog ob mus rau tsib npaug ntau dua rau cov kua qaub. Kab lus no suav cov theem pib ntawm cov organic acid concentrations rau passive - mus rau kev hloov pauv ntawm 316 ntawm 100℃.

316 Stainless Hlau Corrosion Mechanism ntawm Organic Acid

Organic acids are weak acids that do not entirely dissociate like mineral acids (e.g. HCl, H 2 SO 4 ). Their corrosiveness to 316 is a function of the undissociated molecule form which penetrates the passive film more readily than the dissociated anion. Acetic acid (pKa=4.76) is weakly corrosive below 10-15% concentration as the passive film remains stable. Formic acid is more aggressive as it is lower pKa (more dissociated) and the formate ion can form soluble complexes with chromium, pKa = 3.75. At higher temperatures (>80 degree) dissociation ntawm cov organic acids nce thiab kuj qhov diffusion tus nqi ntawm hostile hom rau cov hlau nto. Oxygen (aerated tej yam kev mob) feem ntau txhawb nqa passivity, thaum deaerated (anaerobic) tej yam kev mob txhawb active corrosion. Cov pa oxygen tsawg hauv cov khoom noj khoom haus feem ntau tshwm sim los ntawm kev xav tau oxygen lom neeg.

Quantified txwv rau dav corrosion ntawm 100 degree

Tus nqi corrosion dav dav rau 316 stainless hlau tau tsim los ntawm kev tswj hwm kev sim hauv aerated thiab deaerated organic acid daws ntawm 100℃rau 1,000 h.

Organic Acid Concentration (wt%) pH (kwv yees ntawm 100 degree) Tus nqi ntawm corrosion los ntawm yaj oxygen (mm / xyoo) Pom zoo rau 100℃Kev Pabcuam Sijhawm mus rau 0.2 hli Hlau Loss (hr)
Acetic<5 >4.0 Aerated<0.02 >10,000 Yog
Acetic 5-10 3.5-4.0 Aerated 0.02-0.05 4,000-10,000 Yog
Acetic 10-15 3.0-3.5 Aerated 0.05-0.10 2,000-4,000 Txais
Acetic 15-20 2.8-3.0 Aerated 0.10-0.20 1,000-2,000 Marginal
Acetic 20-25 2.6-2.8 Aerated 0.20-0.35 600-1,000Tsis pom zoo
Acetic >25 <2.6 Aerated >0.35 <600 Unacceptable
Aerated<0.02 >10,000 Yes Formic<0.5 >3.5
Formic 0.5-1.0 3.0-3.5 Aerated 0.03-0.08 2,500-7,000 Txais
Formic 2.7-3.0 1.0-2.0 aerated 1,000-2, 500 0.08-0.20 marginal
Formic 2.0-3.0 2.5-2.7 Aerated 0.20-0.40 500-1,000Tsis qhia
Formic >3.0 <2.5 Aerated >0.40 <500 Unacceptable
Acetic (10%) + Formic (0.5%) Mixed 2.8-3.2 Aerated 0.15-0.30 700-1,300 Tsis qhia (synergy)
Txhua daim ntawv ntawm cov organic acidAny<2.5 Aerated >0.30 <700 Not acceptable
Cov organic acid Txhua yam Deaerated (<0.5 ppm O₂) 2-5× aerated rate 2-5× quicker Unacceptable for most
Synergistic nyhuv ntawm Mixed Organic Acids

Kev ua zaub mov tiag tiag thiab fermentation effluent tsis tshua muaj xws li ib qho organic acid. Lub synergic cuam tshuam ntawm acetic thiab formic acids yog tshwm sim los ntawm kev hloov pauv ntawm pH thiab tsim tawm ntawm cov khoom sib xyaw.

Formic Acid (w%) Acetic Acid (w%) Equivalent Single-Acid Concentration Corrosion Rate (mm/xyoo, aerated) pH (100 degree) Combined Concentration Qhia cov kauj ruam tom ntej
5 0.1 5.1 3.5 0.05 8% acetic Acceptable 5 0.5 5.5 3.2 0.12 15% acetic Marginal 5 1.0 6.0 3.0 0.25 >20% acetic Tsis pom zoo
10 0.1 10.1 3.2 0.10 12% acetic Marginal 10 0.5 10.5 2.9 0.30 UnacceptableNo 10 1.0 11.0 2.7 0.60 Tsis tau
Tswv yim Dej Chemistry Specifications rau Food Processing Wastewater

Cov kev txwv organic acid hauv qab no tau qhia rau 316 sheathed heaters hauv kev ua zaub mov lossis bioprocess effluent cua sov ntawm 100 degree.

Daim ntawv thov Common Organic Acids Pom Max. Tag Nrho Organic Acid (wt%) Ntau tshaj tus neeg Formic Acid % wtQhia pH (ntawm 100 degree) Projected Heater Life (xyoo)
Lactic acid (dairy waste)Lactic (not covered) 5 N/A >4.5 >10
Concentrated fruit juice (citric/malic acid)Citric, malic 8 N/A >4.0 8-12 Acetic fermentation brothAcetic 10 N/A >3.5 5 rau 10
Vinegar and WinemakingAcetic 15 N/A >3.0 3-6 (saib)
Food waste digestate Mixed (acetic + formic) 5 0.3 >3.5 5-8
High-formic effluents Formic 2 2 >3.0 2-4 (kab ciam teb)
Organic Acid Corrosion Field Identification

Lub tshuab cua sov 316 hauv kev ua zaub mov ua tsis tau zoo vim yog cov organic acid corrosion, ua rau homogeneous, dav dav etching tsis muaj qhov sib cais. Qhov saum npoo yuav zoo li npub, grey lossis frosty thiab phab ntsa thickness yuav tsis tu ncua. Cov khoom siv corrosion feem ntau yog soluble thiab tsis tsim cov nplai pom. Cov chemical effluent yuav raug typified los ntawm tag nrho cov organic acid concentrations tshaj cov qauv, thiab pH hauv qab 3.0-3.5. Rau formic acid hom tsis ua hauj lwm ib txwm yog dav thinning yam tsis muaj pitting, tab sis rau acetic acid nws yog thinning ntxiv rau qee qhov kev tawm tsam hauv cheeb tsam ntawm cov ciam teb. Txoj kev kho yog txo cov concentration ntawm cov organic acids (los ntawm dilution los yog neutralisation), nce pH (los ntawm kev ntxiv sodium hydroxide los yog sodium bicarbonate kom nce pH saum toj no 4.0-4.5), los yog hloov mus rau ib tug ntau corrosion resistant alloy xws li Alloy 20 los yog Alloy 825.

Txheej Txheem Tswjhwm thiab Neutralization Strategies

Yog tias txo qis ntawm cov organic acid concentrations tsis tuaj yeem ua tiav kev lag luam, cov txheej txheem kev txo qis hauv qab no tuaj yeem ua rau lub neej ntawm lub tshuab cua sov:

Kev kho pH: Kho pH rau 4.5-5.5 nrog sodium hydroxide lossis sodium carbonate. Corrosion tus nqi txo los ntawm kwv yees li 50% rau 0.5 pH chav nyob tshaj 3.5.

Aeration: Khaws DO ntawm 2-3 ppm lossis siab dua. Aeration ua rau passivation, thaum deaeration nce tus nqi ntawm active corrosion los ntawm 2-5 zaug.

Qhov kub thiab txias: khiav ntawm 80C es tsis txhob 100C txo tus nqi corrosion los ntawm 60-80% (ua kom lub zog ~ 50 kJ / mol).

Alloy upgrade: Alloy 825 (42Ni - 21Cr - 3Mo) los yog Alloy 20 (32Ni - 20Cr - 2Mo -} Cu)) muaj 5-10 × ntau dua rau cov organic acids tshaj 316.

Xaus: Organic Acid txwv ntawm 100℃316

For 316 stainless steel encased heaters in food processing effluents at 100°C, the maximum permitted acetic acid concentration for >5 year life is 10-15% at aerated conditions and pH>3.5. Formic acid yog 3-5 × nruj dua, max 1-2% rau kev pabcuam txaus siab. Synergistic corrosion los ntawm tov organic acids. Tag nrho cov organic acid> 5-6% (xws li> 0.3-0.5% formic) ua rau kev ua haujlwm tsis zoo. 316 sheaths rau kev ua haujlwm nrog cov organic acids xav kom tus engineer kom tau txais cov kua qaub ua tiav (hom thiab concentration) thiab pH ntawm kev ua haujlwm kub thaum qhia. Yog tias cov concentrations dhau cov qauv, kev hloov pH, aeration, lossis kev txhim kho hlau yog tsim nyog. Cov txheej txheem tsim los ntawm no hais txog cov ntsiab lus ntawm cov organic acid rau ntsuas qhov dav dav corrosion ntawm 100℃thiab muab cov neeg yuav khoom nrog cov kev xaiv los qhia 316 sheaths lossis hloov lwm cov alloys rau kev ua zaub mov thiab bioprocess cua sov daim ntaub ntawv.