Anba ki konbinezon silfat-a-pwopòsyon klori ak tanperati 316 Nerjaveèi aparèy chofaj yo rete pasif nan dlo gwo kay won refwadisman simulation

Efè Inhibition nan iyon silfat sou pitting pwovoke pa klori

For the 316 stainless steel clad electric heating tubes in cooling tower water systems, the ratio of sulphate ions (SO4 2-) to chloride ions (Cl-) in the recirculating water is typically more relevant than the absolute chloride level in determining the onset of pitting corrosion. Sulphate ions compete with chloride ions for adsorption sites on the passive film of 316 stainless steel. At sulfate/chloride ratios over a certain critical value, generally 3:1 to 5:1 by weight depending on temperature, the passive film is stable even in the presence of chloride concentrations that would ordinarily induce pitting. Below this level, chlorides dominate and begin pitting. This paper estimates the necessary sulfate-to-chloride ratio for 316 sheaths at normal cooling tower temperatures (30–60 ℃) and provides a foundation for water chemistry specification for dependable heater performance.

Mekanis adsorption konpetitif sou fim pasif.

The passive coating on 316 stainless steel (mostly chromium oxide with enrichment of molybdenum) has a positive surface charge in neutral to slightly alkaline solutions. Chloride ions are tiny and highly polarisable and are strongly adsorbed on the film surface. Once adsorbed, chlorides locally decompose the film by generating soluble chloro-complexes with chromium and iron ions and act as initiation sites for pitting. Sulphate ions are also adsorbed on the passive film but do not induce film rupture. Instead they compete for adsorption sites with chlorides thereby preventing the access to chlorides. The competitive adsorption is described by a Langmuir isotherm: the effective chloride concentration at the surface of the film is lowered by a factor which depends on the sulphate concentration. The critical sulphate to chloride ratio is the threshold at which the sulphate adsorption exceeds the chloride adsorption to the point of inhibiting the chloride driven film breakup. For 316 stainless steel at 50 0C the crucial ratio is about 3:1 (by weight three parts sulphate to one part chloride). The ratio may be as low as 1.5:1 at 30 °C. At 70 °C the ratio must be >5:1. Pi wo pase 80 degre, menm rapò silfat segondè ka pa konplètman anpeche pitting, depi sinetik yo nan adsorption klori yo pi vit pase sa yo ki nan adsorption silfat.

Quantifying Limits pou anpeche Pitting nan dlo gwo kay won refwadisman

Tès elèktrochimik sistematik nan 316 asye pur nan simulation dlo gwo kay won refwadisman (pH 7.5-8.5, alkalinite 100-300 ppm kòm CaCO₃, chanje konsantrasyon klori ak silfat) te revele tanperati a ak konbinezon rapò silfat ak klori ki pral anpeche twou pou 5+ ane. Tablo ki anba la a bay zòn operasyon ki an sekirite ak zòn risk pitting.

Tanperati (degre) Sulfat-a-Rapò klori (wt/wt)Konsantrasyon klori (ppm) Risk pou twou (5 ane sèvis)Aksyon Rekòmande
30 >1.5:1 <1000 No pitting Acceptable 30 0.8-1.5:1 200-1000 Low risk, mild pitting possible Monitor every 2 years 30 <0.8:1 Any High risk Add sulphate or decrease chlorides
40 >2.0:1 <800 No pitting Acceptable 40 1.0-2.0:1 200-800 Moderate risk Add sulphate or upgrade to 316L 40 <1.0:1 Any High risk Not recommended 50 >3.0:1 <500 No pitting Acceptable 50 1.5-3.0:1 200-500 Moderate-high risk Requires treatment 50 <1.5:1 Any High risk 316 unsuitable 60 >5.0:1 <300 No pitting Acceptable with monitoring 60 2.0-5.0:1 100-300 High risk 316 marginal; consider duplex 60 <2.0:1 Any Very high risk 316 not suitable 70 >8:1 <200 Marginal Not recommended for 316 70Any Any High riskUpgrade to Duplex 2205 or Titanium >80 Nenpòt Nenpòt Risk segondè 316 pa apwopriye kèlkeswa rapò
Koreksyon Chimi Dlo Pratik pou Pwoteje Chofaj yo

Refwadisman gwo kay won analiz dlo montre silfat/klori rapò pi ba pase nivo sekirite. Twa chanjman chimik ka pwoteje 316 aparèy chofaj ki anvlòp yo. Metòd prensipal ak pi popilè se adisyon silfat sodyòm (Na2SO4) pou amelyore konsantrasyon silfat la. Pou yon sistèm ki gen 400 ppm klori nan 50 degre, yon rapò minimòm de 3:1 mande pou yon objektif konsantrasyon sulfat nan 1200 ppm. Pou akonpli objektif sa a, yo ajoute silfat sodyòm (48% sulfat pa pwa) nan yon nivo apeprè 1,800 ppm. Pri a pa chè epi silfat pa-korozif epi akseptab pou anviwònman an. Dezyèm ajisteman an se elevasyon pH (soti nan 7.5 a 8.5 -9.0 pa idroksid sodyòm), ki ogmante estabilite nan fim pasif ak diminye silfat ki nesesè -rapò a-klori pa ~ 30%. Ajisteman final la se adisyon a nan zenk oswa fosfat ki baze sou inhibiteurs korozyon. Inibitè sa yo adsorbe fim nan pasif epi bay plis pwoteksyon, diminye kondisyon an rapò pa 40-50%.

Dyagnostik jaden Pitting ki te koze pa sulfat-dezekilib klori

316 aparèy chofaj anvlòp nan sèvis gwo kay won refwadisman. Pitting ka rive menm avèk nivo klori modere (200-500 ppm) si rapò silfat-a-klori ba. Analiz dlo yo ta dwe pou klori (pa iyon kwomatografi oswa titrasyon nitrat ajan) ak silfat (pa metòd gravimetrik oswa turbidimetrik). Si rapò a se mwens pase papòt la nan tablo a pou tanperati a opere, Lè sa a, pitting gen anpil chans rive akòz dominasyon klori. Twou yo tèt yo souvan piti (0.1-1.0 mm), fon (0.1-0.3 mm pwofondè) ak anpil endentasyon olye ke twou yo gwo twou san fon, lajman espace yo te jwenn nan anviwònman ki gen anpil klori. Sa a se akòz lefèt ke fim nan pasif kraze nan anpil pwen ankò se pasyèlman retabli pa konpetisyon adsorption silfat, ki mennen nan anpil twou ti kras olye ke yon kèk gwo. Nan sistèm sa yo, itilizasyon silfat pou kreye yon rapò ki an sekirite ap anpeche plis pwogrè nan twou, men twou ki deja egziste yo ap pèsiste kòm sit konsantrasyon estrès.

Konklizyon: Jere Sulfat-a-Rapò klori pou sèvis chofaj gwo kay won ki konsistan

Rapò silfat ak klori a se yon paramèt chimi dlo enpòtan pou 316 aparèy chofaj asye pur revèti nan sistèm dlo gwo kay won refwadisman pou evalye si kouch pasif la rete entak oswa si pitting kòmanse. Nan 50 degre rapò minimòm lan se 3: 1 (sulfat: klori pa pwa). Pou sèvis plis pase 5 ane. Rapò ki nesesè yo ogmante dramatikman nan ogmante tanperati ak plis pase 70 degre 316 pa konseye nan nenpòt ki rapò. Enjenyè ki espesifye aparèy chofaj pou operasyon refwadisman gwo kay won yo ta dwe fè yon analiz konplè chimi dlo, evalye tanperati fonksyònman an, epi ajiste nivo silfat oswa pwogram inhibitor pou kenbe rapò ki nesesè yo. Achtè yo ka itilize apwòch yo bay la a pou espesifye pwogram tretman dlo ki diminye risk pou echèk twò bonè nan 316 djenn yo lè yo fè rapò silfat-a-pwopò klori ak tanperati a ak yon risk pitting ki mezire.