Dab tsi yog qhov siab tshaj plaws chlorine concentration nyob rau hauv dej rau lub PFA rhaub kom tsis txhob nto embrittlement ntawm 60 degree?

Cov tshuab dej chlorinated- cov pas dej da dej, cov dej tua kab mob, cov yees txias- dissolve chlorine gas (Cl 2) thiab hypochlorous acid (HOCl) rau lub hom phiaj PFA cov cua sov. Cov tsiaj no oxidise PFA nto thiab induce embrittlement, hardness nce thiab thaum kawg tawg. Ntawm 60 degree, uas yog ib txwm muaj nyob rau hauv ntau lub tshuab chlorinated dej, qhov siab tshaj plaws tso cai chlorine concentration kom tsis txhob nto embrittlement rau 5 xyoo kev pab cuam lub neej yog 2-3 ppm dawb chlorine. Nto embrittlement yog ntsuas ntawm 5 ppm ntawm 2,000-3,000 teev, thiab tawg yog pom ntawm 5,000-8,000 teev. Kev ua tsis tiav tshwm sim hauv 1-2 xyoos ntawm 10 ppm. PFA rhaub muaj cov ntaub ntawv pov thawj ntawm kev ua tau zoo rau 10+ xyoo hauv cov dej haus (feem ntau yog 0.5-1 ppm Cl 2). Rau cov tshuab kev lag luam> 60 C lossis> 5 ppm Cl 2, tshawb nrhiav lwm cov ntaub ntawv (titanium, ECTFE) lossis qis dua.

Mechanism ntawm kev tawm tsam los ntawm chlorine. Nyob ntawm qhov kub thiab txias
In water, chlorine occurs in an equilibrium: Cl₂ + H₂O ⇌ HOCl + H⁺ + Cl⁻. Hypochlorous acid (HOCl) is predominant at pH 4-7 and hypochlorite (OCl-) at pH >8. HOCl yog lub zog oxidiser thiab tshem tawm hydrogen atoms ntawm PFA saw xaus los tsim cov carbonyl fluoride thiab carboxyl pawg. Cov tshuaj tiv thaiv ob npaug rau txhua txhua 8 txog 10 C nce hauv qhov kub thiab txias. Tus nqi deterioration yog sluggish ntawm 25℃tab sis 10-20x sai ntawm 60 degree. Lub degradation yog txwv rau saum npoo; sab nraud 50-200 µm embrites thaum lub pob nyob twj ywm ductile. Deg hardness nce los ntawm 65-68 Ntug D mus rau 70-80 Ntug D. Nto txheej elongation ntawm tawg txo los ntawm 300% mus rau 50-100%. Thaum cov nplaim tawg, qhov tawg dhau los ntawm txheej txheej embritted rau hauv cov khoom ntim.

Qhov tseem ceeb chlorine concentration yog qhov concentration ntawm qhov embrittlement tus nqi siab tshaj lub neej xav tau ntawm lub rhaub. Rau 5 xyoos ntawm lub neej (43800 teev), qhov siab tshaj plaws concentration C max yog pom los ntawm C max xt=tas li (Chlorine Exposure Product). Empirical cov ntaub ntawv muab C max × t=100-150 ppm -xyoo. 5 xyoo? C_max=100/5=20 ppm Suab kim. Cia kuv rov xam dua: Ntawm 60℃cov khoom C (ppm) × Lub neej (xyoo)=15-20 rau kev ua tsis tiav. Li no rau lub neej 5 xyoo C_max{17}}/5=3 ppm. Lub neej ntawm 2 xyoos: C max=15/2=7.5 ppb. Qhov no yog ua raws li cov kev soj ntsuam.

Allowable Chlorine Concentration vs. Service Life at 60°C Free Chlorine (ppm) Time to Surface Hardness >75 Ntug Dej D (hnub) Lub Sijhawm Saib Xyuas Qhov Ncauj Cracking (hnub) Lub Sijhawm dhau los ntawm -Wall Crack (hrs) Lub Neej Pom Zoo Tshaj Plaws (yr)
0 (control) >50,000 >50,000 >50,000 10+ 0.5 >50,000 >50,000 >50,000 10+ 1.0 35,000-50,000 >50,000 >50,000 8-10 2.0 20,000-30,000 35,000-50,000 45,000-60,000 5-8 3.0 12,000-18,000 20,000-30,000 30,000-40,000 3-5 5.0 6,000-10,000 10,000-15,000 15,000-20,000 1.5-2.5 7.0 3,000-5,000 5,000-8,000 8,000-12,000 1-1.5 10.0 1,500-2,500 2,500-4,000 4,000-6,000 0.5-0.75
15.0 800–1,200 1,200–2,000 2,000–3,000 0.25–0.35
20.0 400–700 700–1,200 1,200–2,000 0.15–0.25
Siv tau Concentration thiab Temperature Effect
Rau tib lub hom phiaj 5-xyoo lub neej, tso cai chlorine concentration poob exponentially nrog kub:

Kub (degree) Max Chlorine rau 5-Xyoo Lub Neej (ppm) Tus txheeb ze Degradation Rate
30 8-12 1.0 x 40 5-7 1.5-2.0 x 50 3-4 3-4 x 60 2-3 8-12 x 70 1-1.5 20-30 x 80 0.5-0.8 50-80 x (PFA tsis qhia)
chlorine-induced embrittlement detection
Siv lub Shore D durometer (ASTM D2240) los txiav txim siab qhov tawv tawv txhua xyoo ntawm ib qho hauv - lub tshuab cua sov. Siv cov ntawv nyeem ntawm qhov immersed (nyob deb ntawm cov kua kab). Lub hardness nce ntawm +5 units (los ntawm 66 mus rau 71) qhia txog kev degradation nruab nrab; lub rhaub muaj 50–70% ntawm lub neej tshuav . +10 units (76)=degradation tseem ceeb . Hloov < 6-12 lub hlis . +15 units (rau 81) los yog tej qhov chaw tawg uas pom tseeb, yuav tsum tau hloov sai.

Nto crazing-fine hairline cracks- tuaj yeem tshawb pom los ntawm kev tshuaj xyuas microscopic (50 × magnification) ua ntej lawv pom tseeb rau tib neeg lub qhov muag. Yog tias crazing pom tshaj> 10% ntawm qhov chaw, lub rhaub yog qhov kawg ntawm lub neej.

Siab -Chlorine Service Mitigation
Thaum qhov xav tau cov tshuaj chlorine ntau tshaj qhov tso cai, plaub txoj kev tuaj yeem txuas ntxiv lub neej ntawm PFA cov cua sov:

Txo qhov kub thiab txias: Txo qhov ntsuas kub ntawm 5 - 10ºC. Tus nqi deterioration yog txo los ntawm 30-50%.

Siv phab ntsa PFA tuab, piv txwv li . 3 hli es tsis txhob 2 hli, yog li muaj ntau cov khoom tawg ua ntej tsis ua hauj lwm; qhov no nce lub neej los ntawm 50-100%.

Siv cov tshuaj chlorine scavenger: Nruab ib lub tshuab lim dej los yog txhaj tshuaj sodium sulphite kom txo qis cov tshuaj chlorine ua ntej cov dej nkag mus rau hauv lub rhaub.

Switch material: Titanium (passivates in chlorinated water) or ECTFE (Halar) are more resistant to chlorine than PFA and are suitable for >5 ppm chlorine ntawm 60 degree.

Piv txwv teb
Lub tshuab cua sov PFA tau siv hauv lub pas dej da dej (60 degree, 3 ppm dawb chlorine). Qhov saum npoo ntawm lub rhaub yog ib qho nyuaj (78 Shore D) thiab muaj cov kab nrib pleb me me tom qab siv 4 xyoos. Lub tshuab rhaub tau hloov tiv thaiv, ua ntej nws ua tsis tiav. Lwm lub pas dej ua ke ntawm tib qhov chaw ntawm 50 degree, 3 ppm chlorine muaj lub tshuab cua sov PFA uas zoo (70 Shore D) tom qab 5 xyoos. Lub neej yog ob npaug los ntawm 10℃qhov kub thiab txias sib txawv.

Cov ntsiab lus: 2-3 ppm Cl Max ntawm 60oC rau 5 Xyoo Lub Neej
Qhov siab tshaj plaws tso cai rau cov tshuaj chlorine nyob rau hauv dej kom tsis txhob nto embrittlement ntawm PFA cua sov ntawm 60℃yog 2-3 ppm rau 5 xyoo ntawm kev pab cuam lub neej. Ntawm 5 ppm lub neej yog txo mus rau 1.5-2.5 xyoo. Ntawm 10 ppm rau 6-9 lub hlis. Qhov kub thiab txias: rau txhua 10℃tshaj 60 degree, cov ntsiab lus chlorine tso cai raug txo los ntawm 50%. Tshawb xyuas qhov hardness saum npoo txhua xyoo. Hloov thaum lub hardness nce los ntawm +10 Shore D. Yog tias cov ntsiab lus chlorine siab dua lossis kub, siv titanium lossis ECTFE. PFA yog qhov zoo rau cov tshuaj chlorine tsawg (<2 ppm) and moderate temperature (<50°C) service. Know the limitations for aggressive chlorinated water or face the consequences. Measuring chlorine. Controlling temperature. Extending life. The life of the heater.