Qoldiq xloramin kontsentratsiyasi va pH 316 zanglamaydigan po'latdan yasalgan isitgichning qanday o'ziga xos kombinatsiyasi ostida 55 daraja issiq suvda chuqurchalar paydo bo'ladi

Mechanism of pitting corrosion of disinfectant in potable water systems Monochloramine (NH2Cl) is being increasingly used as a secondary disinfectant in municipal hot water systems (domestic hot water tanks, recirculation loops in hotels and hospitals, point of use heaters in commercial buildings) to replace free chlorine and minimise trihalomethane formation for 316 stainless steel sheathed electric heating tubes. Chloramine is less aggressive to stainless steel than free chlorine but can produce pitting at higher temperatures especially when the pH is not in the proper range for chloramine stability. 316 stainless steel is passive at chloramine levels below 2-3 ppm at a common residential hot water temperature of 55 °C and a pH of 7.5-8.5. However, below pH 7.0 chloramine breaks down into free chlorine and ammonia which leads to a more aggressive oxidising environment. Chloramine is unstable at pH > 9.0, and decomposes to dichloramine and nitrogen trichloride. Pitting begins at chloramine levels >4-5 ppm pH 7,0-8,0 yoki pH ekskursiyalari ostida. Ushbu tadqiqot 55 ⁰C da 316 ta qobiqda chuqurchalar paydo bo'lishini boshlaydigan pH chegaralari va xloramin kontsentratsiyasini bashorat qiladi. Xloramin-induktsiyalash mexanizmi va pHga bog'liqlik Monoxloramin (NH2Cl) erkin xlorga (HOCl/OCl-) qaraganda zaifroq oksidlovchi moddadir, ammo xloramin 50 darajadan yuqori haroratlarda ko'plab yo'llar bilan parchalanadi. Neytral va ozgina ishqoriy pH (7,0-8,5) da parchalanish ammiak va azotni beradi, faqat oz miqdorda erkin xlor chiqariladi. PH < 7,0 da parchalanish erkin xlor (HOCl) va dikloramin (NHCl 2) ga o'tadi, ularning ikkalasi ham passiv plyonkani 316 da parchalashi mumkin bo'lgan kuchli oksidlovchilardir. pH > 9,0 da xloramin tez azot trikloridiga parchalanadi va bu yuqori voltli triklorid (NCl) ga aylanadi. Chuqurlik mexanizmi erkin xlorli chuqurchalardir. Cr 2 O 3 passiv plyonkaning mahalliy bo'linishi va keyinchalik xlorid bilan bog'liq chuqurning tarqalishi. Ammo bir xil haroratda chuqurchalar paydo bo'lishi uchun xloramin kuchliroq konsentratsiyaga muhtoj (erkin xlordan taxminan 2-5 marta). 316 zanglamaydigan po'latdan (elektroparatlangan qoplama, Ra=0.2 mkm) 55 daraja haroratda chuqurlashishning miqdoriy chegaralari Sintetik shahar suvida (100 ppm Cl−, 80 ppm SO42−, 120 ppm CaCO3) turli xil monox50 0 0 H konsentratsiyasida va p0 0 0 H konsentratsiyasida boshqariladigan cho'mish sinovlari chuqurlarni boshlash uchun quyidagi chegaralarni aniqladilar. pH (55 daraja) Monoxloramin (ppm Cl2 ekvivalenti sifatida) Xloraminning parchalanish yo'li uchun chuqurchalarni boshlash vaqti (soat) 3000 soatdan keyin maksimal chuqurlik chuqurligi (mikron) Teshilish vaqti (1,5 mm devor) 55 daraja Tavsiya etilgan xizmat<1.0 7.0-8.5 Stable >10,000 <10 >30 yil Ha 1.0-2.0 7.5-8.5 Barqaror 5000-10,000 10-20 15-30 yil Ha 2.0-3.0 7.5-8.5 Barqaror 20-40 yil Koʻpincha 8-15 yil 3000-5000 Qabul qilinadi 3.0-4.0 7.5-8.5 Taxminan 1500-3,000 40-80 4-8 yil Marginal buzilish {{15}ortiqcha buzilish} 800-1,500 80-120 2 dan 4 yilgacha Tavsiya etilmaydi 5.0-7.0 7.5-8.5 Sezilarli parchalanish 400-800 120-200 1-2 yil yoʻq 7.0 7.5-8.5 Tez parchalanish<400 >200 <1 year Unacceptable 2.0-3.0 6.5-7.0 (pH excursion)Free chlorine release 1,000-2,000 60-100 3-5 years Not recommended 2.0-3.0 <6.5 Free chlorine + dichloramine 300-800 100-180 1.5-2.5 years Not acceptable NCl3 formation 2.0-3.0 >9.0 500-1,200 80-150 2 - 3 yeras Unacceptable 3.0 < 7.0 Severe degradation < 500 > 150 < 1.5 years Temperature effect on chloramine aggressiveness Not acceptable The rate of decomposition of monochloramine rises with temperature, hence chloramine is more aggressive at higher temperatures. Water Temperature (oC) Maximum Monochloramine for 5-Year Life pH 7.5-8.0 (mg/L)Maximum Monochloramine for 10 Year Life at pH 7.5-8.0 (mg/L)Recommended Action 40 5.0 3.0 Standard practice 50 3.5 2.5 OK 55 3.0 2.0 Marginal above 2.5 ppm 60 2.2 1.5 Chloramine reduction if >2 ppm 70 1.5 1.0 316 not recommended, upgrade material 80 1.0 0.5 316 not appropriate Chloramine Treatment Practical Water Chemistry Specifications The following specifications will ensure long term pitting free service for 316 sheathed heaters in municipal hot water systems treated with monochloramine at 55oC. System Type Target Monochloramine (ppm) pH Range Max. Temp. (°C) Heater Life Expectancy (years)Hot water heating ideas for households1.0-2.0 7.5-8.5 55 10-15 Commercial (hotel/hospital) OK 1.5-2.5 7.5-8.5 55 8-12 Test for chloramine regularly. big circulation system 2.0-3.0 7.8-8.2 55 5-8Active pH regulation as required Any with chloramine >3.0 >3.0 7.5-8.5 55 2-4 pH ekskursiyalari bilan 316L elektropolish Any-ga yangilang<7.0 <3.0 <7.0 56 2-5 pH control necessary Any at temperatures above 60°C 1.5 7.5-8.5 >60 2-5 2205 Ikki tomonlama yangilash Xloramin tomonidan hosil boʻlgan chuqurchalarning aniqlanishi. Erkin xlor kam boʻlgan, lekin xloramin bilan ishlov berish maʼlum boʻlgan shahar issiq suvidagi 316 isitgich uchun chuqurlar odatda kichik (diametri 0,1-0,5 mm), tez-tez (5-20 chuqur/sm2) boʻladi. Chuqurdagi metall yuzasi xlorid bilan ishlaydigan chuqurchalar morfologiyasidan dalolat beradi. Asosiy farq shundaki, quyma suvda erkin xlor yo'q (xloramin parchalanib borayotganining ko'rsatkichi). Suv kimyo jurnali turli vaqtlarda 3-4 ppm dan yuqori xloramin va pH 7,0 dan past yoki 9,0 dan yuqori bo'ladi. Ommaviy suvda erkin xlor va xloramin mavjudligini tekshirish dezinfeksiya turini tasdiqlaydi. Ushbu nosozliklarni hal qilish xloramin kontsentratsiyasini 2,5-3,0 ppm dan kamroq darajaga tushirish yoki pH ni 7,5-8,5 darajasida ushlab turish yoki dupleks 2205 zanglamaydigan po'latga yangilashdir. Yuqori xloraminli tizimlar uchun davolash eritmalari Agar xloramin kontsentratsiyasini 3 ppm ga kamaytirishning iloji bo'lmasa, quyidagi protseduralar chuqurchalar paydo bo'lish xavfini kamaytiradi: Elektropolishing: Elektropolizlangan sirt (Ra<0.2 µm) increases chloramine threshold by ~1 ppm. pH stability The pH should be maintained in the range 7.8 – 8.2 by adding a pH controller. Decomposes to free chlorine at low pH. Decomposes to NCl3 at high pH. Lower heater setpoint from 55C to 50C (40-50% reduction in chloramine decomposition rate) Alloy upgrade: Duplex stainless steel 2205 (higher pitting resistance equivalent number, PREN >35) yoki titanium nitridi (TiN) qo'shilishi nazorati bilan 316L. Xulosa: 316 isitgichning ishlash muddati @ 55 daraja pH va xloramin nazorati 316 zanglamaydigan po'latdan yasalgan qoplamali isitish moslamalari shahar issiq suvida 55 daraja haroratda 1000-3000 soat ichida pH 7,5-8,5 da 3-4 ppm monoxloramin atrofida chuqurchalar paydo bo'ladi va teshilish 5 yil. Ph 7,0 dan pastga tushishi bilan xloramin erkin xlorga parchalanadi va hatto 2-3 ppm xloramin juda agressiv bo'lib, 1-2 yil ichida chuqurlashadi{17}} xlor va pH, pH diapazoni 7,5-8,5 va monoxloramin.<2.5 ppm for 10 year life shall be specified by engineers for chloramine treated water. Electropolished 316L or duplex 2205 is suggested for chloramine levels over 3 ppm or where pH control is not reliable. The present method, connecting chloramine concentration and pH to measured pitting initiation times at 55°C, allows users to define water treatment programmes which prevent disinfectant-driven pitting in municipal hot water systems.