Amaliy katodik himoya potentsiali va sulfid kontsentratsiyasining o'ziga xos kombinatsiyasi ostida dengiz suvida 25 graduslik 316 l isitgich qobig'i 10 000 soatdan keyin vodorodning mo'rtlashuvidan egiluvchanlik holatiga o'tadi

Dengiz katodik himoyasida vodorod zararining chegarasi

The risk of hydrogen embrittlement (HE) in 316L stainless steel sheathed electric heating tubes in seawater with cathodic protection (CP) such as on offshore platforms, marine vessels or coastal structures is a function of the potential (vs. Ag/AgCl) applied to the tubes. At larger negative potentials (more cathodic) hydrogen evolution (2H2O + 2e- -> H2 + 2OH-) occurs and atomic hydrogen can infiltrate into the 316L sheath producing HE cracking. The presence of sulphides (H2S or HS- ) increases the hydrogen entrance, since sulphide is a toxin for the hydrogen recombination reaction. The ductile-to-HE-dominated transition is established above a critical combination of applied voltage and sulphide content. 316L is still ductile ( no HE ) at potentials exceeding -1000 mV vs . Ag / AgCl in saltwater at 25 C , no sulphides . HE can be seen at -1,050 mV during 5,000-10,000 hours. HE occurs at -1,100 mV within 1,000 hours. In the presence of 10-50 ppm sulphide, the safe potential moves to -900 mV. 316L is prone to HE at >Hatto -800mV da 100 ppm sulfid. Ushbu maqola 10 000 soatlik ta'sirdan keyin HE ning oldini olish uchun CP potentsialining (sulfid konsentratsiyasi) chegarasini baholaydi.

Katodik himoya ostida vodorodning mo'rtlashuvi mexanizmi

Dengiz suvida 316L ning katodik himoyasi odatda qurbonlik anodlari (sink yoki alyuminiy) yoki ta'sirlangan oqim (ICCP) tomonidan amalga oshiriladi. Vodorod evolyutsiyasi Ag/AgCl ga nisbatan -800 mV dan salbiyroq potentsiallarda boshlanadi. 316L ga vodorodning kirish tezligi potentsial pasayish bilan ortadi. Sulfid turlari (H2S, HS- va S2−) metall yuzasida adsorbsiyalanadi va vodorodning rekombinatsiya jarayonini zaharlaydi (2H → H2). Bu metalldagi atom vodorodining barqaror holatdagi kontsentratsiyasini 10 dan 1000 gacha oshiradi. 316L dagi HE uchun vodorodning chegara konsentratsiyasi taxminan 5-10 ppm (og'irlik) ni tashkil qiladi. Bundan yuqorida, material mo'rt bo'lib qoladi va qoldiq yoki qo'llaniladigan kuchlanish ta'sirida intergranular yoki transgranular yorilish orqali ishlamay qoladi.

CP potentsialini miqdoriy aniqlash-Uni kamaytirish uchun sulfid chegaralari

Quyidagi HE boshlash chegaralari 10 000 soat davomida turli xil sulfid konsentrasiyalarida (Na2S sifatida) sintetik dengiz suvida (pH 8,0, 25 daraja) 316L U{1}}burilish namunalarining (uzluksiz uzilish deformatsiyasi) boshqariladigan katodik polarizatsiyasidan olingan.

Applied CP Potential (mV vs. Ag/AgCl) Sulphide Concentration (ppm as S 2- )Hydrogen Entry Rate (relative) Time to HE Cracking (hours) Failure Mode Recommended for 10,000h Seawater Service > -800 0 No H evolution >20,000Yes None -800 to -900 0 Trace >20 000 Yo'q Ha
-900 to -1,000 0 Low >15 000 Yo'q Ha
-1000 dan -1,050 0 Oʻrtacha 8000-15000 Aralash (baʼzi HE) Qabul qilinadi
-1,050 dan -1,100 0 Yuqori 3,000-8,000 HE Tavsiya etilmaydi (uzoq muddatli) < -1,100 0 Juda yuqori<3,000 HE No > -800 10-50 Low (sulphide limited) >15 000 Qabul qilinmaydi
-800 dan -850 10-50 gacha oʻrtacha 8 000-15 000 aralash marginal
-850 dan -900 10-50 Yuqori 4000-8000 HE Tavsiya etilmaydi < -900 10-50Juda yuqori<4,000 HE No > -750 50-100 Sulphide increased) Moderate 8,000-15,000 Mixed Marginal -750 to -800 50-100 High 3,000-8,000 HE Not recommended < -800 50-100Very high <3,000 HE No 
Any >100 Yuqoridan juda balandga<5,000 (≤ -700 mV) HE No (316L not suited)
Harorat funktsiyasi sifatida HE ga sezuvchanlik

Yuqori haroratlar vodorodning tarqalishi va mo'rtlashuv tezligini oshiradi.

Harorat (daraja) 10 000 soat HE-Bepul xizmat uchun maksimal CP potentsial (mV va Ag/AgCl, 0 sulfid) 10 000 soat HE uchun maksimal CP potentsial-Bepul xizmat (10 ppm sulfid)
5 -1,050 -900 15 -1,030 -880 25 -1,000 -850 35 -970 -820 50 -920 -780 
Dengiz suvida 316L zanglamaydigan po'latdan katodik himoya qilish bo'yicha amaliy tavsiyalar

Katodik himoyaga ega dengiz suvidagi 316L o'ralgan isitgichlar uchun sulfidning taxminiy kontsentratsiyasiga qarab quyidagi CP potentsial cheklovlari qo'llaniladi.

Dengiz suvi turi Oʻrtacha sulfid (ppm) CP potentsial diapazoni (mV va Ag/AgCl) Tavsiya etilgan maksimal potentsial xizmat muddati 10 000 soat (mV)Muqobil material
Toza, gazlangan<1 -800 to -950 -1,000 316L acceptable Polluted (harbour) 1-10 -800 to -900 -950 316L with monitoring Polluted (high organic) 10-50 -800 to -850 -880 Duplex 2205
Anoksik/sulfidik 50-100 -750 dan -800 -820 Dupleks 2205 yoki qotishma 825
Severe sulfidic >100 Tavsiya etilmaydi Titanium yoki Inconel 625
CP sabab bo'lgan HE ning dala identifikatsiyasi

Katodik himoya ostida sho'r suvda ishlamay qolgan 316 litrli isitgich ko'pincha kichik shoxlangan va ko'pincha tekis mo'rt sinish yuzasi bilan transgranular (donlar orqali) HE yoriqlarini ko'rsatadi. Buning sababi sulfid (H2S hidi, qora temir sulfid konlari) va -900 dan -1000 mV dan ortiq salbiy CP potentsialining mavjudligi bilan tasdiqlanadi. Javob CP potentsialini (kamroq manfiy) xavfsiz diapazonga oshirish yoki HE ga chidamliroq qotishma (dupleks 2205 yoki titanium) ga oshirishdir.

Xulosa: HE ning oldini olish uchun CP potentsialini va sulfidlarni nazorat qilish

For 316L stainless steel heater sheaths in saltwater at 25°C with cathodic protection, the change from ductile to hydrogen embrittlement occurs at applied potentials more negative than -1,000 to -1,050 mV (sulphide free) or -850 to -900 mV (10-50 ppm sulphide). Maximum safe CP potential during 10,000 hour service is -1000 mV (0 sulphide), -850 mV (10-50 ppm sulphide). 316L is not advised for use at >CP potentsialidan qat'iy nazar 100 ppm sulfid. Dengiz xizmati uchun katodik himoyalangan 316L g'iloflarni belgilovchi muhandislar xavfsiz oynada bo'lish uchun CP potentsialini boshqarishi va sulfidlarni kuzatishi kerak. Bu yerda ishlab chiqilgan model CP potentsialini, sulfid konsentratsiyasini va sho'r suvda 25 graduslik HE boshlanishi vaqtini bog'laydi va xaridorlarga 10 000 soatlik dizayn muddati davomida 316 litrli isitgich qoplamalarining vodorod mo'rtlashuviga yo'l qo'ymaydigan CP belgilangan nuqtalarini aniqlash uchun asos yaratadi.