Anba ki konbinezon espesifik nan potansyèl pwoteksyon katodik aplike ak konsantrasyon sulfid fè 316L aparèy chofaj djenn nan dlo lanmè a 25 degre tranzisyon soti nan dekonpozisyon idwojèn nan konpòtman duktil apre 10,000 èdtan

Limit nan domaj idwojèn nan pwoteksyon katodik maren

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 >100 ppm sulfid menm nan -800mV. Atik sa a evalye papòt potansyèl CP (konsantrasyon sulfid) pou evite HE apre 10,000 èdtan ekspoze.

Mekanis dekonstriksyon idwojèn anba pwoteksyon katodik

Pwoteksyon katodik nan 316L nan dlo lanmè anjeneral fèt pa anod sakrifis (zenk oswa aliminyòm) oswa enpresyone aktyèl (ICCP). Evolisyon idwojèn kòmanse nan potansyèl ki pi negatif pase -800 mV kont Ag/AgCl. Pousantaj antre idwojèn nan 316L ogmante ak diminisyon potansyèl la. Espès sulfid yo (H2S, HS-, ak S2-) yo adsorbe sou sifas metal la epi anpwazonnen pwosesis recombination idwojèn (2H → H2). Sa a ogmante konsantrasyon atomik idwojèn nan eta a nan metal la pa faktè de 10 a 1,000. Konsantrasyon idwojèn papòt pou HE nan 316L se apeprè 5-10 ppm (pwa). Pi wo pase sa a materyèl la vin frajil ak echwe atravè fann intergranular oswa transgranular anba estrès rès rezidyèl oswa aplike.

Quantifier CP Potansyèl-Papòt Sulfid pou atténuation HE

Papòt inisyasyon HE sa yo te jwenn nan polarizasyon katodik kontwole 316L U- espesimèn koube (tansyon kontinyèl tansyon) nan dlo lanmè sentetik (pH 8.0, 25 degre) nan divès kalite konsantrasyon sulfid (tankou Na2S) pou 10,000 èdtan.

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 Okenn Wi
-900 to -1,000 0 Low >15,000 Okenn Wi
-1,000 a -1,050 0 Modere 8,000-15,000 Melanje (kèk HE) Akseptab
-1,050 a -1,100 0 Segondè 3,000-8,000 HE Pa rekòmande (alontèm) < -1,100 0 Trè wo<3,000 HE No > -800 10-50 Low (sulphide limited) >15,000 Okenn Akseptab
-800 rive -850 10-50 modere 8,000-15,000 majinal melanje
-850 a -900 10-50 Segondè 4,000-8,000 HE Pa rekòmande < -900 10-50Trè wo<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 Segondè a trè wo<5,000 (≤ -700 mV) HE No (316L not suited)
Sensibilite nan HE kòm yon Fonksyon nan Tanperati

Tanperati ki pi wo yo ogmante pousantaj difizyon idwojèn ak frajilman.

Tanperati ( degre ) Maksimòm CP Potansyèl pou 10,000h HE-Sèvis Gratis (mV vs Ag/AgCl, 0 sulfid) Maksimòm CP Potansyèl pou 10,000h HE-Sèvis Gratis (10 ppm sulfid)
5 -1,050 -900 15 -1,030 -880 25 -1,000 -850 35 -970 -820 50 -920 -780 
Rekòmandasyon pratik pou pwoteksyon katodik nan asye pur 316L nan dlo lanmè

Pou aparèy chofaj 316L ki anvlòp nan dlo lanmè ak pwoteksyon katodik, restriksyon potansyèl CP sa yo aplike depann sou konsantrasyon ilfid estime a.

Kalite Dlo Lanmè Mwayèn Sulfid (ppm) CP Ranje Potansyèl (mV vs Ag/AgCl) Sigjere Maksimòm Viv Potansyèl 10,000h (mV)Materyèl Altènatif
Netwaye, aere<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/sulfid 50-100 -750 rive -800 -820 Duplex 2205 oswa alyaj 825
Severe sulfidic >100 Pa Rekòmande Pa disponib Titàn oswa Inconel 625
Idantifikasyon jaden CP Enduit HE

Yon aparèy chofaj 316L ki echwe nan dlo sale anba pwoteksyon katodik souvan montre transgranulaire (atravè grenn) HE fant ak ti branch ak souvan yon sifas ki plat frajil ka zo kase. Se kòz la konfime pa prezans nan sulfid (sant nan H2S, nwa fè depo sulfid) ak yon potansyèl CP plis negatif pase -900 a -1,000 mV. Repons lan se ogmante potansyèl CP (mwens negatif) nan seri a san danje, oswa ajou nan yon alyaj ki pi rezistan HE (duplex 2205, oswa Titàn).

Konklizyon: Kontwòl potansyèl CP ak sulfid pou anpeche HE

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 >100 ppm sulfid kèlkeswa potansyèl CP. Enjenyè ki espesifye djenn 316L ki pwoteje katodik pou sèvis maritim yo dwe jere potansyèl CP yo nan fenèt ki an sekirite epi kontwole silfid yo. Modèl la devlope isit la konekte potansyèl CP, konsantrasyon sulfid ak tan inisyasyon HE nan 25 degre nan dlo sale epi li bay yon baz pou achtè yo defini pwen yo fikse CP ki pral evite frajilman idwojèn nan djenn aparèy chofaj 316L pandan 10,000 èdtan lavi konsepsyon.