Yuav Ua Li Cas Ua Ntej Ua Ntej Txias Ua Haujlwm Feem pua ​​​​ntawm 316L Heater Sheath Tubing Tswj Pitting Potential Shift (ΔEpit) hauv Deaerated 1 M NaCl ntawm 60 degree

Electrochemical Kos Npe ntawm Microstructure Induced los ntawm Deformation

Lub peev xwm pitting (Epit), uas yog electrochemical muaj peev xwm ntawm qhov ruaj khov pitting pib, rau 316L stainless hlau sheathed hluav taws xob cua sov tub nyob rau hauv deaerated, siab chloride ib puag ncig (xws li geothermal brines, sib sib zog nqus qhov cub rhaub, los yog kaw- voj tshuab cua txias nrog oxygen scavengers) yog ncaj qha tswj los ntawm cov ua ntej txias ua hauj lwm feem pua. Hauv kev daws teeb meem deeared (solved oxygen<10 ppb) the passive film is less stable than in aerated circumstances and cold work has a strong effect on Epit. Fully annealed 316L (0% cold work) shows a pitting potential of about +200 to +250 mV vs. Ag/AgCl in deaerated 1 M NaCl at 60°C. The rise in dislocation density, strain-induced martensite and deformation banding with increasing cold work, all provide favourable sites for pit initiation leading to a linear drop in Epit with increasing cold work. At 20% cold work, epit drops to +50 to +100 mV; at 30% cold work, to -50 to 0 mV; and at 40% cold work, it turns negative (-100 to -50 mV), indicating that pitting happens spontaneously at open circuit. This paper assesses the link between the percentage of cold work, pitting potential and the risk of spontaneous pitting in deaerated chloride solutions.

Mechanism of Cold Work-Induced Pitting Potential Depression

Pitting peev xwm yog ib qho kev ntsuas ntawm qhov resilience ntawm cov yeeb yaj kiab passive tiv thaiv kev puas tsuaj hauv cheeb tsam. Qhov zoo dua Epit, cov khoom tiv taus ntau dua. Kev ua haujlwm txias ua rau muaj kev hloov pauv microstructural uas txo Epit. Ua ntej, dislocations nucleate ntawm cov hlau nto ua cov kauj ruam uas cov txheej txheej passive yog thinner thiab ntau faulty. Thib ob, strain-induced martensite (') tshwm sim saum 15-25% ua haujlwm txias; martensite muaj cov yeeb yaj kiab tsis tshua ruaj khov dua li austenite. Thib peb, cov deformation bands thiab cov kab hauv qab yog cov chaw adsorption nyiam ntawm chloride ions. Qhov cuam tshuam yog txo qis lub zog thaiv rau qhov pib, thawb Epit kom siab dua qhov tsis zoo.

Kev sib raug zoo ntawm kev ua haujlwm txias thiab lub peev xwm pitting

Pitting muaj peev xwm tau txiav txim siab los ntawm kev tswj xyuas qhov txias txias ntawm 316L tubing (tag nrho annealed pib, 2.2% Mo, 0.02% C) nrog rau tom ntej potentiodynamic polarization kuaj hauv deaerated 1 M NaCl (pH 6.5, 60 degree, scan tus nqi 0.167 mV / s).

Previous Cold Work (%) True Strain α'-Martensite (%) Pitting Potential Epit (mV vs. Ag/AgCl, 3M KCl) Open Circuit Potential (OCP, mV)Recommended Spontaneous Pitting Risk for Deaerated 1 M NaCl at 60°C 0 (annealed) 0.00 0 +200 to +250 -150 to -100 None (Epit >>OCP) Yog 5 0.05 0 +180 rau +230 -150 rau -100 Tsis Yog
10 0.11 0 +200 rau +150 -100 rau -150Tsis Yog
15 0.16 0-1+120 rau +170 -150 rau -100 Tsis Yog
20 0.22 1-3 +80 ~ +130 -140 ~ -90Low (Epit > OCP by >100 mV) Txais tau 25 0.29 3-6 +40 rau +90 -130 rau -80 Nruab Nrab (nplooj) Marginal 30 0.36 6-10 0 rau +50 -120 rau -70 Siab (Epit ze OCP)

Kub (degree F)

Ncej -Kev Kho Mob Alternative Alloy 0.5 (∼18,000 ppm) 60 20 Tsis muaj (raws li - kos tau) 316L 0.5 80 15 Kev ntxhov siab txog 400℃, 1h 316L 1.0 (∼ 46,000 ppm pom zoo) 316L los yog duplex 1.0 80 10 Tag nrho cov tshuaj anneal Duplex 2205 2.0 (∼70,000 ppm) 60 10 Puv tshuaj anneal Duplex 2205 2.0 80<5 Not recommended Titanium or Alloy 625