Vim li cas 316 Stainless Hlau Sheath Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob hauv Hydrofluoric Acid Kev Pabcuam Hauv qab 2% Concentration ntawm 60-80 Degree Exhibit Pitting ntawm Cov Chaw Ua Haujlwm Hauv 500 Teev Thaum Tseem Ceeb Hauv 5-10% Acid Hauv Qhov Kub Zoo?

Ib qho ntawm ob peb cov ntxhia acids uas ua phem rau 316 stainless hlau ntawm qhov nruab nrab thiab qhov kub thiab txias yog hydrofluoric acid (HF). Txawm li cas los xij, cov ntaub ntawv teb los ntawm kev ua haujlwm tshuaj lom neeg, cov hlau pickling da dej thiab semiconductor etching qhia tau hais tias qhov kev cia siab ntawm kev cia siab: 316 sheaths tuaj yeem nyob rau lub hlis hauv 5-10% HF ntawm 60-80℃nrog qhov tsim nyog corrosion (0.1-0.3 mm / xyoo), tab sis poob los ntawm qhov hnyav pitting li ntawm 500-1000. Tus cwj pwm counterintuitive tau piav qhia los ntawm kev sib tw los ntawm cov tshuaj fluoride complexation thiab cov yeeb yaj kiab passive. Hauv dilute HF (<2%) the concentration of fluoride ions is sufficient to locally attack the passive coating but is not high enough to create stable fluoride complexes (FeF 6 3- , CrF 6 3- , NiF 6 2- ) which would uniformly dissolve the corrosion products and allow repassivation. The consequence is localised breakdown at non-metallic inclusions (notably MnS) resulting in deep pits propagating deep into the sheath wall. In more concentrated HF (5–10%) the strong fluoride activity leads to homogeneous dissolution of the entire surface, avoiding localised assault by continuously eroding the passive coating uniformly and producing soluble complexes which do not allow differential aeration cells. Although the uniform corrosion rate is higher in concentrated HF, the absence of significant pitting ensures the sheath will keep its structural integrity for foreseeable service intervals. This article evaluates the pitting vs uniform corrosion transition in HF solutions and provides application guidelines for dilute HF heating service.

Electrochemistry ntawm Dilute vs Concentrated Hydrofluoric Acid ntawm 316 Stainless Hlau
Hydrofluoric acid yog txawv los ntawm lwm yam minerals acids (HCl, H2SO4, HNO3) nyob rau hauv nws muaj peev xwm tsim complexes nrog hlau ions. Fluoride ions (F-) tsim cov complexes ruaj khov nrog hlau (FeF6 3-, log K ~ 16), chromium (CrF6 3-, log K ~ 12) thiab nickel (NiF6 2-, log K ~ 8). Nyob rau hauv dilute HF (0.5-2%) qhov concentration ntawm fluoride (0.25-1.0 M) yog txaus rau complex hlau ions liberated los ntawm corrosion tab sis cov complexes tsuas yog tsim nyob ze rau active corrosion sites. Qhov kev daws teeb meem loj yog qhov tsis yooj yim. Thaum lub qhov dej tsim los ntawm MnS suav nrog (ib qho chaw rau pitting pib hauv cov hlau tsis muaj steel) cov hlau ions yaj los ntawm lub qhov dej hnov ​​​​mob nrog cov tshuaj fluoride los tsim cov complexes uas tsis precipitate li tiv thaiv txheej. Txawm li cas los xij, kev ua haujlwm ntawm cov tshuaj fluoride uas tsis tshua muaj tiv thaiv kom tsis txhob muaj kev sib kis ntawm kev sib kis thiab lub qhov dej txuas ntxiv mus ua ib lub xov tooj ntawm tes.

Hauv cov concentrated HF (5-10%, 2.5-5.0 M fluoride), cov tshuaj fluoride siab ua kom cov hlau, chromium thiab nickel ions sai li sai tau thaum lawv yaj nyob txhua qhov chaw ntawm qhov chaw. Qhov no zam qhov kev loj hlob ntawm cov concentration gradients (hlau ion concentration, pH, chloride) ua rau thaj chaw pitting. Tag nrho saum npoo nyob rau hauv cov ntaub ntawv no yog dissolving aggressively ntawm ib tug ntau los yog tsawg uniform tus nqi. Qhov kev coj cwj pwm no zoo ib yam li cov hlau ntau hauv cov kua qaub uas muaj zog heev. Tus nqi ntawm uniform corrosion yog tswj los ntawm diffusion ntawm complexes deb ntawm qhov chaw.

Quantified Pitting vs Uniform Corrosion hauv HF Solutions
316 stainless hlau daim coupon qauv (kev daws teeb meem annealed, pickled nto) raug kuaj nyob rau hauv kev tswj immersion nyob rau hauv HF kev daws teeb meem ntawm 0.5% mus rau 10% ntawm 70℃mus txog 2000 teev. Tus nqi corrosion tau kwv yees los ntawm kev poob phaus thiab qhov siab tshaj qhov tob tau txiav txim siab los ntawm kev hla -sectioning.

HF Concentration (%) Temperature (degree) Uniform Corrosion Rate (mm/xyoo) Qhov siab tshaj plaws qhov tob tom qab 1000 teev (µm) Qhov siab tshaj plaws qhov tob tom qab 2000 teev (µm) Corrosion Morphology 0.5 70 0.08 110 280 Pitting hnyav ntawm kev suav nrog
1.0 70 0.12 150 420 (perforation) Pitting, qee qhov kev tawm tsam dav dav 2.0 70 0.20 85 180 Mixed pitting + general 3.0 70 0.28 15 35 General nrog me me pitting 5.0 70 0.45 8 12 Uniform general corrosion
10.0 70 0.95 5 10 Uniform, tsis muaj pitting
10.0 50 0.40 3 8 Uniform 10.0 90 2.10 15 40Uniform, me me pitting
Lub pitting-dominated rau uniform-dominated hloov nyob rau hauv corrosion tshwm sim ntawm 2% thiab 3% HF ntawm 70℃. Qhov siab tshaj plaws qhov tob tom qab 1000 teev yog 10-20 lub sij hawm loj dua li qhov tsis sib xws corrosion nkag hauv qab 2%. Ntawm 70℃hauv 1% HF 1.5 hli phab ntsa thickness yuav perforate los ntawm pitting ntawm txog 1200 teev (50 hnub). Uniform corrosion forecasts tsuas yog 0.12 hli poob (8% ntawm phab ntsa). Saum 5% pitting yog me me thiab tsis ua hauj lwm yog los ntawm kev thinning uas yog kwv yees thiab tswj tau los ntawm phab ntsa tuab kam rau ua.

Cov nyhuv ntawm Nto tiav thiab suav nrog ntawm Dilute HF Pitting
Pitting nres hauv dilute HF feem ntau tshwm sim ntawm manganese sulphide (MnS) suav nrog hauv cov qauv 316 stainless hlau ntawm qhov ntom ntawm 10-100 inclusions ib mm2. Cov yeeb yaj kiab ntawm cov chaw no yog qhov tseem ceeb tsis muaj zog hauv lub xeev passive. Nyob rau hauv dilute HF fluoride ions adsorb nyob rau hauv suav ciam teb thiab catalyze disintegration ntawm ib puag ncig matrix. Thaum lub qhov dej tau pib qhov kev ua haujlwm ntawm cov tshuaj fluoride uas tsis tshua muaj tsis cuam tshuam cov tshuaj lom neeg hauv zos thiab lub qhov dej pib autocatalytically.

Kev ntsuam xyuas ntawm 316 cov qauv nrog cov ntsiab lus sib txawv thiab cov khoom tiav hauv 1% HF ntawm 70℃rau 500 teev qhia:

Material Condition MnS Inclusion Density (ib mm²) Surface Finish Ra (µm) Qhov siab tshaj plaws ntawm qhov tob ntawm 500 hr (µm) Qhov ntom ntom (pits / cm²)
Txheem 316 (0.020% S) 15 0.8 95 12 Tsawg sulfur 316 (0.003% S) 2 0.8 25 3 Txheem 316, electropolished 15 0.2 55 6
Txheem 316, passivated nrog nitric acid 15 0.8 70 8
Standard 316, Fluoride Prepassivation (5% HF rau 1 teev) 15 0.8 35 4
316 nrog tsis tshua muaj leej faj (tseem hu ua "316 nrog kev tswj cov sulfur rau kev txhim kho corrosion") txo cov kev sib xyaw ntom ntom thiab ncua sij hawm rau pitting pib. Ua ntej-passivation hauv 5% HF rau 1 teev ua kom muaj cov tshuaj fluoride homogeneous- nplua nuj txheej txheej uas tiv taus qhov chaw tawm tsam hauv dilute HF.

Piv txwv ntawm Field Failure in Industrial Cleaning and Etching
Ib daim ntawv ntsuam xyuas ntawm 316 stainless hlau encased rhaub nyob rau hauv HF kev pab cuam ntawm 14 industrial chaw qhia tau hais tias muaj kev koom tes ntawm HF concentration thiab mechanism ntawm tsis ua hauj lwm:

Daim ntawv thov HF concentration Kub (degree) Hom Kev Pabcuam Lub Neej (1.5mm phab ntsa) Hom Kev Ua Haujlwm Tseem Ceeb
Hlau pickling (HCl-HF sib xyaw acid, HF<1%) 0.5-1% 60-70 2-4 weeksSevere pitting, perforation 
iav etching (5-10% HF, nrog additives) 5-8% 50-60 8-14 hli Predictable, txawm thinning
Semiconductor wafer tu (0.5-1% HF, chav tsev temp) 0.5-1% 25 6-8 hli Pitting (nqi qis dua T)
Kev ntxuav cov tshuaj reactor (3-5% HF nquag siv) 3-5% 80 12-18 hli Mixed pitting/general
Ceramic etching (10% HF, recirculating voj) 10% 40 18-24 hli Thinning nkaus xwb
Roj zoo acidising kua rhaub (0.5-1% HF, ua tiav kev ua haujlwm) 0.5-1% 80 3-5 lub lis piam (ib txoj haujlwm) Perforation nrog pitting
Nyob rau hauv ib qho chaw semiconductor, nce qhov HF concentration ntawm 1% ntawm 25℃mus rau 5% ntawm 25℃rau cov txheej txheem etch txo qhov kev pheej hmoo ntawm pitting tab sis nce tus nqi ntawm cov corrosion tsis sib xws los ntawm 0.03 hli / xyoo mus rau 0.12 hli / xyoo, uas tseem siv tau rau lawv 2 hli phab ntsa sheaths. Counter intuitively txav mus rau ntau dua concentration nce kev ntseeg tau.

Lwm cov khoom siv thiab txo qis ntawm Dilute HF
316 stainless hlau tsis qhia rau kev siv hauv kev pabcuam HF dilute (tsawg dua 2% concentration, kub tshaj 50 degree). Kev txhim kho cov khoom siv lossis cov txheej txheem txo qis yog tsim nyog.

Material Uniform Corrosion Rate nyob rau hauv 1% HF, 70℃(mm/yr) Susceptibility Relative Cost Recommendation Dilute HF (<2% )
316 Stainless hlau 0.08 hnyav, perforation<2000 hrs 1.0 Not recommended above 40°C 316 with low sulphur (0.003% max) 0.08 Moderate, pitting delayed 3-5x 1.5 Acceptable for short duration (<6 months)
Alloy 20 (UNS N08020) 0.12 Tsawg, dav dav tsuas yog 3.0 Zoo rau 1-2 xyoos lub neej
Alloy C-276 (UNS N10276) 0.05 Tsis muaj 8.0 Zoo heev, ncua lub neej
Tantalum<0.001 None 20+ Over-specified
PTFE (sheathed polymer) 0 ( tshuaj inert) Tsis pom zoo 2.0 Pom zoo rau<120°C
Cov pa roj carbon steel (siab kub) 1.5 Pitting hnyav 0.3 Tsis qhia (kev pheej hmoo kis kab mob)
Nyob rau hauv feem ntau dilute HF daim ntaub ntawv hauv qab 100 degree, ib tug hluav taws xob rhaub nyob rau hauv PTFE los yog PFA (polymer sheath over resistance wire) kiag li tiv thaiv corrosion ntawm hlau. Alloy C-276 los yog Alloy 20 yog qhov zoo dua tshaj 316 thaum cov hlau sheath yuav tsum tau ua kom muaj cua sov hloov mus los yog vim li cas cov qauv.

Ib lub chaw tshuaj lom neeg uas tau hloov pauv los ntawm 316 mus rau Alloy C-276 sheaths hauv 1.5% HF, 75℃pickling da dej, txuas ntxiv lub neej nruab nrab ntawm 45 hnub mus rau 28 lub hlis, nrog kev ua haujlwm tsis zoo los ntawm kev tsis sib xws es tsis yog pitting. Tus nqi pib siab dua (8 × rau Alloy C-276) tau rov qab los hauv kev txo qis qis thiab hloov chaw ua haujlwm.

Specification Language for Heaters of Dilute Hydrofluoric Acid
Engineers should carefully consider material compatibility when sourcing electric heating tubes for HF service at concentrations greater than 0.1% and temperatures greater than 40°C. 316 stainless steel is not appropriate for HF concentrations below 2% and temperatures exceeding 50°C. Sheath Material Alloy 20 (UNS N08020) or Alloy C-276 (UNS N10276). For 2% to 5% concentrations, 316 can be considered but with the following requirements: maximum sulphur content of 0.005%, electropolished surface finish (Ra ≤ 0.4 µm) and a corrosion test coupon in the actual process solution for 500 hours with maximum pit depth not exceeding 25 µm. 316 is acceptable for uniform corrosion at HF concentrations >5% yog tias phab ntsa thickness pub (xws li kev tiv thaiv corrosion ntawm ntsuas tus nqi + 50% kev nyab xeeb margin). suav nrog qhov xav tau rau kev tshem tawm roj inert thaum lub sijhawm kaw rau txhua qhov kev pabcuam HF txhawm rau tiv thaiv kev sib xyaw ntawm HF los ntawm cov dej evaporation los ntawm kev daws teeb meem, uas tuaj yeem txhawb nqa HF concentration rau hauv qhov chaw pitting. Ntawm no peb nkag siab qhov tsis yog-monotonic concentration dependence ntawm HF corrosion ntawm 316, nrog rau qhov loj tshaj plaws pitting txaus ntshai nyob rau hauv tsawg concentrations thiab uniform nres ntawm ntau dua concentrations, muab engineers nrog ib tug nkag siab ntawm ib tug ntau thiab counter-intuitive tsis ua hauj lwm scenario.