Qhov siab tshaj plaws uas tso cai rau Residual Solder Flux (Chloride-Raws li) Cov kab mob sib kis ntawm 316 Heater Sheath Surface Initiates Pitting nyob rau hauv Humid Ambient Cia Ua ntej yuav teeb tsa

Hidden Pre-Kev Pabcuam Corrosion Risk los ntawm Kev Tshaj Lij tsis txaus- Kev Tsim Kho Kev Tu

Residual chloride-based solder flux from electrical connection brazing or from contamination during adjacent soldering operations is a severe pitting risk for 316 stainless steel sheathed electric heating tubes stored in warehouse or field conditions prior to installation, particularly in humid environments (relative humidity >60-70%). Fluxes of zinc chloride (ZnCl₂), ammonium chloride (NH₄Cl) or other chloride salts are deliquescent, i.e. they collect moisture from the air and generate concentrated chloride solutions on the sheath surface. Even minuscule flux residues (1-10µg/cm2, almost invisible) can lead to chloride concentrations of 10,000-100,000 ppm at the metal-flux interface, enough to induce pitting on 316 at ambient temperature within weeks to months. The critical flux residue density for pitting initiation is ~0.5-1.0 µg Cl⁻ per cm² at 25°C and 65% RH. Pitting initiates within 30-90 days at >5 -10 µg Cl- / cm2. Hauv kev pabcuam ua ntej ntawm 316 sheaths, qhov sib txuas ntawm cov tshuaj chloride residual flux ntom ntom, av noo thiab lub sijhawm xav tau rau kev pib pitting yog muaj nyob rau hauv tsab xov xwm no.

Mechanism ntawm Atmospheric Pitting Induced los ntawm Deliquescent

Chloride raws li solder fluxes yog hygroscopic. Yog hais tias tus txheeb ze av noo tshaj qhov deliquescence point ntawm cov ntsev muab (li 10% RH rau ZnCl 2 thiab nyob ib ncig ntawm 77-80% RH rau NH 4 Cl), cov flux absorbs noo noo los ntawm qhov chaw thiab ib tug nyias zaj duab xis ntawm concentrated chloride electrolyte yog tsim nyob rau hauv cov hlau nto. Ntawm cov hlau -flux tiv tauj, cov tshuaj chloride tuaj yeem ncav cuag siab li 30-50 wt% (300,000-500,000 ppm Cl⁻), zoo tshaj qhov pib pitting rau 316 txawm nyob rau ntawm qhov kub thiab txias. Cov txheej electrolyte yog nyias thiab nplua nuj nyob rau hauv oxygen ua rau pom qhov tshwm sim rau pitting. Thaum pib lub qhov dej, cov kab hluav taws xob tiv thaiv nws tus kheej thiab lub qhov dej tuaj yeem nkag mus rau phab ntsa 1.5 hli hauv 6-12 lub hlis txawm tias lub tshuab cua sov tsis tau muaj zog.

Kev txiav txim siab ntawm kev sib raug zoo ntawm cov khoom seem chloride Flux thiab Pitting Sijhawm

Tswj cov av noo chamber kuaj (25 degree, 65% RH) ntawm 316 stainless hlau daim coupon nrog tswj deposits ntawm chloride flux (raws li NaCl sib npaug, simulating tov chloride ntsev) yielded cov nram qab no pitting pib thiab propagation sij hawm.

Residual Chloride on Surface (µg Cl-/cm2) Equivalent Flux Residue Visibility Time to Pit Initiation at 65% RH, 25°C (days)Pit Depth after 180 days (µm) Time to Perforation (1.5 mm wall) (hours) at 65% RHRecommended Max Storage >6 hli<0.1 Undetectable >365 (tsis muaj teeb meem)<5 >10 xyoo Yes 0.1-0.5 Kab (tsis pom) 180-365 5-15 5-10 xyoo Yog
0.5-1.0 Lub teeb heev (saib hauv qab UV) 90-180 15-40 2-5 xyoo Txais
1.0-2.0 Lub teeb (pom pom) 60-90 40-80 1-2 xyoo Marginal
2.0-5.0 Nruab Nrab (discoloration) 30-60 80-150 6-12 hli Tsis qhia
5.0-10.0 Hnyav (dawb tso nyiaj) 15-30 150-250 3-6 hli Tsis haum
10-20 Crust (hnyav heev) 7-15 250-400 2-3 hli Unacceptable20 Thick crust<7 >400 <2 months Not suitable
Cov nyhuv ntawm txheeb ze humidity ntawm tus nqi ntawm chloride Induced Pitting

Lub sij hawm rau pitting pib tshwm sim sai heev nrog nce tus txheeb ze humidity. Cov nyhuv ntawm RH ntawm qhov tsis tu ncua 25℃rau qhov seem chloride ntom ntawm 2 µg Cl-/cm2 yog qhia hauv cov lus hauv qab no.

Electrolyte Layer Thickness (kwv yees li μm) Lub Sijhawm rau Pit Initiation (hnub) txheeb ze humidity (%) Lub Sijhawm rau Perforation (mo.) Cov lus pom zoo cia<40 No liquid (salt remains dry) >365 (no pitting) >10 xyoo Safe 40-50 0.1-0.5 180-300 3-5 xyoo Safe 50-60 0.5-1.0 90-180 2-3 xyoo Saib xyuas 60-70 1-2 60-90 1-2 xyoo Desiccant pom zoo 70-80 2-5 30-60 6-12 hli Desiccant tsim nyog
80-90 5-10 15-30 3-6 months Unacceptable >90 >10 <15 <3 months Not acceptable
Heater Manufacture Solder Flux Contamination Sources

Kev tsim cov dej num uas tawm hauv cov tshuaj chloride raws li cov nyiaj tso rau ntawm 316 sheaths:

Terminal brazing: Thaum cov hluav taws xob sib txuas terminals yog brazed mus rau lub rhaub sheath (los yog cov hlau lead), chloride-raws li fluxes (piv txwv li, Handy Flux Type 2, suav nrog ZnCl 2 thiab NH 4 Cl) feem ntau ua haujlwm. Kev ntxuav tsis raug tom qab brazing, flux residues nyob rau ntawm cov ntaub qhwv uas nyob ib sab.

Adjacent Soldering: Cov cua sov hauv cov khoom siv sib dhos tuaj yeem muaj cov raj tooj liab uas nyob ib sab lossis cov hluav taws xob sib txuas uas tau ua nrog flux-cov tub ntxhais solder. Flux spatter los yog vapor tuaj yeem sau rau ntawm lub tshuab cua sov.

Kev cuam tshuam nrog kev sib kis: Cov neeg ua haujlwm uas tswj cov flux- cov khoom siv coated ces hu rau stainless hlau sheaths hloov cov tshuaj chloride tsis pom.

Qhov siab tshaj plaws tso cai flux residue txwv tau muab rau hauv cov lus hauv qab no rau cov xwm txheej sib txawv.

Cia Lub Sijhawm Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntev Ntau Yam Ntawm Cov Chloride (µg Cl- / cm2) Yuav Tsum Tau Tshaj Tawm-Brazing Cleaning Method
Climate controlled warehousing (RH<50%) >12 lub hlis 5.0 Kev soj ntsuam pom thiab hnyav so
Ambient warehouse (RH 50-70%) 2.0 Yaug hauv dej deionised + qhuav 6-12 lub hlis
Ambient warehouse nrog cov av noo raws caij nyoog 3-6 lub hlis 1.0 Ultrasonic tu + DI yaug
Outdoor or uncontrolled (humidity >70%) Ib<0.5 Full passivation + clean checked
Sealed with desiccant >12 lub hlis 10.0 Tus qauv tu OK
Tshaj tawm -Brazing Surface Cleanliness Verification

Rau 316 sheaths nrog brazed terminals los yog rau ib qho txheej txheem soldering, cov kev kuaj xyuas kev huv hauv qab no tau qhia rau tus neeg yuav khoom:

Bresle patch method (ISO 8502-6) Ib thaj yog muab tso rau saum npoo ntawm lub plhaub, cov dej deionised yog txhaj thiab cov conductivity raug soj ntsuam los ntsuas cov tshuaj chloride extraction. Txais:<2 µg Cl⁻/cm² for normal service, <0.5 µg Cl⁻/cm² for high humidity storage.

Kev ntsuam xyuas Ferroxyl: Kev daws ntawm potassium ferricyanide thiab sodium chloride yog muab tso rau saum npoo. Cov xim xiav implies dawb hlau los yog cov tshuaj chlorides. Txais. Tsis muaj xiav.

Water Break Test Tom qab ntxuav cov dej yuav tsum tau daim ntawv sib npaug ntawm qhov chaw thiab tsis txhob hlaws. Beading yog pov thawj ntawm cov organic lossis flux residues.

Field Pre-Service Flux-Induced Pitting

Rau lub rhaub 316 uas tso rau hauv qhov chaw cia ua ntej nws puas tau muab tso rau hauv kev siv, cov pits yuav nyob ze rau lub brazed terminals los yog tej qhov chaw flux tej zaum yuav splattered. Tus so ntawm lub sheath yog immaculate tab sis cov pits zoo li pawg nyob ib ncig ntawm qhov chaw tainted. Nyob rau hauv lub microscope lub pit center yuav tso saib tshuav dawb los yog xim av crystalline flux ntsev. EDS ntawm qhov seem seem yuav pom muaj cov tshuaj chlorine (Cl) thiab zinc (Zn) lossis lwm yam khoom siv flux. Cov kev ua txhaum no yuav tsum tau kuaj xyuas hauv cov chaw tsim khoom cov txheej txheem ntxuav. Hloov cov cua sov yuav tsum tau txiav txim nrog cov lus qhia rau kev tshaj tawm -brazing tu rau<1 µg Cl⁻/cm² and confirmation by Bresle patch.

Xaus: Tsim Kev Tshaj Tawm -Brazing Cleanliness rau Kev Cia Siab

316 stainless steel sheathed heaters stored in humid conditions (RH >60-70%) nrog cov tshuaj chloride residual-raws li solder flux densities ntau dua 1-2 µg Cl-/cm2 ua rau pitting li ntawm 30-90 hnub ntawm kev cia, nrog kev nkag mus los ntawm lub sheath phab ntsa nyob rau hauv 6-12 lub hlis ntawm kev cia-ua ntej lub rhaub. Cov kws tshaj lij qhia txog cov cua sov nrog kev sib txuas ntawm brazed yuav tsum muab cov ntsiab lus ntawm kev ntxuav tom qab brazing nrog cov chloride residue ntau tshaj (piv txwv li,<1 µg Cl- /cm2 for storage >3 lub hlis,<0.5 µg Cl- /cm2 for >6 lub hlis). Cov chav kuaj yuav tsum tau kuaj xyuas los ntawm Bresle thaj chaw lossis kev kuaj ferroxyl. Kev tiv thaiv ntxiv yog muab rau cov ntaub ntawv khaws cia tseem ceeb lossis lub sijhawm ntev nrog cov ntaub ntawv pov tseg tag nrho (nitric acid passivation ib ASTM A967) thiab khaws cia rau hauv lub hnab ntim nrog cov khoom siv desiccant. Txoj hauv kev no tau muab los ntawm no txuas cov chloride flux qhov ntom ntom rau qhov ntsuas pitting pib lub sijhawm nyob rau hauv cov huab cua ntub dej, ua rau cov neeg yuav khoom kom tsis txhob ua ntej -kev pabcuam corrosion tsis ua haujlwm los ntawm kev xa tsis txaus- kev tsim khoom tu.