Ntawm Qhov Kev Sib Txuas Tshwj Xeeb ntawm Caustic Concentration thiab Sheath Surface Temperature Puas Yog 1.2 Millimeter 316 Stainless Steel Sheath Kev Ua Haujlwm Kev Ruaj Ntseg Corrosion Cracking hauv Pulp thiab Ntawv Kev Lag Luam Digester Heater Service?

Kev siv cov txheej txheem engineers lub luag hauj lwm rau hluav taws xob immersion heaters nyob rau hauv cov ntaub so ntswg thiab cov ntawv digesters, kev sib xyaw ntawm sodium hydroxide thiab sodium sulphide ntawm qhov kub siab ua rau ib puag ncig uas caustic stress corrosion cracking yog qhov ua tsis tau zoo. Caustic cracking tsim nkig intergranular tawg uas tuaj yeem nkag mus rau 1.2 hli 316 sheath hauv ib lub lis piam nrog kev ceeb toom me ntsis, tsis zoo li pitting lossis zoo tib yam corrosion. Cov txheej txheem kraft pulping siv dej cawv dawb nrog 15-20% NaOH thiab 5-10% Na₂S ntawm qhov kub ntawm 150-170 degree. Cov cua sov no feem ntau muaj phab ntsa tuab ntawm 1.2 hli vim tias qhov chaw txwv tsis pub muaj nyob hauv cov hlab ntsha digester. Tsab xov xwm qhia txog kev sib xyaw ua ke ntawm caustic concentration thiab sheath saum npoo kub ntawm 1.2-mm 316 sheath yuav tsim kev ntxhov siab corrosion tawg hauv 1000 teev ntawm kev pabcuam txuas ntxiv.

Mechanism ntawm Caustic Stress Corrosion Cracking nyob rau hauv 316
Caustic kev nyuaj siab corrosion cracking ntawm 316 stainless hlau yuav tsum muaj peb yam mob: ib tug caustic concentration tshaj tus nqi pib, kub siab tshaj qhov pib tawg thiab tensile kev nyuaj siab. Txoj kev swaging siv los compact MgO rwb thaiv tsev tsim loj residual tensile hom nyob rau hauv lub puab nto ntawm sheath-feem ntau 150-250 MPa rau ib tug 1.2 hli phab ntsa. Cov residual stresses no yog lub hauv paus ntawm tensile kev nyuaj siab yuav tsum tau rau cracking. Lub caustic concentration rau tawg nyob rau hauv 316 ntawm 150 ° C yog hais txog 5% NaOH. Qhov ntsuas kub tau txo qis rau 130 ° C ntawm 10% NaOH. Kev tawg ntawm 15% NaOH yog siab dua 110 degree. Cracking ntawm 20% NaOH tshaj 100 ° C. Cov xwm txheej hauv cawv dawb (15-20% NaOH, 150-170 degree) zoo tshaj qhov pib tawg. Cov kab nrib pleb hauv 1.2-mm 316 sheath feem ntau pib ntawm sab hauv qhov chaw uas cov kev ntxhov siab seem siab tshaj plaws tom qab 100-500 h raug. Thaum tsim tau, cov kab nrib pleb tawm ntawm tus nqi ntawm 0.1-1.0 hli hauv ib lub lis piam, nkag mus rau phab ntsa 1.2-mm hauv 1-3 lub hlis.

Sheath 1.2 Tseem Ceeb Cracking Thresholds rau 1.2
Raws li kev kuaj sim ntawm swaged 316 sheath qauv hauv cov cawv dawb simulant thiab kev soj ntsuam tsis ua hauj lwm los ntawm cov pob zeb zom zom, cov nram qab no ua ke ntawm caustic concentration thiab sheath nto kub ua rau caustic stress corrosion cracking nyob rau hauv 1,000 teev.

Sodium Hydroxide Concentration ( Nyhav %) Sodium Sulphide Concentration ( Nyhav %) Qhov Kub Kub Tseem Ceeb rau Cracking Onset Lub Sijhawm Ua Haujlwm tawg ntawm 150 ° C Sheath Surface Lub Sijhawm dhau los ntawm - Phab ntsa tawg (1.2 hli) ntawm 150 ° C 5 - 8% 20 - 4% 20 ° C 1,200 - 2,000 teev 8 - 10% 4 - 6% 130 ° C 500 - 800 teev 800 - 1,500 teev 10 - 12% 5 - 7% 120 ° C 300 - 500 teev 500 - 1,000 teev
12 - 15% 6 - 8% 115℃200 - 400 teev 400 - 800 teev 15 - 18% 7 - 9% 110℃150 - 300 teev 300 - 600 teev
18 - 20% 8 - 10% 100℃100 - 200 teev 200 - 400 teev
Ntau tshaj 20% Ntau tshaj 10% Tsawg dua 100℃50 - 150 teev 100 - 300 teev
Rau kraft digester ua hauj lwm nrog 16% NaOH ntawm 155℃tej qhov kub thiab txias, qhov kub ntawm lub plhaub yog li ntawm 155-160℃(xav tias qhov kub me me nce vim qhov tsawg watt ntom hauv cov digesters loj). Qhov no yog tshaj 110 ° C tawg qhov pib thiab yuav tsim cov kab nrib pleb hauv 150-300 teev. Lub 1.2 hli sheath yuav zoo li perforate tom qab 1-2 lub hlis ntawm kev ua haujlwm tas mus li. Cov kev paub dhau los qhia tau hais tias cov dej cawv dawb feem ntau tawg hauv 3-6 lub hlis nrog kev tawg ntawm qhov tseem ceeb ntawm kev ua tsis tiav.

Safe Operating Envelope rau 1.2mm Sheath nyob rau hauv Caustic Service
Cov lus hauv qab no teev qhov siab tshaj plaws kev nyab xeeb caustic concentration rau 1.2 hli 316 sheath ntawm qhov sib txawv sheath saum npoo kub kom tsis txhob muaj kev ntxhov siab corrosion tawg thoob plaws hauv 1,000 teev kev pabcuam lub neej. Cov txiaj ntsig xav tias qhov kev ntxhov siab nyob ruaj khov tom qab swaging, uas tsis tuaj yeem txo tsis tau tom qab -swage annealing.

Sheath Surface Temperature Maximum Safe NaOH Concentration to Prevent Cracking (No Sulfide) Maximum Safe NaOH Concentration nrog 5% Na2S Cia Siab Lub Sijhawm Rau Kev Cracking ntawm Qhov Siab Tshaj Plaws Zoo Tshaj Plaws Pom Zoo Ua Haujlwm 80 ° C 20% 15% 2,000 - 3,000 xuab moos 5% 9000 teev tas li 1% 900C 1,500 - 2,500 teev Txwv kev pab cuam lub neej 100 ° C 12% 10% 1,000 - 2,000 teev 316 tsis pom zoo 110 ° C 10% 8% 800 - 1,500 teev Siv annealed lossis alloy hloov kho 120 ° C 800010% 5 oy tag nrho 6% 4% 300 - 800 teev Alloy upgrade yuav tsum tau 140 ° C 4% 2% 200 - 500 teev 316 tsis haum
Tshaj 150 ° C Tsis muaj kev nyab xeeb Tsis muaj kev nyab xeeb hauv qab 200 teev Siv Nickel Alloy
Lub hnab ntawv ua haujlwm nyab xeeb rau 1.2 hli 316 sheath tsis muaj nyob rau hauv kev pabcuam pulp thiab ntawv digester nrog 16% NaOH ntawm 155 ° C. Kev tawg yuav tuaj nyob rau hauv lub lis piam los yog hli kom paub meej. Cov kws ua choj yuav tsum xaiv cov hlau uas ruaj khov dua.

Tsim cov kev hloov pauv los tiv thaiv caustic cracking
Thaum 316 sheath yuav tsum tau siv rau hauv kev pab cuam caustic, peb qhov kev tsim kho tuaj yeem ua rau lub neej ntev, tab sis tsis muaj leej twg ua rau 316 muaj kev vam khom rau kraft digester tej yam kev mob. Thawj kauj ruam yog txhawm rau txhawm rau tshaj tawm -swage ntawm 1050℃txhawm rau tshem tawm cov tensions seem. Annealing txo cov sab hauv qhov seem seem ntawm 150-250 MPa mus rau qis dua 20 MPa, tshem tawm cov tensile tivthaiv yuav tsum tau tawg. Annealing 1.2 hli 316 sheath hauv 16% NaOH ntawm 150 ° C tuaj yeem txuas nws lub neej mus rau 3-6 lub hlis, tsis yog 1-2 lub hlis. Qhov thib ob hloov pauv yog txhaj tshuaj peen los yog lwm yam compressively kho sab nraud. Cov txheej txheem compressive tiv thaiv kev tawg tawm tab sis tsis txo qis tensile kev nyuaj siab ntawm sab hauv. Qhov kev hloov pauv zaum kawg yog ua haujlwm ntawm qhov qis tshaj qhov ua tau los ntawm qhov kub thiab txias los ntawm kev txo cov watt ntom ntom thiab txhawb kev ncig. Ib qho 10℃txo qis hauv qhov kub thiab txias ob npaug rau lub sijhawm tawg pib. Cov kev hloov no tsis txaus rau feem ntau cov ntaub ntawv thiab daim ntawv thov. Alloy 625 los yog Alloy C-276 yog cov khoom siv rau cov dej cawv dawb. Cov nickel-raws li alloys tiv taus kev ntxhov siab corrosion tawg ntawm tag nrho cov concentrations thiab kub pom nyob rau hauv digesters. A 1.6 hli Alloy 625 sheath yuav ib txwm ua siab ntev 5-10 xyoo nyob rau hauv cov kev pab dawb ntsuj plig li vs 2-6 lub hlis rau 316. Tus nqi pib siab dua yog them rau los ntawm cov nyiaj txuag hauv downtime thiab hloov ua haujlwm. Cov kws tsim qauv xaiv cov cua sov rau kev ua haujlwm digester yuav tsum tsis txhob txais 316 rau txhua daim ntawv thov qhov twg caustic concentration siab tshaj 10% ntawm qhov kub siab tshaj 100 ° C. Tus nqi ntawm kev tawg sai sai nyob rau hauv lub tshuab nqus tsev siab nrog rau cov khoom poob, lub nkoj txias, thiab kev hloov pauv yog ntau dua li tus nqi nce ntxiv ntawm cov nickel alloy siab. Yog tias cov chaw tsim khoom pom zoo 316 rau kev pabcuam dawb dawb thiab tsis tham txog kev ntxhov siab ua rau corrosion tawg lawv tsis muab cov lus ntuas tsim nyog. Cov kab nrib pleb hauv 1.2 hli sheath txhim kho sai thiab tsis muaj pov thawj pom tseeb kom txog thaum lub hnab xau. Qhov tseeb tsuas yog kev daws teeb meem yog kev tiv thaiv los ntawm kev xaiv raug ntawm alloy.