Dab tsi siab tshaj qhov sib npaug los ntawm kev sib xyaw sab hauv siab thiab thermal nthuav dav ntawm 400℃Sab hauv phab ntsa kub tiv thaiv kev ua tsis tiav ntawm 316 Stainless Steel Heater Sheaths

Qhov Kev Txwv Tsis Pub Cyclic Thermal Mechanical Loading

Lub xeev kev ntxhov siab nyob rau hauv 316 stainless hlau sheathed hluav taws xob cua sov raj, kev khiav hauj lwm nyob rau hauv cyclic tej yam kev mob ntawm siab kub (400 C sab hauv phab ntsa kub), xws li intermittent txheej txheem cua sov los yog systems nrog txhua hnub nyob rau hauv - tawm cycles, yog vim muaj kev sib txuas ntawm lub sab hauv siab hoop stress thiab thermal expansion induced axial stress. Yog tias qhov sib npaug ntawm kev ntxhov siab ( von Mises ) mus dhau qhov kev txwv ntawm cov khoom siv, cov ntaub qhwv yuav tsim cov yas yas thaum lub sij hawm txhua lub voj voog cua sov (ratcheting), uas ua rau maj mam nce hauv txoj kab uas hla (o) thiab zaum kawg rupture. Lub shakedown txwv rau 316 ntawm 400℃yog li ntawm 1.5 mus rau 2.0 npaug ntawm cov khoom muaj zog, nyob ntawm qhov kev ntxhov siab piv. Yog tias qhov kev ntxhov siab tsis dhau qhov kev txwv no, cov khoom yuav teb elastically tom qab ob peb lub voj voog (elastic shakedown). ratcheting tus nqi yog 0.01-0.1% strain / voj voog saum toj no txwv, thiab tsis ua hauj lwm tshwm sim tom qab 1,000-10,000 cycles. Nyob rau hauv daim ntawv no, qhov siab tshaj plaws sib npaug kev ntxhov siab yog xam rau ratcheting dawb ua hauj lwm ntawm 316 sheaths nyob rau hauv coupled loads.

Lub ratcheting mechanism nyob rau hauv multiaxial loading

If a heater sheath is fixed at both ends (e.g. flanges or penetrations in the tank wall), thermal expansion during heating will produce axial compressive stress if the sheath is longer than required by its free length. At the same time, hoop tensile stress is induced by internal pressure, whether from sealed gas expansion or from process pressure. The axial stress may surpass yield in compression during heating and be reversed to tension during cooling. If the von Mises equivalent stress exceeds the cyclic yield strength of the material, the hoop direction is incremented by the amount of plastic strain for each complete heat cycle. This incremental strain builds up with each cycle resulting in a gradual increase in sheath diameter (ratcheting). The ratcheting rate is dependent on the axial-to-hoop stress ratio and mean stress level. For similar loads up to around 1.2× the yield strength, no ratcheting occurs (elastic shakedown). Ratcheting is observed at a low rate (10 -4 to 10 -3 per cycle) between 1.2x and 2.0x yield. Rapid ratcheting leads to failure in hundreds of cycles at >2.0x ua.

Quantified Equivalent Stress txwv kev tiv thaiv ntawm Ratcheting ntawm 400 degree

Cov lus hauv qab no muab qhov siab tshaj plaws sib npaug (von Mises) kev ntxhov siab rau 316 stainless hlau ntawm 400℃(yield zog txog 140 MPa) rau ratcheting dawb ua haujlwm rau lub neej tsim sib txawv, sawv cev raws li ntau yam ntawm lub zog tawm los thiab qhov tseem ceeb ntawm kev ntxhov siab.

Sib npaug Kev Nyuaj Siab (von Mises) raws li kev tawm los (400 degree) Sib npaug Kev Nyuaj Siab Tsis Txaus (MPa) Ratcheting Strain Rate (% cycle-1) Lub voj voog mus rau 2% Txoj kab uas hla nce (tsis ua raws cai) Cycles rau ReptureRecommended rau Cyclic Service<1.0× (<140 MPa) <140 0 (elastic shakedown) >100,000 >200,000 Yog
1.0-1.2 × (140-170 MPa) 140-170 hli<0.001 50,000-100,000 80,000-150,000 Yes (low risk)
1.2-1.5 × (170-210 MPa) 170-210 0.001-0.005 10,000-50,000 15,000-80,000 Tau rau kev caij tsheb kauj vab
1.5-1.8 × (210-250 MPa) 210-250 0.005-0.02 2,500-10,000 4,000-20,000 Marginal, saib
1.8-2.0 × (250-280 MPa) 250-280 0.02-0.05 1,000-2,500 1,500-5,000 Tsis haum rau lub voj voog siab
2.0-2.5×(280-350 MPa) 280-350 0.05-0.10 200-1,000 300-2,000 Unacceptable >2.5× (>350 MPa) >350 >0.10 <200 <300 Not acceptable
Combined Loadings: xam qhov sib npaug sib npaug

Rau lub nyias- phab ntsa phab ntsa nyob rau hauv lub siab sab hauv (hoop stress σ_θ) thiab ib qho kev txwv axial (axial stress σ_z) nrog negligible radial stress, lub von Mises equivalent stress yog: σ_vM=sqrt(σ_θ2 + σ_z{{8} σ}). Hoop kev ntxhov siab los ntawm lub siab sab hauv: σ_θ=P × D_mean / 2t. Axial thermal expansion constraint stress: σ_z=× E × ΔT × K, qhov twg K yog qhov txwv tsis pub tshaj (0 rau tag nrho cov kev txwv tsis pub nthuav dav, 1.0 rau tag nrho kev txwv xaus, nruab nrab rau ib nrab txwv). Rau lub rhaub nrog ob qhov kawg ruaj K=1.0 thiab axial kev nyuaj siab yog compressive (tsis zoo) rau cua sov thiab tensile (zoo) kom txias. Qhov siab tshaj $\\sigma_{vM}$ tshwm sim thaum qhov kev ntxhov siab axial yog qhov zoo (txias) thiab ntawm tib lub cim li $\\sigma_\\theta$. σ_z=17e-6 x 180 GPa (ntawm 400C, E ~ 170 GPa) x 380=1100 MPa yog tag nrho txwv - ntau tshaj tawm los. Rau ib txwm 10 hli OD, 1.5 hli phab ntsa sheath ntawm 400C sab hauv phab ntsa kub (Delta T=380C los ntawm ambient). Hauv kev xyaum, kev txo qis los ntawm kev khoov lossis flange yooj yooj yim txo qhov ua tau zoo K rau 0.3-0.7.

Piv txwv ntawm kev siv tswv yim thiab tsim cov lus pom zoo

Cia peb xav tias 316 sheath (10 hli OD, 1.5 hli phab ntsa) nrog lub siab sab hauv ntawm 2 MPa (20 bar) ntawm 400 degree. Hoop stress σ_θ=(2x8.5) / (2x1.5)=5.7 MPa (tsis pom zoo). Rau qhov txwv axial, K=0.5, σz=0.5 × 1,{18}} MPa (compressive cua sov, tensile txias). Qhov sib npaug ntawm kev ntxhov siab σ_vM=550 MPa (vim σ_θ me me) uas yog 3.9 × tawm los ntawm 400℃(140 MPa)-zoo rau hauv qhov chaw nrawm nrawm. Xws li lub rhaub yuav bulge thiab poob hauv 100 mus rau 200 cycles. Kom tau txais σ_vM mus rau 1.2 x tawm los (168 MPa), K yuav tsum tau qis qis rau 0.15, yog li lub mounting yuav luag dawb los nthuav. Rau txhua lub rhaub dej kub ua haujlwm siab tshaj 300 degree, tus qauv tsim yuav tsum muaj kev txhawb nqa zawv zawg, nthuav dav lossis kev sib txuas yooj yim kom txo qis qhov txwv tsis pub tsawg dua 0.2.

Cov ntaub ntawv pov thawj ntawm ratcheting tsis ua haujlwm

Cov tsos mob zoo tshaj plaws ntawm ratcheting tsis ua hauj lwm yog ib qho kev sib txuam thiab kev nthuav dav ntawm cov kab uas hla (o) feem ntau ntawm qhov kub tshaj plaws raws li qhov ntev ntawm 50-200 hli. Tej zaum yuav pom kev loj hlob ntawm txoj kab uas hla ntawm 2-10% ua ntej rupture. Lub rupture yog longitudinally split (parallel rau raj axis) es tsis circumferentially tawg, txij li thaum lub hoop hom los ntawm ratcheting yog ntau dua li axial hom. Cov pob txha tawg tuaj yeem pom cov cim qhia ntawm cyclic yas deformation (cov cim ntug hiav txwv). Rau cov cua sov hauv kev pabcuam, kev ntsuas lub sijhawm ntawm cov kab hauv qab ntawm ntau qhov chaw nrog lub calliper tuaj yeem ntes ratcheting ua ntej tsis ua haujlwm; 1% txoj kab uas hla nce txhais tau hais tias 25-50% ntawm lub neej ratcheting tau siv.

Xaus: Tswj kev txwv los tiv thaiv Ratcheting

Qhov siab tshaj plaws sib npaug rau ratcheting-kev ua haujlwm pub dawb ntawm 316 stainless hlau npog cov cua sov ntawm 400℃sab hauv phab ntsa kub yog li 1.2 × tawm los (168 MPa) nyob rau hauv cov xwm txheej cyclic. Hoop nro vim lub siab sab hauv ib leeg yog tsis tshua muaj loj txaus los tsim ratcheting. Qhov kev ntxhov siab loj yog qhov kev txwv ntawm axial thermal expansion uas tuaj yeem siab dua 1,000 MPa nyob rau hauv rooj plaub ntawm qhov ruaj khov sheath. Lub mounting system yuav tsum tau tsim los pub dawb thermal expansion los ntawm txoj kev zawv zawg seals, expansion pob qij txha los yog saj zawg zog brackets kom lub constraint yam K yog qis dua 0.2. Qhov twg tag nrho cov kev txwv tsis tuaj yeem zam tau (piv txwv li, hauv cov txheej txheem welded), cov khoom yuav tsum tau hloov mus rau lub zog siab dua xws li Inconel 625, lossis qhov kub ua haujlwm yuav tsum tau qis dua 300 degree. Cov qauv tam sim no cuam tshuam qhov sib npaug ntawm kev ntxhov siab nrog ratcheting tus nqi thiab lub voj voog lub neej, tso cai rau cov neeg yuav khoom los qhia txog 316 sheaths uas yuav tsis loj hlob nyob rau hauv txoj kab uas hla los yog tawg los ntawm cyclic thermal- mechanical stressing.