Dab tsi yog erw steel kav? Unveiling cov haujlwm ua haujlwm ntawm cov piping niaj hnub

Taw qhia: Ubiquitous conduit

Nyob rau hauv lub network loj ntawm infrastructure uas unspins pob txha hauv peb tsev thiab cov tsheb thauj khoom hauv tsev thiab cov tsheb thauj khoom ua si ib lub luag haujlwm tseem ceeb. Ntawm cov txheej txheem sib txawv ua haujlwm los tsim cov consuits no, hluav taws xob cuam tshuam vuam (ERW) sawv tawm raws li tus txheej txheem thiab ntau txheej txheem. Kev to taubdab tsi yog erw yeeb nkabyog qhov tseem ceeb rau cov engineers, cov kws tshaj lij, cov ntaub muag khoom, thiab txhua tus neeg koom nrog hauv kev lag luam kom ruaj ntseg ntawm cov tshuab raj. Tsab ntawv no rho tawm tob rau hauvLub ntsiab lus ntawm ERW YEEB, tshawb txog nws cov kev tsim qauv, cov yam ntxwv tshwj xeeb, cov kev siv ntau yam, cov txiaj ntsig zoo, kev tswj hwm zoo, thiab cov qauv kev tswj hwm zoo. Los ntawm demystingingERW STEEL YEEB, peb tau txais kev txaus siab rau qhov no tseem ceeb engineering |.

1. Txhais ERW: Cov Ntsiab Lus Tseem Ceeb thiab Cov Txheej Txheem

Ntawm nws lub siab, tusERW cov yeeb nkab ntsiab lusrevolves nyob ib ncig ntawm cov txheej txheem tsim khoom.Dab tsi yog ERW?ERW sawv rauHluav taws xob tiv thaiv vuamCov. Nws yog qhov siab - Ceev, Nrauv cov txheej txheem siv los tsim cov yeeb nkab ntev welded steel thiab tubing.

• Lub hauv paus ntsiab lus:Lub tub ntxhaisERW txhais tau tiasSiv cov kev tawm tsam ntawm cov hlau mus rau qhov ntws ntawm hluav taws xob tam sim no los tsim kom muaj cua sov. Qhov kub no yog feeb meej meej meej ntawm qhov chaw uas weld yuav tsim.
• Tus txheej txheem yooj yim:

1. Sawb Uncoiling & Txuj Ci:Kev txuas ntxiv coil (skelp) ntawm kub - rolled lossis txias- rolled steel sawb yog ris tsho. Cov kab txaij no dhau los ntawm kev sib sau yob hauv cov pob zeb erw. Cov qaws no txuas ntxiv khoov rau ntawm cov duab cylindrical nrog cov npoo tau coj ua ke nruj me ntsis hauv siab. Qhov tseeb tsim ua ntu zus (piv txwv li, puas yog yob, fin kis, sib sau yob) cov duab sauv kom raug.
2. Qhov tseem ceeb vuam taw tes:Qhov tseem ceeb theem tshwm sim ntawm qhov chaw vuam. Qhov ua kom haum rau lub tog raj kheej ntev ntawm lub tog raj kheej tsim ua ke ntawm ob lub tooj liab alloy tiv tauj khau (elecodes). Ib tug heev siab - zaus} zaus hloov pauv tam sim no (AC) tau thov los ntawm cov hluav taws xob no rau cov npoo. TusERW txhais tau tiasKev cia siab rau cov hluav taws xob tsis kam ntawm cov hlau nws tus kheej los tsim kom muaj kev mob siab, cov cua sov hauv zos ntawm lub sib txuas ntawm ob npoo - joule cua sov. Qhov kub no sai sai tsa qhov kub ntawm cov steel sawv kom zoo saum toj no melting point (feem ntau rau kev sib tw kub).
3. Forging Unvent:Ib txhij nrog daim ntawv thov ntawm tam sim no, cov neeg ua tshuab siab siab tau siv los ntawm cov electrodes thiab kev sib sau yob. Qhov kev siab no tsis pub ua ke molten lossis yas npoo ua ke, nthuav tawm cov impurities lossis oxides thiab tsim cov khoom- lub xeev weld. Kev sib xyaw ua ke ntawm kev mob siab rau cov cua sov thiab kev kub siab tsim cov kev sib tw weld yam tsis muaj kev sib ntxiv ntawm cov muab tub lim hlau.
4. Kev Kho Mob Weld:Sai li sai tau tom qab vuam, sab nraud thiab sab hauv weld hlaws (flash) tsim tau siv cov cuab yeej txiav (phuam qhwv caj dab) thaum lub weld tseem kub thiab muag. Qhov no tsim ib qho chaw du. Qee cov mills tseem ua cov kev kho cua sov online (normalizing lossis annealing) ntawm Weld Seam Cov Qauv thiab txhim kho cov khoom siv neeg kho khaub ncaws.
5. Sizing & Wraftening:Welded yeeb nkab ces dhau los ntawm ib qho sizing rolls. Cov khaub thuas - ua haujlwm cov yeeb nkab kom ua tiav nws qhov kawg ncaj qha sab nraum lub taub (OD), kev sib tw, thiab kev ncaj ncees.
6. Txiav rau ntev:Nruam cov yeeb yog thaum kawg txiav kom teev qhov ntev siv ya saw lossis lwm yam kev txiav cov tshuab.
7. Xov & Kuaj:Kev txiav cov kav dej hla ntau cov kauj ruam tag (hy6, kev kuaj xyuas hydrostatic, tsis yog} Kuv yuav tsum tau siv) ua ntej ntim khoom kawg nkaus thiab cov zaub mov xa tuaj.

Cov kev ua tau zoo thiab nrawm ntawm cov txheej txheem txuas ntxiv no yog qhov tseem ceeb hauv kev sib kis tau thiab tus nqi- ua hauj lwm zoo ntawmERW kav.

2. Muaj qhov txawv ntawm lwm cov yeeb nkab tsim cov txheej txheem

Kev to taubdab tsi yog erw yeeb nkabkuj yuav tsum paub nws yog dab tsitsisCov. ERW yog ib qho ntawm ntau txoj hauv kev rau kev tsim cov welded steel yeeb nkab, txhua tus muaj cov yam ntxwv sib xws:

• ERW vs. Seamless (sms) yeeb nkab:Seamless cov yeeb nkab yog tsim los ntawm tho ib lub nplua fillet ntawm cov hlau thiab tom qab ntawd elongating nws los ntawm dov thiab kos cov txheej txheem. Nws tsis muaj kev sib tw weld ntev.

• Qhov sib txawv:Seamless cov yeeb nkab inherently tsis muaj txoj kab ntev ntev, feem ntau pom tias yog qhov xwm txheej ntawm qaug zog (txawm tias niaj hnub txhim khu kev ntseeg tau). SMLS feem ntau nyiam rau qhov siab heev - qhov siab, tseem ceeb, lossis cov ntawv thov corrosive uas yuav tsum muaj kev loj tshaj plaws. Txawm li cas los xij, cov yeeb nkab uas tsis muaj nqi yog qhov tseem kim dua thiab muaj qhov loj me txwv piv rau qhov loj- txoj hauj lwm hla.
• ERW vs. Submerged Arc Welded (pom) Yeeb Nkab:Pom cov yeeb nkab tseem pib nrog tsim tus ntses, tab sis cov kab ntawv ntev (LSAW) lossis KAUV) lossis KAUV) lossis KAUV) lossis KAUV) lossis KAUV) lossis KAUV Ib lub arc hluav taws xob melts lub electrode thiab flux, tsim lub pas dej weld thiab tiv thaiv nws los ntawm cov kev paug atmosphric.

Qhov sib txawv:Pom siv cov hlau sib tov sab nraud thiab flux, tsim cov tuab dua, txhawb weld hlaws dai. Nws yog feem ntau siv rau cov kab mob loj dua, cov roj ntsa uas tau qeeb dua qub Erdw excels me me rau nruab nrab diameters ntawm kev siv tsheb siab ntau lawm.

• Erw thiab rauv taws taub hau welded (FBW) yeeb nkab:Ib qho txheej txheem qub, FBW koom nrog cua sov cov npoo ntawm cov txheej txheem tsim nyob rau hauv lub cub tawg thiab tom qab ntawd ua ke los ua ke los ua ke ntawm weld. Nws feem ntau ua yeeb nkab nrog qis qhov tseeb thiab muaj weld zoo piv rau ERW.

Rooj 1: kev sib piv ntawm cov khoom siv steel hlau tsim cov txheej txheem

Qhov kev sib piv ntawm qhov teeb meem uasERW kavNyob hauv ib qho tseem ceeb tshaj plaws ntawm cov nqi, kev ua kom nrawm nrawm, tshwj xeeb nyob rau hauv cov ntawv thov loj, tshwj xeeb hauv}- nruab nrab txoj kab ntau.

3. Cov yam ntxwv thiab cov khoom ntawm ERW hlau kav

Cov khoom ntawmhluav taws xob tiv thaiv welded steel yeeb nkabqia ncaj qha los ntawm kev tsim khoom lag luam thiab cov khoom siv hauv paus siv (Skelp):

• Khoom siv:ERW kav yog tsim los ntawm tsawg - carbon, nruab nrab {{{{{}}}} alloy (hsla) cov hlau. Cov qib kawm feem ntau suav nrog AFTM A53 (Qib A & B), ASTM A135, AVI 5L (DIN (DIN, LOSSIS BS sib npaug. Kev xaiv ntawm qib steel txiav txim siab cov yeeb nkab cov cuab yeej siv tshuab (tawm lub zog, hardness) thiab haum rau qee qhov chaw ib puag ncig.
• Weld Reld Muaj Peev Xwm:Qhov zoo tshaj ntawm ERW Weld Weld Seam yog qhov tseem ceeb. Niaj hnub nimno siab - zaus erw cov tswv yim, sib xyaw ua ke nrog kev tiv thaiv tshav kub, ua kom muaj kev ncaj ncees rau cov hlau. Lub weld microstructure yog kho kom zoo nkauj yog kho kom zoo, thiab tsis muaj qhov tsis muaj fusion lossis suav nrog cov txheej txheem tswj thiab kuaj nruj. Kom tsimERW STEEL YEEBCov khoom ua pov thawj zoo ntev ntev zog.
• Qhov tseeb ntawm qhov tseeb thiab nto tiav:Cov txheej txheem txias sizing kom ntseeg tauERW TubeThiab cov yeeb nkab muaj cov khoom siv tau zoo sib xws (OD, Phab Ntsa Thickness, Roundness) thiab Ncaj. Lub saum npoo tiav yog feem ntau du, tshwj xeeb yog tom qab sab nraud / sab hauv weld hlaws tshem tawm. Qhov no ua rau cov yeeb nkab tsim nyog rau cov ntawv thov uas yuav tsum tau ua kom pom tseeb thiab zoo nkauj zoo.
• Cov Khoom Siv Neeg Kho Tshuab:Kev ua haujlwm txias thaum lub sijhawm ua thiab sizing tuaj yeem nce ntxiv kom nce ntxiv thiab tensile lub zog ntawm cov yeeb nkab lub cev nyob ze ntawm cov npoo, thaum muaj peev xwm txo qis me ntsis. Tshaj tawm - Weld Kev Kho Mob Kub pab txhawb cov khoom nruab nrab thiab daws kev ntxhov siab. Qhov ntau tshaj plaws ua tau raws li cov ntaub ntawv tshwj xeeb ntawm cov ntaub ntawv tshwj xeeb (piv txwv li, ASTM A53 qib B muaj qhov tsawg kawg nkaus lub zog ntawm 35,000 psi).
• Sib xws:Lub tshuab automatic, txuas ntxiv xwm ntawm ER kev tsim cov khoom ua kom zoo sib xws thiab cov yeeb nkab rau cov yeeb nkab thiab los ntawm cov yeeb nkab rau hauv ib pob.

4. Daim ntawv thov: qhov twg ERW kav yog qhov tseem ceeb

Qhov tshwj xeeb ua ke ntawm tus nqi ntawm tus nqi ntawm tus nqi ntawm tus nqi ntawm cov nqi- ua tau zoo, lub zog zoo, thiab muaj peev xwm uaERW kavindispensable nyob rau hauv ntau cov haujlwm:

• Kev Ntsuas Cov Dej:

Dej muab & Distribution:Tus caj qaum ntawm cov dej thiab dej tshuab rau cov dej muaj txiaj ntsig, dej, thiab wastewater (ob qho tib si siab thiab tsis {{}} qhov kev thov siab). Dominates me dua txoj kab uas hla thiab cov kab pabcuam.

Roj & Roj:Siv ntau yam rau kev sib sau cov kab (thauj roj / roj los ntawm Wellheads los ua cov chaw ua haujlwm), xa cov khoom ntuj (xa cov khoom siv qis {}} siab} siab {}} siab {milling xa cov kab. API 5L cov qib kawm muaj ntau. Kuj siv rau casing thiab tubing hauv qee hom zoo.

Chav kab:NYIAS rau nruab nrab -} h siab tawv kab hauv cov nroj tsuag muaj cov nroj tsuag thiab cov cua sov.

Hydraulic Kab:Tubing rau cov tshuab hydraulic hauv tshuab.

Hlob Cua Tshuab:Cov khoom siv hluav taws xob tsis pub dhau lub Hoobkas.

• Cov ntawv thov txheej txheem:

Kev Tsim Kho:Dav siv raws li cov qauv txheej txheem, chav vov ru tsev, cov chaw thav duab, scaffolding, lub laj kab, thiab cov neeg tiv thaiv. ASTM A500 (puag ncig, xwmfab, duab plaub) yog qhov tshwj xeeb rau cov qauv kev coj ua. Qhov tseeb ntawm qhov tseeb thiab lub zog - rau {{4 4} Qhov hnyav nyhav yog qhov tseem ceeb.

Muaj:Txhawb nqa qauv, thav ntawv rau kev siv Machinery, conveyor tshuab, khoom siv cov khoom siv tua khoom.

Infrastructure:Signposts, teeb pom kev zoo, choj railings.

• Kev Lag Luam Automotive:Cov khoom sib xyaw tseem ceeb hauv kev tsim cov khoom lag luam hauv tsheb, chassis Cheebtsam, cov tawb kaw (cov seem), thiab ntau yam dej. Yuav tsum tau muaj qhov ntev tiag tiag thiab zoo ib yam. ASTM A513 yog ib qho kev qhia tshwj xeeb rau cov neeg kho tshuab tubing.
• Cov Ntawv Siv Neeg Kho Tshuab thiab Kev Lag Luam Kev Lag Luam:Shafts, muab chais, lub tes tsho, thooj voos kheej, thiab lwm yam uas muaj qhov uas hollow yog qhov zoo rau kev txuag hluav taws xob lossis kev ua haujlwm.ERW Tubepom cov kev siv dav dav ntawm no.
• Rooj tog thiab khoom siv tau khoom lag luam:Siv nyob rau hauv ntas rau rooj tog zaum (rooj zaum, rooj, khoom siv (tshuab ntxhua khaub ncaws (tshuab ntxhua khaub ncaws txhawb), thiab cov khw muag khoom fluctures. Muaj lub zog thiab tsim qauv.
• Khoom siv Agricultural:Irrigation tshuab, cov txheej txheem ua ke rau cov tsheb laij teb thiab siv.

Cov ntawv sau loj no uas tsis tau nkag siab ntawm qhov kev sib txuas ntawmhluav taws xob tiv thaiv welded steel yeeb nkabHauv kev tsim kho tshiab tshiab thiab kev lag luam. Nws cov versatility thiab kev khwv nyiaj txiag ua rau nws xaiv thawj qhov kev xaiv rau cov ntawv thov suav tsis txheeb qhov twg yog qhov tsim nyog uas tsim nyog.

5. Tswjhwm thiab cov qauv tswj hwm Erw kav

Ua kom muaj kev cia siab thiab kev nyab xeeb ntawmERW STEEL YEEBYuav tsum tau tswj kev lag luam nyuaj thoob plaws hauv kev tsim khoom lag luam thiab kev tsim qauv los tsim cov qauv thoob ntiaj teb. Cov ntsiab lus tseem ceeb xws li:

• Tshuaj Ntsuam Xyuas Raw:Xyuas cov tshuaj lom neeg muaj kuab lom thiab cov khoom siv neeg kho mob ntawm cov khoom siv steel tuaj steel (skelp) tiv thaiv cov lus qhia kom meej.
• Txheej Txheem Tswj:Kev saib xyuas tas mus li thiab tswj cov tsis tseem ceeb thaum lub sijhawm ERW:

Sawb dav, thickness, thiab ntug.

Tsim cov yob sib ncab thiab siab.

Vuam qhov tsis: Tam sim no (amps), volts (volts), zaus (HZ), HZ

Weld twv yuav raug tshem tawm thiab xwm yeem.

Sizing tsis thiab kawg qhov ntev (OD, Phab Ntsa Thickness, Ncov, ncaj).

Post - Weld Thaum Tshav Kub Kub Kho Kub Kub Thiab Duration (Yog Siv).

• Tsis - Kev sim tshuaj (ndt):Qhov tseem ceeb rau kev kuaj pom sab hauv thiab nto tawm hauv Weld Seam thiab cov hlau yam tsis muaj cov yeeb nkab. Cov hau kev rau ERW suav nrog:

Eddy kev sim tam sim no (ect):Ceev thiab ua tau zoo rau kev kuaj xyuas saum npoo thiab ze - npoo npoo (tawg, tsis muaj fusion) feem ntau hauv Weld Seam. Feem ntau siv rau cov hlab me me.

Kev sim ultrasonic (UT):Ua tau zoo rau kev kuaj pom cov flaws sab hauv (cov lus teb, kev tsis pom zoo weld (tsis muaj kev sib txawv, tsis muaj qhov nkag) thoob plaws lub phab ntsa tuab. Tuaj yeem siv tshuaj rau siab - ceev soj ntsuam. Tseem ceeb rau cov ntawv thov tseem ceeb.

Sib nqus Particle kuaj (MT):Siv los tshawb xyuas nto - breaking flaws, tshwj xeeb yog tom qab Weld Bead tshem tawm. Feem ntau thov xaiv.

Kev Ntsuam Xyuas Pom:Txheeb xyuas qhov chaw nyob, ncaj, thiab pom tseeb thiab tsis xws luag.

• Kev sim ua txhaum:Ua rau cov qauv txiav los ntawm cov yeeb nkab lossis los ntawm cov coupons sim ua ke nrog cov yeeb nkab khiav:

Tensile xeem:Kev ntsuas cov khoom siv lub zog, lub zog lub zog, thiab elongation ntawm lub hauv paus hlau thiab hla ntawm Weld.

Kaj ntsuam xyuas:Kev ntsuas ductility los ntawm flattening lub nplhaib qauv txiav los ntawm cov yeeb nkab kom txog thaum cov phab ntsa sib ntsib lossis cov kab nrib pleb tshwm sim los yog tawg tshwm. Ntsuas kev tsom kwm weld.

Kuaj Hardness:Kev ntsuas lub hardness ntawm cov hlau thiab weld cheeb tsam, kom nws ua tau raws li cov kev cai tshwj xeeb.

Rov qab khoov ntsuas (rau cov diamet me me):Yuav cov qauv hlua khi hlua hla ntawm Weld los kuaj Weld Ductility thiab Suab.

Kev Cuam Tshuam (Charpy V - Itch):Kev ntsuas kev sib tw ntawm lub hauv paus hlau thiab weld ntawm cov ntsuas kub teev (tshwj xeeb yog rau qis - Cov ntawv thov kub).

• Hydrostatic kuaj:Filling cov yeeb nkab nrog dej thiab nias nws mus rau theem qib siab dua nws cov kev ua haujlwm siab. Qhov kev ntsuas no lub siab tag nrho -} muaj cov muaj peev xwm thiab txeej, suav nrog Weld kev ncaj ncees. Yuav tsum tau rau feem ntau cov piping specifications.
• Ua raws li cov qauv:ERW cov yeeb nkab tsim thiab kev soj ntsuam yog kev tswj hwm los ntawm ntau haiv neeg thiab kev ua kom loj, thev naus laus zis, kev soj ntsuam cov qauv, thiab kev soj ntsuam cov qauv. Cov Qauv Tseem Ceeb suav nrog:

ASTM (American Society rau kev sim thiab cov ntaub ntawv):

ASTM A53: Cov Qauv Qhia Tshwj Xeeb rau cov yeeb nkab, Hlau, Dub thiab Kub -} (}

ASTM A135: Txuj Ci rau hluav taws xob {{}} Tsis kam {} Welded Steel Yeeb Nkab Zoo li Conduit).

ASTM A500: Cov Qauv Qhia Tshwj Xeeb rau Cold-} mive welded thiab seamless cov hlau txheem tubing hauv rounds thiab duab.

ASTM A513: Cov Qauv Qhia Tshwj Xeeb rau Hluav Taws Xob {{}} Tsis kam {} welded carbon thiab alloy steel neeg siv tshuab tubing.

API (American Petroleum Lub Koom Haum):

API 5L: Kev qhia tshwj xeeb rau kab yeeb (npog seamless thiab welded yeeb nkab rau cov roj thiab roj kis). Piav cov qib nyiam B, X42, x52, thiab lwm yam.

ASME (AMERICANCE LUB TSEV NEEG NTAWM COV NEEG KHO TSHUAB

ASME B36.10M: welded thiab seamless wrought steel yeeb nkab (choverse thiab tes taw hnyav li cas).

ISO (International rau cov qauv):Piv txwv li, ISO 3183 (roj av thiab ntuj muaj kev lag luam - Cov yeeb nkab hlau rau cov tshuab xa hluav taws xob ntxiv).

Cov Qauv Hauv Tebchaws:JIS (Nyiv), Din (Lub teb chaws Yelemees), BS (UK), GB (Suav teb) thiab lwm yam, muaj cov lus qhia sib npaug.

Qhov no cov qauv hauv cov txheej txheem ntawm cov txheej txheem tswj, tshuaj xyuas, kev sim, thiab qauv ua kom ntseeg tau tiasERW kavXa mus rau kev ua lag luam Raws li txoj kev tsim nyog rau kev ua tau zoo thiab kev nyab xeeb hauv lawv cov ntawv thov. Nkag siab lubLub ntsiab lus ntawm ERW YEEBInherently muaj feem cuam tshuam txog cov tshuab ua kom khov kho tsis tau nws ntau lawm.

Xaus: Qhov kev ua tiav kev cuam tshuam ntawm ERW thev naus laus zis

Kev tshawb nrhiav ntawmDab tsi yog erw steel kavQhia tawm cov khoom lag luam uas muaj deb tshaj li ntawm lub raj yooj yim. Nws sawv cev rau cov txheej txheem tsim kev tsim khoom lag luam -hluav taws xob tiv thaiv vuam- Zoo meej dua xyoo lawm kom xa cov siab - Zoo, nqi - {} {} Kev siv cov kev daws teeb meem zoo tshaj plaws. Nkag siab lubERW cov yeeb nkab ntsiab lusPom meej nws txoj haujlwm txawv: Muab qhov tshwj xeeb ua kom muaj zog, qhov chaw zoo, thiab kev lag luam, tshwj xeeb}- nruab nrab diameters.

Thaum Seamless Tus Yeeb Nkab Tuav Cov Khaub Ncaws Rau Qhov Tseem Ceeb Tshaj Plaws {{} {}- Inch Inch Ua Lag Luam Kev Lag Luam,ERW STEEL YEEBtseem yog tus undisputed workorsed ua haujlwm rau lub staggering array ntawm txhua hnub kev lag luam thiab muaj kev lag luam xav tau. Los ntawm cov dej loj hauv qab peb txoj kev thiab cov roj nkev pub peb cov cuab yeej siv, rau cov qauv txheej txheem ntawm cov tsev thiab cov chassis ntawm peb cov tsheb,ERW kavyog cov khoom siv tseem ceeb ua rau lub neej niaj hnub.

Kev nce qib txuas ntxiv hauv zeb thev naus laus zis, txheej txheem tswj, thiab tsis - Kev sim ua kom muaj kev cia siab ntxiv txhim kho thiab muaj xwm yeem ntawmERW Tubethiab cov yeeb nkab. Kev ua raws li cov qauv thoob ntiaj teb muab kev paub tseeb ntawm kev ua tau zoo thiab kev nyab xeeb rau lub hom phiaj. Yog li ntawd, thaum ntsuas kev xa ntawv rau cov khoom siv kom haum, cov kev siv tshuab, siv tshuab, lossis kev siv tsheb kho tsheb, tusLub ntsiab lus ntawm ERW YEEBtxhais ua pov thawj, muaj ntau yam, thiab kev lag luam suab paj uas txuas ntxiv mus zoo li peb ib puag ncig kev ua tau zoo thiab muaj txiaj ntsig. Nws txoj kev ua kom muaj qhov tseeb yog qhov ua tim khawv rau cov ingenuity thiab kev ua tau zoo ntawm cov txheej txheem erw tsim.