Ob Lub Ntsiab Failure Mechanisms
Thaum twgtooj dag fittingsua tsis tiav, forensic engineers feem ntau txheeb xyuas ob tus thawj culpris. Cov no yog dezincification (DZ) thiab kev nyuaj siab corrosion cracking (SCC). Nkag siab txog cov txheej txheem no yog thawj kauj ruam los tiv thaiv kev ua tsis tiav yav tom ntej hauv koj cov kav dej.
Dezincification yog dab tsi?
Dezincification yog ib hom kev txhim kho corrosion. Brass yog ib qho alloy ntawm tooj liab thiab zinc. Thaum lub sij hawm dezincification, zinc reacts nrog tshuaj nyob rau hauv dej. Nws yog rub tawm ntawm tooj dag matrix. Qhov no tawm tom qab cov khoom tsis muaj zog, spongy tooj liab.
Qhov "Copper Sponge" tshwm sim
Cov tooj liab uas tseem tshuav no tsis tuaj yeem tiv taus dej siab. Ib daim ntawv tshaj tawm forensic piav txog zinc li "ua tiav leached ... tawm hauv cov ntxiab matrix los ntawm tag nrho cov phab ntsa tuab". Lub haum poob tag nrho cov neeg kho tshuab lub zog. Cov dej xau yuav tshwm sim rau ntawm qhov chaw ntawd.
Zinc Content Risk Threshold
Brass nrog cov ntsiab lus siab zinc yog qhov yooj yim tshaj plaws. Qhov kev pheej hmoo pib thaum zinc cov ntsiab lus yog 15% lossis siab dua. Qhov phom sij ua rau hnyav ntawm 35% zinc lossis ntau dua. Ntau tus qauvtooj dag fittingssiv C36000 alloy, uas muaj kwv yees li 34% zinc. Qhov no alloy yog heev susceptible rau dezincification.
Plug Type vs. Layer Type
Muaj ob hom kev dezincification. Plug hom tsim qhov chaw sib sib zog nqus "spongy" thaj chaw uas nkag mus sai. Nws tshwm sim nyob rau hauv nruab nrab los yog alkaline dej nrog siab ntsev cov ntsiab lus thiab siab kub. Txheej hom kis ib txheej nyias, txheej corroded thoob plaws saum npoo. Qhov no tshwm sim nrog me ntsis acidic dej.
Lub Luag Haujlwm ntawm Dej Kub
Cov dej kub tseem ceeb accelerates dezincification. Ib qho kev tshawb fawb ntawm ib lub tsev nyob tau pom tias muaj kev puas tsuaj loj "vim yog qhov muaj zog ntawm cov khoom siv sab hauv, dej kub kub, ... Cov dej kub siab dua ua kom cov tshuaj tiv thaiv kab mob.Brass yeeb nkab fittingsnyob rau hauv cov dej kub kab tsis sai npaum li cas.
Chlorine thiab Dej Chemistry
Cov tshuaj lom neeg hauv cov khoom siv dej pej xeem ua rau muaj kev tawm tsam. Cov tshuaj chlorine thiab chloramines pab txhawb cov tshuaj tiv thaiv corrosion. Cov dej pH, cov ntsiab lus chloride, thiab cov dej ntws qis tag nrho ua rau kev puas tsuaj. Kev tshawb nrhiav forensic xaus lus tias kev txhoj puab heev hauv dej chemistry yog qhov tseem ceeb hauv kev ua tsis tiav.
Kev ntxhov siab Corrosion Cracking (SCC)
SCC yog qhov sib txawv tsis ua haujlwm. Nws yuav tsum muaj peb yam ua ke. Cov no yog cov tensile kev nyuaj siab, ib puag ncig corrosive, thiab cov khoom raug mob. Qhov siab dua qhov kev ntxhov siab lossis qhov corrosive ntau dua qhov chaw, qhov tawg sai dua.Brass yeeb nkab fittingsnyob rau hauv tensions muaj kev pheej hmoo.
Overtightening raws li Thawj Kev Nyuaj Siab
Kev ntxhov siab ntawm kev teeb tsa yog ib qho ua rau SCC. Thaum tus neeg siv kav dej overtightens ib threaded haum, nws tsim muaj zog tensile kev nyuaj siab nyob rau hauv cov hlau. Ib qhov chaw sau tseg tias overtightening tsim "cov ntsiab lus kev ntxhov siab hauv zos, ua rau cov khoom siv tsis muaj zog thaum lub sijhawm". Qhov kev ntxhov siab seem no yog thawj tus tsav tsheb rau kev tawg yav tom ntej.
Ammonia Factor
Ammonia yog ib qho muaj zog corrodent rau kev nyuaj siab tooj dag. Qee qhov ammonia yog "yuav luag ib txwm muaj nyob hauv cov khoom siv dej pej xeem". Ib qho me me heev, ua ke nrog kev ntxhov siab thiab ua rau cov tooj dag, ua rau SCC. Txawm tias muaj kev tu cov kua dej nyob ze ntawm lub cev tuaj yeem ua rau muaj kev phom sij.
Kev Pom Kev Pom Kev ntawm Degradation
Dezincification tuaj yeem nyuaj rau pom. Qhov haum feem ntau "tseem tsis hloov pauv rau sab nraud, ib sab ntawm cov xim me me". Kev tawg ntawm SCC tuaj yeem pom, tab sis kev puas tsuaj sab hauv tsis yog. Ib qho haum uas zoo li tsis zoo tuaj yeem ua rau muaj kev cuam tshuam. Ib qhotooj dag fittingsnyob rau hauv cov dej kub kab uas qhia staining yuav tsum tau soj ntsuam ze.
Kev Tiv Thaiv Kev Tiv Thaiv
Kev tiv thaiv yog lub tswv yim zoo tshaj plaws. Hloov cov qauv tooj dag fittings nrog DZR (dezincification-resistant) tooj dag hauv cov dej kub. Txo koj lub rhaub dej kub kom qeeb cov tshuaj tiv thaiv. Ntsuam xyuas koj cov dej rau pH thiab cov ntsiab lus chlorine. Yog tias cov dej txhoj puab heev, txhim kho tag nrho - tsev kho mob.
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