Thaum tshav kub kub preservation yeeb nkab (Hub preservation yeeb nkab) yog cov yeeb nkab steel uas tau ua tiav los ntawm kev txuag hluav taws xob thiab nyob rau hauv kev ua haujlwm ntawm cov chaw ua haujlwm sib txawv thiab cov xov xwm sab nraud kom ntseeg tau tias qhov kub thiab txias ntawm qhov chaw ua haujlwm steel yeeb nkab ua tau raws li qhov yuav tsum tau ua. rau siv.
