Insimbi engagqwali ayigqwali kalula, igqwalile noma ingcole ngamanzi njengoba kwenza insimbi evamile. Kodwa-ke, ayiqinisekisi amabala ngokuphelele ezindaweni ezinomoya-mpilo omncane, ezinosawoti omningi, noma ezindaweni ezingezinhle zokujikeleza komoya. Kunamamaki ahlukene kanye nokuqedwa kwangaphezulu kwensimbi engagqwali ukuze kuhambisane nemvelo ingxubevange okufanele ibekezelele. Insimbi engagqwali isetshenziswa lapho kokubili izakhiwo zensimbi nokugqwala zidingeka.

Insimbi engagqwali ihluka ku-carbon steel ngenani le-chromium ekhona. I-carbon steel engavikelekile igqwala kalula uma ibekwe emoyeni kanye nomswakama. Le filimu ye-iron oxide (ukugqwala) iyasebenza futhi isheshisa ukugqwala ngokwakha i-iron oxide eyengeziwe[ukucaciswa kuyadingeka]; futhi, ngenxa yomthamo omkhulu we-iron oxide, lokhu kuvame ukuphephuka futhi kuwa. Izinsimbi ezingenasici ziqukethe i-chromium eyanele ukwenza ifilimu ye-passive ye-chromium oxide, evimbela ukugqwala okuqhubekayo kwendawo ngokuvimbela ukusakazeka komoyampilo endaweni yensimbi futhi ivimbe ukugqwala ukuthi kungasakazeki esakhiweni sangaphakathi sensimbi. Ukudlula kwenzeka kuphela uma ingxenye ye-chromium iphezulu ngokwanele futhi kukhona umoya-mpilo.