Electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP) were used to study the failure of the coating modified with air-plasma treatment in 3.5 % mass fraction of NaCl. The results show that the failure process can be divided into three stages including water penetration, accumulation of corrosion products at the location of a defect, water penetration of the entire coating and coating failure. The EIS results show that the plasma-treated samples exhibit an additional electrical double-layer capacitor that delays the coating failure during the second stage. The potential of the non-plasma-treated samples decrease faster than that of the plasma-treated samples according to the SKP study. As the transition layer, air plasma delays the coating failure due to the chemical bond between the metal substrate and the coating. Keywords: air-plasma treatment, electrochemical impedance spectroscopy, scanning Kelvin probe, coating failure, hydrostatic pressure Elektrokemijsko impedan~no spektroskopijo (angl. EIS) in vrsti~no Kelvinovo sondo (SKP) smo uporabili za preu~evanje po{kodb na prevleki, modificirani s plazmo, v 3,5 mas. % raztopini NaCl. Rezultati ka`ejo, da se nastajanje po{kodb lahko razdeli na tri faze, vklju~no s penetracijo vode: na akumulacijo korozijskih produktov na mestu napake, na prodiranje vode v dele celotne prevleke in na odpoved prevleke. Rezultati EIS ka`ejo, da imajo vzorci, obdelani v plazmi, dodaten elektri~ni dvoslojni kondenzator, ki v drugi fazi upo~asni po{kodbo prevleke (premaza). SKP-analize so pokazale, da se potencial plazemsko neobdelanih vzorcev zmanj{uje hitreje kot tistih vzorcev, ki so bili obdelani s plazmo. Kot prehodna plast, obdelava z zra~no plazmo upo~asni po{kodbo premaza zaradi kemijske vezi med kovinskim substratom in prevleko. Klju~ne besede: obdelava s plazmo, elektrokemijska impedan~na spektroskopija, skeniranje s sondo Kelvin, odpoved prevleke, hidrostati~ni tlak