MHD potentials on the electrodes were investigated while MHD pressure drop for insulating coatings with and without the cracking or flaking was studied. MHD duct may be seen in Fig. 1 of Ref. [1]. We measure the potential difference between the MHD potentials on the electrodes were investigated while MHD pressure drop for insulating coatings with and without the cracking or flaking was studied. MHD duct may be seen in Fig. 1 of Ref. [1]. We measure the potential difference between the