Ideal and resistive MHD interchange instabilities play a crucial role with increasing beta in tokamak SOL plasmas. Applying the mixing length argument the perpendicular transport coefficients are derived in different regimes, i.e. λi < L|| and λi > L||, taking into account volume (Spitzer) resistivity and sheath resistance. Single-Null and Double-Null SOL configurations give different results. For larger beta these MHD instabilities can regulate the SOL width.