a method for removing calcium , iron , other metals , and amines from crude oil in a refinery desalting process includes the steps of adding a wash water to the crude oil ; adding the wash water to the crude oil to create an emulsion ; adding to the wash water , the crude oil or the emulsion an acid additive consisting of at least one of the following : oxalic acid , citric acid , water - soluble hydroxyacid selected from the group consisting of glycolic acid , gluconic acid , c . sub . 2 - c . sub . 4 alpha - hydroxy acids , malic acid , lactic acid , poly - hydroxy carboxylic acids , thioglycolic acid , chloroacetic acid , polymeric forms of the above hydroxyacids , poly - glycolic esters , glycolate ethers , and ammonium salt and alkali metal salts of these hydroxyacids , and mixtures thereof ; heating at least one of the crude oil , the wash water or the emulsion to a desired temperature ; resolving the emulsion containing the acid additive into a hydrocarbon phase and an aqueous phase using electrostatic coalescence , the metals and amines being transferred to the aqueous phase ; measuring at least one desalting process characteristic at at least one process point ; performing a statistical calculation of the desalting process performance based upon the measuring ; and adjusting a control setting of the desalting process as a function of the statistical calculation . other methods and devices are also provided .