The present invention relates to the field of processing hydrocarbons which causes corrosion in the metal surfaces of processing units. The invention addresses the technical problem of high temperature naphthenic acid corrosion and sulphur corrosion and provides a solution to inhibit these types of corrosion. The three combination compositions are formed by three mixtures separately, with one mixture obtained by mixing compound A, which is obtained by reacting high reactive polyisobutylene (HRPIB) with phosphorous pentasulphide in presence of catalytic amount of sulphur with compound B such as trialkyl phosphate and second mixture obtained by mixing compound A with compound C such as phosphite like di-isodecyl phenyl phosphite, and third mixture obtained by mixing compound A with compound D such as a phosphonate, wherein each of these three mixtures independently provide high corrosion inhibition efficiency in case of high temperature naphthenic acid corrosion inhibition and sulphur corrosion inhibition. The invention is useful in all hydrocarbon processing units, such as, refineries, distillation columns and other petrochemical industries.