A specific nonionic surfactant is added to a component mainly comprising hydrocarbons before passing through a heat exchanger in a petrochemical plant or a polyolefin production plant, whereby fouling of the heat exchanger can be efficiently prevented, that is, the performance of the heat exchanger can be prevented from being deteriorated, and long-term operation is feasible without sacrificing the speed of production. The nonionic surfactant is preferably a polyoxyalkylene compound represented by the general formula [I] below, more preferably a compound represented by the general formula [II] below. R.sup.1--O--[CH.sub.2--CH(R.sup.3)--O].sub.k--R.sup.2[I] wherein R.sup.1, R.sup.2 and R.sup.3 are selected from a hydrogen atom, a C1 to C20 alkyl group, a C6 to C20 aryl group and a C1 to C20 acyl group, and may be the same or different from each other. HO--(CH.sub.2CH.sub.2O).sub.m--[CH.sub.2CH(CH.sub.3)O].sub.n--(CH.sub.2CH- .sub.2O).sub.pH[II] wherein m, n and p each represent the average number of repeating units, and m is in the range of 1 to 20, n is 2 to 50 and p is 1 to 20.