The heat transfer oil system of a petrochemical company occurs oil blackening and a large amount of scaling in a short period of time,which affects the normal use of the entire heating system.Through the test of physical and chemical indexes,pollution indexes and wear indicators of the heat transfer oil,the performance and state information of the heat transfer oil were obtained.The composition information of the scaling was obtained by X-ray fluorescence spectroscopy,X-ray diffraction analysis,and scanning electron microscope and energy spectrometer analysis.According to the comprehensive analysis of the testing results and the fault background,the reason for the abnormal blackening of the heat transfer oil is that there are lots of scale particles in the heat transfer oil.Scaling particles are composed of high-temperature degradation and carbonization products of heat transfer oil,corrosion products of steel components,and reaction products of external pollutants.The main component of scaling particle is carbon deposition.The excessively high working temperature of the heat transfer oil is the cause of a large number of carbon deposits in the system in a short time.In addition,the intrusion of corrosive elements such as Cl and S into the heat transfer oil system causes corrosion of the steel parts,and Fe oxides accumulate in the carbon particles.