Method for determining carbon steel corrosion rate in coexisting environment of naphthenic acid and sulfur

Abstract

The invention discloses a method for determining the carbon steel corrosion rate in a coexisting environment of naphthenic acid and sulfur. The method is characterized in that in the coexisting environment of naphthenic acid and sulfur, carbon steel equipment has two dominant injury mechanisms which are respectively a naphthenic acid dominant mechanism and a sulfur dominant mechanism, and the two mechanisms simultaneously have the inhibiting effect on of the sulfur on the naphthenic acid; and the total corrosion rate of the carbon steel equipment is the summation of the corrosion rates of the two dominant injury mechanisms and the corrosion rate of the naphthenic acid under the inhibiting effect of the sulfur. In the method, the factors such as the interaction of the dominant mechanisms, the influence of secondary mechanisms on the dominant mechanisms, and the like are considered while determining the corrosion rate, and related methods in API581 are improved so that the probability analysis of equipment failures in risk evaluation are more scientific, reasonable and practical.

Description

technical field [0001] The invention relates to a method for determining the corrosion rate of carbon steel in an environment where naphthenic acid and sulfur coexist. Background technique [0002] The determination of the corrosion rate of steel in the medium environment is crucial to the determination of material selection and structural size in the design stage, and in the use stage, the determination of the possibility of equipment failure is even more important for the estimation of the inspection period and remaining life of the equipment. [0003] In the 2008 edition of API 581, "Risk-Based Inspection Techniques", the failure probability of equipment is calculated according to the following formula: [0004] P f (t)=G ff ×DF(t)×F MS In the formula: [0005] P f (t) is the probability of equipment failure; [0006] G ff is the average failure probability of similar equipment, given in Table 4.1 of API 581; [0007] f MS It is the management level impact co...

AI Technical Summary

Problems solved by technology

However, the irrationality in the API581 method will mislead people to think that as long as the material selection and the determination of the structure size meet the high-acid and high-sulfur medium environment, the high-acid and low-sulfur environment must be satisfied. Obviously, this will cause unsafe conditions.