ABSTRACT

A large compilation of corrosion data for metals and alloys in high-temperature gases has been created. The data compilation represents about 70 commercial alloys, 4100 corrosion data measurements, and five million exposure hours. The data compilation has been developed and organized to allow prediction of sound metal thickness losses by several corrosion mechanisms at high-temperatures as functions of gas composition, temperature, time, and alloy type. Several charts and tables have been prepared as examples of predicted metal losses of alloys corroding in standard conditions for several corrosion mechanisms expected in high-temperature gases. Use of the data compilation to assess corrosion will be illustrated for corrosion in oxidizing, sulfidizing, sulfidizing/ oxidizing, and carburizing conditions.

BACKGROUND

This paper discusses the potential of high-temperature gases to corrode metals and recommends how to predict sound metal losses for a wide range of conditions. Corrosion of metals and alloys used in equipment handling high- temperature, corrosive gases is a potential concern in processes used in petroleum refining, gas processing, fired equipment, process heaters, burners, flares, furnaces, boilers, thermocouples, instrumentation, process heaters, hydro cracking, coking, vacuum flashing, hydro treating, coal/coke/oil gassing, gas processing, petrochemical production and catalytic reforming. Corrosion can define the maximum allowable temperature for metals and alloys, although mechanical properties or other considerations may require a lower maximum allowable temperature.

Determining the extent of sound metal loss by corrosion is intended to assess the remaining useful strength as equipment corrodes. It is therefore important to review how the characteristics of the exposure conditions and the alloys can combine to influence the rate of corrosion.

Most corrosion data for alloys exposed to high-temperature gases have been reported interims of weight change/area for relatively short exposures and inadequately defined exposure conditions. The weight change/area information is not directly related to the thickness (penetration) of corroded metal, which is often needed in assessing the strength of equipment components. Corrosion is best reported in penetration units, which indicate the sound metal loss, as discussed earlier?-2. Corrosion in high-temperature gases is affected by key parameters of the corrosive environments such as temperature, alloy composition, time, and gas composition. Summaries of metal penetrations for some typical conditions for four different corrosion mechanisms are shown in this presentation, which extends beyond the traditional corrosion weight change data by reporting total metal penetration for an extensive number of alloys over a wide range of conditions. Compositions of the alloys discussed in this paper are shown in Table 1.

The names of the corrosion mechanisms discussed in this paper are determined by the most abundant dominant corrosion products. For example: oxidation implies oxides, sulfidation implies sulfides, sulfidation/oxidation implies sulfides plus oxides, and carburization implies carbides.

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