Service testing high-temperature corrosion

High-temperature service test standards are available from ASTM. No other technical organization has yet published any standards pertaining to high-temperature corrosion service. 

Examples of specific service tests for selected applications are cited below that have achieved a high degree of acceptability. Additional discussion on high temperature corrosion testing in specific laboratory and field environments can be found in the chapter on Testing in Environments. 

Laboratory Methods for the Evaluation of Protective Coatings Used as Lining Materials for Immersion Service Dynamic Corrosion Testing of Metals in High Temperature Water... 

Autoclave corrosion tests are a convenient means for laboratory simulation of many service environments for the purpose of evaluating the corrosion resistance of materials and for determining the effects of metallurgical, processing, and environmental variables on corrosion processes. The reason for such tests is to more closely recreate the high temperatures and pressures commonly occurring in commercial or industrial processes. 

Focus here is on service tests that evaluate materials in applications that involve both high-temperature and corrosive conditions. B lsic chemical, thermodynamic, and physical principles are discussed. Specimen preparation, environment synthesis and evaluation are briefly reviewed and, where appropriate, reference is made to more detailed information and studies available in the technical literature. 

Kinetics, chemical, thermodynamic, and physical principles will all be operating in high-temperature service test environments, requiring each investigator to have an adequate huniliarily of basic mechanisms and corrosion phenomena. A brief introduction to these aspects of service testing is presented here. 

High-temperature chlorides can require unique chloride resistance testing [9]. In aqueous solutions, it is common to use electrochemical testing to evaluate pitting potential or crevice corrosion. In nonaqueous base solutions, this must usually be evaluated by in-service tests in pilot plants or in existing process equipment. 

Acceleration of Stress Corrosion Cracking Test for High-Temperature, High-Purity Water Environments by Means of Artificial Crevice Application Conference Application of Accelerated Corrosion Tests to Service Life Prediction of Materials, Miami, Florida, USA,... 

Under extreme conditions of high temperature and corrosion, the surface film may not be protective at all. Based on this, service tests are recommended. 

For high-temperature applications in particular, it is recommended to run laboratory corrosion tests to confirm that sufficient inhibition will take place. However, only in rare cases is it necessary to have more than 12 hours of corrosion protection. Often, 6-8 hours of protection is plenty. Service companies should not be placed in the position of overloading with inhibitor and intensifier to meet an unreasonable request for the sake of providing insurance. Table 6-7 summarizes the industry s acceptable corrosion limits. 

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