The paper describes several approaches to perform computer simulation of corrosion occurring in the chemical process industries. While the present state of the art does not permit simulating all modes of corrosion observed in process systems, useful insights can be gained at the design stage by the inclusion of corrosion simulation tools. A thermodynamic speciation model coupled to electrochemical kinetic model is used to calculate the uniform corrosion rates in a variety of mixed acid systems. Such a model can also compute the corrosion potential; an important parameter that can determine the occurrence of a variety of localized corrosion processes. For systems undergoing localized corrosion, a semi-empirical model, involving repassivation and corrosion potentials is described, Other approaches to corrosion prediction are described briefly. Areas for further development are identified.
In charting the evolution of the process industry over the next 20 or so years Keller and Bryan delineate seven themes for future process improvements:
* Raw material cost reduction
? Capital investment reduction
? Energy use reduction
? Increased process flexibility and inventory reduction
? Process safety
? Increased attention to quality
? Better environmental performance
They argued that three quarters of the products that will be sold in the year 2020 will be produced with equipment operating in 1999 and that much of the process engineering improvements will also be done using the existing units. This is because capital costs constitute 25-50 percent of the total product sales price. In its Technology Roadmap, 2 The Materials Technology Institute of the Chemical Process Industries, Inc. identified the prediction of material performance in complex chemical systems without empirical tests as a priority research need and a key barrier to process improvement. This assessment, combined with the seven themes outlined by Kellar and Bryan, would suggest that the process engineers in the future will have to contend with the need to use the same equipment to implement new processes or manufacture new products while ensuring safe and trouble-free operation. Additionally, the time period between process conception and commercialization has become shortened, so that the process engineers do not always have the luxury of the traditional scale-up route involving laboratory development and pilot plant testing 3.
Generally, materials selection for new processes is made through a combination of previous process experience, laboratory testing, or plant testing in a related process or pilot plant. Staehle 4 has delineated the following steps in a corrosion based design approach:
Environment definition
Material definition (characterization)
Failure mode assessment
Failure criteria
Statistical treatment and scale-up
Accelerated testing
Prediction of performance
Monitoring and feedback
This paper discusses approaches to defining the environment causing the corrosion and assessing the failure modes. Ideally, corrosion based design approach should be a part of process simulation software because these simulation tools are often used by chemical engineers in designing new processes. However, the process simulation software available today does not incorporate models to evaluate the performance of process equipment 3, which would make risk assessment and informed investment decisions possible. A variety of heuristic methods (expert systems, neural network models) have been published to tackle this problem, but none are completely satisfactory for new applications.
The objective of the paper is to review the pro
