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The need for life prediction of structures corrosion processes has increased because of several factors, including:

• Aging engineering structures that have often exceeded their original design life

• Energy conservation

• Environmental preservation

• Improvement of the readiness of weapon and nonweapon systems

Corrosion prediction of systems with extremely long design life of the order of tens of thousands of years has become importance in high-level radioactive waste disposal. Southwest Research Institute (SwRI) has been engaged in developing corrosion life prediction models for a broad range of applications, including:

• Radioactive waste disposal containers

• Chemical process industry equipment

• Marine structures

• Underground natural gas pipelines.

Localized Corrosion Modeling

Localized corrosion is one of the most important and feared corrosion processes because, once initiated, it can propagate rapidly, it is difficult to inspect, and it can lead to other failure modes such as stress corrosion cracking and corrosion fatigue.

The predicted repassivation potentials (colored rectangles) are compared to measured corrosion potentials in the chemical plant. The model predicts that type 316L stainless steel and AL6XN would suffer severe localized corrosion whereas alloy C-276 would only marginally suffer corrosion in agreement with this plant's experience.

	ICDA utilizes the gas temperature, pressure, and flow velocity in conjunction with the inclination of the pipe to predict likely locations of water accumulation.

SwRI has, for the last decade, developed a simple methodology to predict the occurrence of localized corrosion and validated this methodology using both long-term (multiyear) laboratory tests and field studies. In collaboration with OLI Systems, this model has been incorporated in their Corrosion Analyzer^TM software to predict localized corrosion in complex environments that occur in a number of industries.
 

Pipeline Internal Corrosion Modeling

Internal corrosion is an important cause of pipeline ruptures that has led to loss of life, property, and contamination of the environment. Although periodic inspection of pipelines will ensure such failures are minimized, inspection of pipelines is expensive, and, in many cases, the pipeline features prevent automatic inspection using in-line inspection tools (also called pigs). SwRI developed a method, Internal Corrosion Direct Assessment, which combined flow modeling, to predict the locations along a pipeline where water hold-up would occur, with corrosion rate models, to compute the extent of corrosion penetration.

Comparing the critical angle determined using fluid flow model to the inclination angle of the pipeline identifies locations along the pipe where water accumulation is likely and subsequent inspection and excavation are needed.

	SwRI has developed a simple probabilistic methodology that can be implemented in spreadsheet version to prioritize locations where detailed inspections must be done.

Many sources of uncertainties exist in this model, including:

• Uncertainties in flow parameters

• Pipeline elevation profile, and corrosion models

Several corrosion models exist, each with its own input uncertainties. SwRI has developed a simple probabilistic methodology that can be implemented in spreadsheet version to prioritize locations where detailed inspections must be done.

High-Level Nuclear Waste Container Life Prediction

• Center for Nuclear Waste Regulatory Analyses

For more information about our corrosion life prediction capabilities, or how you can contract with SwRI, pplease contact James F. Dante, at jdante@swri.org or (210) 522-5458.

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

January 03, 2013