To help operators make monitoring and repair decisions, as well as prioritize their replacement programs, GTI experts developed a cast iron (CI) fitness-for-service (FFS) model, calculator, and method. DOT PHMSA funded the effort that will help operator characterize and grade graphitic corrosion defects on cast iron natural gas pipe. This FFS guidance is critical to ensure safety and stability of natural gas supply.
GTI’s 200-page report provides validated engineering guidance to identify and prioritize the highest risk piping for replacement programs. It summarizes the history, use, composition, microstructure, mechanical properties, metallurgy, and corrosion characteristics of cast iron used for natural gas distribution systems.
Providing a remaining factor of safety for cast iron assets provides a go/no-go decision for immediate threat mitigation by operators. A CI FFS model was developed for use in determining the critical defect size and characteristics that could lead to premature piping failure. A first-pass validation of the model with field failure data illustrated the basis and specific recommendations for a comprehensive, testing-based validation program.
The results of the model were incorporated into a calculator, along with guidelines for operators to characterize the type and severity of graphitic corrosion to allow for consistent and reliable input data.
Next steps are for the project team to augment the solution for large-diameter cast iron pipes from 14-48 inches and provide a geo-spatial implementation example of the FFS solution applied to a cast iron pipe network. Individual operators, recognizing GTI’s expertise and extensive capabilities in this area, are approaching GTI regarding consulting on their replacement programs.
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