Mechanical Metallurgy on Vintage X100 Experimental Pipe

Overview

Main Objective

The National Institute of Standards and Technology (NIST) will conduct metallurgical testing on Columbia Gas X100 experimental pipe to provide valuable information on property changes due to degradation and property differences due to microstructure. The project will provide insight on vintage vs modern high strength steels.

Public Abstract

The research will utilize more recent test methods such as small-scale fracture testing, miniaturized Charpy specimens, instrumented indentation, and atomic force microscopy on the vintage pipe and compare it to such tests completed on modern high strength steels. The mechanical properties will be correlated with microstructure and chemical information via analytical electron microscopy, thereby providing processing-structure-property-performance relations for vintage and modern X100.

The project will encompass two phases. The first phase of the project will include microstructure and chemistry characterization and Charpy testing and hardness mapping on both vintage Columbia Gas X100 experimental pipe and modern X100 pipe from a previous project, as this will facilitate valuable information on property changes due to degradation (via comparisons with original values3) and property differences due to microstructure (via comparisons with modern X100 pipe). The second phase of the project will extend these studies via more recent test methods such as small-scale fracture testing and multi-scale indentation mechanics, thereby enabling processing-structure-property-performance relations.

Summary and Conclusions

The comprehensive analysis of vintage X100 steel line pipe revealed that while the pipes generally meet current API 5L standards for X100Q steel, there are some variations in properties and performance. Microstructural analysis identified inconsistent chemical composition and a bainite-ferrite microstructure in all base metal pipe sections. Mechanical testing, including tension and impact tests, demonstrated that most specimens satisfy the required criteria. However, some individual specimens, particularly in the heat affected zone of girth welds, exhibited lower impact toughness than expected. Micro-indentation analysis revealed variations in hardness across the heat affected zone of girth welds, differing from previous findings. Overall, the results suggest that the vintage X100 steel line pipe is generally in good condition but exhibits some localized variations that should be considered in future assessments.

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