St. Petersburg State Polytechnical University (St.Petersburg, Russia):

A. Kazakov, kazakov@thixomet.ru

D. Kiselev

O. Pakhomova

Standards currently used to assess the quality of steel plate for pipelines are out of date and cannot be used for this purpose. The motorized hardware-software complex “Thixomet SmartDrive” has been developed and installed in dozens of enterprises and companies to provide an objective quantitative estimation of all types of structural inhomogeneity in modern pipeline steels, such as microstructural banding, general anisotropy, blocks of bainite with lath morphology and centerline segregation.

All developed standards are either unique and have no analogues (general anisotropy and blocks of bainite with lath morphology), or are compatible but exceed in efficiency and objectiveness of quality estimation: current Russian (GOST 5640-68) and foreign (ASTM 1268, GB/T 13298) standards. Our work has demonstrated that structural heterogeneity evaluated by the volume fraction and size of elongated areas of bainite blocks with lath morphology parallel to the rolling direction will adequately describe mechanical properties obtained from tensile and impact tests of pipeline steels with yield strength from 485 up to 625 N/mm².

The “structure - properties" relationships determined can be used as a background for developing a quality estimation system that includes acceptance tests for steel products between suppliers and consumers of pipeline plate, and also for the improvement of production technology.

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