HIGH-TEMPERATURE STRENGTH OF METAL OF BOILER TUBES MADE FROM CONTINUOUSLY CAST BILLETS PRODUCED BY MZ DNIPROSTAL LLC

Keywords: high-temperature strength, boiler tubes, non-worked continuously cast billets, macrocrystalline structure, remains of cast structure, microstructure, ultimate long-term strength, long-term ductility, fracture, fracture form

Abstract

Purpose. Investigation of ability of the new process technology to provide manufacture of "20" grade steel boiler tubes of high operational reliability in a wide size range by applying the method of hot rolling at Interpipe Niko Tube LLC TPA 30-1-2 tube rolling unit immediately from non-worked continuously cast billets manufactured by MZ Dniprostal LLC.
Methods. Examination of macrostructure (for a presence of residues of cast structure) and microstructure of the tube metal, conduction of long-term strength test, fractographic and metallographic examination of form of fracture of tube specimens following the tests for high-temperature strength.
Results. Characteristics of high-temperature strength (long-term strength and long-term ductility) in various conditions (hot-rolled and normalized from a single heat) of the boiler tube metal. The tubes were rolled at various elongation coefficients in the Interpipe Niko Tube LLC TPA 30-102 tube-rolling unit incorporating a continuous mill. Non-worked continuously cast billets of "20" grade steel manufactured by MZ Dniprostal LLC were used. The processes taking place in the tube metal structure under long-term loading at high temperatures and the form of fracture of the tube specimens during high-temperature strength tests have been studied. Influence of structural characteristics and technological factors of production of tube billets and tubes on the level of high-temperature strength and behavior of tube metal under long-term loading at high temperatures has been established. A necessity of improvement of the process of manufacture of continuously cast billets for boiler tubes at MZ Dniprostal LLC with the aim of obtaining required macrocrystalline structure (i.e. with a developed zone of fine equiaxed disoriented crystals and a limited zone of columnar crystals) and norming this indicator of metal of non-worked continuously cast billets in specification TU U24.1-05757883-216:2019 (Round Continuously Cast Steel Billets for Manufacture of Boiler Tubes) has been shown. A possibility of supplying the power generating facilities of Uktaine with boiler tubes of "20" grade steel manufactured with elongation coefficients of at least 17.0 at Interpipe Niko Tube LLC TPA 30-102 tube rolling unit from billets manufactured by
MZ Dniprostal LLC without obligatory normalizing from a separate heat specified in normative documents for such tubes was established.
Originality. Ultimate long-term strength for operation during 100 thousand hours at temperature of 450 °C was determined for the first time for the boiler tubes rolled with various coefficients of elongation at Interpipe Niko Tube TPA 30-102 tube rolling unit from MZ Dniprostal LLC non-worked continuously cast billets of "20" grade steel. This strength is normed in TU 14-3-460:2009/TU U 27.2-05757883-207:2009 and is the main characteristic used when calculating strength of power generating equipment. Behavior of metal of such tubes in various conditions (after hot rolling and normalizing from a separate heat) in conditions of long-term loading at high temperatures has been investigated.
Practical implications. The results obtained in this study will serve as the basis for improving the technology used at MZ Dniprostal LLC in the manufacture of non-worked continuously cast billets further used in rolling boiler tubes at Interpipe Niko Tube LLC. This will ensure production of boiler tubes of high operational reliability due to application of the new technology. Use of domestic billets will allow Interpipe Corporation to reduce costs of production of boiler tubes according to specification TU 14-3-460:2009/TU U 27.2-05757883-207:2009 and be a strong competitor to foreign tube companies.

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Published
2019-12-27
How to Cite
Opryshko, L., Holovniak, T., HerasymenkoР., & Poltava, I. (2019). HIGH-TEMPERATURE STRENGTH OF METAL OF BOILER TUBES MADE FROM CONTINUOUSLY CAST BILLETS PRODUCED BY MZ DNIPROSTAL LLC. Metallurgical and Ore Mining Industry, (5-6), 67-75. https://doi.org/10.34185/0543-5749.2019-5-6-67-75