Novel Proposal for Dissimilar Girth Welding of API 5 L X65 Steel Pipe with Internal Alloy 625 Cladding Using Both Low-Alloy Steel and Alloy 22 Combined Filler Metals

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2024-09, Vol.55 (9), p.3689-3705
• Main Authors: Miná, Émerson M., Ferreira, Gabriel M., Silva, Rafaella D., Marinho, Ricardo R., Dalpiaz, Giovani, Paes, Marcelo T., Motta, Marcelo F., Miranda, Hélio C., Silva, Cleiton C.
• Format: Article
• Language: English
• Subjects: Bend strength; Characterization and Evaluation of Materials; Chemistry and Materials Science; Clad metals; Cladding; Corrosion resistance; Corrosion resistant alloys; Corrosion resistant steels; Dilution; Dissimilar material joining; Ductile fracture; Ductile-brittle transition; Energy absorption; Ferritic stainless steels; Filler metals; Fracture toughness; High strength low alloy steels; Impact strength; Martensite; Materials Science; Mechanical properties; Metallic Materials; Microstructure; Nanotechnology; Nickel base alloys; Original Research Article; Solidification; Steel pipes; Structural Materials; Surfaces and Interfaces; Tensile tests; Thin Films; Transition temperature; Welded joints; Welding
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-024-07503-8

In this study, a new method for welding an API 5L X65 steel pipe that is internally clad with Alloy 625 cladding using Alloy 22 and AWS ER100S-G steel was developed. The first and second weld passes were made using Alloy 22 to provide excellent corrosion resistance for the Alloy 625 cladding region. The remaining weld passes were made using 100S-G steel to provide high mechanical strength. The welded joints were evaluated for their microstructure and mechanical properties. No significant solidification defects were found in the welded joints, as confirmed by bending and transverse tensile tests. The yield strength of the welded joint showed that welding was capable of delivering the necessary strength compatible with API 5L X65, X70, and X80 steels for subsequent installation using the reel lay process. The microstructure of the welded joint was complex, with the first two weld passes having a soft Ni-fcc matrix composed mainly of Alloy 22, while the first three 100S-G steel weld passes had a hard martensite matrix. The main region of the welded joint had a soft acicular ferritic matrix. Impact toughness testing showed that the energy absorbed by the notch positioned at the first steel weld pass was better than that for the notch positioned at the steel weld pass without a dilution effect for Alloy 22 (approximately 46 J and 14 J, respectively). The toughness of the weld pass increased due to the high Ni incorporation by dilution with Alloy 22, even at −  15 °C, while the steel weld passes that were not affected by dilution with Alloy 22 exhibited very low energy absorption, which is characteristic of steel materials assessed under conditions below the ductile-to-brittle transition temperature (DBTT). The fracture toughness tests confirmed this result, as the major steel weld passes exhibited brittle features that caused abrupt failure during the test at − 15 °C.