Welding of P355NH steel for the construction of a medium-pressure gas pipeline

• Published in: Continuum mechanics and thermodynamics 2024, Vol.36 (1), p.107-118
• Main Authors: Szczucka-Lasota, Bożena, Węgrzyn, Tomasz, Szymczak, Tadeusz, Łazarz, Bogusław, Pereria Silva, Abílio, Jurek, Adam
• Format: Article
• Language: English
• Subjects: Additives; Argon; Bend strength; Chemical composition; Classical and Continuum Physics; Construction materials; Engineering Thermodynamics; Gas pipelines; Gas tungsten arc welding; Gases; Heat and Mass Transfer; Heating; Helium; Impact strength; Inclusions; Interpass temperature; Light microscopy; Magnetic particle testing; Mechanical properties; Microscopy; Natural gas; Nondestructive testing; Nucleation; Optical microscopy; Original Article; Penetration tests; Physics; Physics and Astronomy; Pipelines; Service life; Steel pipes; Structural Materials; Tensile strength; Theoretical and Applied Mechanics; Thermodynamics; Thickness; Welded joints; Welding; Yield point
• ISSN: 0935-1175; 1432-0959
• DOI: 10.1007/s00161-023-01265-1

There is an increasing demand for welding of steel pipes meant for pressure purposes. P355NH (1.0473) steel became an important construction material used for structuring and restructuring of a medium-pressure gas pipeline due to its properties, such as significant tensile strength at the level of 600 MPa and increased yield point. These properties ensure appropriate service life of the principal pipeline structures. When welding P355NH steel, processes that enable high-quality welds without significant changes in the chemical composition of the base material, are applied. It is recommended to use the TIG welding process to produce joints, although P355NH steel joints are considered as difficult to weld. During welding, various welding defects might appear, which mainly include sticking and lack of fusion. Creation of joints with the desired properties, including those used in the construction of medium pressure gas pipelines, with the required class B quality, requires selection of appropriate parameters and compliance with the welding process practice. This is very important for the service life of the structure. Therefore, the article aims to select the most appropriate parameters and thermodynamic conditions for welding P355NH steel in order to obtain the best mechanical properties. The most important of the tested welding parameters of P355NH steel is welding speed, welding current, preheating temperature, interpass temperature and, above all, the role of various shielding gases. (Three different shielding gases containing argon and helium additives were tested.) The obtained joints were tested by: non-destructive tests, such as VT—visual examination; MT—magnetic particle testing, PT—penetration tests, UT—ultrasonic testing and by the destructive methods, such as tensile strength, impact toughness, bending test, light microscopy and scanning electron microscopy. The cause-and-effect relationships between the obtained joint structure and its mechanical properties were determined. The considerations were supported by the nucleation model and the mechanisms of formation of the acicular ferrite phase in the joint material. The chosen parameters of TIG process allow to obtain joint with adequate strength for the production of the gases pipeline, without welding defects. The results have a practical implication, the developed production technology for the obtaining the joints. The presented solution gives the possibility of producing correct welded joints,