International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

High-frequency electric resistance welding (HFERW) is one of the most common process for production of longitudinal welded carbon steel pipes, suitable for line pipes, casing, and tubing. In the edges joining line of hot rolled coils is formed decarburization layer which sometimes appeared negative impact on the microstructure and mechanical properties of the welded joint, so the aim of this paper is to investigate impact of this layer on the crack propagation in the pipes welded joint, obtained by high frequency electric resistance welding (HFERW). Crack propagation in the pipes welded joint monitored by macro and microscopic analysis as well as by the hardness testing, along and transverse through decarburization layer. Results of this investigation brings additional knowledge about impact of the decarburization layer on the crack propagation in the high frequency electric resistance welded joint.

Hot rolled steel coils, as a result of the history of production, respectively processing, shows anisotropy of the mechanical properties, i.e. different mechanical properties in different direction. Therefore, the mechanical properties of hot rolled steel coils should be known in advance, respectively prior to its use as raw material for the production of various final products, particularly for spiral and longitudinal welded steel pipes, where mechanical anisotropy of hot rolled steel coils even more appears during the formation of hot rolled coils into the pipe. Mechanical testing of the hot rolled steel coils in transversal (T) and longitudinal (L) direction related to the rolling, were conducted.

The aim of this paper is to investigate anisotropy of the mechanical properties of the hot rolled steel (S355 EN 10025:2004) coils, used for the production of spiral and longitudinal welded steel pipes.

In this paper are presented some macrofractographic and microfractographic analysis of welded joint fracture surfaces, respectively welded seam (W), heat affected zone (HAZ) and base metal (BM), of spiral and longitudinal steel welded pipes after conducting the laboratory destructive testing. Destructive testing are conducted to assess the quality of the steel welded pipes and besides the numerical results, the fracture surface of the tested samples offers additional information, very important for assessing the quality of steel welded pipes. Given this, in the paper are treated the macrofractographic and microfractographic analysis (LOM-Light Optical Microscopy and Scanning Microscopy-SEM) of the fracture surfaces of samples which are fractured after destructive testing. The morphology of the fracture surfaces is compared with the numerical results and it concludes that there is a direct correlation between the obtained results and deformation that causes fracture, providing thus additional information for assessing the quality of the welded pipes.

In this paper, local post weld heat treatment (LPWHT) effects on the metallurgical and mechanical properties of high frequency electric resistance welded (HFERW) steel pipes were investigated. Local post weld heat treatment (LPWHT) of the welded joint was carried out by an induction heating device which selectively heat only the weld area from the outside surface of the welded steel pipes. Optical microscopy, tensile testing, Charpy-V-notch testing, hardness testing and flattening testing were used to evaluate local post weld heat treatment (LPWHT) effects on the metallurgical and mechanical properties of high frequency electric resistance welded (HFERW) steel pipes.

The steel for the production of welded pipes must possess good weldability to achieve high efficiency and effectiveness of the production process in production lines (in line) and ground, during welding of pipes in long distance pipelines and in lower temperature conditions. The main focu of this research was on weldability assessment of API Grade X52 steel at low temperature (0°C), which is used for the production of welded pipes, respectively pipelines. Carbon equivalent (C_E), mechanical testing and metallographic analysis of the welded joint were conducted in order to assess the weldability. The results of mechanical tests and metallographic analysis show that steel API Grade X52, at low temperature (0°C) has excellent weldability, so the pipes produced can be welded in long distance pipelines, easy and unhindered, thereby ensuring high production efficiency and effectiveness.

Submerged-arc welding (SAW) may be considered as a miniature casting and the final microstructure of a weld and a casting are both dendritic, but the differences are much greater than the similarities. The microstructure produced in a weld deposits is very complex and may contain several phases and hence has pronounced effect on the mechanical properties, such as hardness, strength and toughness.

The microstructure of the double sided welds joint is generally non-uniform, being composed of areas of as deposited weld metal (first weld) and areas that have reheated by subsequent pass (second weld). The hardness values (HV1/15) within double sided submerged-arc weld metals are different and depends to the exact positioning of the measurements. The obtained results using LM (Light Microscopy), SEM (Scanning Electron Microscopy) and Vickers hardness testing (HV1/15) are presented in this work and this is an attempt to clarify a correlation between microstructure and hardness gradient within double- sided submerged-arc weld metals from microalloyed steel API grade X60.

High frequency electric resistance welding is one of the most extensively used methods for production of longitudinally welded carbon steel pipes suitable for line pipe, casing and tubing. In this pipe production process, the hot rolled steel strip goes into the continuous cold forming process and its edges are continuously joined by a combination of localized high-frequency electric resistance heating and plastic deformation. The heated edges up to the welding temperature squeezed together at the “Vee” apex by the forge pressure rolls, plastically deformed and a forge type weld is formed. The plastic deformation which is realized under the action of the squeezing rolls caused changes of the microstructure constituents in the bond line and in the heat affected zone and plays principal role on the quality of the welded joint. In this paper microstructure and plasticity of the welded joint were investigated by light microscopy and flattening testing.

The obtained results shows that plastic deformation plays principal role on the microstructure and plasticity of the welded joint.

High-frequency electric resistance welding is one of the most common process for production of longitudinal seam welded carbon steel pipes suitable for line pipe, casing and tubing. In this pipe production process, the hot rolled strip goes into the forming mill where it is gradually cold formed into a tubular shape in several stages of forming rolls and its edges are continuously joined by a combination of localized electrical resistance heating and forge pressure. High frequency electric resistance welding generally involves high temperature, forge pressure and subsequent cooling, and as the result of this thermal cycle occurs significant microstructural changes. These microstructural changes provides a wealth of information on weld seam quality and edge preparation of hot rolled strips.

In this paper, microstructural changes in the forge weld area during high frequency electric resistance welding (HFERW) of longitudinal seam welded pipes Ø114.3×5.21mm were investigated.