CAST HOLLOW BILLET STRUCTURE SIMULATION MODELING FOR OIL GRADE PIPES

Purpose – The purpose of this paper is to study the effect of feeding scheme on melt flow and temperature field during the steady-state of level-pour direct-chill (DC) casting of A390 alloy hollow billet and optimize the design of feeding scheme. Design/methodology/approach – Melt flow and temperature field are investigated by numerical simulation, which is based on a three-dimensional mathematical model and well verified by experiments. Findings – The numerical results reveal that both melt flow and temperature field are obviously affected by the feeding scheme. The homogeneity of melt flow and temperature field in hollow billet with the feeding scheme of modified four inlets are better than the other feeding schemes. Experimental results show that crack can be eliminated by increasing the number of feeding inlets. The primary Si size appears unaffected while the distribution of primary Si particles is highly affected by the change of feeding scheme. Only with the feeding scheme of modified four inlets can fine and uniformly distributed primary Si particles be achieved. Practical implications – The paper includes implications for the design of feeding scheme in level-pour DC casting of hollow billet for practical use. Originality/value – This paper develops different feeding schemes for level-pour DC casting of hollow billet and optimizes the design of feeding scheme.

The two-phase zone continuous casting (TZCC) technique was used to continuously cast high-strength aluminum alloy hollow billets, and a verified 3D model of TZCC was used to simulate the flow and temperature fields at casting speeds of 2–6 mm·min−1. Hollow billets under the same conditions were prepared, and their macro/microstructures were analyzed by an optical microscope and a scanning electron microscope. During the TZCC process, a circular fluid flow appears in front of the mushy zone, and the induction heated stepped mold and convective heat transfer result in a curved solidification front with depressed region near the inner wall and a vertical temperature gradient. The deflection of the solidification front decreases and the average cooling rate in the mushy zone increases with increasing casting speed. Experimental results for a 2D12 alloy show that hot tearing periodically appears in the hollow billet accompanied by macrosegregation near the inner wall at casting speeds of 2 and 4 mm·min−1, while macroscopic defects of hot tearing and macrosegregation weaken and the average size of columnar crystals in the hollow billets decreases with further increasing casting speed. 2D12 aluminum alloy hollow billets with no macroscopic defects, the finest columnar crystals, and excellent mechanical properties were prepared by TZCC at a casting speed of 6 mm·min−1, which is beneficial for the further plastic forming process.

The article solves the problem of determining the temperature of calibrated strikers in a unit of combined casting and deformation during production of hollow steel billets. The authors substantiate the relevance of determining temperature fields and thermoelastic stresses in calibrated strikers when compressing the wall of a hollow billet and at full speed when cooling the strikers with water, and describe the strength and thermophysical properties of the steel from which the strikers are made. Geometry of the striker for producing a hollow billet in one pass is shown. The paper considers the initial data and temperature boundary conditions for calculating the temperature field of the striker during production of hollow billets in a unit of combined casting and deformation. The boundary conditions are given to determine the striker temperature as well as the values of heat flow and effective heat transfer coefficient. The results of calculating the temperature fields are performed in four sections and are presented for cha­racteristic lines and points located on the striker contact surface and in the contact layer at a depth of 5 mm from the working surface. Dimensions of the finite element grid were used in calculating the temperature field of the strikers. The temperature field of the strikers with collars was determined based on solution of the unsteady thermal conductivity equation with the corresponding initial and boundary conditions. The values and patterns of temperature distribution in a calibrated striker are presented when the wall of a hollow billet is compressed and when a hollow billet is produced in one pass in a unit of combined casting and deformation.

The most productive and modern method is the production of pipes on pipe-rolling machines using continuous rolling mills with a retained mandrel. The production of seamless hot rolled tubes on such aggregates can be accompanied by the appearance of defects on the surface of the pipes, which leads to an increase in the amount of defective products. Taking into account the current state of the art, the process of defect formation in the production of pipes has not been studied sufficiently. Defects occur on the surface of pipes when rolling in the mills of the line of the pipe-rolling unit. Typical types of surface defects are surface cavity, rolling skin on the outer and inner surfaces of the pipes, pigeon hole. In this article, we consider the quality of pipes with an outer diameter in the range of 219÷325 mm with a wall thickness in the range of 8÷24 mm obtained by rolling on aggregates that have continuous rolling mills with 2- and 3-roll stands in the line. The quality is considered from the point of view of the influence of technological factors of rolling (the drawing coefficient, the reduction in the external diameter, the wall thickness, etc.) on the amount of reject for certain types of surface defects. As a universal, previously little studied, the size of which can be judged on the level of defectiveness of technology, we consider the factor of the ratio of deformations in diameter to deformation along the wall thickness in the rolling mill. A number of models have been obtained by statistical methods, guided by which it is possible to predict the expected level of defects in surface defects in the production of seamless pipes, and also to select deformation conditions that minimize the amount of defect.

The crystallizer is the most critical and most important functional unit of a continuous casting machine (hereinafter referred to as CCM). It is the main technological unit of the CCM, an assembly for removing heat during the solidification of the solidifying metal and the formation of the ingot. The main requirement for the crystallizer is to provide maximum heat removal from the solidifying steel to the cooling water, and to obtain a strong ingot shell with a good surface at the outlet of the crystallizer, which would not be destroyed by the heat of the liquid phase and the ferrostatic pressure. During the reconstruction of the CCM by the contractor company, drawings of crystallizers and crystallizer sleeves with a double‑cone internal geometry for casting 200 mm continuous cast billets were developed. The 200 mm continuous cast billet is a billet for the production of hot‑rolled seamless steel pipes. During the operation of the crystallizer sleeves with a double‑cone internal geometry, an accelerated wear of the protective coating in the lower part of the sleeve was noted, as well as an increased rejection of hot‑rolled pipes due to defects on the outer surface of the pipes. In order to identify the cause of the defect formation, complex metallographic studies of the outer surface of the pipes were carried out. As a result of the metallographic study, surface defects classified as steel mill scale on the outer surface of the pipes were identified. To minimize the “steel mill scale” defect and reduce the wear of the protective coating of the crystallizer sleeves, work was carried out to select the optimal conditions for the crystallization of the continuous cast billet: the use of crystallizer sleeves with a three‑cone internal geometry compared to a double‑cone was investigated; maintaining the temperature difference of the water at the inlet and outlet of the crystallizer within specified limits (ΔT) was tested. It was found that the use of a crystallizer sleeve with a three‑cone internal geometry for casting 200 mm billets and the stable behavior of the ΔT parameter made it possible to ensure the required quality of the surface of seamless pipes, reduce the wear of the protective coating of the crystallizer sleeves and increase the productivity of the CCM.

In this research, a new semi-analytical model is presented for the strand surface temperature in the continuous casting of steel. Firstly with a dimensional analysis approach a general relation between the strand surface temperature and the other effective variables such as conductivity of the steel, pouring temperature, casting velocity, distance from the meniscus, volume rate of cooling water, solidus temperature and heat flux density at the meniscus is deduced. The constants appeared as coefficients or powers of variables in presented relation were computed by a numerical simulation of continuous casting for a breakout bloom. The resulted semi-analytical model for strand surface temperature was extended to predict the solidified shell thickness. The resulted semi-analytical model was validated with comparison to experimental, analytical and numerical results of slab, billet and bloom and good agreement was seen. The new presented model at this research is in versus of controllable parameters and specifications of the mold and it can be used for design of a process control system for continuous casting of slab, billet and bloom.

A modern pipe-rolling unit intended for the production of seamless pipes includes a continuous rolling mill with a retained mandrel. During operation, the working portion of the mandrel unit of a continuous rolling mill is subject to high temperatures and constant cyclic alternating loads, which results in its wear. The magnitude and nature of the wear of mandrels affect the quality of the inner surface of finished pipes. Also, a significant problem in the production of pipes on a continuous rolling mill is the short service life of mandrels. Moreover, mandrels are mostly imported and very expansive. In normal operating conditions, the amount of wear along the length of the mandrel is not uniform. The wear of mandrels can be made uniform and their service life can be increased by changing the velocity of the mandrel, changing the position of the mandrel at the beginning of the rolling process, or using mandrels of a new design. In this article, the main developments and research aimed at increasing the service life of mandrels of FQM-type continuous rolling mills are described.

A joint industrial program (JIP), termed “Seamless 100 ksi weldable” was launched in order to address the complex design issues of high strength Q&T seamless pipes for ultra deep water applications. The JIP was split in two main phases, the first one devoted to the development and production of seamless pipes, with minimum yield strength of 90 ksi (620 MPa) to 100 ksi (690 MPa), and the second one to evaluate their field weldability. Phase I was recently completed. The role of chemical composition and Q&T process conditions on microstructure and precipitation was analyzed, together with relevant effects on strength and toughness, for both laboratory and industrial steels. The main microstructural features which control the strength-toughness combination of these high strength Q&T steel grades were identified and results were exploited for the set-up of a production route for pipelines and risers. The 100 ksi grade was achieved in 16 mm (0.630 in) and 25 mm (0.980 in) WT pipes. Phase II is in progress.

As a result of work carried out by institutes and enterprises in the refractories and metallurgical industry of the USSR, various types of refractories have been developed for continuous steel casting plant that is widely used in production conditions. The speeding up of the work of continuous casting plant, the extension of the range of steels being cast, and the development of continuous casting plant of various designs all require decisions to be made in the field of refractory materials. It is necessary to continue research into the mechanism responsible for the formation of the contact layer between the steel and the refractory, the way in which it reacts, and the movement in various boundary conditions; it will also be necessary to develop further scientific experimental theories for the contact layer, and through the accumulation of the necessary data to approach the problems of constructing a mathematical model for the process.

In this paper, a comprehensive three-dimensional mathematical model is built to investigate the effect of rotating electromagnetic stirring on solidification process of copper hollow billet during horizontal continuous casting. The finite element package ANSYS and the commercial finite volume package FLUENT are employed for simulating electromagnetic field and thermal flow field respectively. The Lorenz force and Joule heat are transferred between them with a special data communication method. The model involves the solution of Maxwell equations, Navier—Stokes equations and energy equation for the turbulence characteristics κ and ϵ. The measured magnetic flux density is used for validating the proposed model. The simulated results show that rotating electromagnetic stirring causes a swirling motion in the hollow billet and makes the temperature field uniform. In the present study, the temperature gradient decreases from 748 to 196 K m−1, and the sump depth is reduced from 48·8 to 29·0 mm.

A wide variety of tools are used in the production of corrosion-resistant pipes. These include dies and die rings, mandrel needles, press washers, bushings, expanders, rollers, support plates, mandrels, and gauges. Their operating conditions are characterized by significant loads, high temperatures, strong friction, and significant specific pressures. In most processes, pipe tools have low stability, which requires stopping mills and presses, constant retooling, and reduces the efficiency of rolling and pressing corrosion-resistant pipes. With low tool stability, the quality of the inner surface of the pipes and their stability in operation also decreases. This is especially important in the difficult operating conditions of these pipes: in the energy, aviation, machine building, chemical, and food industries. Therefore, the search for modern ways to strengthen and improve the corrosion resistance of pipe tools is an important task of modern materials science. The relevance of the topic stems from the need to create highly productive and durable tools for the production of corrosion-resistant pipes, which is primarily associated with the problem of obtaining and processing materials that can withstand the harsh operating conditions of the tools (high temperatures, intense sliding speeds, and high wear rates). primarily with the problem of obtaining and processing materials that could withstand the harsh operating conditions of the tool (high temperatures, intense sliding speeds and significant specific pressure, alternating loads, dynamic impacts). Thus, there is a certain interest in improving heat treatment methods and using modern types of chemical-thermal treatment to increase the wear resistance and performance characteristics of tools. The aim of the work is to find modern ways to strengthen the main pipe tools (pipe pressing tools – die rings, expanders) for pressing corrosion-resistant pipes on pipe pressing machines and tools for cold rolling of pipes (rollers, support strips of HPT mills) used in the production of thin-walled pipes from corrosion-resistant steels using new technologies of ion-plasma nitriding and modern methods of alloy structure research, as well as real testing of tools in production conditions and implementation of the results of the work at existing pipe enterprises in Ukraine.

Physical experiments allow to obtain maximum information on a studied process at minimal cost, ensuring its higher accuracy comparing with data, obtained by mathematical simulation and avoiding risks, which can occur at industrial testing of new technological modes. Results of studies of deformation in the process of pipes production by extrusion presented. The studies were accomplished at laboratory test units, developed by specialists of the laboratory of drawing and extrusion of JSC “RusNITI”. One of the basic problems at pipes production by extrusion is ensuring minimal possible wall non-uniform thickness. It was noted that the relation between plunger die moving speeds during sleeve pressing-out and immediate pipe extrusion has a significant effect on pipe wall non-uniform thickness. Computer simulation of the pipe extrusion process, accomplished by application QForm program shown that minimal values of wall non-uniform thickness corresponded to relation abovementioned speeds as 0.5–0.8. To check the data, a physical simulation of extrusion process of lead cylinder samples, having outside diameter of 18.94 mm and wall thickness 5.19–5.32 mm was accomplished. For the extrusion, a universal servohydraulic system of dynamic test Shimadzu Servopulser was used. Within the physical experiment a dependence was established between pipe wall non-uniform thickness on relation between speeds of pressing-out and extrusion. The revealed regularity was confirmed during pilot production of a pipe lot at the 55 MN force extrusion line. Another physical simulation of extrusion of 10.0×2.0 mm pipe-samples made of C1 grade lead was accomplished with one- and twothread helical ribbing of internal surface. For its accomplishment an experimental module was designed and manufactured. It was established that rotation speed of the extrusion mandrel had no significant effect on extrusion force. Metallographic studies shown that the extrusion mandrel rotation speed contributes to considerable increase of pipes surface hardness and obtaining finer grain comparing with the classic extrusion method. The technical ability of pipes production with internal helical ribbing by hot extrusion method was confirmed. The results of the study became a base for elaboration of a technology of pipes production at Volzhsky pipe plant according to ТУ 14-3Р-157–2018 “Steel seamless hot-extruded pipes with helical ribbing of internal surface for steam boilers”. Results of physical simulation of pipe drawing process at self-adjusting mandrel with application of lubricant materials of various viscosity. The data obtained were used for elaboration of a technology for production of cold-deformed pipes with internal diameter of 6.0–12.0 mm at Sinarsky pipe plant.

Non-uniform friction and lubrication are the key factors affecting the surface quality of the casting billet. Based on the three-layer structure of the casting powder in the mold, the frictional stress in the mold was calculated and analyzed by using the relationship between the frictional stress and the thickness and viscosity of the liquid slag film, and the lubrication state between the cast billet and the mold was evaluated. Based on the actual production data of 40Mn2 steel and combined with the numerical simulation results of the solidification and shrinkage process of the molten steel in the mold by ANSYS 2022 R1 software, the frictional stress on the cast billet in the mold was calculated. It was found that within the range of 44~300 mm from the meniscus, the friction between the cast billet and the mold was mainly liquid friction, and the friction stress value increased from 0 to 145 KPa. Within 300–720 mm from the meniscus, the billet shell is in direct contact with the mold. The friction between the cast billet and the mold is mainly solid-state friction, and the friction stress value increases from 10.6 KPa to 26.6 KPa. It indicates that the excessive frictional stress inside the mold causes poor lubrication of the cast billet. By reducing the taper of the mold and optimizing the physical and chemical properties of the protective powder, within the range of 44~550 mm from the meniscus, the friction between the cast billet and the mold is mainly liquid friction, and the friction stress value varies within the range of 0–200 Pa. It reduces the frictional stress inside the mold, improves the lubrication between the billet shell and the mold, and completely solves the problem of mesh cracks on the surface of 40Mn2 steel cast billets.

Ever since continuous casting was introduced, nozzle clogging has been a recurring subject of metallurgical research and publications. Nozzle clogging is caused by the deposition of non‐metallic inclusions – on the casting equipment – which are solid at the temperature of casting. Calcium treatment already represents a possible solution to eliminate this phenomenon, but there are special steel grades which do not allow its application either because they are price sensitive or for certain other reasons.3 Cleaning the steel melt by agitation is an alternative solution, but it has time constraints due to the cooling of the melt. Over extensive cooling can be prevented by heating the melt (in ladle), but its introduction and operational costs per heat are often too high for an individual steelmaking plant to afford. The goal of our research is to find metallurgical solution to reduce the rate of nozzle clogging in plants which do not possess a ladle furnace and the time devoted to treatment or the price of the product do not allow Ca‐treatment to be applied.

Trends in pipe-steel development, smelting technologies, and hot-rolling and heat-treatment methods are reviewed, in the context of growing requirements on seamless pipe for oil and gas extraction in challenging conditions. As new resources become available, PAO Gazprom is developing appropriate requirements on high-strength, low-temperature borehole pipe and pump and compressor pipe that is resistant to H2S and CO2 corrosion. In the present work, metallurgical principles are outlined for the development of new grades of high-quality steel with minimum content of sulfur, phosphorus, and dissolved gas and corresponding treatment conditions. This involves the selection of the chemical composition so that martensite structure is formed on quenching and subsequent high-tempering, thereby ensuring the required combination of strength and ductility. It is shown that the optimal combination of strength and ductility may be attained at–60°C if chromium–molybdenum steel containing around 0.25 wt % C is alloyed with vanadium and niobium, which readily form carbides. Resistance to sulfide stress cracking may be afforded by microalloying of the steel so as to decrease the initial austenite grain size and by calibrating the content of molybdenum, which ensures high hardenability and slows softening on tempering. New compositions for martensitic stainless steel with 13% Cr are developed. That ensures the required resistance to CO2 corrosion and improves the strength and cold strength in comparison with the basic composition of 20X13 steel. Reconstruction of the electrosmelting and rolling systems at OAO Volzhskii Trubnyi Zavod (VTZ) ensures the required quality of the new products, from continuous-cast steel billet to the final pipe.