Steel Tube Joint Research Articles

Multi-response optimisation of rotary friction welding of austenite stainless steel tube joints for improved strength and corrosion resistance

Multi-response optimisation of rotary friction welding of austenite stainless steel tube joints for improved strength and corrosion resistance

Feasibility of Recycled Aggregate Concrete in a Novel Anchoring Connection for Beam-to-Concrete-Filled Steel Tube Joints

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper proposed a novel full-bolted beam-to-concrete-filled steel tube (CFST) joint and investigated the anchoring behavior of the steel plates embedded in RAC-filled steel tubes, which represents the behavior of the tensile zone in this joint, to demonstrate the feasibility of utilizing RAC in composite structures. The specimen consisted of a CFST and a connecting plate embedded in the CFST. In total, 18 specimens were tested to study the effects of concrete type (i.e., recycled aggregate concrete and natural aggregate concrete), anchoring type (i.e., plate with holes, notches, and rebars), and plate thickness on the pullout behavior, such as anchorage strength, load–displacement response, and ductility. Based on experimental results, the aggregate type of the concrete does not affect the pullout behavior obviously but the influence of anchoring type is significant. Among the three anchoring methods, the plate with rebars exhibits the best performance in terms of anchorage strength and ductility, and is recommended for the beam-to-CFST joint. In addition, plate thickness obviously affects the behavior of plates with holes and notches, the bearing area of which is proportional to the thickness, whereas the pullout behavior of the plates with rebars is independent of thickness. Finally, design formulas are proposed to estimate the anchorage strength of the connecting plates, and their reasonability is validated using the experimental results.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Optimizing rotary friction welding parameters to attain maximum strength in duplex stainless steel tube joints

Optimizing rotary friction welding parameters to attain maximum strength in duplex stainless steel tube joints

Microstructures and properties of a novel 115 mm thick 08Cr9W3Co3VNbCuBN heat-resistant steel tube joints welded by shielded metal arc welding

A novel heat-resistant steel tube, 08Cr9W3Co3VNbCuBN (G115), is the primary choice for crucial components of ultra-supercritical (USC) thermal power plants. In this paper, the 115 mm thick G115 steel tube was welded successfully by shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW), and the microstructures and mechanical characteristics of joint were studied. The results indicated that the microstructure of the weld zone (WZ) was mostly ferrite and martensite, and the content of ferrite at the weld root was 19.9% lower than that at the weld center. However, at the weld toot the grain size was reduced by about 20%, and the content of M23C6 was increased by 30.9%. Previous austenite grain boundaries (PAGBs) and martensite occurred in the heat-affected zone (HAZ) because to varying heat input, and a tiny quantity of fine Cu-rich phase precipitated from the root of HAZ. The hardness distribution of joint from the base metal (BM) to WZ demonstrated a low to high phenomena, with the average hardness of the BM being 235 HV and the average hardness of WZ being enhanced by 1.16 times. The fine secondary phases precipitated and diffused in the WZ, therefore reinforcing the martensite and improving its mechanical properties. The average impact absorption energy of the weld zone was 43.89 J, and the average impact energy of the HAZ was 54.57 J, both of which were sufficient to fulfill the actual standard (>31 J). The fracture morphology revealed a complex fracture mechanism with dimples and cleavages on the surface of joint, and the toughness was positive. The causes of the decrease in hardness and the rise in toughness might be the Cu-rich phase precipitated from the root of HAZ. Furthermore, the corrosion resistance of the welded joint (WZ: Icorr = 10.542 μA cm−2, HAZ: Icorr = 11.241 μA cm−2) was lower than that of the BM (Icorr = 9.4844 μA cm−2).

Study on dynamic behavior of tubular T-joints subjected to out-of-plane impact loading

In this study, the failure mode, impact resistance, and other key factors affecting the deformation of T-shaped circular steel tubular joints subjected to out-of-plane impacts are studied using a combination of numerical and analytical methods. The finite element (FE) analysis for circular hollow section (CHS) tubular T-joints subjected to in-plane impact is carried out. The simulation results are in good agreement with the test results, and the error is <6%. For common joint sizes in engineering, 63 FE models of CHS tubular T-joints subjected to out-of-plane impacts are created, and the deformation patterns and impact force development processes are described. In particular, following previous research into the deformation laws of steel tube structures, this study proposes a modified equal area axis method and utilizes it to distinguish the bending displacement and local indentation. Using the displacement changes and research results for T-joint failure modes, the criteria for judging the failure modes of the specimen are proposed, and the failure mode is categorized into three types. By discussing the influence of four parameters [length-to-diameter ratio of the chord (α), diameter ratio of the brace-to-chord (β), impact energy (Ek), and length-to-diameter ratio of the brace (αh)] upon the joint deformation of the specimen, a prediction formula for the global and local deformation of a T-shaped steel tube joint under out-of-plane impact loads with respect to the four abovementioned parameters is obtained via data fitting, and the accuracy of the formula is verified via error analysis.

Fatigue and Fracture Performance of a Pedestrian Bridge with a Circular Steel Tube Girder

Pedestrian bridges with I-shaped girders exhibit frequent construction errors and difficulties in the construction of curved sections because the bridges are composed of straight girders mounted on piers. Therefore, a pedestrian bridge utilizing circular steel tubes as the main girder, which is easy to construct and more economical, is proposed to resolve these problems. When steel pedestrian bridges are used for long periods, fractures can occur owing to fatigue in the joints between the main girder and the bottom support. Full-scale circular steel tube joint test units were fabricated and subjected to two million cycles of fatigue performance tests and one million cycles of fatigue fracture tests to quantify the fatigue behavior of a new pedestrian bridge design comprising circular steel tubes. Finite element analysis (FEA) was used to verify the results of the fatigue fracture tests. The proposed pedestrian bridge exhibited excellent stability in terms of fatigue behavior. Moreover, the fatigue fracture of the bridge was successfully predicted using FEA.

Structural behaviour of inner set bolted joints in steel tubes under tension

In this article, the structural behaviour of a new continuous joint of steel tube under tension is systematically studied. Structural analyses of six typical joints under tension are carried out. The experimental set-up and details of the specimens are introduced, followed by descriptions of the results and experimental observations. Based on the experimental results, the main behavioural patterns are discussed and the salient response characteristics related to stress concentration and capacity are examined. An ideal elastoplastic stress–strain relationship, Mises yield criterion and geometric nonlinear finite element analysis model are established, and a detailed description of the modelling assumptions is presented. A large number of finite element parameters are further analysed. The experimental and numerical findings presented in this article offer direct information on the influence of key bearing capacity properties, such as the plugged length of the cross-gusset, the area of the cross-gusset and the area of the cushion-plate, on the main response characteristics. The results also provide essential data for future analytical and design-oriented studies.

Force transmission mechanism of a new joint of concrete-filled rectangular steel tubular column under axial compression

In this study, a new joint of concrete-filled rectangular steel tube column was proposed and analyzed. The force transmission components include distribution beams and inner periphery ribs in the floor node area. The stress behavior of the new proposed concrete-filled rectangular steel tube column under axial compressive load was investigated. It was found that the force transmission components coordinate the force and deformation of external steel tube and internal concrete. This indicates that the steel tube and concrete can work together to bear external load. Our previous test results also show that arranging force transmission components in the floor node area can improve the mechanical behavior of a concrete-filled rectangular steel tube column. Finally, a design method of force transmission component distribution beam is proposed, which provides a reference for the structural designer to use the new concrete-filled rectangular steel tube joint in actual engineering.

Stress reduction effect of concrete-filled steel tube joints

Stress reduction effect of concrete-filled steel tube joints

Optimization of process parameters for friction weld steel tube to forging joints

In this study, structural durability of continuous drive friction welding (CDFW) of steel tube/forging joints is inspected. The relationship between the welding parameters and the mechanical properties is developed by using response surface methodology (RSM). While keeping rotation speed constant, friction pressure, friction time, forging pressure and forging time are used as input variables, and the tensile strength, elongation (%) and petal crack length are selected as output variables. For setting optimum condition parameters, the desirability function is used.According to the confirmation experiment, the difference between the values of tensile strength, elongation (%) and petal crack length, predicted by response surface curve and the experimental data for the maximum desirability is 1.06%, 13.37% and 2.44%, respectively. Furthermore, the predicted model looks reasonably accurate based on the analysis of variance (ANOVA). Using the response curve, one may estimate the tensile strength, elongation (%) and petal crack length for similar joints.In comparison to previous studies, optimization of CDFW parameters for forging bracket to steel tube joints is investigated for the first time. Petal test for the optimization of friction welding is also utilized for the first time.

モルタル充填接合工法による杭頭接合部の開発に伴う耐力評価法の検討

A new steel column and ready-made pile joint system is proposed by the authors. This new joint system has been using mortal in-filled steel tube joint. These abilities can enable to reduce costs and construction period by omitting mold construction work, rebar construction, and concrete work for building the foundation.In a structural design according to the present joint system, evaluation method of ultimate strength for mortar-filled joints should be clear. Therefore, in this paper, ultimate strength evaluation method in the case of the development of pile head joint by mortal in-filled method is clarified obtained by the present experiments.

A numerical approach for evaluating the stiffness of steel tube–R.C. beam composite joint

A numerical approach has been developed for the analysis of composite joints of steel tubes embedded in reinforced concrete. This kind of joint is typically found at the foundation of composite columns and in open pile supported wharves. The performance of such joints is thought to have a considerable effect on the overall behaviour and ductility of the structures containing them as indicated by previous experimental and analytical work. The developed approach was based on a two-stage two dimensional analysis to account for the three dimensional nature of the joint behaviour. The validity of the new approach was proven by applying it to previously experimentally tested composite joints. Good agreement was observed between the joint behaviour as produced by the numerical analysis using the new approach and the experimental measurements. Considerable saving in computer run time was also achieved compared to the case of using three dimensional analysis.

Microstructure and tensile properties of friction welded SUS 304HCu austenitic stainless steel tubes

Austenitic stainless steels are used in superheater/reheater tubing for their oxidation resistance and fireside corrosion resistance, in addition to their creep strength. The addition of 3 wt. % Cu to SUS 304HCu austenitic stainless steel to reduce the corrosion, has found to increase the creep performance in temperature range of 650°–750 °C. The addition of Cu to steels can have adverse effects on the mechanical properties of the fusion welded joints. During fusion welding, Cu can form low temperature eutectic phases that preferentially segregate to the grain boundaries and embrittle the alloy. There is a need for a better welding procedure/technique to fabricate this alloy. Friction welding is a solid state welding process which nullifies the adverse effects of low temperature eutectics segregation. Hence, in this investigation an attempt has been made to study the microstructural and tensile properties of the friction welded SUS 304HCu austenitic stainless steel tube joints fabricated using optimized parameters.

Experimental Investigation and Finite Element Analysis on Concrete-Filled Steel Tubular Gusset Plate Connections

The use of concrete-filled steel tubes in different areas of construction is becoming an attractive solution because of its remarkable performance. It provides not only an increase in the load carrying capacity but also good seismic behaviour. It is often adopted as compression member especially for structure under large axial pressure. Concrete-filled steel tubular composite truss can be used as main load-bearing structure of long-span and mega structure. But the composite trusses were connected by mutually intersecting joints which the welding construction process is complicated and the quality is unstable. Therefore, gusset plate joints are more suitable. So experimental study and finite element analysis are carried out in 12 specimens. Test results indicate that bearing capacity of hollow circular steel tube joints filled with concrete is provided obviously, and local buckling performance of steel tube under gusset plate is also improved. In order to study the mechanical performance and interaction of steel tube and core concrete, the ANSYS program is adopted in finite element analysis. And the analysis results is agreed well with the test. Regression analysis is carried out at the same time, thus simplified calculated formula of this type joints is concluded which can give reference for the designers.

Failure analysis of a steel tube joint perforated by corrosion in a well-drilling pipe

The corroded steel tube joint belonging to an offshore oil well-drilling pipeline was investigated. All of the pits and punctures distributed along the “steps” are formed by off-centre machining on the internal tube surface, and the pits have a horse’s hoof and hemispherical contour. The metallurgical structure of some spots on non-penetrating corrosion pits and penetrating punctures looked markedly curved, i.e., curved deflections in the banded structure (or streamlines) were visible. The pits contour and metallurgical structure indicate that the pits and punctures are characterised by cavitation erosion. The chemical composition of the corroded steel tube joint is similar to 1320, 1330 and L80-1 steels specified in ASTM standards, and the content of non-metallic impurities in the failed steel tube was identified as Grade 1.0–1.5, which is within the permitted range. Corrosion pit surfaces and the tube joint showed a deposit layer and a clay-like substance that was rich in Fe, Mn, Ca, Ti, Cu, C, O, S and Cl, and “crystal sugar-like” appearance observed on location of the penetrating puncture, indicating H2S- and CO2-assisted corrosion mechanisms. These investigations indicated that failure of the pipeline occurred by erosion corrosion, cavitations erosion and chemical corrosion, which is from both mechanical and chemical actions.

Static Performance Analysis on Combined Truss with Steel Tube and Concrete-Filled Steel Tube Based on Total Strain Crack Constitutive Model

Based on the total strain crack constitutive model and the available testing data, finite element model on three trusses were established by the finite element procedure MIDAS/FEA and the analysis were executed in order to verify the validity of constitutive model and study the static performance of combined truss. The results show that the finite element model based on total strain crack constitutive can reflect the static performance of combined truss and can carry the affective parameters analysis, which can offer theory evidence for engineering application of combined truss. The failure of three trusses were due to joint failure, however the failure modes were different and changed by the concrete filled in chord. The bearing capacity of three trusses was controlled by the jionts and the strength and stiffness of jionts were increased by the concrete filled in the chord, therefore the bearing capacity of trusses was increased while the deformation was decreased. In combined truss with steel tube and concrete filled steel tube, the concrete-filled steel tube joints can improve the bearing capacity and the steel tube joint can satisfy the requirements of plastic deformation, which have obvious advantages in the engineering application.

Finite Element Analysis on Static Performance on Combined Truss with Rectangular Steel Tube and Concrete-Filled Steel Tube

Finite element analysis on three trusses was carried out in order to study the performance of combined truss with steel tube and concrete filled steel tube. The first specimen was a RHS truss, the second one was a combined truss with steel tube and concrete filled steel tube, and the third one was a concrete-filled steel tube truss. The results show that the finite element model can reflect the static performance of combined truss and can carry out the affective parameters analysis, which can offer theory evidence for engineering application of combined truss. The damage of three trusses was all due to the joint failure and the failure mode was all punishing shearing failure, but the concrete filled changed by the failure place of joints. The bearing capacity of three trusses was controlled by the jionts and the strength and stiffness of jionts were increased by the concrete filled in the chord, therefore the bearing capacity of trusses was increased while the deformation of trusses was decreased. In combined truss with steel tube and concrete filled steel tube, the concrete-filled steel tube joints can improve the bearing capacity and the steel tube joint can satisfy the requirements of deformation, which have obvious advantages in the engineering application.

An analysis of weld geometry in creep of welded tubes undergoing internal pressure

The purpose of this paper is to present the complex problems of creep in welded joints of steel tubes. The following sections are contained in this paper: formulation of the equations for nonlinear thermomechanics, discussions of the creep law and the flow rule as well as presentation of equations for the finite element method. A numerical algorithm for solution is explained. Theoretical considerations are supplemented by solving a practical engineering problem.

The Internal Creep Rupture Strength of Joints of Steel Tubes Welded with Dissimilar Metals

Hereunder is given an account of the uniaxial tension and internal pressure creep rupture tests conducted of the joints of 2. 25 Cr-1 Mo, 5 Cr-0.5 Mo, 9 Cr-1 Mo low alloy steel tubes, and of 18-8 Mo, 18-8 Ti, 18-8 Nb stainless steel tubes, welded with dissimilar metals, to investigate the effect of the weld defects, and of the decarburized layer, on the internal pressure creep rupture strength of the welded joints, as well as the relationship between the uniaxial and the internal pressure creep rupture strength.The results are summarized as follows:(1) When poor penetration is formed at the welded joints, fracture often occurs in the welded metal under the internal pressure, and leaves the internal pressure creep rupture strength poor.At sound joints, fracture always occurs in the base metal in the internal pressure test, and the strength of the welded joints is equal to that of plain tubes.(2) A decarburized layer is formed at all dissimillar metal joints, regardless of electrodes, stainless steels or Inconel alloys.At the joints of 2.25 Cr-1 Mo and stainless steels with 24 Cr-13 Ni stainless steel electrode, fracture occurs in the decarburized layer in uniaxial tests lasting for a longer time than 700∼2000 hours, but in the internal pressure tests, fracture occurs in the base metal even after a longer duration. At other joints, fracture always occurs in the base metal both in the uniaxial and the internal pressure tests.Thus it is evident that the internal pressure creep rupture strength of joints with dissimilar metals is not affected by the formation of a decarburized layer.(3) The uniaxial and internal creep rupture data of the plain tubes and the welded joints which fractured in the base metal, are analyged by the statistical method to determine the relationship between the uniaxial and the internal creep rupture strength.The mean diameter formula is fairly applicable to the result of 2, 25 Cr-1 Mo tubes, and of 9 Cr-1 Mo tubes, either in the received condition or in the stress relieved condition, while the ASME or the Tresca formula is applicable to the result of 5 Cr-0.5Mo steel tubes.