Duplex Stainless Steel Tubes Research Articles

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

Axial compressive property of square and rectangular UHPC-filled duplex stainless steel tube stub columns

This study presents experimental and numerical investigations of the axial compression performance of square and rectangular ultrahigh performance concrete (UHPC)-filled duplex stainless steel tube (UFSST) stub columns. A total of twelve UFSST stub columns, six ordinary concrete filled duplex stainless steel tube (CFSST) stub columns, and six hollow duplex stainless steel tube (HSST) stub columns were tested under axial compression. The test parameters include the section type, three kinds of concrete strength grades, and three kinds of duplex stainless steel tube thicknesses. The test results showed that UFSST stub columns behaved with high bearing capacity and favourable ductility. In the UFSST stub columns with ξ ≥ 1.87, the square and rectangular duplex stainless steel tubes could well confine the shear failure of UHPC. The developed finite element model could effectively reflect the compressive behavior of the HSST, CFSST and UFSST stub columns. The available experimental database was employed to evaluate the feasibility of current design codes and existing calculation models in the literature to design UFSST stub columns. Finally, a modified computational model was proposed that takes into account the nonuniform confinement effect induced by square and rectangular section tubes on concrete and showed a higher prediction accuracy.

Axial compression behaviour of circular and square UHPC-filled stainless steel tube columns

To improve the durability and mechanical behaviour, an ultra-high performance concrete (UHPC)-filled duplex stainless steel tube stub column is proposed in this study. To explore the axial compression performance of UHPC-filled duplex stainless steel tube (UFSST) stub columns, a total of 12 UFSST, 6 confined concrete-filled duplex stainless steel tube (CFSST) and 6 hollow duplex stainless steel tube (HSST) stub columns were subjected to axial compression. The experimental parameters included the section type, the tube thickness and the core concrete strength. For the UFSST stub columns, when the constraining index (ξ) exceeds 0.82 and 1.52 for circular and square stub columns, respectively, the failure mode changes from shear-type failure to waist-drum failure. The concrete contribution rate (CCR) is positively correlated with the concrete strength and negatively correlated with the tube thickness, whereas the variation law for the strength index (SI) is the opposite. The circular UFSST stub columns have a higher CCR than the square columns. A test database, including UFSST and UHPC-filled steel tube (UFST) stub columns, was established to evaluate the applicability of existing design codes. Furthermore, a modified ultimate load prediction formula with higher accuracy is proposed and verified.

Surface morphology and experimental investigation on joint characteristics of solid-state welded duplex stainless steel tubes

The aim of this work was to systematically find the optimum parameter combination using the response surface methodology (RSM) technique for welding of UNS S31803 tubes and to find the effect of parameters on mechanical and metallurgical properties. In the present work, the experimental investigations of friction-welded UNS S31803 tube joints are discussed in detail with characterization, radiography, and corrosion studies. The most important parameter that has the greatest impact on the tensile strength of the joints is the upset pressure, which is followed by heating time, heating pressure, and upset time. As the upset pressure and time increased, the joint strength also increased. The radiographic evaluation of the weldments revealed no significant flaws at the weld contact. In comparison to the parent metal zone, the microstructure indicated coarse grain structure in the weld metal zone, with grain orientation changing with upset time. For the optimal parameter combination, the austenite phase is primarily spread in the weld metal zone. In comparison to the partially deformed zone and the parent metal zone, the weld zone had lower hardness values. In the high strength and optimum parameter joints, fractography investigation revealed ductile failure.

Axial compressive performance of novel square coral concrete-filled duplex stainless steel tubes

In this paper, a novel square coral concrete-filled duplex stainless steel tube (SCCFDSST) is proposed, and its axial compressive behavior is systematically investigated. Totally forty-five square steel columns welded with 2205 duplex stainless-steel plates are tested. Forty-two specimens are filled with coral concrete, and three columns are hollow steel tubes. The influential critical factors include the strength of coral concrete, the width-to-thickness ratio of steel tube and the constraint factor of SCCFDSST. The results indicate that SCCFDSSTs present satisfying ductility and bearing capacity. Moreover, the composite action provided by coral concrete and duplex stainless-steel tubes (DSST) is significant. For the purpose of guiding structural design, a mechanical model is established to determine the sectional capacity and the relationship between axial load and axial deformation of SCCFDSST. The accuracy of proposed formulas has been fully validated by experimental results, presenting higher precision than that of existing specifications. The results of this research can provide guidance for the application of the novel columns in engineering structures.

Effects of reducing atmospheres of bright annealing on the surface and corrosion characteristics of super duplex stainless steel tubes

The influence of the gas composition in the reducing atmospheres of bright annealing on the surface and corrosion characteristics of super duplex stainless steel tubes was investigated using a variety of experimental and analytical methods. This study showed that the addition of N2 to the reducing atmosphere increased [N] pick up on the surface, promoting the phase transition to a single γ phase with a fine-sized δ remaining along the grain boundary of γ. The increase in partial pressure of N2 in the reducing atmosphere resulted in a thicker single γ phase with Cr2N precipitates along the grain boundary of γ. The corrosion resistance decreased substantially as a result. On the other hand, after annealing in 100% H2 at 1100 °C, some cracks with phase transformation to ɛ-martensite were formed mainly on the top surface region. The corrosion resistance of the annealed sample could be recovered only when the degraded surfaces had been removed, exposing the original phase structure with equivalent phase fractions of δ and γ. Based on the experimental results, more desirable bright annealing conditions for steel tubes with superior corrosion resistance are proposed.

Compressive strength of concrete-filled stainless steel tube stub columns

Concrete-filled stainless steel tube (CFSST) members combine the advantages of the outstanding corrosion resistance of stainless steel and the composite action in concrete-filled steel tube (CFST) system. However, accurate calculation methods for this type of structures are currently limited and research into CFSST members with hot-rolled stainless steel tubes are not available. In this paper, the compressive behavior of CFSST stub columns has been investigated through a comprehensive experimental and numerical program. A total of 18 specimens, including 9 concrete-filled austenitic stainless steel tube (austenitic CFSST) and 9 concrete-filled duplex stainless steel tube (duplex CFSST) stub columns, were tested under compression. The varying parameters in the experimental study included the thickness of the stainless steel tube and the strength of the concrete. Finite element (FE) models duplicating the tests were developed, which were subsequently used in parametric study to generate a wider range of data and to investigate the influence of the tube thickness and concrete strength on the ultimate capacities of CFSST stub columns. Based on the generated data, it was found that the current European and Chinese standards for concrete-filled carbon steel tubes underestimate the resistances of CFSST members significantly. To this end, new calculation methods developed based on these European and Chinese design rules have been proposed, which were shown to provide improved strength predictions for both the austenitic and duplex CFSST members.

Experimental and numerical study of cold-drawn duplex stainless steel square tube columns

ABSTRACT Cold-drawing is one of typical cold-forming techniques in producing stainless steel tubes. Compared with cold-rolling, cold-drawing can be used to manufacture large scale stainless steel tubes. In this study, material properties tests of 14 coupons taken from cold-drawn duplex stainless steel square tubes were reported, along with six stub and seven long column tests under axial compression. Stress-strain curves, ultimate loads and failure characteristics of stub and long columns were obtained. Test results indicate that cold-drawn duplex stainless steel tubes have pronounced cold-forming effect, the yield strength of the flat region reaches up to 750 MPa and the elongation at the fracture decreases significantly. And, all the stub columns show local buckling mode, while most of the long columns undergo overall flexural buckling mode. Finite element models were developed, validated using test data, and then used to generate more results over a wider range of cross-sectional and member slenderness. Both the results of test and numerical modeling were compared with the design strengths of the European, American, Australian/New Zealand and Chinese codes, the design method proposed by Afshan, and the deformation based continuous strength method (CSM). Comparisons show that: for stub columns, design strengths according to all the design codes are underestimated, while the continuous strength method provides reasonable predictions especially for both the stocky and slender cross-sections; for long columns, design strengths calculated using the European, Australian/New Zealand, Chinese codes and the method proposed by Afshan are conservative, while those calculated using the American code are unsafe.

Hydrogen induced stress cracking in UNS S32750 super duplex stainless steel tube weld joint

In this work, the hydrogen embrittlement of super duplex stainless steel tubes UNS S32750 under different hydrogen charging conditions was investigated. Hydrogen charging was performed both in unloaded and in elastically stressed specimens. The tubes were charged and tested under two conditions: as-received and welded. The samples were submitted to tensile tests in order to evaluate how the mechanical properties are affected by the hydrogen inserted into the microstructure. The fracture surfaces were analyzed in order to identify the failure active micro mechanisms. Combined tensile test results and microstructural investigations indicated that elastic stress applied to samples during hydrogen charging enhanced hydrogen solubility and permeability, resulting in greater loss of ductility. As pointed by fractographies of welded H-charged tubes, the microstructural changes induced by welding increased hydrogen diffusivity. The fracture surface of the hydrogen charged as-received tubes exhibited a quasi-cleavage aspect, indicating a mixed failure mechanism composed by plastic strain in austenite and cleavage on ferrite. Otherwise, the main mechanism of failure on welded tubes was cleavage.

Nondestructive Evaluation for Duplex Stainless Steel Tube Using Multi-Frequencies Remote Field Testing

This paper presents the determination of Remote Field Testing (RFT) frequencies to accomplish the inspection of duplex stainless steel tubes grade ASME/ASTM SA 789. The tube specimen was 25.4 mm of outside diameter, and thickness of 1.65 mm with the different artificial flaws. A dual-pickup coils type of RFT probe was employed to inspect the specimen by inserting a probe within the tube. Optimum of testing frequency Range was determined based on an eddy current through transmission generation to produce different magnetic field density. RFT inspection frequency range for duplex stainless steel was consequently determined from 5 to 25 kHz which was different than those inspection frequencies of general ferromagnetic steel tube. In the experiment, calculated frequencies were then generated to the Eddy current (ET) and RFT probes for detecting the flaws of the tube specimen. The inspection signals were specifically shown in function of impedance plane to identify the flaw characters. The results showed that the RFT can be utilized to quantify the wall loss levels of duplex stainless-steel tube better than the ET. Especially, phase angle of inspection signals can be used to evaluate the different depths of the wall losses. Sensitivity of RFT showed the detection performance at minimum 20% of tube wall loss.

Effect of bright annealing process on the properties of TIG welded duplex stainless steel tube

Passivation is the process of forming a protective oxide film on stainless steel. It is accomplished through an appropriate inline bright annealing process. Duplex stainless steel exhibits optimum mechanical and corrosion properties with the austenite-ferrite phase balance in its structure. However, the ferrite-austenite equilibrium in duplex structure can also be affected by inline bright annealing process, in which the heating of stainless steel to a suitably high temperature in a reducing atmosphere takes place. For this reason, the effect of inline bright annealing process on the microstructure and mechanical properties of TIG welded AISI2205 stainless steel tube was evaluated in this study. The results point out that the structure and mechanical properties of the duplex stainless steel tube are affected by the inline bright annealing process. In light of foregoing findings, the sample that was inline bright annealed in reducing nitrogen gas atmosphere has given optimum mechanical properties.

Behaviour of circular concrete-filled lean duplex stainless steel tubular short columns

Lean duplex stainless steel material (EN 1.4162) has recently gained significant attention for its higher structural performance and corrosion resistance compared to the austenitic type. Circular lean duplex stainless steel tubes filled with concrete are innovative composite columns which have not been studied experimentally or numerically. This paper presents the fundamental behaviour of circular concrete-filled lean duplex stainless steel tubular (CFSST) short columns under axial compression. Three dimensional finite element (FE) models for CFSST columns subjected to axial compression are developed using the FE package ABAQUS. The lean duplex stainless steel material is modelled using the two-stage constitutive laws while the concrete is simulated using accurate concrete confinement models. The FE models are verified by comparisons with existing experimental results on hollow stainless steel columns, concrete-filled steel tubular columns and CFSST columns. Parametric studies are undertaken to investigate the effects of concrete compressive strength and diameter-to-thickness (D/t) ratio on the behaviour of CFSST columns. The results show that the ultimate axial strength of circular CFSST columns increases with increasing the concrete compressive strength but decreases with an increase in the D/t ratio. Circular CFSST columns with different D/t ratios exhibit the same initial stiffness. The lean duplex stainless steel tubes cannot provide good confinement on the concrete when D/t ratio is large. The ultimate axial strengths of CFSST columns predicted by the FE models are also compared with those calculated by the Eurocode 4, ACI code, the continuous strength method (CSM) by Lam and Gardner and Liang and Fragomeni's design formulas. The comparative study shows that Eurocode 4 and the CSM give good estimates of the ultimate axial strengths of CFSST columns with D/t<40 but overestimates the strengths of columns with D/t≥40. The ACI code gives too conservative estimates of the ultimate loads of CFSST columns as it does not consider the concrete confinement effects. Finally, it was found that the modified Liang and Fragomeni's design formulas yield the best predictions of the ultimate axial strengths of CFSST columns over the entire range of D/t ratios.

Collapse of geometrically imperfect stainless steel tubes under external hydrostatic pressure

This paper reports on an investigation into the buckling behaviour of 5 geometrically imperfect duplex stainless steel tube models, subjected to external hydrostatic pressure. The research was partly experimental and partly theoretical, where in the latter case; both analytical & numerical theoretical analyses were carried out.The experiments were carried out on five stainless steel tube models of different lengths, using two mild steel end bungs to seal the models. The experimental results showed that the Duplex stainless steel specimens behaved similarly to other isotropic materials tested by other researchers.The theoretical calculations and analyses were made by MisesNP, a DOS-based computer program, together with the ANSYS finite element structural analysis software.Combining the results of the present series of models, together with the results of other experimenters, a design chart was produced, which can be used for designing full-scale vessels. It should be emphasised that this design chart has been extended to those from previous studies, so that shorter and thicker vessels can now be designed.

Comparison of Residual Stresses in the Mechanical Roll Expansion of HX Tubes Into TEMA Grooves

The mechanical roll expansion of heat exchanger tubes into tubesheets containing TEMA grooves, which are thought to aid in the mechanical integrity of the tube-to-tubesheet (TTT) joint, has for many years provided an acceptable means of completing a TTT joint. Inherent with the intentional roll expansion of the tube is the creation of a tensile residual stress field within the tube that is greatest in the transition region between the expanded and unexpanded zones of the tube. An additional complicating factor in the tube-to-tubesheet joint design is the choice of utilizing a seal weld or a “full strength” weld at the tube end in conjunction with a level of roll expansion quantified by the degree of tube wall reduction. This paper presents the results of an initial study of the mechanical roll expansion of 1in. diameter tubes into a typical TEMA-R designed tubesheet, utilizing two grooves in the tubesheet hole. Two combinations of tube and tubesheet materials are studied that include duplex stainless steel tubes and tubesheet, while the second combination includes type 321 tubes roll expanded into a 2‐1∕4 Cr-1 Mo tubesheet, clad with 321 SS overlay. The residual stress fields are calculated by the finite element method and employ a simplified two-dimensional nonlinear axisymmetric model.

Corrosion failures of AISI type 304 stainless steel in a fertiliser plant

A urea plant, operating on ammonia and carbon dioxide (CO 2) gases, had to be shutdown due to corrosion in the intercooler and aftercooler of its CO 2 gas cleaning circuit. Extensive general corrosion of AISI type 304 stainless steel parts, such as sealing strips, fins, demisters and the shell, of these two components which were in contact with the duplex stainless steel tubes, caused the shutdown of the fertiliser plant within 6 months. Investigations of the corrosion products by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques showed the presence of carbon and ammonia based compounds, thus suggesting the role of ammonia and CO 2 gases, or the product of their reactions, in the corrosion of type 304 stainless steel. Electrochemical polarisation studies showed that duplex stainless steel possessed a more positive open circuit potential and a nobler critical pitting potential than type 304 stainless steel thus confirming that the corrosion of type 304 stainless steel was caused by the galvanic action with the duplex stainless steel heat transfer tubes. Hence, it was recommended that (i) the same material (type 304 stainless steel) be used for all parts of the intercooler and aftercooler to avoid galvanic corrosion, (ii) condense water carried over by CO 2 gas by cooling it to low temperatures immediately after it comes out from the scrubber, (iii) slight modification of the process to add up to 0.8% oxygen in the CO 2 gas before entry into the intercooler, which will help in retaining/formation of an effective passive film on type 304 stainless steel.

接合 二相ステンレス鋼管の液相拡散接合法の開発

The transition liquid-phase (TLP) diffusion bonding process was recently tailored to join the tubes of duplex stainless steel, Fe-25Cr-6.5Ni-3Mo-2W-0.5Cu-0.3N, with a Ni brazing filler, Ni-7Cr-3Fe-4.5Si-3B. The butts cramped by a hydraulic system are heated up locally with an induction coil in Ar shield gas. While the bonding at the holding temperatures lower than 1250°C introduces a large amount of boron nitrides at the interface which degrade extremely the tensile strength of the joint, the higher temperature bonding eliminates them from the joint, whose strength is about 850MPa close to 1000MPa for the base metal. The coarser recrystalized grains in the stronger joint scatter the ultrasonic wave so significantly that the joint efficiency is judged non-destructively with the ultrasonic transmission test. The precipitates Fe-Cr-Mo in HAZ reduce substantially the impact value of the joint, which recovers to the original level after the post-heat treatment at 1100°C to dissolve them. Another precipitates Cr7C3 in HAZ don't impair the localized corrosion and the stress corrosion cracking resistance. The developed TLP process is a promising technology for joining the duplex stainless steel tubes at the site of oil fields.

Quantitative phase analysis of duplex stainless steel using incomplete pole figures

The use of a single, accurate, and relatively quick experimental method suitable for determination of crystallo graphic texture and amounts of phases in the final product is of interest to some manufacturers. The suitability of an X-ray method for this purpose is evaluated in the present paper. The Schulz back reflection technique has been used to record incomplete pole figures of ferrite and austenite in a sample of commercial duplex stainless steel tube. The orientation distribution function was calculated for each phase and then used for the reproduction of complete pole figures. The complete pole figures were applied in quantitative phase analysis (QPhA), by a new method, free from texture induced errors. For comparison, the volume fraction of austenite and ferrite was also determined by means of the classic direct comparison method of Averbach and Cohen as well as by standard quantitative metallography. The proposed method of QPhA was applied for the examination of the amount of retained austenite in certain bearing construction elements.

Eddy current examination using an inner coil with strongly magnetizing efficiency for duplex stainless steel tubes : Journal of JSNDI, vol. 42, no. 9 (September 1993) p. 520 Sakamoto, Takahide; Fujisaka, Yuzo; Arita, Yoshio

Eddy current examination using an inner coil with strongly magnetizing efficiency for duplex stainless steel tubes : Journal of JSNDI, vol. 42, no. 9 (September 1993) p. 520 Sakamoto, Takahide; Fujisaka, Yuzo; Arita, Yoshio

Effects of metallurgical factors on service performance of duplex stainless steel for deep sour gas wells

This paper deals with the effects of alloying elements on hot workability, mechanical properties, pitting corrosion, and stress corrosion cracking of duplex stainless steel. Test materials are laboratory-melted 20 to 30 pct Cr duplex stainless steels, containing different amounts of Ni, Mo, N, and other elements. Corrosion resistance, tensile properties, and hot workability depend on the ferrite content in the microstructure. Cr, Mo, and N are beneficial in improving the resistance to pitting and general corrosion. Susceptibility to stress corrosion cracking in sour gas environments depends on the microstructure. Based on these test results, duplex stainless steel tube containing 22 pct Cr-5.5 pct Ni-3 pct Mo-0.15 pct N for deep corrosive well service has been developed on a mill production basis. This tube has a ferrite content of about 50 pct and can be produced in three grades of yield strength, 9.4, 16, and 20 MPa (65, 110, and 140 ksi).