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Benefited by its high efficiency and low cost, the narrow gap welding has been widely used in thick wall pressure equipment. Considering the fact that defects in welded joints inevitable, the safety assessments for welding equipment with residual stress are crucial. However, for the thick-wall equipment using narrow-gap welding, the current safety assessment standards specifying the residual stress distribution are not detailed or missing. In this paper, the through-wall residual stress of thick wall girth welds with narrow gap welding is studied. The stress components (bending stress, membrane stress and self-equilibrating stress) at the evaluation point are obtained by stress decomposition. The effects of the heat input, the wall thickness, the radius thickness ratio and the number of welding passes on residual stress are considered, respectively. The results show that the heat input only affects the distribution of bending stress and membrane stress. The axial and hoop bending stresses decrease with the increase of the wall thickness, and the hoop membrane stress is about 0.75 times material yield strength. With the increase of radius thickness ratio, the bending stress decreases while the hoop membrane stress increases. The stress distribution is fluctuating when the number of welding layers is small, which be expressed by trigonometric function. The distribution model of welding residual stress through the wall thickness is proposed. The stress distribution obtained by the proposed prediction model is in good agreement with the finite element calculation results. • >The universal model of residual stress and stress components for girth weld with thick wall was proposed. • The stress components (bending stress, membrane stress and self-equilibrating stress) of the evaluation point are also obtained. • The effects of heat input, wall thickness, radius thickness ratio and number of welding passes on residual stress are considered, respectively. • Heat input only affect the amplitude of bending stress and hoop membrane stress. • The stress on inner surface using narrow gap welding for thick walls is compressive stress. [ABSTRACT FROM AUTHOR]

Abstract This paper studied the distribution of weld residual stress in a spiral welded pipeline by finite element method (FEM) and experimental measurements, and the effect of helix angle on residual stress has also been investigated. Both the FEM and experiment results show that the residual stresses in HAZ are larger than those in weld. The error between FEM and experiment results is within 14%, proving that our FEM is correct. There is a peak-shape stress distribution through the weld thickness and the residual stresses in the inner surface are larger than those in the outer surface. Different helix angle has a different equivalent weld length along the hoop and axial directions, which generates different hoop and axial plastic strains, leading to different hoop and axial residual stresses. As the increase of the helix angle, both the radial and hoop residual stresses decrease, while the axial residual stresses increase. As the helix angle increases from 20° to 50°, the hoop stresses in HAZ decrease by 65%, while the axial stresses increase by 120%. The residual stresses are influenced by the pipe dimension (pipe diameter, thickness, weld profile), welding technology (heat input, welding speed) and material grade. When the helix angle is between 40° and 45°, both the hoop and axial residual stresses are reduced to the minimum. The most suitable helix angle is suggested to design around 40°–45°. Graphical abstract Image 1 Highlights • Effect of helix angle on residual stress for oil pipelines is investigated. • HAZ is a weakest zone for X70 steel spiral pipes. • The residual stresses are easily influenced by the pipe dimension and welding technology. • The most suitable helix angle is suggested to design around 40°–45°. [ABSTRACT FROM AUTHOR]

In this study, we present a creep analysis for an anode-supported tubular solid oxide fuel cell (SOFC). The effects of tube radius on creep and stress are also studied. The as-sintered residual stress is measured by an X-ray diffraction instrument. Simulated result is consistent with the measurement data. The finding shows that the fracture starts in the electrolyte for the big tube radius after 50 000 h because of the mismatch creep properties between SOFC layers. As tube radius increases, the hoop stress in the electrolyte also increases because the growth of elastic strain is dominant compared with creep relaxation. Hoop stress in the electrolyte exceeds the tensile strength when the tube radius is larger than 30 mm for our SOFC system. The tube radius should be designed to be in millimeter level or sub-millimeter level to decrease the growth of hoop stress in the electrolyte and ensure long-term reliability at high temperatures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Residual stress reduction in penetration weld nozzle by overlay welding was studied. [•] The overlay weld can decrease the residual stress in the weld root. [•] Long overlay welding is proposed in the actual welding. [•] Overlay weld to decrease residual stress is more suitable for thin nozzle. [ABSTRACT FROM AUTHOR]

In this paper, an energy difference method is proposed to estimate biaxial stress components based on indentation technique. The indentation energy is chosen as an analytical parameter, which can be calculated directly from the load-depth curve. The presence of residual stress in a material causes the change of indentation energy. The mapping relationship between uniaxial stress and indentation energy difference was established by finite element analysis. Meanwhile, the Knoop tip was applied since the indentation response varies according to the indenter orientation. Using this feature, a biaxial stress state can be transformed into two equivalent uniaxial stress states by indentation energy conversion. Finally, the biaxial residual stress components can be solved by the energy difference functions of two orthogonal indentations. A portable indentation instrument was developed to implement this approach, which is suitable for in-site measurement. The obtained results show good agreements with the artificial stresses applied by cross-shape sample experiment. • A new methodology is proposed to estimate biaxial stress components based on indentation method. • The Knoop indenter is applied to correlate the stress direction. • A biaxial stress state can be transformed into two equivalent uniaxial stress states by indentation energy conversion. • An indentation testing instrument was developed to validate this approach. • The biaxial stress components can be solved from the load-depth curves, without the need for contact area. [ABSTRACT FROM AUTHOR]

The localized defects, including the ruptured truss and debonding joint, have been severely threatening the structural integrity of the pyramidal lattice truss panel structure (PLTPS). In this paper, a series of analytical models, i.e., equivalent elastic modulus, plastic and creep strain rate models, were developed to study the effects of localized defects on the mechanical properties and creep performance of the PLTPS, which have been verified by the experiments and finite element (FE) simulation. Based on the experimental data, the equivalent elastic modulus model was modified when the defect fraction exceeds the threshold value. The complete stress–strain curve was plotted by the proposed analytical models. At elevated temperature, both the analytical model and finite element results indicate that the equivalent creep rate increases exponentially with the increase of the defect fraction. In addition, for the long-term service, the total equivalent strain is the superposition of the steady-state creep strain and the saltatorial strain stimulated by the inconsecutive stress once the truss or joint fails, which is more susceptible to the effective stress comparing with the servicing time. The proposed analytical model which considering the effect of localized defects of the PLTPS provides an efficient criterion to justify whether the structure with certain defects satisfies the engineering requirements. • The creep properties of PLTPS with defects were studied by analytical methods. • The analytical models have been verified by the experiments and FE simulation. • An efficient criterion for sample test is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Clad plates are widely used in the construction of corrosion resistant equipment. During the repair of clad plates, residual stresses are generated and influence the structure integrity. This paper uses the finite element method (FEM) to predict the residual stresses in a repair weld of a stainless steel clad plate. The effect of repair width on residual stresses has also been investigated by numerical simulation. Due to the material mismatching between clad metal and base metal, a discontinuous stress distribution has been generated across the interface between clad and base metals. The peak residual stress occurs in the heat affected zone (HAZ) of the base metal, because the yield strength of the base metal is larger than that of the clad metal. With an increase in repair width, the residual stresses are decreased. When the repair width is increased to 24 mm, the residual stresses in the weld have been decreased greatly and the peak residual stresses have been reduced to less than the yield strength. Therefore, the recommended repair width should not be less than 24 mm, which provides a reference for optimizing repair welding technology for this stainless steel clad pate. [ABSTRACT FROM AUTHOR]

Abstract: This paper uses finite element method (FEM) to predict the residual stress and plastic strain in the brazed joint of sealing foil-to-window frame in bonded compliant seal (BCS) design in a planar solid oxide fuel cell (PSOFC). The effects of window frame material type, sealing foil thickness, filler metal thickness and window frame thickness on residual stress and plastic strain are discussed. Large residual stress is generated in the joint, and the stress and strain are concentrated around the fillet. It is proved that the BCS design can mitigate and trap some residual stress by plastic deformation within the sealing foil. The residual stress and the ability of trapping stress of sealing foil are affected by window frame material and structure thickness. Based on the comprehensive considerations of the impact of residual stress and plastic strain, Alloy 625 as a window frame material is found to be better than Haynes 214, Hastelloy X and SUS 316L. The optimum thickness of sealing foil and filler metal BNi2 are found to be 150μm and 75μm, respectively. The residual stress and plastic strain are increased with the increase of window frame thickness. [Copyright &y& Elsevier]

Abstract: This paper presents a study of the effect of filler metal thickness on tensile strength for a stainless steel plate-fin structure by finite element method and experiment. The results show that the filler metal thickness has a great effect on tensile strength. The tensile strength is increased with the filler metal thickness increase, then it keeps stable when the filler metal thickness is 105–140μm. But it decreases rapidly when the filler metal thickness is larger than 140μm. The fracture location is shown at the end of vertical fin when the filler metal thickness is 105–140μm. Specimens with filler metal thickness smaller or larger than 105–140μm rupture in the brazed filler metal. The optimal filler metal thickness is 105μm, using which can get higher strength for 304 stainless steel plate-fin structures. [Copyright &y& Elsevier]

Austenite and duplex stainless steels are widely used in engineering, and the latter exhibits a more excellent combination of mechanical properties and corrosion resistance due to the coexistence of austenite and ferrite and higher nitrogen. However, fatigue failure still threatens their structural integrity. A comprehensive comparison of their cyclic deformation behavior is a major foundation to understand the role of duplex-phase microstructure and nitrogen in the safety assessment of engineering components. Thus, in this paper, the cyclic deformation behavior of fully-austenitic stainless steel 316L and duplex stainless steel 2205 was studied by a series of low cycle fatigue tests with various strain amplitudes, loading rates and tensile holding. A theoretical mechanism diagram of the interaction between nitrogen and dislocation movements during cyclic loads was proposed. Results show that the cyclic stress response of 2205 was the primary cyclic hardening, followed by a long-term cyclic softening regardless of strain amplitudes and rates, while an additional secondary hardening was observed for 316L at greater strain amplitudes. Cyclic softening of 2205 was restrained under slower strain rates or tensile holding due to the interaction between nitrogen and dislocations. The cyclic plasticity of 2205 started within the austenite, and gradually translated into the ferrite with the elevation of the cyclic amplitude, which lead to a decreased hardening ratio with the increase in amplitude and a shorter fatigue life for a given smaller plastic strain amplitude. [ABSTRACT FROM AUTHOR]

Abstract: Stainless-steel plate–fin heat exchanger (PFHE) has been used as a high-temperature recuperator in microturbine for its excellent qualities in compact structure, high-temperature and pressure resistance. Plate–fin structure, as the core of PFHE, is fabricated by vacuum brazing. The main component fins and the parting sheets are joined by fusion of a brazing alloy cladded to the surface of parting sheets. Owing to the material mismatching between the filler metal and the base metal, residual stresses can arise and decrease the structure strength greatly. The recuperator serves at high temperature and the creep would happen. The thickness of the filler metal plays an important role in the joint strength. Hence this paper presented a finite element (FE) analysis of the brazed residual stresses and creep for a counterflow stainless-steel plate–fin structure. The effect of the filler metal thickness on residual stress and creep was investigated, which provides a reference for strength design. [Copyright &y& Elsevier]

Larger residual stresses and deformations are inevitably generated during local post-weld heat treatment (PWHT) for ultra-large pressure vessels, which may lead to cracking in weld joint. In this paper, a new control method with reinforced plate was proposed to prevent cracking during local PWHT for ultra-large pressure vessels. And the evolution of stresses and deformation during local PWHT and the reason of cracking were discussed. The results show that bigger inconsistent deformation along axial direction and larger axial stresses in weld toe are the main reason to cause cracking. The hoop, axial and maximum principal stresses in welded joint can be reduced by reinforced plate. And the maximum radial deformation during holding stage of PWHT was decreased by reinforced plate because of the decreased elastic and plastic strain. The maximum radial deformation was decreased by more than 50%. The inconsistent deformation at heating stage can be improved, so the stress concentration in weld toe resulting in cracking could be also improved. This work will provide a good guidance for the manufacture of ultra-large pressure vessels. [Display omitted] • A new control method was proposed to avoid cracking during local PWHT. • The inconsistent deformation along axial direction is main reason to cause cracking. • The stress concentration in weld toe during PWHT were decreased by new control method. • The inconsistent and maximum deformation at holding stage can be improved greatly. • The new control method can reduce the elastic and plastic strain during PWHT. [ABSTRACT FROM AUTHOR]

Local post welding heat treatment (PWHT) is a feasible method to eliminate weld residual stress for ultra-large pressure vessels. This paper is focused on the discussion of weld residual stress and deformation for the typical ultra-large mechanical penetration inserted plate (MPIP) during the local PWHT. The reason why the MPIP subjected to local PWHT causes cracking is clarified. A rigid-flexible coordinated control method is proposed to prevent cracking during local PWHT for the ultra-large pressure vessels. The results show that the inconsistent deformation and greater stress concentration in weld toe are the main reason to result in cracking during PWHT. The axial stresses and radial deformation in the welded joints can be reduced by the rigid-flexible coordinated control method. The axial stress is changed to compressive stress, and the radial deformation is reduced by about 58%. And the inconsistent deformation in welded joints during the heat treatment can be obviously improved, which is of great significance to ensure the safe service for ultra-large pressure vessels. [Display omitted] • The greater stress concentration induced by bend deformation is the main reason of cracking. • A rigid-flexible coordinated method was proposed to avoid cracking during local PWHT. • The axial stress and radial deformation in weld during PWHT were improved by new method. • The inconsistent and maximum deformation at insulation stage can be improved greatly. • The smooth weld can reduce the risk to occur cracking during local PWHT. [ABSTRACT FROM AUTHOR]

The welding residual stresses (WRS) in a cracked head-cylinder joint of a large rectifying tower were studied by finite element method (FEM) and experimental study. The effects of welding layer sequence, cover welding direction and weld reinforcement have been fully studied. The results showed that the stress concentration and plastic strain accumulation caused by unreasonable welding process and structural discontinuity are the main reasons of cracking. Furthermore, the order of welding layers has a significant influence on the distribution of axial stress: the inside and outside alternating welding process is superior to non-alternating welding process. The direction of cover welding markedly influences the hoop stress: the location of maximum stress is related to the welding start-end position. Besides, the removal of weld reinforcement after welding helps to release sub-surface tensile stress and solve the stress concentration problem. • Recommendations regarding welding procedure in large pressure vessels were proposed by FEM and experiment study. • High tensile WRS and large PEEQ at the weld toe directly contributed to the cracking. • The axial stresses can be effectively reduced by alternating welding. • The position of peak stress is related to the cover welding direction. • Removing the weld reinforcement helps to further control WRS. [ABSTRACT FROM AUTHOR]

• The underlying mechanism of relaxation and redistribution of residual stress under cyclic loading were analyzed. • The correlation between redistributed residual stress and fatigue fracture behavior was discussed. • The role of residual stress on the fatigue performance of weld joints was revealed. • A fatigue life prediction model of weld joints was proposed by considering the residual stress and its redistribution. Weld residual stresses have a great effect on the fatigue strength of welding structures. As an internal stress, the residual stress is unfounded to be treated as the conventional mechanical load during the fatigue safety assessment due to its relaxation and redistribution under cyclic loading. Thus, establishing an accurate model considering the effects of residual stress is critical for fatigue strength design. Therefore, this paper develops a sequential coupling residual stress analysis and a cyclic viscoplastic constitutive model to predict the residual stress evolution and its role on the fatigue life, which has been validated by an experimental measurement of residual stress and a SEM-based observation fatigue fracture morphology. The results show that the role of residual stress on fatigue life is mainly reflected by the increase of mean stress, and its increased magnitudes depends on the stress redistribution. The redistribution of residual stresses is closely correlated to the fatigue fracture behavior of weld joints. And a fatigue life prediction model of weld joints is proposed based on the experimental data of base metal by further considering the residual stress and its redistribution. Finally, the experimental results verify the proposed model on predicting both the fatigue failure location and lives of weld joints, and the predicted lives are within the 1.5 error band. [ABSTRACT FROM AUTHOR]

This paper presents a study of the residual stress in the welding connection between hydrogen nozzle and spherical head in a hydrofining reactor. A sequential coupling finite element program is developed to analyze the residual stress in nozzle-to-sphere connection. The results show that large residual stresses are generated in the weld and weld/parent interface during the welding of hydrogen nozzle. Large axial stress is generated on the internal surface of hydrogen nozzle due to the angular deformation, which has a great effect on hydrogen induced cracking (HIC) and stress corrosion cracking (SCC). Based on the residual stress distribution character, a new connection structure between hydrogen nozzle and head is developed. A stressless flanging is proposed to insert into the nozzle to isolate the residual stresses, which can be useful to prevent HIC and SCC. To cover all the residual stresses effectively, the arc length of flanging should be not less than 80 mm. [ABSTRACT FROM AUTHOR]

Due to the limited testing methods and high costs, researches on the evolution law of residual stress in the post-weld heat treatment (PWHT) process of pressure equipment are mainly by numerical simulation, in which the selection of a reasonable and reliable creep constitutive model is crucial to ensure the accuracy of numerical predictions. It is worth noting that the temperature changes and residual stress variation during the heat treatment process result in the following creep characteristics: the creep occurs under different temperatures during the heat treatment processes of heating, holding, and cooling; the creep occurs under different residual stress level where the residual stress varies during the heat treatment stages. Thus, to accurately simulate the stress release behavior during the PWHT process, the proper creep constitutive model must involve the influences of the temperature and the stress state. Meanwhile, current heat treatment simulation usually adopts simplified qualitative approaches, and the creep constitutive models often ignore the physical mechanisms and characteristics of actual creep processes, such as the Norton, the Norton-Bailey, and the Omega models. As a result, the accuracy of heat treatment simulation is limited. In this paper, a new creep constitutive relation under varying temperature and stress is proposed. The hyperbolic-sinusoidal function is used to represent the complete three stages of creep, which compensate the inaccuracy prediction at the first and the third creep stages. Moreover, the Arrhenius function is introduced to characterize the creep response under varying temperature conditions, which enables the prediction of residual stress evolution throughout the entire heating-holding-cooling process of heat treatment. Then, a typical pressure vessel cylindrical circumferential weld is simulated. The stress release during the heat treatment is calculated, and the efficacy of the proposed model is validated through surface residual stress testing. It is found that the creep behavior is a crucial factor in numerical simulation of heat treatment, and the creep constitutive relation can significantly affect the accuracy of heat treatment simulation. The simulation utilizing the hyperbolic-sinusoidal temperature-dependent creep model is much more accurate compared to the classical simulation. The simulation results are much more consistent to the experimental results. Specifically, the traditional model often underestimates the stress state, the residual stress drops abruptly during the heating stage. The residual stress evolution mechanism is simulated using the new model: The majority of residual stress are released during the heating process which primarily relies on the creep strain transformation (contributes up to 85%). The stress state does not change during the holding stage and slight higher at the cooling stage. • A new creep constitutive relation suitable for post weld heat treatment under varying temperature and stress is proposed. • It is found that the creep behavior is a crucial factor in numerical simulation of heat treatment. • The mechanism of residual stress evolution during heat treatment has been summarized. [ABSTRACT FROM AUTHOR]

The support platform is an essential component of a hydrogenation reactor, providing stable support for internal components and ensuring efficient reactions. However, the manufacturing method of overlay welding and complex structure of support platform unavoidably generates welding residual stresses (WRS) and stress concentration, posing a threat to operational reliability. In this paper, the WRS distribution and cracking causes of the support platform of hydrogenation reactor was studied by the finite element method (FEM) combined with experimental research. Four manufacturing processes for the support platform were compared in terms of their residual stresses, and the influence of welding heat input and fillet size on the WRS was discussed. The results indicate that the abrupt increase in residual stresses at the fillet region following the machining of the base layer has enhanced the likelihood of crack occurrence. The cumulative effect of stress concentration resulting from improper welding processes and structural discontinuities, along with the tensile stress during normal operating conditions, renders the surface layers susceptible to cracking during service. The manufacturing process significantly influences the distribution of residual stresses. To obtain a reliable and crack-resistant large-sized hydrogenation reactor support platform, a welding procedure with a certain machining allowance at the support platform location prior to overlay welding should be adopted. The fillet size has a notable effect on the residual stresses at the fillet region of transition layer. Recommended fillet sizes are 15 mm radius for the base layer, 11 mm radius for the transition layer, and 8 mm radius for the surface layer. Additionally, the heat input greatly affects the hoop stresses in the transition layer, in order to avoid the occurrence of cracks, a recommended heat input of approximately 20 kJ/cm is suggested. • Residual stress distribution and crack causes of the support platform were analyzed. • Surface layer fillet is more prone to cracking. • Manufacturing with a machining allowance as the root has optimal stress distribution. • Increasing fillet size significantly reduces residual stress of transition layer. [ABSTRACT FROM AUTHOR]

• The correlation among heterogeneous microstructure, cyclic hardening/softening and fatigue failure behavior was analyzed extensively. • The fracture location was changed with the fatigue amplitude due to the amplitude-dependent and heterogeneous cyclic hardening/softening of BM and WM. • A modified cyclic constitutive model was proposed to precisely predict the heterogeneous cyclic mechanical response and failure location for both stress-controlled and strain-controlled conditions. This work performed experimental and modeling investigations on the fatigue failure mechanism of duplex stainless steel welded joints, and the correlation among heterogeneous microstructure, cyclic hardening/softening and fatigue failure behavior was analyzed extensively. A series of experiments including the characterization of microstructure by the electron back-scattered diffraction observation and fatigue mechanical tests assisted by digital image correlation technique were performed. The results show that at the lower stress amplitudes (approximately 520 MPa), the fatigue failure occurred in the weld metal, while it shifted to the base metal at higher amplitudes. Due to the grain refinement, the strain amplitude of weld metal was lower than that of base metal, particularly at the higher amplitudes, leading to the final failure at the base metal. However, at the lower amplitudes, due to the effect of Kurdjumov-Sachs orientation relationship at the weld metal, its cyclic softening behavior was much drastic than that of base metal, resulting in the overshoot of strain amplitude during fatigue process and finial rupture at the weld metal. A cyclic constitutive model was developed by considering the amplitude-dependent and heterogeneous cyclic hardening/softening, to accurately predict the cyclic mechanical response and fatigue failure location for both stress-controlled and strain-controlled conditions. This work can be used as guidance of structure integrity assessment and life prediction for the engineering components of duplex stainless steel. [ABSTRACT FROM AUTHOR]

Highlights • A more appropriate FE model was proposed to predict the CCI and CCG behavior. • The effects of simulation method on CCI and CCG of brazed joint are investigated. • The brazed RS can promote CCI and enhance CCG rate, thus reducing creep life. • The predicted results by single-material method agree well with the experiment. • Bigger uniaxial creep strain can prolong the CCI time and reduce the CCG rate. Abstract In this paper, a more appropriate finite element (FE) model was proposed to predict the creep crack initiation (CCI) and growth (CCG) behavior of HastelloyC276-BNi2 brazed joint at high temperature. The effects of single-material, bi-material and three-material method on CCI and CCG behavior have been discussed fully. The relationships between CCG rate and parameter C ∗ for different simulation methods were obtained. The results show that the simulation method has a great influence on CCI and CCG behavior of brazed joint. The brazed residual stress (RS) can accelerate CCI and enhance CCG rate, leading to the reduction of creep life. The CCI time and creep life predicted by single-material method is smaller than those by bi-material and three-material method. The creep life and crack growth morphology predicted by single-material method have a good consistent with the experimental results. The single-material method can accurately predict the CCG behavior of brazed joints. Bigger uniaxial creep strain can prolong the CCI time and reduce the CCG rate. The creep life of brazed joint can be enhanced by increasing uniaxial creep strain. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) is the main failure mode of tube-to-tubesheet welded joints in a heat exchanger, and weld residual stress can play an important role in the development of these cracks. Local post welding heat treatment (PWHT) is a feasible method to reduce weld residual stress for tube-to-tubesheet welded joints. In this paper, the residual stress evolution and relaxation mechanisms during local PWHT were discussed in depth. The effects of PWHT temperature and hold time on residual stress were clarified. A compressive stress manufacturing method based on local PWHT was proposed. The results show that the stress concentration at the root of tube-to-tubesheet welded joints is the main reason for the SCC of heat exchangers. The residual stresses in the weld and heated affected zone (HAZ) are significantly reduced during local PWHT. The residual stress relaxation of tube-to-tubesheet welded joints can be attributed to the creep strain development and deformation during local PWHT. The extrusion of the tube and tubesheet at cooling stage results in the generation of compressive stress at the root of tube-to-tubesheet welded joints. PWHT temperature has significant effect on the residual stress in the weld and HAZ in comparison with PWHT hold time. The application of the proposed compressive stress manufacturing method realizes the fabrication of compressive stress at the root of tube-to-tubesheet welded joints, and improves the economic benefit by reducing PWHT hold time. This work will provide a good guidance to reduce the SCC risk of heat exchangers. • The stress concentration at the root of tube-to-tubesheet welded joints was found to be the main reason for SCC. • The residual stress relaxation mechanisms of tube-to-tubesheet welded joints during local PWHT were clarified. • PWHT temperature had significant effect on the residual stress in the weld and HAZ in comparison with PWHT hold time. • The proposed local PWHT method realized the fabrication of compressive stress at the root of tube-to-tubesheet welded joints. [ABSTRACT FROM AUTHOR]

Local hydrogen enrichment would increase the risk of hydrogen embrittlement in welded structures, so the dynamic hydrogen diffusion process and final concentration distribution were investigated numerically by finite element simulation for a hydrogen gas transport X80 steel spiral welded pipe. The results show that the change of microstructure induced by weld thermal cycle would decrease the hydrogen concentration in welded joint, but welding residual stress could cause local hydrogen enrichment. Equivalent hydrogen pressures for base metal, weld metal and three subregions in heat-affected zone were put forward in order to scientifically evaluate the influence of hydrogen enrichment on hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Revealing the hydrogen permeation behavior in steel is the foundation to analyze hydrogen induced fracture. Herein, slow strain rate tension tests were used to investigate the susceptibility of X70, X80 and X100 steel to hydrogen embrittlement induced by cathodic polarization, and the subsurface hydrogen concentration ( C 0 ) of three steels was accurately determined by two kinds of hydrogen permeation tests. Results showed that the HE index range of ductile-to-brittle transition should be determined by fracture analysis. The C 0 increased in turn from X70, X80 to X100 at any given applied potential, that’s why X100 presented the highest hydrogen embrittlement susceptibility. [ABSTRACT FROM AUTHOR]

Bipolar plates are regarded as the core of the proton exchange membrane fuel cell. In order to obtain a connected stainless steel bipolar plate with low residual stress and small deformation, the brazing process is commonly used for bipolar plate connection. In this study, a numerical model was developed to calculate the residual stress in a brazed joint. Clamp pressure, brazing gap, and solder type were investigated. The results showed that clamping pressure had little influence on residual stress and the residual stress decreased with an increase in the brazing gap, which provided a reference for controlling brazed residual stresses for stainless steel bipolar plates. [ABSTRACT FROM AUTHOR]