Nondestructive Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Plates

This article investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of austenitic stainless steel plates (AISI 304L). Longitudinal critically refracted (L _CR ) waves are employed to measure the residual stresses. Measuring the acoustoelastic constant through the tensile test is eliminated on the main investigated sample to keep it intact. Another welded plate with the same welding specification, geometry, thickness, and the same material is used to extract tensile test samples. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to produce microstructure similar to that of the HAZ in a tensile test sample. A finite element model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic stress measurements which is accomplished nondestructively.     

Ultrasonic inspection of a welded stainless steel pipe to evaluate residual stresses through thickness

This study investigates ultrasonic method in axial and hoop stress measurement through thickness of an austenitic stainless steel pipe. Longitudinal critically refracted (L_CR) waves are employed to measure the welding residual stresses while outer and inner surfaces of the pipe are inspected by using different frequency range of ultrasonic transducers. The acoustoelastic constant is measured on a plate with the same material and thickness of the investigated pipe to keep the pipe intact. Welding process of the pipe is simulated by a 3D finite element (FE) model which is validated by hole-drilling method performed on 25 points. The residual stresses calculated by FE simulation are then compared with those obtained from the ultrasonic measurement while a good agreement is observed. It is demonstrated that the residual stresses through thickness of the stainless steel pipe can be evaluated by combining FE and L_CR method (known as FEL_CR method).     

Using finite element and ultrasonic method to evaluate welding longitudinal residual stress through the thickness in austenitic stainless steel plates

This paper uses a 3D thermo-mechanical finite element analysis to evaluate welding residual stresses in austenitic stainless steel plates of AISI 304L. The finite element model has been verified by the hole drilling method. The validated finite element (FE) model is then compared with the ultrasonic stress measurement based on acoustoelasticity. This technique uses longitudinal critically refracted (L_CR) waves that travel parallel to the surface within an effective depth. The residual stresses through the thickness of plates are evaluated by four different series (1 MHz, 2 MHz, 4 MHz and 5 MHz) of transducers. By combining FE and L_CR method (known as FEL_CR method) a 3D distribution of residual stress for the entire of the welded plate is presented. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to reproduce HAZ microstructure in a tensile test sample. It has been shown that the residual stresses through the thickness of stainless steel plates can be evaluated by FEL_CR method.     

Comparison between contact and immersion ultrasonic method to evaluate welding residual stresses of dissimilar joints

This paper presents a comparison of contact and immersion waves used to measure residual stresses. The residual stresses are produced due to a dissimilar welding of stainless steel (304) to carbon steel (A106). Longitudinal critically refracted (L_CR) wave propagated by 2 MHz contact and immersion ultrasonic transducers is employed to measure the residual stresses. A Finite Element (FE) model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results while an acceptable agreement is achieved. The best agreement is observed in the parent material while the maximum difference is measured in the heat affected zone (HAZ). The results show no considerable difference between using contact and immersion transducers in ultrasonic stress measurement of dissimilar joints.     

Comparison Between Using Longitudinal and Shear Waves in Ultrasonic Stress Measurement to Investigate the Effect of Post-Weld Heat-Treatment on Welding Residual Stresses

Fusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (L_CR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the L_CR method is employed.     

Residual stress measurement in steel plates and welds using critically refracted longitudinal (LCR) waves

The application of acoustoelasticity using critically refracted longitudinal (L_CR) waves is described for measuring residual stress in welded steel plates. Residual stresses are self-equilibrating and may exist in a material that has been deformed in a nonhomogeneous manner. When unknown residual stress is present in a structure, the true stress may become significantly greater than the working stress. In a corrosive environment, highly stressed areas that have not been properly stress relieved are prone to stress corrosion cracking. Areas near welds are particularly susceptible to stress corrosion cracking.Two welded plates were investigated for the present work: one hot-rolled and the other cold-rolled. Residual stresses are usually greatest after welding. Further, longitudinal stress (i.e., stress parallel to the weld bead) is typically greater than the component transverse to the weld bead. Since the acoustoelastic behavior of the L_CR wave is largest when propagated parallel to a uniaxial stress, the L_CR wave traveling parallel to the weld bead was used to investigate the stress changes after stress relieving of the welded plates. Both 1 MHz and 2.25 MHz probe frequencies were used in this study. The stress changes in the welds and in the cold-rolled plate were clearly indicated by the L_CR data.Two verification methods were used: hole drilling (HD) and neutron diffraction (ND). The stress relief was verified by the hole-drilling technique. While the HD technique showed about the same stress magnitude as found by the L_CR results, the orientation was reversed. The stress orientation was probably caused by the grinding process used to flatten the weld bead. Texture was also investigated using a neutron diffraction (ND) technique on the (001)[110] texture. The through-the-thickness technique yields an average of the orientation distribution of the (110) planes. At locations in the parent metal and in the weld, the distribution was found to be very similar, indicating uniform texture throughout the weld and parent metal zones.     

Residual Stress Measurement in Steel Plates and Welds Using Critically Refracted Longitudinal (LCR) Waves

Abstract

The application of acoustoelasticity using critically refracted longitudinal (L_CR) waves is described for measuring residual stress in welded steel plates. Residual stresses are self-equilibrating and may exist in a material that has been deformed in a nonhomogeneous manner. When unknown residual stress is present in a structure, the true stress may become significantly greater than the working stress. In a corrosive environment, highly stressed areas that have not been properly stress relieved are prone to stress corrosion cracking. Areas near welds are particularly susceptible to stress corrosion cracking.

Two welded plates were investigated for the present work: one hot-rolled and the other cold-rolled. Residual stresses are usually greatest after welding. Further, longitudinal stress (i.e., stress parallel to the weld bead) is typically greater than the component transverse to the weld bead. Since the acoustoelastic behavior of the L_CR wave is largest when propagated parallel to a uniaxial stress, the L_CR wave traveling parallel to the weld bead was used to investigate the stress changes after stress relieving of the welded plates. Both 1 MHz and 2.25 MHz probe frequencies were used in this study. The stress changes in the welds and in the cold-rolled plate were clearly indicated by the L_CR data.

Two verification methods were used: hole drilling (HD) and neutron diffraction (ND). The stress relief was verified by the hole-drilling technique. While the HD technique showed about the same stress magnitude as found by the L_CR results, the orientation was reversed. The stress orientation was probably caused by the grinding process used to flatten the weld bead. Texture was also investigated using a neutron diffraction (ND) technique on the (001)[110] texture. The through-the-thickness technique yields an average of the orientation distribution of the (110) planes. At locations in the parent metal and in the weld, the distribution was found to be very similar, indicating uniform texture throughout the weld and parent metal zones.     

Taguchi optimization and ultrasonic measurement of residual stresses in the friction stir welding

The main goal of this study is optimization of residual stresses produced by friction stir welding (FSW) of 5086 aluminum plates. Taguchi method is employed as statistical design of experiment (DOE) to optimize welding parameters including feed rate, rotational speed, pin diameter and shoulder diameter. The optimization process depends on effect of the welding parameters on longitudinal residual stress, which is measured by employing ultrasonic technique. The ultrasonic measurement method is based on acoustoelasticity law, which describes the relation between acoustic waves and internal stresses of the material. In this study, the ultrasonic stress measurement is fulfilled by using longitudinal critically refracted (L_CR) waves which are longitudinal ultrasonic waves propagated parallel to the surface within an effective depth. The ultrasonic stress measurement results are also verified by employing the hole-drilling standard technique. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the longitudinal residual stress peak is related to the feed rate while the pin and shoulder diameter have no dominant effect. The rotational speed variation leads to changing the welding heat input which affects on the residual stress considerably.     

Grain size correction of welding residual stress measurement in a carbon steel plate using the critical refraction of longitudinal waves

In this, a method to measure welding residual stress in butt-welded joints of carbon steel plates using longitudinal critically refracted wave (L_cr wave) is proposed. Cross-correlation was employed to calculate the difference in time of flight between L_cr wave, and the optimal step length for the measurements is discussed. To determine L_cr wave acoustoelastic coefficient of the heat affected zone (HAZ), the relationship between the L_cr wave acoustoelastic coefficient and the grain size is established. The results show that one cycle is the optimal step length for the difference in the time-of-flight calculation, and with increasing grain size increase, L_cr wave acoustoelastic coefficient decreases in the form of a power function. In addition, grain size can be determined by using amplitude of the L_cr wave, so that the measured value of welding residual stress in HAZ can be corrected. The welding residual stress in melted zone (MZ) is corrected by calibrating acoustoelastic coefficient of the MZ. The acoustoelastic coefficient of the MZ is larger than that of parent material (PM). At last, welding residual stress in the butt-weld joint is measured and corrected with the L_cr wave technique. The results are verified by the hole drilling method.     

Characterization of the Critically Refracted Longitudinal (LCR) Waves and Their Use in Defect Detection

The critically refracted longitudinal (L_CR) waves are used in various domains of nondestructive evaluation, especially for residual stress measurements. However, few works have characterized the associated ultrasonic beam. In this article, the characterization of the L_CR ultrasonic beam, both numerically and experimentally, is first clarified in order to provide some answers to questions that arise about its behavior in elastic solids. The aim of the second part of this work is to investigate the use of the L_CR waves for the detection of surface defects of different sizes in aluminum. For that, the effect of defects at fixed depth (5 mm) with various diameters (2, 4, 6, and 8 mm) and fixed diameter (8 mm) with various depths (5, 7, and 10 mm) in an aluminum sample have been investigated at frequencies around 1 MHz. It has been experimentally found that the amplitude of the (L_CR) wave decreases and its frequency spectrum changes with a given defect. The rate of the decrease of the amplitude and the change in the spectrum is related to the increase of the defect depth. The study shows that the effect on the propagating of the L_CR waves is larger as the defect depth increases.     

高钢级大口径焊管残余应力的测试方法

针对X80钢大口径UOE,JCOE和SAWH(螺旋缝埋弧焊)三种焊管,研究了盲孔法、切块法和切环法在高钢级大口径焊管残余应力测试中的应用.结果表明:对于这三种管型,通过切环法估算的残余应力与盲孔法和切块法的测试值较为接近,三种方法的结果重合性较好.     

Numerical and experiment analysis of residual stress on magnesium alloy and steel butt joint by hybrid laser-TIG welding

Hybrid welding technology has received significant attention in the welding of dissimilar materials recently. While, great welding residual stress and deformation often result by the difference of coefficient of thermal expansion This study describes the thermal elastic–plastic analysis using finite element techniques to analyze the thermo mechanical behavior and evaluate the residual stresses and welding distortion on the AZ31B magnesium alloy and 304L steel butt joint in laser-TIG hybrid welding. A new coupled heat source model was developed which combined by double-elliptic planar distribution, double-ellipsoid body distribution and Rotary–Gauss body distribution model. From the results, it can be concluded that the temperature distribution at the hybrid weld region is exposed to faster rate of heating and cooling in hybrid welding than TIG. Furthermore, compared to the welding stress distribution on the TIG weld, residual stress σ_y is found about 20% higher on hybrid weld joints, and the residual stress on the 304L steel plate is lower than that on the AZ31B magnesium plate.     

Application of low Ms temperature consumable to dissimilar welded joint

Abstract

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe–Cr–Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with M_s temperature below 200°C and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.     

Constraint loss correction for assessment of CTOD fracture toughness under welding residual stress - Part II: Application of toughness correction methodology

This part II paper presents the verified results of the toughness correction methodology for welded joints of wide plates. The equivalent CTOD ratio, β_r, is applied to the fracture data of the welded joints from lower to upper ductile-brittle transition temperature region. In the part I paper, β_r is defined as the ratio of CTOD in the standard fracture toughness specimen to CTOD in the wide plate with welding residual stress at the same level of the Weibull stress. In this part II paper, the equivalent CTOD ratio, β_r, under the welding residual stress field has been verified for assessment of constraint loss effects on CTOD fracture toughness of wide plate. Fracture assessments have been conducted by applying the methodology for “After Weld Notch” and “Before Weld Notch” type welded joints. It has been found that an excessive conservatism observed in the conventional procedure is reasonably reduced by applying the proposed methodology.     

Constraint loss correction for assessment of CTOD fracture toughness under welding residual stress. Part I: Methodology using the equivalent CTOD ratio

This part I of a two-part paper presents a method of assessing the effects of welding residual stress and constraint loss on the cleavage fracture of a wide plate subjected to membrane stress based on the Weibull stress criterion. It has been found that the Weibull stress criterion is efficient for evaluating the fracture instability of wide plates with and without a welding residual stress field. The concept of an equivalent crack-tip opening displacement (CTOD) ratio β_r under a welding residual stress field is introduced for assessment of constraint loss effects on CTOD fracture toughness of wide plates. The equivalent CTOD ratio β_r is defined as the ratio of the CTOD in the standard fracture toughness specimen to the CTOD in a wide plate with a welding residual stress at the same level of the Weibull stress. Fracture assessment procedures using β_r for wide plates are shown within the framework of the failure assessment diagram. It has been found that the excessive conservatism observed in the conventional procedure can be reduced reasonably by applying the proposed method. The companion part II of the paper presents applications of the CTOD toughness correction method using β_r to the fracture test data of welded joints and verifies the proposed method in the ductile-brittle transition temperature region.     

Prediction of residual stresses in welds of similar and dissimilar steel weldments

The fabrication of structural member using dissimilar steels renders steel structures lighter and more economical. However, it always involves welding process and produces different residual stresses in welds as compared with welding of similar steels. This paper presents the characteristics of residual stresses in welds of similar and dissimilar steel weldments by carrying out three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis. The materials used in this investigation were SM400, SM490, SM520 and SM570, widely used structural steels in welded structure. Results show that the maximum longitudinal residual stresses in welds of the similar steel weldments increase with increasing yield stress of the steel welded (SM400 < SM490 < SM520 < SM570). In case of the dissimilar steel weldments, the difference between the longitudinal residual stresses in welds increases with increasing yield stress of the steel welded together with SM400 (SM490 < SM520 < SM570).     

Mechanical properties of friction welded 6063 aluminum alloy and austenitic stainless steel

Friction welding of dissimilar metal combination of aluminum alloy and austenitic stainless steel was examined to investigate the effect of welding conditions on mechanical properties of the dissimilar metal combination. The welded joints were produced by varying forge pressure (F _g), friction pressure (F _r), and burn-off length (B). The joints were subjected to mechanical testing methods such as the tension, notch Charpy impact tests. The tensile strength and toughness decrease with an increase in friction pressure. The tensile strength decreases with an increase in burn-off length at a low forge pressure while tensile strength increases with an increase in burn-off length at a high forge pressure. The tensile failure of the welded joint occurred in aluminum alloy just away from interface in the thermo-mechanically affected zone indicates good joint strength at the condition of low friction pressure, high forge pressure, and high burn-off length. The maximum tensile strength was observed with low friction pressure and high forge pressure. The tensile strength of dissimilar joint is approximately equal to tensile strength of 6063 aluminum alloys at the condition of low friction pressure, high forge pressure, and high burn-off length. The tensile and impact failure of joints was examined under scanning electron microscope and failure modes were discussed.     

DP590双相钢点焊接头的正交试验及超声检测分析

对DP590双相钢点焊接头进行正交试验,研究不同工艺因素对点焊接头失效载荷和焊核直径的影响,确定最优点焊工艺参数,并探讨点焊接头压痕深度的超声测量方法.采用超声波水浸聚焦入射法对1.5 mm厚的DP590双相钢点焊接头进行超声C扫描,获得接头焊核直径,利用超声A扫信号,计算点焊接头压痕深度,并与实际测量结果对比.研究表明:焊接参数对DP590点焊接头的失效载荷与焊核直径的显著性影响一致,从大到小依次为焊接电流、焊接时间、电极压力;DP590点焊接头最优的焊接工艺参数为:焊接时间70 ms,焊接电流15.0 k A,电极压力6.5 k N,在此参数下接头的抗拉强度为9 521.4 N;超声A扫信号计算得到的点焊接头表面压痕率与实际压痕率的误差在2.5%~9.7%,超声计算所得压痕深度与实际测量压痕率较为接近.     

Failure Analysis of AISI-304 Stainless Steel Styrene Storage Tank

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler wire. The failed base plate was replaced with the new AISI 304 base plate of same thickness. After a short period of time, seepage was observed along the weld bead. Upon nondestructive testing cracks were found in the heat-affected zone and in the base plate. The failure investigation was carried out on welded and base plate samples using spectroscopy, optical and scanning electron microscopy, fractography, SEM–EDS analysis, microhardness measurements, tensile and impact testing. The results revealed transgranular cracks in the HAZ and base plate, and the failure was attributed due to stress corrosion cracking. Cracks initiated as a result of combined action of stresses developed during welding and the presence of a chloride containing environment due to seawater. It was further observed that improper welding parameters were employed for weld repair which resulted in sensitization of the structure and postweld heat treatment to remove weld sensitization and minimize the residual stresses was not done.     

铝-镀锌钢板异种金属Pulsed DE-MIG熔钎焊方法研究

为精确控制焊接热输入,从而控制铝钢异种金属界面区金属间化合物生长,提出一种新型高效低热输入的脉冲旁路耦合电弧MIG焊(Pulsed DE-MIG)方法,用ER5356铝合金焊丝在镀锌钢板上利用平板堆焊实验对工艺参数进行优化.在焊丝总电流保持不变,不同的Pulsed DE-MIG焊接参数下焊接,结果表明随着旁路电流的增大,焊缝宽度显著变小,且焊缝堆高明显变高.采用OM、SEM、EDS等测试手段观察和分析连接界面区的微观组织,发现在连接界面区形成Fe2Al5、FeAl3金属间化合物层,且母材热输入大时,FeAl3析出得多,随着母材热输入的减小,FeAl3析出逐步减少直至FeAl3无析出.