Longitudinal Weld Research Articles

Validation of Welding Simulations Using Thermal Strains Measured with DIC

Residual stresses can affect the performance of steel tubes in many ways and as a result their magnitude and distribution is of particular interest to many applications. Residual stresses in cold-rolled steel tubes mainly originate from the rolling of a flat plate into a circular cross section (involving plastic deformations) and the weld bead that closes the cross section (involving non-uniform heating and cooling). Focus in this contribution is on the longitudinal weld bead that closes the cross section. To reveal the residual stresses in the tubes under consideration, a finite element analysis (FEA) of the welding step in the production process is made. The FEA of the welding process is validated with the temperature evolution of the thermal simulation and the strain evolution for the mechanical part of the analysis. Several methods for measuring the strain evolution are available and in this contribution it is investigated if the Digital Image Correlation (DIC) technique can record the strain evolution during welding. It is shown that the strain evolution obtained with DIC is in agreement with that found by electrical resistance strain gauges. The results of these experimental measuring methods are compared with numerical results from a FEA of the welding process.

Pitting corrosion in pipeline steel weld zones

Steel pipelines externally exposed to seawater pit more severely in heat-affected weld zones but longer-term quantitative data are scarce. Maximum pit depths and variability are reported for the longitudinal weld in API X56 Spec 5 L grade steel pipeline samples exposed continuously to natural Pacific Ocean seawater for 3.5 years. For the first year maximum pit depths and pit depth variability for the different weld zones were very similar. Both became much greater subsequently, with the greatest increases for the heat affected zone. This is compared with steel composition and grain size and potential reasons for the observations discussed.

Experimental Investigation and Design of Aluminum Beams with Longitudinal Welds

This paper presents an experimental investigation of longitudinally welded aluminum I-section beams subjected to concentrated force. The specimens were fabricated using 6061-T6 heat-treated aluminum. The test program included 10 beam tests contained 2 test series according to different welding section, i.e. T-shape section and P-shape section. The test results were compared with the design strengths predicted by the European Code and the suggested formula in the paper for welded aluminum beams. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section aluminum beams, and to validate the accuracy of the recommended design formula.

Residual Stress Effects and Fatigue Behavior of Friction-Stir-Welded 2198-T8 Al-Li Alloy Joints

Applications of friction stir welding in a fuselage structure were studied. Samples with two different friction-stirweld orientations in the fuselage panelwere tested: one is along the fuselage longitudinal direction and the other one is along the fuselage circumferential direction. Then fatigue cracks were investigated that were set in three different types: parallel and perpendicular to friction stir welds and between doublewelds. Sample geometries weremachined from identical welds in order to remove the effect of theweld process on fatigue behavior. Tests were conducted onM (T) specimens with either longitudinal or transverse welds. Cracks growing into or growing away from the weld center, as well as in the nugget zone, were investigated. It is shown that fatigue crack growth for cracks growing away from the center seems similar to that of the parentmaterial; for crack growing in the nugget, crack grows slower than in the parent material; and for cracks starting between double welds, the crack grows slower than in the other two types. The virtual crack-closure technique method was used to calculate stress intensity factor from residual stress (Kres) and effective R ratio in an attempt to explain the experimental findings.

Weld zone representation during the formability prediction of friction stir welded blanks with similar thickness sheets

During formability prediction of friction stir welded (FSW) blanks, it is necessary to incorporate nugget zone and heat-affected zone (HAZ) properties separately for better accuracy. In general, it is observed that the weld zone is represented as a single entity, in which only global weld zone properties are implemented. In this work, it is proposed that there is a domain of weld conditions in which the single-zone assumption (nugget and HAZ are modelled without incorporating their individual properties) breaks down and the double-zone assumption (nugget zone and HAZ are represented separately) should be followed. During limiting dome height simulations, a representative base material is considered from the literature with changing nugget zone and HAZ properties. The punch displacement at failure and maximum load are compared between FSW blanks modelled with single- and double-zone assumptions. It is observed that modelling FSW blanks with double-zone assumption plays a vital role for accurate formability prediction. The single-zone assumption is not valid for all the FSW conditions. Both in transverse and longitudinal weld orientations, there are possibilities of multiple domains in which the double-zone assumption is valid. It is found that there exists a relationship between the thickness distribution and availability of single-zone or double-zone models. Whenever the thickness distribution of a particular double zone is closer to the reference case modelled with single zone, it is sufficient to model that weld zone case with a single zone. Double-zone representation is required in cases when the thickness distribution is very different. The domains for weld zone modelling in FSW blanks are sensitive to failure location. Put simply, it is advisable to model HAZ separately, when failure occurs in it. But this is not always the case. It depends on a compromise between the accuracy and availability of HAZ properties.

Size effects on residual stress and fatigue crack growth in friction stir welded 2195-T8 aluminium – Part I: Experiments

Residual stress fields were measured in three different sizes of Compact-Tension (C(T)) and eccentrically loaded single edge notch (ESE(T)) specimens containing transverse or longitudinal welds. The effect of size on residual stress profiles was studied. Fatigue crack growth tests were carried out with cracks growing into or away from the weld line, as well as growing along the weld centre line. Effects of weld residual stresses on fatigue crack growth rates parallel and perpendicular to the friction stir welds were studied. It was found that compressive residual stresses around the sample notch had significant retarding effects on both crack initiation and crack growth rates for cracks growing towards the weld line. Effects of residual stress on crack growth rates declined with increasing crack length. When cracks grew parallel to the weld line in C(T) samples the crack growth rate was around 20% lower than in parent material.

Crane runways – Fatigue evaluation of crane rail welds using local concepts

The introduction of the wheel loads into a crane runway with a hot rolled I-section and a block rail fastened by longitudinal fillet welds forms a multiaxial fatigue problem. At the point of wheel load application the top region of the runway girder is subjected to a stress field comprising local stress components induced by the concentrated load, i.e. local transverse pressure and local shear stress in addition to the direct and shear stress components due to global bending. The superposition of all aforementioned stress components (and stress ranges, resp.) during each single crane pass results in a so-called non-proportional cyclic stressing of the rail welds with alternating principal stress direction. Due to the variation of the principal stress direction the conventional fatigue evaluation procedures appear not to be reliable. To approach the complex issue two crane runway girders were tested under proportional multiaxial loading, i.e. under flexural bending and stationary wheel load, both simultaneously pulsating. The paper presents the fatigue evaluation of these tests using different local concepts.

Experimental investigation and design of aluminum columns with longitudinal welds

This paper presents an experimental investigation of longitudinally welded aluminum alloy I-section columns subjected to pure axial compression. The specimens were fabricated using 6061-T6 heat-treated aluminum alloy. The test program included 20 column tests which were separated into 2 test series of different types of welding sections. Each test series contained 10 columns. All the specimens were welded using the Tungsten Inert Gas welding method. The length of the specimens ranged from 442 to 2433 mm in order to obtain a column curve for each test series. The observed failure mode for the column tests includes mainly flexural buckling around the minor axis and the major axis by applying support except for one column (ZP1217-1) which buckled in the local zone and some columns which failed in the weld. The test strengths were compared with the design strengths predicted by the European Code and China Code for aluminum structures. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section columns, and to check the accuracy of the design rules in the current specifications.

Compression Behaviors of Thickness-Reduced Steel Pipes Repaired with Underwater Welds

Underwater welding is commonly used to repair corroded offshore steel structures. Corrosion-damaged portions are covered by welded patch plates. According to the current design manual, a thickness of patch plate and a weld length can be determined. However, different weld patterns can be designed to achieve the same required weld length. In order to examine the effectiveness of these different weld patterns, this paper first proposes a method to model underwater welds in the finite element analysis based on mechanical properties of fillet welds obtained from weld strength tests. The weld model was firstly validated against a theoretical shear stress distribution in a longitudinal fillet weld and then further validated against experimental results of thickness-reduced steel pipes repaired with welded patch plates under compression. The proposed model was then applied to thickness-reduced steel pipes repaired by welded patch plates with different weld patterns that have the minimum required weld length. Behaviors of these repaired pipes under a compressive load were examined with respect to stiffness, load-carrying capacity, load share of patch plates, and failure modes. It was found that stiffness and load-carrying capacity of the thickness-reduced steel pipes under compression cannot be fully recovered by the welded patch plate repair when a patch plate thickness is the same as the thickness reduction of the damaged pipe. Among different weld patters, the one with four slits was found to show better performance.

Case studies on virtual extrusion of aluminium alloys in real size

Two case studies were conducted to illustrate the capabilities of the state-of-the-art computer simulation technology applied to the aluminium extrusion process and demonstrate the usefulness of virtual extrusion in real size to the die designer and extrusion process engineer alike. A deform 3D software package was used for virtual extrusion in real size to manufacture a hollow profile through a porthole die (case I) and two precision solid profiles through a two-hole multi-step pocket die (case II). Temperature, stress and velocity distributions were revealed. In case I, the filling of the ports, welding in the welding chamber and forming of the hollow profile were visualised. The quality of the longitudinal welds along the hollow profile length was assessed. In case II, the deflection of two solid profiles from the centreline to different extents was predicted, thereby providing the guidelines for die design modification. The modified die indeed performed better.

Assessing the Validity of Original and Modified Failure Criteria to Predict the Forming Limit of Unwelded and Tailor Welded Blanks with Longitudinal Weld

The main objective of the work is to assess the validity of modified failure criteria proposed by Naik et al. [1] and original failure criteria in predicting the forming limit of unwelded and tailor welded blanks (TWBs) with longitudinal weld, during stretching and drawing operations. The four different failure criteria, namely, effective strain rate-based, major strain rate-based, thickness strain rate-based, and thickness gradient-based failure criteria, both in original and modified forms, are used to predict the forming limit strains of unwelded and welded blanks. In the case of unwelded sheet, the forming limit predictions are consistent with the experimental result in the drawing side, but considerable difference is observed in the stretching side of forming limit diagram (FLD). In the case of tailor welded blanks (TWB), whenever failure is seen near the weld region, the strain rate-based criteria are modified as RC1 ≥ 25, RC2 ≥ 32, RC3 ≥ 32 for failure to occur. TWB forming limit curve (FLC) predicted using the modified criteria show better accuracy than the original failure criteria in the stretching side of the FLD. In the drawing side, FLC predicted by original criteria is the same as that from modified criteria, where in strain path change is witnessed instead of limit strain improvement. Through this work, it is demonstrated that using modified failure criteria, forming limit of TWBs can be predicted with better accuracy during stretching operation, while original failure criteria are sufficient for a drawing operation or in the drawing side of FLD

Evaluation of the intrinsic crack growth rates of weld joints

A method is presented for evaluating the intrinsic fatigue crack growth rate (FCGR) by excluding the effect of welding-induced residual stresses. Calculation procedures have been developed and demonstrated via an example of crack growth across a longitudinal weld subjected to constant amplitude loads and also constant applied stress intensity factor ranges. Trends of intrinsic FCGR in different weld regions are identified. The methodology should also be applicable for crack propagation within and parallel to a weld for establishing intrinsic FCGR laws.

Effect of Weld on Axial Buckling of Cylindrical Shells

Large oil storage tank (oil tank for short) shells are vulnerable to buckling damage when suffering the seismic loads. Numerical simulation analysis was taken to estimate the effects of the weld form, number and their location to axial buckling stress of cylindrical shells, considering not only the characteristic of welding processes, but also the effects probably caused by magnitude of residual stress and deformation on elephant foot buckling to oil tanks. It is revealed that the existence of circumferential welds had obvious negative effect on axial buckling critical stress compared with the structure without welds, while the effects of weld number and location were not as much; longitudinal welds had no visible effect on axial buckling critical stress; controlling the residual stress and deformation range caused by circumferential welds should be the key point during the tanks welding process.

Failure analysis of a stainless steel hydrotreating reactor

This paper presents an analysis of a failed AISI 316L austenitic stainless steel (SS) hydrotreating reactor that produces flavors and fragrances. Pitting and cracking were observed mainly in the vicinity of the circumferential and longitudinal shell welds on the internal surface of the reactor by dye penetrant testing (DPT). Ultrasonic evaluation revealed the cracks were within near-surface area, therefore remedial grinding was performed to remove them. In situ metallographic investigation revealed that the cracks were predominantly transgranular and multi-branching. Thickness gauge, hydraulic pressure testing, and acoustic emission validated the reusability of the repaired vessel. Analysis of the catalysts showed the source of chloride. SCC (stress corrosion cracking) susceptibility testing of the identical material proved its liability to chloride SCC in the environment of the suspect catalysts. Studies revealed that the failure was caused by chloride SCC. Recommendations are made to prevent the recurrence of the similar failure.

An inverse method for evaluating weld residual stresses via fatigue crack growth test data

This paper presents an inverse method for calculating the thermal residual stresses in welded specimens via measured fatigue crack growth rates. Firstly, fracture-mechanics superposition law has been used to extract the stress intensity factor due to residual stress contribution from measured crack growth rate. Secondly, a so-called B matrix has been established by performing finite element analysis. Residual stress distribution is then determined by solving linear algebraic equations relating the B matrix and residual stress intensity factors obtained from crack growth test data. The inverse method has been validated by a well-established residual stress distribution and corresponding stress intensity factor, and then applied to an M(T) sample in 2024-T3 alloy with a longitudinal weld. Agreement with the measured residual stresses is reasonably good and reasons for certain differences between the calculated and measured are discussed.

Effects of process parameters and die geometry on longitudinal welds quality in aluminum porthole die extrusion process

By using the rigid-visco-plasticity finite element method, the welding process of aluminum porthole die extrusion to form a tube was simulated based on Deform-3D software. The welding chamber height (H), back dimension of die leg (D), process velocity and initial billet temperature were used in FE simulations so as to determine the conditions in which better longitudinal welding quality can be obtained. According to K criterion, the local welding parameters such as welding pressure, effective stress and welding path length on the welding plane are linked to longitudinal welds quality. Simulation turns out that pressure-to-effective stress ratio (p/σ) and welding path length (L) are the key factors affecting the welding quality. Higher welding chamber best and sharper die leg give better welding quality. When H=10 mm and D=0.4 mm, the longitudinal welds have the best quality. Higher process velocity decreases welds quality. The proper velocity is 10 mm/s for this simulation. In a certain range, higher temperature is beneficial to the longitudinal welds. It is found that both 450 and 465 °C can satisfy the requirements of the longitudinal welds.

Crack Analysis of Induction Heating Bent Pipe

There were 20 of 103 length of pipe found cracks on the extrados surface of the bent pipe made of Φ406.4×10mm L360 Longitudinal Submerged Arc Welding (LSAW) pipe, the cracks were mostly distributed in the extrados surface and the arc initial point of the bent pipe, the cracks were spindle-shaped and narrow at both ends with the longitudinal direction vertical to the axis of bent pipe. The mechanism and the causes of the cracks were studied by macro inspection, mechanical property test, microscope, scanning electron microscopy and energy spectrum analysis, which shown that the cracks were result from the contamination of copper or its alloy during or before the bent pipe production. The contaminated material like copper infiltrated and diffused into the base metal at high temperature, and could hardly stead to and transfer the normal stress from the base metal where the inertial crack was shaped. Meanwhile, the new crack was formed at the tip of inertial crack after the new infiltration and diffusion under the condition of both high temperature and tensile stress, so that the crack progressed and extended in this way.

Determination through the distortions analysis of the best welding sequence in longitudinal welds VATS electron beam welding FE simulation

This paper presents a detailed finite element simulation of the longitudinal rib welds of Vessel Advanced Technology Segment (VATS) by e-beam welding. Nine different simulation sequences were carried out to explain the different mechanisms that drive the distortions process during welding and to lead to an optimum sequence which minimizes the final distortions. The simulations were used to guide the manufacture of the final sequence of the VATS. Distortion measurements taken after welding compared very well with the simulated results.

Degradation of impact fracture during accelerated ageing of weld metal on microalloyed steel

The effect of accelerated ageing on the toughness and fracture of the longitudinal weld metal of an API5L-X52 linepipe steel was evaluated by a Charpy V-notch impact test, fracture analysis and transmission electron microscopy. Ageing was performed at 250°C for 100–1000 h. The impact results indicated a significant reduction in the fracture energy and impact toughness as a function of ageing time, which were achieved by the scanning electron microscope fractographs that showed a decrease in the volume fraction of microvoids by Charpy ductile failure with the ageing time, which promoted brittle fracture due to transgranular cleavage. The minimum volume fraction of microvoids was reached at 500 h due to the peak age. The microstructural analysis indicated the precipitation of transgranular iron nanocarbides in the aged specimens, which was related to the deterioration of toughness and change in the ductile to brittle behaviour.

Design and Behavior of Multi-Orientation Fillet Weld Connections

Several independent research projects have demonstrated that the strength and ductility of fillet welds are a function of the angle between the weld axis and the line of action of the applied load. It has been demonstrated that transverse welds are about 50% stronger than longitudinal welds, but have considerably lower ductility. This difference in behavior can have a significant impact on the design of welded connections with multiple weld orientations within the same joint. Tests on concentrically loaded welded double lapped joints have recently been conducted to investigate the strength of connections with multiple weld segments of different orientations. The tests indicate that these joints possess capacities significantly lower than the sum of the individual weld segment strengths. The tested connections' capacities are a function of the interaction of the load versus deformation characteristics of the individual weld segments. A general approach for the design of welded joints that combine welds in various directions that reflects the individual segments' load versus deformation interaction is recommended.