Longitudinal Weld Seams Research Articles

Physical Simulation Method for the Investigation of Weld Seam Formation During the Extrusion of Aluminum Alloys

Extrusion through the porthole die is a predominant forming process used in the production of hollow aluminum alloy profiles across the aluminum extrusion industry. Longitudinal weld seams formed during the process may negatively influence the quality of extruded profiles. It is therefore of great importance to understand the formation of weld seams inside the welding chamber during extrusion, as affected by extrusion process variables and die design. Previously developed physical simulation methods could not fully reproduce the thermomechanical conditions inside the welding chamber of porthole die. In this research, a novel physical simulation method for the investigation of weld seam formation during extrusion was developed. With a tailor-designed tooling set mounted on a universal testing machine, the effects of temperature, speed, and strain on the weld seam quality of the 6063 alloy were investigated. The strains inside the welding chamber were found to be of paramount importance for the bonding of metal streams, accompanied by microstructural changes, i.e., recovery or recrystallization, depending on the local deformation condition. The method was shown to be able to provide guidelines for the design of porthole dies and choice of extrusion process variables, thereby reducing the scrap rate of aluminum extrusion operation.

A framework for estimating residual stress profile in seam-welded pipe and vessel components part I: Weld region

A recent comprehensive investigation into residual stress distributions in pipe and vessel longitudinal seam welds is presented in this paper, covering component wall thickness from 1/4″ (6.35 mm) to 10″ (254 mm), component radius to wall thickness ratio from 2 to 20, and linear welding heat input from low (50 J/mm) to high (6000 J/mm). Through the use of a residual stress decomposition technique, two key parameters that govern through-thickness residual stress distributions in terms of their membrane and bending content have been identified. One is component radius to wall thickness ratio (r/t) and the other is a characteristic heat input density (Q^) having a unit of J/mm3. With these two parameters, a unified functional form for estimating through-thickness residual stress profile in seam welded components is proposed in this paper (Part I) for supporting fitness for service assessment for crack-like flaws in weld region. A curved beam bending theory based model is introduced in Part II as a means of analytically describing through-thickness residual stress profile as a function of circumferential position away from the weld region until residual stresses become zero. The effectiveness of this proposed framework for achieving residual stress profile estimation within weld region (Part I) for longitudinal seam welds in pressure vessel and piping components has been confirmed by finite element residual stress analysis results on a large number of component configurations and different welding conditions.

Analysis of longitudinal weld seam defects and investigation of solid-state bonding criteria in porthole die extrusion process of aluminum alloy profiles

In porthole die extrusion process of aluminum alloy profiles, the formation of longitudinal weld seams (L-seams) is inevitable. Analysis of L-seam defects and investigation of solid-state bonding criteria are important issues for practical production. In this study, a set of modular porthole extrusion dies with different depths of welding chambers were designed and manufactured. The profiles extruded with different depths of welding chambers were obtained by performing extrusion experiments.The welding quality of extruded profiles was characterized by means of microstructure observation, tensile test and fracture analysis. The true stress-strain curves of homogenized AA6063 aluminum alloy with various strain rates and deformation temperatures were obtained by means of isothermal hot compression test. Three-dimensional transient numerical simulation models of the porthole die extrusion processes were established. Flow behaviors of aluminum alloy in porthole die extrusion process were investigated, and the formation processes of L-seams and their defects were revealed. The solid-state bonding processes of metal particles were traced and their welding paths were determined. Finally, based on the plastic deformation and diffusion mechanisms for closure behaviors of micro voids on contact interfaces, a new dimensionless solid-state bonding criterion related to stress triaxiality, effective strain rate, temperature and contact time was proposed. The bonding quality of L-seams of extruded profiles without any macro defect was predicted successfully by using this new criterion. In addition, it was found that the formation of a macro hole in the profile extruded with a shallow welding chamber is attributed to metal flow behavior, and does not relate to solid-state bonding process.

Test Apparatus for On-line Butt-Welding Evaluation of Aluminum Layer in PEX-AL-PEX Multilayer Pipes

Considering the advantages of multilayer pipes over metal and single layer ones as well as their new and increasing application in construction industry, testing these pipes has come into consideration to guarantee the quality of the pipes, and, consequently, prolong their life and increase the quality of building. A most prominent factor in multilayer pipes is the longitudinal seam-weld. If the aluminum layer is applied without welding, it may not affect the pipe’s strength. The welding normally employed involves butt or overlap using laser, ultrasonic, or tungsten inert gas (TIG) techniques. A defect-free weld can play a significant role in the pipe’s strength. Thus, a defect-free weld on the aluminum layer is a major factor in guaranteeing pipe’s quality. In this article, an apparatus for on-line testing of aluminum layer seam weld in multilayer pipes is presented which functions via an inductive proximity sensor. Finally, the results of several tests and defects detected are described.

Investigation of interface evolution, microstructure and mechanical properties of solid-state bonding seams in hot extrusion process of aluminum alloy profiles

Solid-state bonding is an important problem in hot extrusion process of aluminum alloy profiles, especially for hollow section profiles. Predicting and decreasing the length of transverse weld seam (T-seam), improving the solid-state bonding degree and controlling microstructure of longitudinal weld seam (L-seam) are major concerns. In this work, a set of porthole extrusion dies with different shapes of legs (pointed and square) and depths of welding chambers were designed and manufactured. A series of extrusion experiments for different die structure parameters were performed, and microstructure observations, tensile tests and fracture feature analyses for the extruded profiles were conducted. The influences of the shapes of legs and the depths of welding chambers on the evolution and the length of T-seams and on the formation, microstructure and mechanical properties of L-seams were respectively investigated by means of experiment and numerical simulation. The distribution law of the ratio of pressure to material flow stress, p/σ, and the material flow behavior in welding plane were studied by using numerical simulation method. The results showed that the profiles extruded by the dies with pointed legs have single-convex T-seams and straight L-seams on their cross sections, and their T-seams are relatively shorter but their ductility is relatively inferior. While, the profiles extruded by the dies with square legs have double-convex T-seams and cross-shaped L-seams, their ductility is relatively superior but their T-seams are longer. With the increase of the depth of welding chamber, the ductility of the extruded profiles is increased, but the lengths of T-seams are almost invariable. In addition, it was found from numerical simulation results that, in the welding plane, the deforming material with a higher flow velocity has a lower value of p/σ, and vice versa. It was concluded that an effective welding zone should exist in the welding plane, and the deforming material only in this effective welding zone can flow into the extrusion die bearing to form an L-seam in extruded profile.

Liquid Metal Embrittlement of Austenitic Stainless Steel Fitting Caused by Copper Contamination

A failure was observed in an 1800 long radius elbow of ASTM A403 WP 304-WX grade, during site fabrication and erection activities. All the welded fittings used were manufactured from SS 304 plates by the Monaka process [1], which involves cold forming of plates and subsequent welding of the formed halves. The fabrication sequence followed by the fitting manufacturer is shown in Fig. 1. The cracked fitting was an 1800 Sch. 10 90 long radius elbow. This elbow was welded to a pipe and radiographic testing (RT) was carried out for this joint to ensure soundness of the weld. A crack was seen in the RT film, away from the circumferential weld seam and perpendicular to the same. The location of the crack with respect to the circumferential weld seam, as seen from the RT film, is provided in Fig. 2. On careful visual inspection of the component, it was observed that the crack was present on the inside diameter of the fitting, perpendicular to the circumferential weld, the orientation on cross section being 90 to the two longitudinal weld seams of the fitting. The image of cracked portion after dye penetrant testing (DPT) is shown in Fig. 3. Assuming this was a superficial crack, an attempt was made to grind it off. However, the crack found on the ID was not removed completely, even after grinding up to a depth of 3 mm. To ascertain the exact root cause of the failure, the defective piece from the component was sectioned and analyzed thoroughly. Analysis

Lessons for effective integrity management from the San Bruno pipeline rupture

In September 2010, eight members of the public were killed when a gas transmission pipeline ruptured at San Bruno, California. This article describes the causes of this serious organizational failure with a view to learning by other organizations that operate hazardous facilities. The rupture occurred when a longitudinal seam weld failed. The weld had been poorly made at the time the pipeline was fabricated and installed in 1956. The line had not been inspected or tested since that time. While the details are specific to the case at hand, organizational lessons are valid for other organizations operating complex sociotechnical systems that face the problem of sleeping or latent faults that can remain dormant for many years. This analysis focuses on the organizational arrangements that led to such ineffective integrity management, in particular how the potential for an event such as the one that occurred was systematically ignored by the operating company for many years. The key to effective management of the potential for disaster is to ensure that risk management does not become a “fantasy” but remains grounded in the reality of the dangers that the assets pose to workers, the public, and to the organization itself. © 2015 American Institute of Chemical Engineers Process Saf Prog 34: 202–206, 2015

Non-destructive Testing of Longitudinal and Charge Weld Seams in Extruded Aluminum and Magnesium Profiles

The present study focuses on the influence of longitudinal and charge weld seams on the possibility for their non-destructive testing in extruded profiles. For this, aluminum and magnesium alloys were extruded at different extrusion conditions using porthole dies and prepared for non-destructive testing. First, the electrical conductivity of profiles containing charge welds was measured on two measuring paths over the length of the profile and correlated to the respective mechanical properties and microstructures. Second, detailed measurements on specimens taken from similar profiles were done in order to evaluate and compare the detectability of longitudinal weld seams for different alloys.

Relationship between Process Conditions and Seam Weld width in Extruded Shapes through a Porthole Die with Customized Geometry

Extrusion porthole die plays an important role in hollow profile manufacturing of light alloys. The reliability of extruded parts is strongly affected by the quality of extrusion longitudinal seam welds. In the proposed work, a special test die was designed and manufactured with three mandrel supporting legs, each one of a different width. The extruded billet is split into three metal streams, all of the same cross section geometry; however, the legs are not symmetrically positioned. Experimental and numerical campaigns were carried out to analyze the influence of the leg size, ram speed and extrusion ratio on the welding line width.

Comparison of weld characteristics between longitudinal seam and circumferential butt weld joints of cylindrical components

The control of weld induced residual stresses and distortions are very important in longitudinal seam (L-Seam) and circumferential (C-Seam) butt joints of cylindrical components. In this study, a three-dimensional, sequentially coupled thermo-metallurgical-mechanical analysis was performed for L-Seam and C-Seam butt weld joints of AISI 304 cylindrical components to evaluate weld characteristics during gas tungsten arc welding (GTAW) process. Initially, weld experiments were carried out to obtain the heat input and the macrographs which were further validated with the predicted weld molten pool sizes during heat source fitting (HSF) analysis. The Goldak's double ellipsoid heat source function obtained in HSF analysis was employed in the thermal and mechanical analysis. The results reveal that there are significant differences in residual stress distributions between L-Seam and C-Seam butt joints. Full scale shop floor welding experiments were performed to verify the effectiveness of the proposed numerical models and these are in good agreement with the experimental measurements.

A physical simulation of longitudinal seam welding in micro channel tube extrusion

Micro channel tube is a newly developed type of aluminum profiles with sub-millimeter-diameter ports in the cross-section designed for heat transfer enhancement. Micro channel tube is formed with porthole extrusion die, and the longitudinal seam welding problem is the key issue related to both the design of the delicate mandrel in the extrusion die and the pressure bearing capacity of the tube. This paper proposes a novel method to evaluate the seam welding strength of the micro channel tube at the stage of extrusion die design. First, a finite element (FE) simulation of the tube extrusion process is performed for the seam welding conditions in the die chamber and effect of the welding chamber height on hydrostatic pressure. Then, a thermo-mechanical experiment is carried out for a quantitative relationship between the welding strength and the weld condition parameters. Combining this relationship to the numerical results, the welding strength under different die design can be evaluated. Pressure bearing tests on the tube prove the reliability of this evaluation method. This study quantitatively connects the seam welding strength of the profile to the extrusion die parameters, which is helpful for optimizing the design of the extrusion process.

The origin of weld seam defects related to metal flow in the hot extrusion of aluminium alloys EN AW-6060 and EN AW-6082

Longitudinal weld seams are an intrinsic feature in hollow extrusions produced with porthole dies. As these joins occur along the entire extruded length, it is desirable that these weld seams have a minimal impact on the structural integrity of the extrudate. In particular, defects associated with weld seam formation should be avoided. In this research, the occurrence of defects related to material flow inside the extrusion tooling is studied. In lab-scale experiments, EN AW-6060 and EN AW-6082 aluminium alloy billets are formed into strips by means of the direct hot extrusion process. By utilising model dies with an internal obstruction similar to the supports present in porthole dies, a strip with a central longitudinal weld seam is formed. The effects of different geometries of the weld-chamber and the processing conditions on the quality of the weld seam are investigated. Characterisation is performed through mechanical testing, focusing on the ability of the weld seam area to accommodate plastic deformation, and microstructural analysis provides insight into the defects related to unsound metal flow. Through computer simulations, conditions related to weld seam formation are modelled and correlated with the experimental results. The experimental results demonstrate that metal flow controlled by the die geometry causes defects leading to inferior mechanical performance of the extrudate. It is further argued that current weld seam formation criteria utilised in finite element modelling need enhancement to incorporate these flow related defects.

Non-Destructive Detection of Weld Seams in Extruded Aluminum Profiles

The present study focuses on the feasibility of non-destructive testing methods for the detection of transverse and longitudinal weld seams in extruded aluminum alloys. Two extrusion trials using billet on billet extrusion with a porthole die producing both types of weld seams were conducted. First, two billets of different types of alloy, AlMgSi1 (EN AW-6082) and AlZn4.5Mg1 (EN AW-7020), were extruded. In a second trial, two billets of AlZn4.5Mg1 were processed. The produced profiles were then tested by non-destructive testing using a tactile eddy current sensor as well as an encasing sensor at room temperature. The measured signals of both sensors were then evaluated and compared. Microstructural analyses have been carried out to correlate the occurrence of transverse and longitudinal weld seams with the results of the non-destructive testing.

Numerical Approach for the Evaluation of Seam Welding Criteria in Extrusion Processes

The accurate simulation and the optimization of extrusion processes can be a helpful technique to ensure producibility of complex aluminum profiles, for example for the automobile industry. Currently, the die designing is based on expert’s knowledge and cost-intensive prototyping. The paper deals with numerical investigations based on finite element simulations as well as experimental investigations of an industrial extrusion process. A newly developed method for longitudinal seam weld prediction is applied to analyze the position of the longitudinal welding line and the welding quality.

Stress and Strain Evolution Rule Research on Aerospace Aluminum Alloy Cylinder Structure Welding

The stress and strain in Aluminum cylinder longitudinal and circumferential weld seam are simulated by finite element analysis tools-ANSYS.Tube structure in aerospace is welded by the variable polarity plasma arc welding process.According to the characteristics of variable polarity plasma arc weld,surface heat source and cylindrical heat source are used to simulate variable polarity plasma arc weld.The program which is used to achieve loading and moving variable polarity plasma arc(VPPA) welding heat is wrote by using the ANSYS parametric design language(APDL) in ANSYS software.The same structure in different type of weld is presented by the different ways of loading heat source.The use of sweep meshing method to build complex cylinder structure analysis model is proposed.Through the simulation results,the complex cylinder welding deformation evolution process is explained.It is found that longitudinal seam ends have obvious stress-strain release in the process,and cross section deformation directly influenced the size precision of whole structure.

Practical use of defect assessment procedures for industrial component integrity assessment

The practical use of defect assessment procedures for industrial component integrity assessment is described through two practical examples in this paper. In the first example, the procedure is used to perform low temperature fitness-for-service (FFS) analysis of a longitudinal seam welded vessel manufactured from a duplex stainless steel. The impact energy obtained from the Charpy impact test performed on the weld of the vessel was found lower than the value of the minimum impact energy criteria given by the British Standard BS 5500. Charpy impact energy and fracture toughness correlation and failure assessment diagram (FAD) methodology were used in this FFS analysis to determine the fracture resistance of the vessel. For the assumed defect size used in the assessment, the weld was found to meet the fracture resistance criteria and therefore would still be fit-for-purpose. The FAD analysis was, however, repeated using the J-values obtained from the CTOD test to gain better confidence as the Charpy impact test does not provide direct measurement of the fracture toughness. The FAD was later used to determine the critical surface crack length which was then represented as a function of crack depth. The Charpy impact energy correlation method was found to be more conservative than the method of evaluation using the CTOD J-values. The lack of side wall fusion (LOF) which is a typical defect in this type of vessel would usually be influenced by the size/diameter of the electrode wire used in the weld and the number of runs. In this case, the fracture resistance of the 15mm thick vessel with the longitudinal seam weld should be adequate if less than 5mm diameter of electrode wire is used.The second example illustrates defect assessment of a high temperature plant component. A defect was found in the high pressure final superheater header. A defect assessment incorporating FAD on the header showed that the defect was non-critical. This led to the need to perform creep and fatigue crack growth calculations and remaining life assessment in order to determine the mitigation plan for the engineers. The deterministic approach, which mainly considers the worst case scenario, suggested that the remaining life of the header was approximately 4.5 years. Probabilistic analysis showed that the component could still be fit for service up to 6 years. This will allow the engineers to mitigate a more efficient plan with a decision to either repair or replace the header and when. The use of probabilistic lifing methodologies and algorithms could consequently bring considerable financial benefits to the plant owners/operators e.g. by avoiding premature component repair or replacement. Nevertheless, it would be in the management’s interest to avoid a forced outage. The recommendation would be that the component could still be fit to use until their next minor outage (in 3 years). From then, the remedy option would be to grind down to a depth of suspected crack, excavate a small area/surrounding which might be affected, followed by correct and regular monitoring, or alternatively replace the component.

Towards Predictive Control of Extrusion Weld Seams: An Integrated Approach

Longitudinal weld seams are an intrinsic feature in hollow extrusions produced with porthole dies. The formation of longitudinal weld seams is a solid bonding process, controlled by the local conditions in the extrusion die. Being the weakest areas within the extrusion cross section, it is desirable to achieve adequate properties of these weld seams. In our research, the concept of a weld seam integrity indicator as a means of quantifying bonding efficiency is introduced. The value of this indicator depends on a number of factors: the material flow within the die weld chambers, an adequate pressure level acting on the weld planes and finally the evolution of the metal microstructure. Optimisation of the welding conditions leads to a higher value of the weld seam integrity indicator and thus to improved weld seam properties. The objective of the research presented in this paper is to assess the feasibility of this concept. In lab-scale experiments, AA6060 and AA6082 aluminium alloy billets were formed into strips by means of the direct hot extrusion process. By utilising porthole dies a central longitudinal weld seam is formed. The effect of different geometries of the weld chamber and the processing conditions on the quality of the weld seam are investigated. Characterisation of these weld seams through mechanical testing, focusing on the ability of the weld seam area to accommodate plastic deformation following the onset of plastic instability, and microstructural analysis provides insight into bonding performance. The outcome of this characterisation provides a basis for an estimation of the weld seam indicator. Through computer modelling, the particular process conditions related to weld seam formation are calculated and correlated with the experimental results. The experimental results clearly demonstrate that weld seam formation is controlled by a combination of factors as described above. Inadequate fulfilment of these conditions, verified by the FE-simulations, is the cause of inferior weld seams, associated with low values of the weld seam integrity indicator. Through further elaboration of the concepts presented in this work, the weld seam integrity indicator is to be developed, with the future aim of predicting the weld seam performance through finite element simulations.

Physical Simulation of Longitudinal Weld Seam Formation During Extrusion to Produce Hollow Aluminum Profiles

Uniaxial compression tests were performed to understand the solid-state bonding process that occurs in porthole dies during the manufacturing of hollow aluminum extrusions. Strain, strain rate, and temperature applied during the tests were those typically encountered during aluminum extrusion. For a good bond, strain was found to be the most influential parameter, along with bonding time. The effect of temperature on bonding depended on alloy composition. Bonding stress was less influential within the range investigated. Surface stretching was introduced to the AA6060, AA6082, and AA7020 aluminum alloys as a criterion to quantify the bonding phenomena and distinguish their bondabilities.

Three Dimensional Analysis of High Frequency Induction Welding of Steel Pipes With Impeder

High frequency induction welding is widely employed for longitudinal seam welding of small scale tubes and pipes due to its relatively high processing speed and efficiency. This research is aimed at understanding the variables that affect the quality of the high frequency induction welding. The welding variables include the welding frequency, weld speed, vee angle, and tube thickness. Temperature distribution of the tube is calculated through three dimensional coupled electromagnetic and thermal finite element analysis. The skin and proximity effects are considered in the electromagnetic analysis. The influence of the impeder is also analyzed. The effects of the operating welding variables on the temperature distribution are investigated quantitatively by exhibiting the heat affected zone. The results explain the mechanism of significant enhancement of welding efficiency when the impeder is used. Not only good weld state can be obtained but also overheated edge can be avoided by understating the effect of welding variables. Suggestions are made for the better induction welding conditions.

Analysis of Metal Flow through a Porthole Die to Produce a Rectangular Hollow Profile with Longitudinal Weld Seams

A detailed analysis of metal flow through a porthole die to produce a rectangular hollow aluminium profile was performed by means of three-dimensional FE simulation using DEFORM 3D. It was aimed at revealing the flow patterns of a medium-strength aluminium alloy 7020 through a porthole die and gaining an insight into the formation of longitudinal weld seams inside the welding chamber during extrusion. In the case of extruding a rectangular hollow profile through a porthole die with four ports, two neighbouring ports were different from each other. Using an FE model including these two ports, different flow patterns of two individual metal streams were revealed. The 3D FE simulation also showed how two unequal metal streams contacted each other and became bonded in the welding chamber under a certain hydrostatic pressure and at a certain temperature, before the metal flew through the die bearing. The difference in velocity between the metal streams led to uneven flow at the die bearing and thus a wavy extrusion nose.