Longitudinal Seam Research Articles

Acoustic Emission Waveform Analysis From Weld Defects in Steel Ring Samples

Acoustic emission (AE) signals from weld defects, incomplete penetration (IP), slag inclusion (SI), and porosity (PR), in longitudinal seam welding of UOE steel pipes were evaluated by using an envelope analysis system and waveform analysis system. In test results, the location accuracy of the envelope and the waveform systems during the loading tests were a few 10 mm and a few mm, respectively. AE activity and intensity and waveform type could identify the welding defect types. Three types of AE spherical radiation patterns (AERPs), a monopole mode, a tensile fracture of dipole mode, and a tensile and shear mixed of dipole mode, were observed during the test. Information from cross section observation of the IP by SEM and AERP suggested that activity and intensity of AE signals from welding defects could depend on both stress concentration of the defect and brittleness of the microstructure around the defect.

Investigation of the stability of imperfect cylinders using structural models

A combined analytical and experimental programme on the buckling of cylinders under axial compression, external pressure, and combined loading was conducted to develop a methodology for predicting the buckling of shell structures with manufacturing induced imperfections. A unique method of fabricating test cylinders from Lexan without longitudinal seams was developed. Cylindrical blanks formed by blow moulding were thermoformed and machined to the correct wall thickness to form perfect cylinders. The co-ordinates were measured and the cylinders tested. After testing, the cylinders were thermoformed on a second mandrel containing the desired imperfection shape and amplitude, remeasured, and tested. Excellent correlation to predictions from the BOSOR 4 and ABAQUS computer codes was achieved.

Some issues in life assessment of longitudinal seam welds based on creep tests with cross-weld specimens

In order to reduce production costs, it is of great interest to use longitudinal seam welds when manufacturing large diameter pipes. The cost reduction can be as high as 30%. However, severe inservice accidents for this type of pipes working in the creep regime have occurred mainly due to mismatch in weldment creep properties. In many cases, creep tests of cross-weld specimens, taken from the seam weld, are used to predict the behaviour of the seam weld, assuming that the creep behaviour of specimen and weldment is equivalent. Experiences of this procedure indicate that further knowledge is required before translation between specimen and component can be made. In the present paper, both full scale seam welded pipes and cross-weld specimens are studied with the damage mechanics concept using finite element, FE, technique. The same mechanical model of multiple material zones is used for the two components. Both the influence of differences in creep properties between the weldment constituents and the size effect of the cross-weld specimen, are studied. It is found that the cross-weld test results can not directly be translated to the full scale component. Factors such as the creep properties and the relative geometry of the weldment constituents and the size of the cross-weld specimen have to be considered when performing creep life assessment.

Three-dimensional calculation of the distribution of eddy currents and the heating effect on slit tubes when welding longitudinal seams

A numerical model is presented for the process of the inductive longitudinal-seal welding of tubes. This model refers to a three-dimensional, quasi-stationary electromagnetic field and a three-dimensional temperature field. The characteristics of the material dependent on the field in both cases are taken into consideration in iterative ways in the form of local functions. The differential equations describing the electromagnetic field are integrated as an A-/spl phi/ formulation into the method of finite elements. The discretization, adapted to suit the problem, leads to grid networks with up to 100.000 nodes. The results of the calculations shown permit the determination of optimum process parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

COMPARISON OF FATIGUE LIFE PREDICTIONS IN WELDED JOINTS USING 2D AND 3D K SOLUTIONS

AbstractThe paper presents the results of fatigue life predictions in non‐loaded carrying tee and cruciform joints and also longitudinal seams of tubes, obtained with 2D and 3D stress intensity factor solutions. The 2D computational method uses the standard Bueckner weight function solution to obtain the 2D values of the stress magnifying factor MK. In the 3D approach a modified 3D weight function solution was used in conjunction with the Raju and Newman base stress intensity formulation.Comparison of results is shown between the 2D and 3D fatigue life predictions and experimental results of fatigue strength obtained by the authors. Results are also given showing the influence of crack aspect ratio, thickness and the ratio of tube radius to tube thickness.

A study of the dynamic stability of anisotropic thin-walled beams

The dynamic stability of an anisotropic thin-walled beam subjected to harmonically varying axial compression is studied in this paper. The analysis is based on the assumption that the shape of the cross-section of the beam does not change during deformation. The shear of the middle surface of the beam is taken into account. The dynamic equations are reduced to a set of coupled Mathieu equations by using the Galerkin method. Then Hill's infinite-determinant method and a shooting-type numerical method are used to investigate the Mathieu equations to determine the stability regions of the beam in the parameter space. Two examples, one of which is a complete circular tube and the other is a circular tube with a longitudinal seam, are given.

Influence of misalignment on the fatigue strength of butt welds

A study is presented concerning the influence of misalignment on the fatigue behaviour of transversely loaded butt welded joints. The following main types of misalignment were analysed: parallel misalignment between two plates with equal or different thickness, longitudinal seams in tubular connections and also angular misalignment. An LEFM approach was used to predict crack propagation life. The theoretical predictions for the joints between plates with equal thickness and with parallel and angular misalignment were compared against experimental results taken from the literature, and good agreement was found. In the case of parallel misalignment and equal plate thicknesses a crack initiation model was applied and the total S-N curves were obtained for the fatigue life of the joint.

A More Accurate Method for Predicting the Prestresses in a Multilayer Wrapped Cylindrical Vessel

The prestresses in the walls of multilayered weld-wrapped cylindrical pressure vessels are mainly created by the transverse shrinkage of the welded layers. Current design practices consider only the shrinkage of longitudinal weld seams, resulting from constant temperature gradients. Such practices ignore the contribution to shrinkage from the remaining part of the welded plate and would, therefore, yield approximate values for the corresponding prestresses. In the present work the shrinkage of the full layer is determined, and hence a more accurate method for predicting the weld wrapping stresses is offered. The heat transfer problem during welding is addressed and modeled. A three-dimensional heat conduction problem with a heat source traveling at constant speed is formulated and solved. Using Green’s function, the transient temperature distribution is determined. A two-dimensional model is also employed, and the corresponding temperature solution is obtained. A numerical example for the two-dimensional model is worked out for a single welded layer. Comparison between the value of the layer shrinkage calculated by the method described in this paper (variable layer temperature) and that obtained by the current industry method (constant temperature gradient) shows that the latter yields a higher (more conservative) value, and hence will underpredict the prestresses in the layer and the vessel.

Life Assessment of Hot Reheat Steam Pipe

A methodology for assessing the remaining life of hot reheat steam pipe with longitudinal flaws, such as those typically associated with the longitudinal seam welds, has been developed. The approach uses three levels of analysis. Level 1 employs handbook data, assumed flaw sizes, and design parameters. Level 2 employs handbook data, assumed flaw sizes, and actual operating parameters. Level 3 is tailored to a specific case and uses measured data, inspection results, and actual operating parameters. A computer code was developed to apply this approach to hot reheat steam pipe of 2-1/4Cr-1Mo and 1-1/4Cr-1/2Mo-Si steel. Using data from an EPRI survey (RP2596-7), the results of Level 1 analysis were found to predict the potential for creep damage and fracture and to correlate well with past experience, whereas the traditional lower-bound Larson-Miller approach was generally overly optimistic in predicting remaining service life. The approach predicts creep-crack-growth life and assesses the potential of rapid, unstable fracture occurring before a significant amount of leaking takes place. The usefulness of the methodology is illustrated by means of example analyses of a typical cases that might be expected in service. The parameters that were varied in these analyses include type of material (base metal or weld metal), pressure, temperature, pipe wall thickness, and initial flaw size. The approach provides a preliminary tool to help make inspection, operating, and replacement decisions; but additional work is required to validate it as a general tool.

Stand for the automatic welding of longitudinal seams on shells made of thin sheets

Stand for the automatic welding of longitudinal seams on shells made of thin sheets

Improvement of notch toughness and soundness in longitudinal seam weld of line pipe.

Multiple-electrode submerged arc welding process with three or four electrode is used for the production of longitudinally welded pipe. Increased welding speed is limited by the properties of flux against weld defects such as undercutting and slag inclusion and the toughness of weld metal deteriorated by impurity gas contamination.A flux with a solidification temperature of 950 to 1050°C and with a viscosity of 2.5 to 4.5 poise at 1400°C can minimize slag inclusion and undercutting. Welding of heavy wall thickness UOE pipes with a heat input above 100kJ/cm requires a flux with a high melting point and high viscosity.In order to obtain good notch toughness of weld metal at low temperature service, it is necessary to control the nitrogen content foreffective utilization of titanium and boron in weld metal. Optimum range of titanium to get high notch toughness is shifted by nitrogen content in weld metal.HAZ notch toughness of high strength line pipe is affected strongly by carbon and boron contents in base metal. Excellent notch toughness of HAZ was obtained by decreasing the carbon content in base metal below 0.05wt%.

An Assessment of the Impact Performance of Bonded Joints for Use in High Energy Absorbing Structures

Using an instrumented impact test, the strength and energy absorption of bonded single lap joints have been measured for single lap joints with four epoxy adhesives and three aluminium alloy adherends. Compared with the static values, joint strength is not significantly affected by the high loading rates. Energy absorption is large when joint strength is sufficient for plastic deformation to occur in the adherends prior to failure, which is only the case for certain adherend/adhesive combinations. Spot welded joints are shown to be inferior in performance in the tests. The effect of loading rate on bonded joint strength has been analysed using a non-linear finite element method, from which predictions of joint strength in keeping with the experimental results have been obtained. Crush tests carried out on open-ended cylinders have been used to simulate the impact behaviour of an energy absorbing structure. Similar performance was observed for cylinders with either bonded or spot welded longitudinal seams, although the large deformations in the crumple zones led to some debonding and weld fracture.

直流アーク溶接法による管内面溶接時の磁気発生とアークの偏向防止策

This investigation was carried out to clarify the mechanism of the magnetic arc blow occurred in UOE pipe longitudinal inside seam welding by large current MIG arc welding process, and to establish the preventions against this phenomenon.The magnetic flux density around the arc was measured with aid of simulated model. The results obtained are summarized as follows.(1) The magnetic flux density around the arc in inside welding of pipes showed asymmetrical distribution.(2) Welding arc is blown toward the lower density side i.e. molten pool.(3) The asymmetrical disribution of magnetic flux density is caused by the earth current and welding current through the boom inserted to the pipe.(4) The prevention against the arc blow is established on the basis of the results obtained.

Differences in the Apparent Permeability of Spore Walls and Prothallial Cell Walls in Onoclea sensibilis

The spores of Onoclea sensibilis L. undergo marked changes in their apparent permeability during germination. For example, spores do not stain with an acetocarmine-chloral hydrate mixture until germination has proceeded for about 20 hr (Towill & Ikuma, 1975; Fisher & Miller, 1978), whereas after that time stain is absorbed readily. During the early stages of germination, the spores of Onoclea, Matteuccia struthiopteris (L.) Tod., and other species are difficult to prepare for electron microscopy because embedding resins fail to penetrate adequately (Marengo, 1973; Gantt & Amott, 1976; Raghavan, 1976). Spores in later stages can be processed with no difficulty. This impermeability seems to be associated with the inner spore coat (intine). Fisher and Miller (1978) noted that when the intine of Onoclea spores was artificially ruptured during the early stages of germination and the protoplast was directly exposed to acetocarmine-chloral hydrate, the protoplast stained rapidly, whereas no intact spores could be stained. The time at which Matteuccia and Onoclea spores normally become penetrable by embedding resins coincides with the time the intine ruptures naturally during germination (Gantt & Amott, 1965; Marengo, 1973). If the intine of Onoclea is caused to open by treatment with sodium hypochlorite, even dormant spores and those in early stages of germination may be infiltrated readily with embedding resin (Bassel, Kuehnert & Miller, 1981). Dormant spores of both Onoclea and Matteuccia have a loose outer spore coat and a thick intine, along which there is a longitudinal seam, the raphe (laesura), on the flattened, proximal face of the spore; the spore protoplast is naked within the intine (Gantt & Arnott, 1965; Bassel, Kuehnert & Miller, 1981). Germinating spores synthesize a new wall around the protoplast inside the intine between 8 and 16 hr. At the time the intine ruptures and is cast off, this new wall becomes the bounding wall of the young protonema. Clearly there is a difference in which materials will penetrate the spore intine and which will cross the normal prothallial cell wall. Carpita et al. (1979) published a method for obtaining quantitative information about the apparent capillary pore size of plant cell walls, which limits the passage of solutes. The cells are placed in a solution of a non-ionic solute having a water potential lower than that of the cells, which causes water to leave the cells. If the solute can pass through the wall, and thus the solution can be in contact with the plasma membrane, one observes plasmolysis (retraction of the protoplast from the cell wall). If, however, the solute particles are too large to penetrate the wall, exit of water from the cell causes cytorrhysis (collapse of the cell wall around the protoplast as it shrinks). I applied this technique to spores and young gametophytes of Onoclea and observed differences in the apparent capillary pore sizes of the spore intine, prothallial cell walls, and rhizoid walls.

Stability of cylindrical shells with unreinforced holes

and 8 had no holes. Shells with an internal surface of radius 100 mm were made from sheets of tin plate (E = 9.2 �9 101~ N/m2; an = 2.14" 108 N/m2; a t = 2.6.108 N/m2; crr = 3.16.108 N/m 2) of thickness 5 = 0.54 mm. Flat rectangular b~anks of 320  635 mm, the width of which corresponded to the shell length l = 320 mm, were prepared for the cylinders and the holes were cut. An overlap of 5 mm was allowed for the longitudinal seam, which was made along a generatrix equidistant from the holes. The flexible blank was shaped on a drum to cylindrical form. The longitudinal seam was soldered on a special mandrel with a clamp, the excess solder was removed, and the shell was held with the clamp. The edge of the shell 4 (Fig. 1) was fixed to the base 1, which had two annu= lar grooves. Since the inner diameter of the base and the clamp was the same, self-centering of the shell and the base in assembly was possible. The shell was rolled past the annular grooves onto the base and then the spring circular clips 3 were put in place and secured by the collar 2. At the center of the base a conical depression was drilled, to position the spherical bearing through which the shelI is axially loaded. This method of fixing the shell edges and axially loading the shell ensures a uniform distribution of axial forces over the shell perimeter, as verified by tensometry. The shells were divided into six groups. The zero group consisted of eight shells without holes. Shells in groups t-V had four holes: square with unrounded corners, square with rounded corners, and round. A single group consisted of shells of the same linear dimension but holes of different shapes. Each i-th shell in the various groups had holes of the same shape; for example, all the third shells had round holes. All the shells were prepared in the same conditions on the same equipment. The initial flexure was not measured.

Tests of Fabricated Tubular Columns

Described herein are tests of 10 long fabricated tubular steel columns, of relatively large diameter, with essentially pine-ended conditions. In addition to the behavior, strength, and the manner of failure of the long columns, a number of stub column tests were also made along with the measurements of residual stresses. These residual stresses are both circumferential, due to formation of a flat plate into a cylindrical shape; and longitudinal, resulting from the welding of longitudinal seam needed to complete the fabricated cylinder. Measurement of these stresses is considered essential to any theoretical analysis of column behavior. The maximum strength of the 10 long columns tested (at diameter-to-thickness ratios of 48 and 70 and with a range of slenderness ratio between 39 to 83) is compared with the CRC column curve and good agreement is generally observed.

Surface Transfer Impedance of Cable Shields Having a Longitudinal Seam

The magnitude of noise induced into communication cable from electromagnetic influences is reduced by the shielding properties of the metallic shield. One of these properties is the surface transfer impedance. The surface transfer impedance relates the current induced on one side of a shield to the longitudinal voltage appearing on the other side due to that current. At low frequencies the surface transfer impedance for nonpermeable materials is equal to the dc resistance of the shield. At high frequencies it decreases rapidly. The frequency at which the decrease begins is a function of the thickness and conductivity of the metal. For cylindrical shields having longitudinal seams, the transfer impedance increases at somewhat higher frequencies. The size of the seam opening determines the frequency at which the increase begins. Although the size of the seam opening is difficult to control, experimental results are in relatively good agreement with theoretical calculations.

Surface Transfer Impedance of Cable Shields Having a Longitudinal Seam

The magnitude of noise induced into communication cable from electromagnetic influences is reduced by the shielding properties of the metallic shield. One of these properties is the surface transfer impedance. The surface transfer impedance relates the current induced on one side of a shield to the longitudinal voltage appearing on the other side due to that current. At low frequencies the surface transfer impedance for nonpermeable materials is equal to the dc resistance of the shield. At high frequencies it decreases rapidly. The frequency at which the decrease begins is a function of the thickness and conductivity of the metal. For cylindrical shields having longitudinal seams, the transfer impedance increases at somewhat higher frequencies. The size of the seam opening determines the frequency at which the increase begins. Although the size of the seam opening is difficult to control, experimental results are in relatively good agreement with theoretical calculations.

Automatic welder for longitudinal seams in short tubes and shells

Automatic welder for longitudinal seams in short tubes and shells

Special welding head for automatic welding of longitudinal seams in shells

Special welding head for automatic welding of longitudinal seams in shells