Cap Pass Research Articles

Comparisons of microstructure and mechanical properties of MAG joints welded under 2G and 3G conditions

MAG welding of 07MnMoVR steel was performed at the 2G and 3G positions, and weld formation, microstructure, residual stress, and tensile properties were compared. In this study, welds without defects were obtained at the 2G and 3G positions. The results showed that a larger distortion of the weld at the 3G position was present because of the higher heat input and that the perlage morphology was related to the introduction of the arc weaving process. In addition, the grain size of the filling pass was coarser than that of the cap pass because of the repeated heating process, and the grain sizes of the filling and cap passes increased by approximately 33% for the weld at the 3G position compared with that at the 2G position. In this case, the weld at the 3G position showed a larger residual stress and lower yield and tensile strengths, and the elongation rates and microhardness of the weld at the 3G position were lower than were those of the weld at the 2G position, regardless of the root pass, filling pass, or cap pass.

Combined Gas Tungsten Arc Welding and Shielded Metal Arc Welding Processes for Joining Tube to Tubesheet in Shell and Tube Heat Exchangers

Abstract Flawless tube and tubesheet joints are necessary for shell and tube heat exchanger with high leakproof ability and durability. The consequence of mixing of transfer fluids due to the defective welded or expanded tube-to-tubesheet joint results in complete malfunctioning of the heat exchange process. In this case, there is a high demand for quality assessment of the fabricated tube-to-tubesheet joints (TTS) based on the international standards. Additionally, the literature on assessing the mechanical and metallurgical characteristics of tube-to-tubesheet joints using any one welding technique is available; however, articles dealing with the use of multiple welding techniques are scanty. In the current work, the quality assessment of strength welded and light expanded (3%) tube-to-tubesheet joints followed by light expansion was performed whereas for welding, combined gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) as root pass and cap pass were adopted in the fabrication stage. Quality and sound tube-to-tubesheet joints were produced using welding and tube expansion process. Linear and circular indications representing the cracks were absent on the developer in the liquid penetration test. The minimum leak path (MLP) was greater than the two-third of tube wall thickness. The results strongly qualify the use of combined gas tungsten inert gas and shielded metal arc welding process for manufacturing of tube-to-tubesheet joints. The methodology and results in the current article are beneficial for researchers and industrialists working close to shell and tube heat exchangers and boilers.

Structural integrity and corrosion behavior assessment of the dissimilar gas tungsten arc welded joint of sDSS 2507/ IN625 superalloy

This study investigates the effect of filler materials on the structural integrity of dissimilar welded joints (sDSS 2507/IN625) employed in marine subsea manifold applications. Multi-pass gas tungsten arc welding (GTAW) using ER2594 and ERNiCrMo-3 fillers investigates microstructure evolution, solidification mechanisms, mechanical characteristics, residual stresses, and corrosion behavior. Optical and scanning electron microscopy revealed an unmixed zone (peninsula/island-shaped) at the weld interface and weld zone (WZ) in both filler weldments. Segregation of Mo, Nb, and Ni was observed in the interdendritic region of ERNiCrMo-3 filler WZ, whereas the skeletal ferrite matrix of ER2594 filler WZ revealed the existence of the Laves phase (Fe2Nb form). Electron beam scattered diffraction (EBSD) investigation showed austenitic solidification for ERNiCrMo-3 and fully ferritic solidification for ER2594 with distinct dendrite formations. Inhomogeneity has been observed in microhardness maps, with ER2594 and ERNiCrMo-3 WZ averaging 310 ± 7 Hv0.5 and 270 ± 10 Hv0.5, respectively. ERNiCrMo-3 (165 ± 5 J and 180 ± 3 J) and ER2594 (100 ± 3 J and 110 ± 6 J) fillers exhibited distinct effects on toughness in the weld cap and root due to laves phase precipitation. Additionally, ER2594 (750 ± 6 MPa) and ERNiCrMo-3 (790 ± 7 MPa) fillers exhibited lower tensile strength than base metals. The structural integrity of WZ can be better understood by residual stress analysis, which showed compressive cap pass and tensile root pass residual stresses for both fillers. In a 3.5 wt% NaCl solution, both fillers exhibited outstanding corrosion resistance in marine conditions. These findings improve subsea manifold structure integrity and performance in corrosive marine environments.

Microstructural characterization of the physical simulated and welded heat-affected zone of 9% Ni steel pipe

The microstructure, Vickers microhardness, and prior austenite grain size (PAGS) of the heat-affected zone (HAZ) in a circumferential welded joint of a 9% Ni steel pipe were compared with those of a physically simulated (Gleeble machine) HAZ to validate a developed methodology for evaluating the HAZ via finite element method simulation. The welding of the cap pass was computationally simulated; subsequently, the thermal cycles of the HAZ subzones were reproduced (thermomechanical simulator), and the HAZ (physically simulated and of the welded joint) microstructures were compared. The HAZs in these conditions showed similar microstructures, microhardnesses, and PAGSs, thereby validating the developed methodology. The subcritical (SCHAZ), intercritical (ICHAZ), fine-grain (FGHAZ), and coarse-grain HAZs (CGHAZ) exhibited base metal unaltered microstructure, dual-phase microstructures (martensite and ferrite), refined martensite, and coarse martensite with coalesced bainite, respectively. The physically simulated HAZ was investigated using X-ray diffraction spectroscopy and transmission electron microscopy, and it exhibited globular and thin-film austenite morphologies, with minimum and maximum contents in the CGHAZ and ICHAZ, respectively. The developed computational and physical simulation methodology can be reliably reproduced and can evaluate the HAZ microstructure of the 9% Ni steel welded joint.

Study on the Effect of Heat-Input on the Thickness of the Heat-Affected Zone of the SUS316L Steel Welded Joint by Numerical Simulation

The thickness of the heat-affected zone (HAZ) has a great influence on the strength of the welded joint, so one of the important tasks is to control the HAZ to a small enough level, through using the suitable heat-input (qd). In this study, the authors use SYSWELD software to compute and build a relationship between the heat-input and the thickness of the heat-affected zone in the plate thickness direction to find the right heat-input for researched welding joint. The simulation results show that when welding the root pass with qd > 552 J/mm and the cap pass with 754 J/mm < qd < 1066 J/mm, the thickness of HAZ were increased with a function almost linearly.

Probability of detection of discontinuities by ultrasonic phased array inspection of 9% Ni steel joints welded with alloy 625 as the filler metal

For the first time, the 9% Ni steel is being used in CO2 injection units in floating production storage offloading vessels. Pipe joints welded with nickel-based superalloy 625 as the filler metal present difficulties in ultrasonic inspection owing to the sonic attenuation and deviation caused by the anisotropic and coarse-grained weld metal. This study aims to conduct a probability of detection (POD) to evaluate the discontinuity detection reliability in 9% Ni steel arc welded joints. The inspections were performed using ultrasonic phased array transducers with transversal and longitudinal waves, by using both a conventional wedge formed of Rexolite® and an adapted wedge filled with water to simulate the immersion inspection. POD curves were developed using the hit/miss and â vs a models. The inspection performed with transversal waves detected much fewer discontinuities than that performed with longitudinal waves. Furthermore, inspection performed with longitudinal waves after weld metal cap pass removal exhibited much more reliability in 9% Ni steel welded joints. The obtained POD curves were shown to be a suitable tool to evaluate the inspection of 9% Ni steel welded joints, as they confirmed that the best inspection procedure involves a combination of three different phased array ultrasonic testing configurations.

Determine The Suitable Heat Input Range for Butt Joint Made by Heat Resistance Stainless Steel SUS316L by Using the Numerical Simulation

One of the methods for reducing the production costs to increase competitiveness is to minimize waste products as well as the cost of testing products, and numerical simulation is a useful tool to solve this task. In this study, the authors use SYSWELD software to compute in advance the suitable heat input range to weld specific layers in heat-resistant stainless steel butt welded joints in chemical plants, oil and gas, and energy. The simulation results show that with the butt-welded joint made by SUS316L steel in 8 mm thick and welded by the MIG welding process, the appropriate heat input of the root pass is 506 J/mm ≤ qđl ≤ 650 J/mm and the heat input suitable for cap pass is 754 J/mm ≤ qđl ≤ 1066 J/mm.

Advanced Automatic Welding System for Offshore Pipeline System with Seam Tracking Function

Automatic welding technology is a solution to increase welding productivity and improve welding quality in offshore pipe welding. To increase welding productivity, it is necessary to save time during the assembly/disassembly of the guide track from the welding carriage and pipe to move the next station. The guide track consists of a pneumatic system that does not separate the welding carriage, and two welding carriages operate on a half-pipe joint to increase productivity. These welding carriages automatically operate under the controller command. An automatic welding system consists of a DC motor module, a step motor module, a welding control module, a welding monitoring module, and a central control module. The control systems incorporate control modules and transmit commands to each module for an automatic welding system. In order to minimize the inevitable misalignment between the centerline of the welding seam and the welding torch for each welding pass, a moving average algorithm for seam tracking is proposed, which was proven to be suitable for the root pass, filling pass, and cap pass. Welding experiments were also carried out to verify the validity of the weld seam tracking system.

Shielded metal arc welding of UNS S32750 steel: microstructure, mechanical properties and corrosion behaviour

In the present investigation, ER2594 (conventional) and ER2595 (consisting of additional Cu and W) electrodes were used to produce butt joints of 5.5 mm thick super duplex stainless steel (UNS S32750) sheets using shielded metal arc welding (SMAW) process. During SMAW process, the heat input was 0.81 kJ mm−1 for ER2594 electrode and 0.75 kJ mm−1 for ER2595 electrode. Optical microscope and scanning electron microscope were used to observe the microstructures of different zones, namely, fusion zone (FZ), heat affected zone (HAZ) and base metal (BM). Tensile test, impact test and micro-hardness measurements were carried out for both the weldments on samples cut across the weld. The microstructures of the FZ consisted of inter-granular austenite (IGA), grain boundary austenite (GBA) and Widmanstatten austenite (WA). There was minor change in the width of the HAZ of the weldments with the change in electrode. This is expected to be due to the minor change in the heat input during SMAW process. The weld zone (cap pass) of both the weldments predominantly showed WA and mode of solidification was found to be ferritic (F mode). The tensile strength of both the weldments was approximately same as that of base metal and both the samples fractured through the BM. Cr, Fe and Mo rich precipitates were found in the FZ (weld region), which are expected to be formed due to pick of gaseous content from the atmosphere during welding. The FZ of the weldments produced by ER2595 electrode showed better pitting corrosion resistance than those produced by ER2594 electrode.

Comparative study of evolution of residual stress state by local mechanical tensioning and laser processing of ferritic and austenitic structural steel welds.

Complex thermal stresses generated in welded structures are undesirable but inevitable in fusion welding. The presence of residual stresses can be detrimental to the integrity of a welded joint. In this research, redistribution of residual stress magnitude and profile was studied and compared in two multi-pass welded structural alloys (API X100 and 304L stainless steel) after cold rolling and laser processing. The residual stress field was studied by neutron diffraction using the SALSA strain scanner at their reactor neutron source at ILL, Grenoble. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements may result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements in certain areas. The modification of as-welded residual stress state was done by cold rolling which was followed by laser processing to create a recrystallized microstructure to minimise segregation. The main objective of this study is to understand the suitability of this novel manufacturing technique to create a stress free weldment with recrystallised grain structure. Hardness evolution in the welded structures was scanned following welding, post weld cold rolling and cold rolling followed by laser processing. Hardness distribution in both the structural alloys showed a significant evidence of plastic deformation near the cap pass of the weld metal. Residual stress redistribution was observed up to 4 mm from the capping pass for ferritic steel, while in austenitic steel weld, post weld cold rolling was effective in modifying the residual stress redistribution throughout the entire thickness. Laser processing in both cases reinstated the as-welded residual stress distribution and resulted in softening of the strained area.

An Investigation into Strain Partitioning in Mismatched HSLA-65 Steel Welds

The aim of this study was to quantify strain partitioning in HSLA-65 joints, welded with three types of weld filler: 6011 undermatched weld filler, 7018 matched weld filler, and 9016 overmatched weld filler. Strain measurements were made using a three-dimensional digital image correlation system while specimens were tested on a displacement controlled servo-hydraulic test frame. Crosshead displacement rates ranged from 0.056 mm/s to almost 56 mm/s. Coupons were cut from flux-core arc welded HSLA-65 plates to characterize the base metal, weld filler materials, and mismatched welds. Constitutive material properties could be extracted reliably for all coupons at the lowest displacement rate and showed that, as expected, all weld fillers had similar elastic modulus values but different yield strengths. A comparison of the peak strains at 85 per cent of maximum elongation showed that overall the failure strain was inversely related to the crosshead displacement rate. Analysis of the mismatched coupons found that the failure location was a function of weld filler and was independent of strain rate. Higher magnification imaging of the weld nugget showed that strain partitioning occurred within the weld zone, with slightly lower strains in the cap pass as opposed to the root pass.

A review of the fishery and the investigations of Roughhead Grenadier (Macrourus berglax) in Flemish Cap and Flemish Pass

We review the fishery and biological investigations carried out in the Flemish Cap and Flemish Pass area during the 25 years of NAFO history. In particular, we examine the information available on the biology and population structure of roughhead grenadier recorded in the following 7 research surveys carried out in the Flemish Cap and Flemish Pass area (NAFO Div. 3LMN): Russian bottom trawl research survey (1974–86), Russian longline research survey (1982), Canadian deepwater bottom trawl research survey (1991, 1994 and 1995), European Union longline research survey (1996), European Union Flemish Cap bottom trawl research survey (1988–2004), Canadian autumn bottom trawl research survey (1978–2004) and Spanish 3NO bottom trawl research survey (1995–2004). In addition, biological data collected aboard Spanish commercial fishery vessels were analysed from 1997 to 2004. Indices of biomass from various surveys suggest stability during recent years. Most surveys indicated catch rates as well as average fish size increased with depth. Growth studies by sex demonstrated both sexes grew similarly up to 9–10 years, but the male growth was slower thereafter. Estimates of size and age at 50% maturity and fecundity were very similar for the different data sets studied, showing a late maturity and low fecundity. All the studies examined found that the roughhead grenadier show a very wide feeding spectrum.

Population structure, growth and reproduction of roughhead grenadier on the Flemish Cap and Flemish Pass

Roughhead grenadier Macrourus berglax were collected during the Flemish Cap bottom survey (1991–2001, NAFO division 3M, depth of 200–720 m) and on commercial vessels (1998–2000, NAFO divisions 3L, M and N, depth of 700–1700 m). The abundance of roughhead grenadier, as well as their average size, increased with depth. Age and length composition of the catches showed clear differences between the sexes. The proportion of males in the catch declined in the larger length classes and there were no males in the largest length classes (25 cm). There were differences in the growth trajectories of the two sexes; both sexes grew similarly up to 9 years, but the male growth was slower thereafter. The pre‐anal fin length at first maturity (LPA50) for roughhead grenadier females was 28·5 cm, whilst the age at 50% maturity was 15–16 years. Individual total fecundity varied between 8522 and 61 844 oocytes. Macrourus berglax had a prolonged life cycle and multi‐aged population structure, with differences in growth and mortality between males and females, slow maturation and low fecundity.

Relaxation of Residual Stress in AISI 347 Welded Pipe: A Time-of-Flight Neutron Diffraction Study

Abstract The residual stress state in an AISI 347 welded pipe for nuclear applications has been investigated by means of neutron time-of-flight diffraction. Two kinds of welds were compared: a ‘bare’ manual and a dressed tungsten inert gas (m-TIG with and without last pass heat sink, respectively). Thorough investigations along a line transverse to the weld seam and through-thickness have been carried out with very fine-step scans. Complementary microstructural investigations have been carried out by means of optical microscopy. Results show that the grain size varies from the parent material to the heat affected zone and weld pool. Some martensite is present in the parent material because of the cold working following each welding pass. In the weld pool, the heat flow seems to be redistributed effectively by the cap pass of the LPHSW. Although the microstructural heat affected zone is rather small, the effect of the weld on the stress state seems to extend further (the so-called strain affected zone). In...

The polar cap environment of outflowing O+

Ion composition measurements by Dynamics Explorer 1 often show upward O+ beams at polar latitudes, with streaming energies of 1–20 eV or more. Here we utilize measurements of core (0–50 eV) and “energetic” (∼0–1 keV) ion composition, plasma waves, and auroral images from DE 1 and plasma ions and electrons from DE 2 to examine some of their properties in the context of the polar cap environment. It is found that two distinct populations of O+ beams are observed: “high‐speed” (10–30 eV or higher streaming energies) and “low‐speed” (generally <10‐eV streaming energies). The “high‐speed” polar beams show an “auroral” connection; i.e., they are observed on or near field lines threading auroral arcs seen in DE 1 images. The “low‐speed” streams are on or near field lines threading the dark polar cap and may be convected from the cleft ion fountain. The low‐speed streams are generally much more stable in energy and flux, while the high‐speed streams tend to be bursty. In general, the streams are convecting antisunward, with velocities of 5–14 km/s in the orbital plane. We sought to obtain plasma density estimates from plasma wave measurements, through analysis of features of auroral hiss as well as upper hybrid emissions. Densities in the range 1–5 el/cm³ were indicated for one segment of a DE 1 polar cap pass; however, the measurements generally indicate little auroral hiss or upper hybrid emissions in the polar cap for the other cases considered here. Estimates of electrostatic potential drops above the DE 2 satellite have been made using energy‐angle spectrograms of photoelectron data, under the assumption that the field lines of observation are “effectively” open. Potential drops often are in the 20‐ to 40‐V range. At other times the potential falls below the ∼5‐V instrument threshold, or there are insufficient photoelectron fluxes for estimation. These limited data suggest that the largest potential drops are just poleward of the cleft or near its poleward edge and there is a decline of the drop in the antisunward direction. No obvious correlation between the potential estimates and “nearby” O+ streaming energies is seen.

全姿勢プラズマキーホール溶接法の検討

In this study, a pulsed current plasma arc is applied to the keyhole operating mode to control solidification of the molten pool. Further, the pulse time, peak current, and plasma gas flow rate are especially investigated.A one-pulse/one-keyhole range of pulse times by low frequency is obtained at each of four positions (Flat, Overhead, Vertical-up, and Vertical-down). As a result, suitable pulse times for some combinations of the plasma gas flow rate (Q) and the peak current (Ip) are the peak time (tp)=0.2-0.4 sec and the background time (tb)=0.4-0.6 sec at welding speed (ν) of 120 mm/min in case of stainless steel pipe (JIS SUS304, 4 mm thickness).Then fixed pipes are welded, and it is found that orbital welding is possible by starting from the 4:30 position and by control of the plasma gas flow rate, the peak current, and the welding speed according to the welding position at 6:00 or 7:30, 9:00, and 12:00 (o'clock) positions.And effect of joint alignment error is studied, and it is found that permitted limits with cap pass welding are miss-matching=1.0 mm, root-gas=0.5 mm, arc-length=±1.0 mm, and arc-deviation=1.0 mm in case of mild steel pipe (JIS STPG38, 4 mm thickness).

“Electron conic” signatures observed in the nightside auroral zone and over the polar cap

A preliminary search of the Dynamics Explorer 1 high‐altitude plasma instrument data base has yielded examples of “electron conic” signatures. The three example passes show an association with regions of downward electron acceleration and upward ion beams, but this is not true of all the electron conic events. The electron conic signatures are clearly discernible on energy‐flux‐versus‐time color spectrograms as pairs of discrete vertical bands which are symmetric about a pitch angle of approximately 180°. One of the examples is a polar cap pass with electron conic signatures observed at invariant latitudes from 84° to 75°. The other two cases are nightside auroral zone passes in which the regions of detectable electron conies are spatially more confined, covering only about 1° in invariant latitude. The conic signatures have been found at energies that range from 50 eV < E < 2 keV, with the lowest‐energy examples found in the polar cap. The distribution of the electrons about a pitch angle of 180° is larger than expected for a loss cone feature. If the electrons conserve the first adiabatic invariant in a dipole magnetic field, and in some cases a parallel electric field, the mirroring altitude varies between about 500 km and 8000 km, which is above the atmospheric loss region. For this reason, and in analogy with the formation of ion conics, we suggest that the conic signatures are produced by heating of the electrons perpendicular to the magnetic field.

配管の高速自動溶接に関する研究 Ｉ 溶接施工

Pipeline installation requires the use of a welding method presenting high pipe-laying efficiency and therefore high welding speed.The present report describes the development of welding procedure by the automatic one side downhill welding method using high-current-density GMAW with regard to the girth welding of pipe. In this method, the groove root is made tight and non-gapped, and welding is performed in the narrow gap with little deposit metal, in order to shorten the pipe alignment and welding time. An appropriate procedure for this method was established by developing the downhill welding which uses copper backing on the pipe inside and small diameter solid wire on the pipe outside. When the standard welding conditions are deviated from, the welding arc will touch the copper backing sometimes causing the copper to deposit on the root bead. This deposition of copper on root beads causes not only cracking of beads, but decreasing pipelaying efficiency due to consumption of copper backing. As a result of various researches, this problem was resolved by preparing another groove on the pipe inside in addition to the groove on the pipe outside. The use of the improved shape of groove expanded the zone of appropriate welding conditions for root pass toward the high-speed welding side. The built-up sequence was divided basically into three kinds of passes, the root pass, intermediate pass and cap pass, and each pass was expressed graphically to facilitate the selection of welding conditions for assuring no welding defects and high welding efficiency.This welding method was applied into a welding system with the development in computor control technique and with the development in internal clamp.