Showing papers in "Welding Journal in 1995"

Thermal efficiency of arc welding processes

Abstract: A study was conducted on the arc and melting efficiency of the plasma arc, gas tungsten arc, gas metal arc, and submerged arc welding processes The results of this work are extended to develop a quantitative method for estimating weld metal dilution in a companion paper Arc efficiency was determined as a function of current for each process using A36 steel base metal Melting efficiency was evaluated with variations in arc power and travel speed during deposition of austenitic stainless steel filler metal onto A36 steel substrates The arc efficiency did not vary significantly within a given process over the range of currents investigated The consumable electrode processes exhibited the highest arc efficiency (084), followed by the gas tungsten arc (067) and plasma arc (047) processes Resistive heating of the consumable GMAW electrode was calculated to account for a significant difference in arc efficiency between the gas metal arc and gas tungsten arc processes A semi-empirical relation was developed for the melting efficiency as a function of net arc power and travel speed, which described the experimental data well An interaction was observed between the arc and melting efficiency A low arc efficiency factor limits the power delivered to the substrate which, in turn, limits the maximum travel speed for a given set of conditions High melting efficiency is favored by high arc powers and travel speeds As a result, a low arc efficiency can limit the maximum obtainable melting efficiency

Abrasion resistance of iron-based hardfacing alloys

Abstract: A study was undertaken of numerous iron-based hardfacing compositions as arc weld deposits (SMA, FCA and SA) to evaluate quantitatively their low-stress abrasion resistance as a function of composition and hardness. The method of evaluation is the ASTM G65, Procedure A, dry sand/rubber wheel test, determining weight loss after a fixed number of revolutions of the wheel. A broad spectrum of deposits was prepared from commercial and experimental electrodes. One-, two-, and four-layer cladding permitted examination of dilution effects. The compositions studied included buildup alloys, martensitic deposits, austenitic manganese, primary austenite with austenite-carbide eutectic, near-eutectic austenite-carbide, and primary carbides with austenite-carbide eutectic. Composition and abrasion resistance are determined generally on one, two, and four layers of hardfacing on mild steel. In all, about 200 hardfacing deposits were evaluated. The most important variable in determining low-stress abrasion resistance was found to be carbon content. Above about 4% carbon, numerous primary carbides are obtained and abrasion resistance is greatest. Hardness and chromium content (alloy content) have, at best, secondary effects on abrasion resistance. Dilution has an important effect, often causing an alloy that consists of primary carbides in multiple layers to be primary austenite in the first layer, with resulting inferior abrasion resistance.

Computer simulation of resistance spot welding in aluminum: Part 1

Abstract: A computer-based model of resistance spot welding with hemispherical electrode tips has been developed to include simulation of elastic-plastic mechanical deformation as well as ohmic heating and thermal conduction. The primary effect of the mechanical deformation is in its influence on the contact read and current density developed at the faying surface. The model was used to simulate spot welding in aluminum alloys. Preliminary results show the effects of variations in input current, contact resistance, applied force and position of the cooling water with respect to the electrode tip. It is shown that the value of the contact resistance has a large effect on nugget formation in the spot welding of aluminum alloys and that the applied force has a significant effect arising from its effect on the area of contact at the faying surface. The formation of a resistance spot weld in aluminum is also sensitive to the position of the cooling water-electrode interface because of the high thermal conductivity of aluminum alloys.

Study of metallurgical phenomena in the HAZ of 6061-T6 aluminum welded joints

Abstract: An area of minimum hardness in the HAZ appears to be the location of initial failure regardless of welding variables

Microstructure and properties of ferritic steel welds containing Al and Ti

Abstract: The combined effect of Al and Ti, in the range 5 to 500 ppm, on the microstructure and properties of C-Mn shielded metal arc welds has been studied. It was found that Ti, in contrast to Al, dramatically enhanced the formation of acicular ferrite and improved notch toughness. A strong interactive effect was encountered, with Al at low concentrations tending to diminish the influence of Ti. Unless a critical balance is achieved, with regard to oxygen content, it is concluded that Ti be optimized at 30 to 40 ppm and that Al be kept as low as possible.

The role of failure mode, resistance spot weld and adhesive on the fatigue behavior of weld-bonded aluminium

Abstract: Fatigue behavior of the weld-bonded (combination of welding and adhesive bonding) aluminium joint was investigated as part of a study attempting to replace steel with aluminium in the lightweight vehicle structure. Aluminium 5754-H40 alloy and bis-phenol-A epoxy adhesive were used in specimen fabrication. Test results showed that weld-bonded aluminium has a slightly lower fatigue resistance than the adhesive-bonded aluminium (i.e., the presence of the resistance spot weld decreases the fatigue strength by 11% at 3 × 10 6 cycles) but a much higher fatigue resistance than the aluminium of weld-bonded aluminium occurred by either «nugget-through» where failure originated from the weld nugget, or «adherent-tearing» where failure started from the edge of adherend overlap. Statistical analyses of the test results of weld-bonded aluminium indicated that fatigue strength is not significantly affected by the failure modes

A study on the effect of contact tube-to-workpiece distance on weld pool shape in gas metal arc welding

Abstract: Computer simulations of the three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding have been studied for analyzing the effect of contact tube-to-workpiece distance on the weld pool shape by considering the driving forces for weld pool convection, the electromagnetic force, the buoyancy force and the surface tension force at the weld pool surface, and also the effect of molten electrode droplets In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously The experiments are performed to show the variation of the weld bead geometry due to the change of the contact tube-to-workpiece distance The calculated weld shapes correspond well with those of experiments, and both these resu Its demonstrate that the contact of tube-to-workpiece distance exerts a considerable influence on the formation of the weld pool and the resulting weld shape by affecting the arc length and welding current

Gas metal arc welding fume generation using pulsed current

Abstract: While the fume generation rate of gas metal arc welding (GMAW) is lower than some other arc welding processes, the further reduction of welding fumes is of interest to companies using GMAW. Several researchers have reported lower fume generation rates for pulsed welding current compared to steady current. However, the range of welding parameters where these reduced fume levels can be expected has not been well documented. This paper describes a study of the effects of pulsed welding current on the amount of welding fume and ozone produced during GMAW using a range of welding parameters. Fume generation rates were measured for steady current and pulsed current GMAW of mild steel using copper-coated ER70S-3 welding wire and 95%Ar-5% CO 2 and 85% Ar-15% CO 2 shielding gases. The amount of fume generated during welding was determined by drawing fume through a fiberglass filter using the standard procedures contained in ANSI/AWS F1.2. Results of these measurements show that pulsed welding current can reduce fume generation rates compared to steady current. There is a range of welding voltage that produces the minimum fume generation rate for each wire feed speed with both pulsed and steady current. The data also show that using pulsed current does not guarantee lower fume generation compared to steady current. Welding parameters must be correctly controlled if pulsed current is to be used to reduce fume levels. Fillet welds were made to demonstrate that the pulsed current welding parameters that reduce fume also produce acceptable welds. No significant difference was found in the chemical composition of fumes from pulsed current compared to steady current. Fumes generated by both types of current are mixtures of iron, manganese and silicon oxides. Measurements of ozone generation rates show that the pulsed current welding parameters that reduce fume also increase ozone generation compared to steady current welding

Heat treatment of welded 13%Cr-4%Ni martensitic stainless steels for sour service

Abstract: For many years, the petroleum industry has employed martensitic stainless steels for wellhead and valve applications, and increasing use has been made of 13%Cr-4%Ni alloys. This material type was originally developed as a cast alloy (e.g., ASTM A487/A487M-89a Grade CA6NM). The combination of a low-carbon content and the addition of 3.5 to 4.5% nickel produces a fine, lath martensite structure which, after a tempering heat treatment, can exhibit superior mechanical properties. Thus, CA6NM and its forged variant ASTM A182/A182M-91 F6NM find application for production fluids containing CO{sub 2} and H{sub 2}S environments, particularly when hardening occurs, as is the case with fusion welds. Sensitivity to sulfide SCC increases at high material hardness levels, and the NACE MR0175 standard limits 13%Cr-4%Ni alloys to HRC 23 maximum for sour service. Attainment of such a hardness level requires careful consideration of tempering procedure. In this paper, the roles of welding procedure, material composition and postweld heat treatment are examined in relation to producing the minimum hardness levels in the weld zone.

Precipitation of intermetallic phases in 22% Cr duplex stainless weld metals

Abstract: The effect on corrosion resistance and impact toughness of intermetallic phases, formed in the temperature range of 675--1,000 C (1,247-1,832 F), was studied for 22%Cr 9%Ni 3%Mo 0.15%N-type duplex stainless weld metals. R-phase precipitated rapidly below 800 C (1472 F). [sigma]-phase successively replaced R-phase at 800 C and was the only phase forming at higher temperatures. Minor amounts of [chi]-phase formed at 800 C and continuous, Cr- and Mo-rich, grain boundary films were found after aging at 675 C. The decrease in impact toughness was most rapid around 900 C (1,652 F). Deterioration of corrosion resistance took place most quickly at 700 (1,652 F) and 900 C due to formation of R- and [sigma]-phase, respectively. Corrosion resistance and toughness are affected simultaneously above 800 C; whereas, loss of corrosion resistance precedes embrittlement at lower temperatures. A significant decrease of ferrite content or an increase in hardness indicates a lowered corrosion resistance and embrittlement. However, ferrite content or hardness cannot be used to guarantee unaffected properties. Loss of corrosion resistance or embrittlement of the weld metal will not occur if recommended welding procedures are followed.

Flux cored arc welding : arc signals, processing and metal transfer characterization

Abstract: Metal droplet transfer in flux cored arc welding (FCAW) was studied using electrical arc signals and droplets collected from the welding process. A large number of metal droplets from the FCAW experiments was collected. According to the size distribution of the droplets, several metal transfer modes could be identified amongst which spray transfer predominated. The electrical arc signals, in particular, voltage, were processed using the fast Fourier transform (FFT) technique. Characteristic spectral frequencies corresponding to different metal transfer modes were identified. The size distribution of the collected droplets correlated extremely well with these characteristic frequencies. The electrode melt rate, calculated using the characteristic frequencies identified from the FFT analysis, agreed closely with the measured melt rate. Results from the arc signal analysis and the FFT analysis showed that both arc voltage fluctuations (Δu) and characteristic frequencies of the FFT spectra were adequate to distinguish the different kinds of metal transfer modes in FCAW. Metal transfer mode maps, constructed using the two sets of results, were used to determine the optimal parameters for E71T-1, 1/16-in.-diameter electrode, and Ar-25%CO 2 shielding gas.

The Influence of Oxygen Additions on Argon-Shielded Gas Metal Arc Welding Processes

Abstract: It has been observed experi- mentally that small additions of oxygen to the argon shielding gas affect the gen- eral operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxy- gen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophys- ical transport and thermodynamic prop- erties caused by the oxygen addition. Therefore, it is concluded that the addi- tion of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxides initiates arc- ing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the elec- trode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.

Laser beam welding and formability of tailored banks

Abstract: Laser beam welding of sheet steel for tailored blanks is increasingly being used in the automotive industry as high-quality laser welded blanks can be produced having good formability and corrosion resistance. As part of an experimental formability analysis, complete penetration welds in square-butt joints were produced at different laser power levels and multiple travel speeds on a drawing-quality special-killed steel sheet having different sulfur contents. In the unwelded condition, no differences in formability were observed between the two steels. However, for a given heat input, differences in formability were observed between the welded steel blanks because of a reduction in the weld fusion zone ductility due to the presence of sulfide inclusions. It was also found that the weld, heat-affected zone and base metal composite yield strength, as measured on tension specimens with the weld in the middle and parallel to the loading axis, decreased with increasing travel speed. Since travel speeds at a given power directly affected the weld mechanical properties and weld geometry, the results showed that work hardening efficiency was enhanced with welding speed. It was concluded that both impurity level in the steel and the weld geometry are important factors governing the formability of laser-welded blanks.

Building tomorrow`s automobiles

Abstract: Detroit is awhirl these days with speculation about the next generation of automobile. Pressures are clamping down on the industry to produce cars that are free from emissions, much more fuel efficient, and, through it all, salable. Right now, a great deal of attention is being paid to the body-in-white or that part of the automobile represented by the frame and the body parts. Will it be high-strength steel, aluminum, plastic, composite, or a combination of different materials? Will resistance spot welding and gas metal arc welding still be used? What role will the laser play in all of this activity? Can welding expect severe competition from other joining processes, like adhesive bonding and riveting? The best answers to the above questions are yes, maybe, and no. Whatever happens, it seems the jury is still out. Nevertheless, the verdicts will be critical to the welding industry because the automotive industry is the largest single market for welding. Competitively, welding technology has its hands full. A number of Fortune 500 companies are developing improved adhesives. There is also a quasi-riveting process popular in Europe that is being introduced here in the States. And there is a rivet bonding version of thatmore » process. Also, weld bonding or the technique of making resistance spot welds through adhesives is gaining ground among the designers of the next generation of automobile. Over the years, the number one market for arc welding and resistance welding has been the automotive industry. Changes in the designs of automobiles have required adjustments on the part of welding technologies, but there has not been anything unusual in that respect. For the most part, the requirements have been met.« less

Power characteristics in GMAW: experimental and numerical investigation

Abstract: The voltage and power distributions in gas metal arc welding (GMAW) were studied both experimentally and numerically. The principal voltage drop takes place in the arc, which also constitutes the dominant power contribution. Within the arc, the dominating voltage contributions are from the arc column and the cathode fall, while the anode fall and the electrode regions are less significant. The power input to the arc column increases with both increasing current and increasing arc length. These results indicate that it is critical to control the arc length in order to control the power input to the system.

Effect of hydrogen in an argon GTAW shielding gas: Arc characteristics and bead morphology

Abstract: The influence of hydrogen additions to an argon shielding gas on the heat input and weld bead morphology was investigated using the gas tungsten arc welding process. Variations in weld bead size and shape with hydrogen additions were related to changes in the ability of the arc to generate heat and not to generate perturbations in the weld pool caused by Marangoni fluid flow

Particle-reinforced metal matrix composite as a weld deposit

Abstract: Weld metal consisting of particulate-reinforced metal matrix composite structure was produced with ceramic or refractory metal powder filled cored wire. Results are presented for both gas tungsten arc and gas metal arc weldments on Type 304 stainless steel. The effect of powder particle density and size distribution on the dispersion of particulates in the weld deposit was investigated. The motion and final distribution of particulates in the weld pool were evaluated with a fluid mechanics-based model, and critical welding criteria for the production of uniform particle distributions were identified. With particulates of optimum size and density in powder-filled cored wire it was possible to produce arc welding particulate-reinforced metal matrix weld deposits having uniform spatial particle distributions.

Effects of welding parameters on weld zone toughness and hardness in 690 MPa steel

Abstract: Specifications for the welding of high-strength steels are generally intended to control hydrogen cracking and provide adequate weld zone toughness for resistance to fatigue cracking and shock loading. The specifications should also allow welding to be undertaken safely and profitably. The work described here was designed to identify the optimum match of welding parameters, notably preheat, interpass temperature and heat input, for the welding of a 690 MPa (100 ksi) microalloy quench and tempered steel. The paper covers investigations into two aspects of weldability: toughness and hardness. The first part involved shielded metal arc (SMA) butt joint welding of carefully designed plates at a range of preheat and interpass temperatures and heat input values, to identify welding procedures that give maximum HAZ and weld metal toughness. The second is a laboratory study of bead-on-plate submerged arc welds to clearly identify the relationship between hardness and welding parameters. The test procedure for the first investigation involved SMA welding at preheat and interpass (P and I) temperatures from -20°C to 220°C (-4° to 428°F) using heat input values of (approximately) 1.3, 2.9 and 4 kJ/mm (33, 74 and 102 KJ/in.) Charpy V-notch energy and fracture appearance transition curves were then generated with the Charpy notches being carefully located to give the lowest toughness values. Results showed that the minimum preheat and interpass temperature for control of weld metal hydrogen cracking was 60°C (140°F) and that low values of toughness in both weld and heat-affected zone consistently occurred in the weld root region. Low preheat techniques and one-sided welding should therefore be avoided for critical applications. For weld metal, greatest toughness occurred at high preheat and interpass temperatures (160°C; 320°F) combined with low welding heat input (1.2 kJ/mm; 30 KJ/in). For high heat input welding, preheat and interpass temperature had little influence on toughness over the range of temperatures examined. For heat-affected zone regions, levels of toughness obtained when using the high preheat/low heat input and low preheat/high heat input techniques were similar. It was found, however, that careful control of preheat and interpass temperature was essential, for each heat input value, because toughness can drop off rapidly on either side of the optimum interpass temperature. For some applications, optimum preheat and interpass temperatures were found to lie between 60° and 90°C (140° and 194°F). In the second study, a series of bead-on-plate submerged arc welds was deposited using a wide range of preheat and interpass temperatures, voltages, currents and travel speeds. In each case, the welding parameters were chosen so that the welding power input (V x I) could be held constant while varying heat input, or vice versa. For each weld, hardness readings were taken in both the weld deposit and HAZ at approximately 1 mm (0.04 in.) from the weld interface. It was found that: 1) HAZ hardness readings (390-430 HV 30 for heat input values up to 2 kJ/mm) were consistently higher than weld metal hardness readings. 2) Heat input has a marginal effect on HAZ hardness up to about 2 kJ/mm (51 kJ/in.), however, above 2 kJ/mm the hardness drops off at a rate of approximately HV 30 for each increase of 1 kJ/mm (25 kJ/in.). 3) Weld metal hardness dropped continuously over the range of 0.5 to 4.5 kJ/mm (13 to 114 kJ/in.). 4) Both HAZ and weld metal hardness drops approximately 1 HV 30 for every 4°C (7.2°F) increase in preheat and interpass temperature. The results of this work have been used to develop an optimized weld design for butt joint welding of 35-50 mm (1.4-2 in.) plate. This uses high heat input for all but the weld capping passes, where high interpass temperatures and low heat input techniques are employed.

A comparison of pulsed and conventional welding with basic flux cored and metal cored welding wires

Abstract: The results of a comparison between the use of a programmable pulsed power supply and a conventional (constant voltage) power supply with both basic flux cored and metal cored welding wires are described. Investigations were made of welding behavior and bead characteristics for both horizontal and uphill fillet welds for each combination of wire and power supply. In addition, all-weld-metal tensile and low-temperature impact properties, as well as weld composition and metallographic features are reported for each wire and power supply combination. The results for the basic flux cored wires indicate that the use of pulsed welding allows a major extension to the usable range of welding currents and some positional welding capability, without significant changes to deposition rates, weld metal mechanical properties, composition or microstructure. With metal cored wires, the use of pulsed welding not only resulted in a major extension to the range of usable welding currents and improved positional welding capability, but also in improved weld metal mechanical properties.

Welding and joining: moving from art to science

Abstract: The field of welding and joining has progressed markedly during the 76 years since the American Welding Society was formed, but the rate of progress must increase if one is to keep pace with the rapidly advancing technology. This can be done if the approach emphasizes simple, quantitative explorations that contain the essential physics of the process. Unfortunately, too much effort is often spent on refining existing analyses with even more sophisticated mathematics. While this does demonstrate mathematical proficiency, it does not advance the field of welding and joining very far. It is necessary to step back and critically question what is known and why it is known. Only by quantifying the hypotheses and by testing them experimentally can one hope to progress as rapidly as one must.

Optimized postweld heat treatment procedures for 17-4 PH stainless steels

Abstract: The postweld heat treatment (PWHT) procedures for 1 7-4 PH stainless steel weldments of matching chemistry was optimized vis-a-vis its microstructure prior to welding based on microstructural studies and room-temperature mechanical properties. The 17-4 PH stainless steel was welded in two different prior microstructural conditions (condition A and condition H 1150) and then postweld heat treated to condition H900 or condition H1150, using different heat treatment procedures. Microstructural investigations and roomtemperature tensile properties were determined to study the combined effects of prior microstructural and PWHT procedures.

Surface temperature distribution of GTA weld pools on thin-plate 304 stainless steel

Abstract: A transient multidimensional computational model was utilized to study gas tungsten arc (GTA) welding of thin-plate 304 stainless steel (SS). The model eliminates several of the earlier restrictive assumptions including temperature-independent thermal-physical properties. Consequently, all important thermal-physical properties were considered as temperature dependent throughout the range of temperatures experienced by the weld metal. The computational model was used to predict surface temperature distribution of the GTA weld pools in 1.5-mm-thick AISI 304 SS. The welding parameters were chosen so as to correspond with an earlier experimental study that produced high-resolution surface temperature maps. One of the motivations of the present study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate excellent agreement, thereby verifying the model.

Contact tube wear detection in gas metal arc welding

Abstract: A real-time algorithm has been developed to detect contact tube wear during gas metal arc welding. The integral from 0.3 to 4 Hz of the power spectral density of voltage (constant current and pulsed current power sources) or current (constant voltage power sources) is called the wear parameter and is used to measure wear. The contact tube is predicted to be worn when the parameter grows nonlinearly or exceeds a threshold. For 11 contact tubes worn by welding on a rotating pipe, the wear parameter predicted the observed increase in the area of the contact tube`s exit bore of 140% of the original area within a standard deviation of 20%. Welds were made with a constant voltage power source and with a pulsed current power source at two different voltages. The pulsed current welds were made with and without automatic voltage control by wire feed speed and with and without weaving in a V-groove. No significant differences were detected between the wear parameters for all test welds, indicating that the algorithm can be used under these welding conditions.

An evaluation of CO2 laser beam welding on a Ti3Al-Nb alloy

Abstract: The CO 2 laser beam weldability of Ti-14.3.wt-%-Al-21 wt-% Nb, a Ti 3 Al-Nb (alpha 2 aluminide) alloy, was investigated. A sequence of pulsed and continuous wave (CW) CO 2 laser beam welds was made on 1.7 mm (0.067-in.) thick coupons of Ti-1421. The weld cross-sections were subjected to microhardness evaluation and characterized by optical metallography. The hardness values were plotted with respect to calculated cooling rates to reveal possible trends in microhardness. Laser welds were produced without cracks, porosity or other discontinuities. Laser welding with calculated cooling rates between 195° and 10, 400°C/s produced relatively constant microhardness values. These values ranged between 373 and 432 DPH for the heat-affected zone (HAZ), and between 364 and 416 for the fusion zone (FZ). These results are in contrast to Mascorella's results for gas tungsten arc welding, which showed microhardness values have an increasing trend with increased cooling rate (from 297 to 488 HAZ and from 292 to 459 FZ for coolings rates from 2 to 50°C/s). Bend ductility values within the unaffected base metal (UBM) range were obtained in full penetration longitudinal bend specimens for laser welds with calculated cooling rates above 3400°C/s. For cooling rates of 1380°C/s and lower ductilities were well below the UBM range. The slower cooled welds exhibited a larger flat cleavage fracture area and lower ductility than the rapidly cooled welds. The results of this investigation show that careful selection of CO 2 laser welding conditions will result in cooling rates that will yield more ductile HAZs and FZs when compared to gas tungsten arc welding (GTAW)

Welding stainless and 9% nickel steel cryogenic vessels

Abstract: Gases are often more efficiently stored and shipped as liquids at cryogenic temperatures. Pure gases commonly stored below liquefaction temperatures include oxygen {minus}297 F ({minus}183 C), argon {minus}302 f ({minus}186 C), nitrogen {minus}320 F ({minus}196 C), hydrogen {minus}423 F ({minus}253 C) and helium {minus}452 F ({minus}269 C). Natural gas is also transported and frequently stored as liquefied natural gas (LNG) at temperatures below {minus}261 F ({minus}163 C). Storage tanks for the pure gases are generally shop fabricated in sizes that can be shipped by conventional carriers. Smaller LNG vessels for over-the-road and railroad fuel applications are also shop-fabricated. Shown in a figure is a rail-mounted tank designed to supply liquefied natural gas to locomotives. Another example of a tank installation is also shown. LNG terminal storage tanks are generally field-erected vessels fabricated from 9% nickel steel in sizes of 50,000 to 100,000 m{sup 3} (315,000 to 630,000 bbls). This article focuses on welding practices for shop-fabricated vessels and equipment.