A ferritic filler submerged arc welding (SAW) process has been developed and applied to the manufacture of UOE pipes.
In order to achieve sufficient cryogenic toughness of ferritic weld metal, the welding wire and flux compositions are recommended to be designed so that the oxygen and silicon contents in the weld metal become approximately 250ppm and 0.25%, respectively. To prevent cold cracking, it is suggested that the difusible hydrogen content should be less than approximately 3.5cc/100g of the weld metal. The combination of a fused type flux (CaF₂-Al₂O₃-SiO₂ system) with a ferritic welding wire of low Si-12%Ni was found adequate for satisfying the above two conditions.
Next, rapid quenching and tempering conditions to maximize both the cryogenic toughness of the weld metal and the productivity of UOE pipes were determined. A unique quenching thermal pattern having a holding period at 600°C before quenching from 790°C was found crucial to satisfy the above requirements. The subsequent tempering was carried out by raising the temperature continuously to 600°C, and then immediately water cooled. Under this thermal pattern, a heating time as short as 6min is required to reach the target temperature of quenching and tempering, and to yield a toughness o f as high as 10kgf-m. This rapid heat treatment technique enables the use of a high frequency induction heating system on the production line of UOE pipes. The satisfactory toughness is believed to be a result of the austenitic grains being refined and the carbide precipitation being accelerated by holding the welds at 600°C.
The UOE pipes manufactured by the ferritic filler SAW process have satisfactory tensile properties as well. The strength of the ferritic weld matches that of the 9% Ni steel plate, so that the expanding strain applied to the pipe wall for improving its dimensional accuracy does not concentrate in the weld metal as it does in the case of an austenitic weld.

抄録全体を表示

To reduce P_CM value for prevention of cold cracking in girth welding and for sour environment service, low carbon steel is required. Strengthening of low carbon steel necessitates microstructural change from ferrite-pearlite to low temperature transformation products. Microalloying technique and dynamic accelerated cooling process after controlled rolling were applicable to develop low P_CM high grade line pipe steel. Lowering nitrogen content is very preferable to make boron effective.
From the metallurgical studies of microalloying, low G-Nb-Ti-B steel was developed.
The HAZ toughness was improved by adding small amount of titanium. The risk of hot cracking was decreased by lowering carbon content. The hardenability of new type steel was considered by the effective boron contents. The P*_CM formula was newly developed. The strength can be obtained with extremely low P_CM level in boron treated new type steels, resulting low hardness in the HAZ.

抄録全体を表示

The method for improving the weld metal toughness and new welding process for high speed welding have been investigated.
The formation of acicular ferrite microstructure is essential for high weld metal toughness, for which Ti-B bearing low oxygen weld metal is needed.
Highly basic fused flux has been developed, which could maintain low oxygen content in spite of increasing the welding speed.
To increase the welding speed, use of DC power supply for first arc is effective. Based on the knowledge for three-wire welding process, DC AC-AC-AC powered four-wire submerged arc welding process has been developed and applied for line pipe production, which contributed to high productivity and high quality.

抄録全体を表示

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%.

抄録全体を表示

A new welding process has been introduced in the manufacture of large-diameter UOE pipes at the Kimitsu Works, Nippon Steel Corp. The new process includes the following methods which have been developed on the basis of fundamental research.
(1) Observation of molten pools by X-rays was made during welding to find effective means for the prevention of undercuts. Multiple electrode welding is successfully applied to prevent the undercuts because of its dispersion of the arc in the direction of welding line.
(2) Four wire welding has been adopted in place of three wire welding to increase the welding speed without loss of the toughness.
(3) Metal inert gas welding can be combined with submerged arc welding to manufacture the line pipes for low temperature service.
(4) A flux cored tubular wire with melt-type flux is used for large heat-input welding.

抄録全体を表示

Spurred by the growing demand for heavy wall UOE pipes with excellent toughness, recent progress by the 4-wire submerged arc welding (SAW) method is reported from the aspects of productivity and weld quality. The 4-wire SAW method is found to bring about 10-30% improvement in productivity and to result in a remarkable suppression of slag inclusion under optimized welding conditions, for example, in current pha se and current ratio. It is also confirmed that the speedup by the 4-wire SAW method does not deteriorate weld quality.
Special attentions are paid on the weld quality of heavy wall pipes to meet the recent market situation. This was because there are two problems, i.e., the formation of coarse microstructures of low toughness owing to slow cooling rate and the deterioration of external bead appearance. To cope with them, firstly, the control of nitrogen, oxygen and boron contents in weld metal must be conducted. The optimum ratio between nitrogen and boron contents for excellent toughness is found to be B=0.7•[N]±15 (ppm) for [N]≤80ppm. Secondly, a fused type flux is developed, which has excellent performances in both lowering oxygen content in weld metal to 250-300ppm and suppressing the deterioration of bead appearance. Charpy V-notch Energy more than 100J at -60°C has, then been achieved based on above studies.

抄録全体を表示

Undercut restricts the upper limit of welding speed in submerged arc welding (SAW). The mechanism of formation of undercut has been, however, incompletely known because of the difficulty in process observation. Accordingly, in the present study, a direct observation of the process by X-ray and simulations of the weld puddle phenomena by a heat conduction model and an arc pressure measurement were undertaken. This study aimed to understand the dominant controlling factors of undercut and to develop a new technique for high speed welding.
A quantitative investigation of the process of undercut which restricts the upper limit of welding speed in submerged arc welding was undertaken in an attempt to gain a clear understanding of the dominant factors of this defect and to develop a high speed welding technique.
Two variables mainly affect the occurrence of undercut. One is the displacement of molten metal (X_m) and the other is the solidification point along a weld puddle toe (X_s). When the molten metal is displaced more than the solidification point (X_m>X_s ), undercut occurs.
As a result of these effects, the linearization of an arc heat source by a group of fine electrodes allows a much higher critical travel speed than the conventional arc heat source.

抄録全体を表示

High quality large diameter welded pipes have been developed by UOE process followed by induction heat treatment such as quenching and tempering, stress relieving, or solution annealing. This paper describes about the manufacturing process, selections of welding consumables, and mechanical properties of products such as heavy wall and high strength steel pipes, low alloy steel pipes (3.5% Ni and 21/4Cr-1Mo) and Type 304L stainless pipe.
The advantages of heat treatment after welding are summarized as follows;
1) Enlargement of manufacturable range for wall thickness and grade of strength (QT), and
2) Improvement of properties of seam welds as well as pipe body (QT, SR, ST).

抄録全体を表示

Trial induction hot bends as well as laboratory tests were carried out in order to develop the heavy wall bent pipe with high strength (API-5LX60 to 70) and high toughness.
The Mo-V, Nb-V, Cr-Mo and high Nb line pipe steels with the carbon equivalent range of 0.35 to 0.43% were selected in this experiment. The thermal history of actual bending was simulated in the laboratory test. According to test results in laboratory, the tempering following the bending process was necessary to maintain the high yield strength and high toughness at low temperatures. Low temperature toughness of weld metal after bending and tempering was improved greatly by decreasing oxygen levels less than 350ppm, while the carbon equivalent of weld metal is also important. Trial bends were performed with UO pipe of 28-30inch in OD, 1.250-1.375inch in WT. The strength of X60-X70 and high toughness at -30 °C (-22°F) were obtained in the Nb-V and Cr-Mo line pipe steels.

抄録全体を表示

The properties of heat-treated weld metal of X-52 to X-70 class steel pipes are studied. To satisfy the requirement that vE_-46°C>50ft-lb, oxygen content of weld metal must be kept at 180ppm or under. Even when nitrogen content is high, high toughness can be obtained by the addition of aluminum. The high toughness obtained in the weld metal of low oxygen content and high aluminum content seems to be due to the precipitation of aluminum nitride that suppresses the coasening of austenite grains. The oxygen content of weld metal is governed by the basicity of flux and CaF₂, K₂O and CO₂ ratios in flux, and is determined by the following equation;
[O]=g(B+f(R_CaF2)•N_CaF2)+h(R_K2O)+k(R_CO2).
An increase in basicity of fused flux aimed at a decrease in oxygen content causes an increase in diffusive hydrogen and nitrogen contents of the weld metal. Hydrogen and nitrogen contents can be decreased by the addition of carbonate minerals, control of flux grain size distribution and increased addition of calcium fluoride. The quantity of hydrogen can be also decreased effectively by, an air-cooling treatment of molten flux and preventing the crystallization of hydrotropic minerals.

抄録全体を表示

The studies were carried out to increase welding speed in the spiral pipe mill. The problems which prevent the increase of the welding speed are the occurrence of undercut, concave bead, convex bead.
Investigations were carried out to solve these problems. Main results obtained are as follows;
(1) The optimum welding conditions for the high speed welding were found.
(2) The good bead appearance could be obtained by the use of the new flux bearing optimum amount of titanium dioxide.

抄録全体を表示

Spiral pipe mill in which submerged arc welding is made immediately after pipe forming limits the productivity by the welding speed. The higher welding speed is restrained by occurrence of inner bead defects such as undercutting and concave shape.
The high speed spiral welding techniques including development of new flux and determination of proper welding parameters were established by laboratory simulation tests.
By applying these techniques to actual spiral pipe mill, it became possible to obtain 4m/min in welding speed.

抄録全体を表示

A new welding process which combines ERW and SAW has been developed to improve the productivity and product quality of spiral pipe manufacturing lines. The features of this process are as follows.
(1) Construction of a compact and highly efficient spiral pipe mill is made possible by the combination of ERW and SAW in one welding line.
(2) Lap type ERW is applied in which the pipe-side edge and the strip-side edge approach each other in the vertical direction.
(3) High-speed cosmetic SAW is applied with the use of multiple twin wire system to cover the weld from both inside and outside after ERW.
The features of the cosmetic SAW are low heat input, high-efficiency deposit and high oblate ratio of heat source shape to prevent formation of undercuts.
(4) The welding speed of the new ERW-SAW process is 5-6m/min, compared with the 3m/min maximum of the conventional process, and the joint performance is equal to or higher than that by the conventional SAW process.

抄録全体を表示

It was found that monitoring the variation in oscillator frequency of welding current enables to detect the optimum welding state that produces the fewest weld defect. Applying this finding, new automatic power input control system was developed.
This new system establishes and maintains the optimum welding state rapidly by the feed-forward system and precisely by the feed-back system. Besides the power input, other welding conditions were also optimized. Synthesizing these techniques, it has been possible to produce ERW pipes without weld defect.

抄録全体を表示

In order to manufacture a fairly heavy walled pipe, the distribution of the electric current in the strip edge of Vee apex zone was analyzed by comparing the measured and calculated electric circuit constants in Vee apex zone.
From the result of the analysis it can be concluded that the current in strip edges has a tendency to flow uniformly as the strip thickness increases and, also, that the overheat at the corner of strip edges can be reduced to an allowable level by employing a small apex angle and mild welding condition.
In addition, it is found that the large amount of upset is needed to obtain a sound quality of welding. So, the proper welding conditions of heavy wall are selected to be as follows, mild welding condition, i.e., slow welding speed, small apex angle and large amount of upset. A fairly heavy walled ERW pipe with large outside diameter of 24inchφ×19.05^t are manufactured by applying the proper conditions. The toughness of the weld part is proved to have excellent toughness.

抄録全体を表示

The quality of chromium, chromium-molybdenum and austenitic stainless steel tubes manufactured by an electric resistance welding (ERW) is highly dependent on the sophisticated technologies of non-oxidizing welding, precise control of welding energy and smooth cutting of inside flush. In this report a newly developed manufacturing technology for ERW alloy steel tubes is described on the following items; oxygen content in the welding atmosphere for a non-oxidizing welding and its control equipment, appropriate welding energy and its control system and a high performance impeder.
Furthermore, the quality of the mass-produced ERW alloy steel tubes by the new technology is investigated focusing on their corrosion resistance, high temperature creep rupture strength and fatigue strength.

抄録全体を表示

Basic characteristics of electric resistance welding (ERW) were studied by using a Bead Shape meter and a temperature distribution measuring system with a silicon photodiode array in order to establish the controlling technique of ERW. Based on the information from these studies, the integrated heat control system, which is composed of on-line bead shape monitoring system and the automatic temperature distribution control system, has been developed. These systems were installed in small, medium and large diameter pipe mills.
These systems are proved to be very effective to produce high quality tubes and pipes.

抄録全体を表示

Thin wall welded titanium tubes require high quality and reliability, because they are used as an important element in power plant condensers or desalination plants. Direct current (DC) TIG welding power source was conventionally used for titanium tube making but the products did not satisfactorily meet the severe quality requirements. The investigation on application of high frequency pulsed current power source to titanium tube making was made and its results were successfully used in a mill production process. The main features of the high frequency pulsed arc welding confirmed in the application tests were as follows:
(1) High quality weld bead with superior surface smoothness was obtained.
(2) Tube making speed was improved because welding arc stability was maintained even at the speeds over 10m/min.

抄録全体を表示

5kW CO₂ laser welders for sheet steel production process have been installed on production floor. The welders combine high accuracy cutting technology, high accuracy machine assembly, accurate grinding techniques, and filler wire supply welding technology.
Laser welding applied to electrical and high carbon steels has improved the process efficiency of pickling and rolling.

抄録全体を表示