Fully automatic welding of large-diameter, thick-walled (greater than 21mm) pipelines often uses U-shaped grooves or compound grooves. Because the processing of type 1 grooves and compound grooves is time-consuming and labor-intensive, the efficiency of pipeline welding is restricted. The processing of V-shaped grooves is simple, saving time and effort. However, when welding V-shaped grooves of large-diameter, thick-walled pipelines automatically, improper selection of joint process parameters will lead to welding defects.
As the strength grade of steel pipes used in pipeline construction has increased to X70 and X80 levels, and the pipe diameter and wall thickness have increased, automatic welding technology has gradually begun to be applied in pipeline construction since 2003. Automatic pipeline welding technology has great potential in the application of large-diameter, thick-walled pipeline construction due to its advantages of high welding efficiency, low labor intensity, and the welding process is less affected by human factors.
However, my country’s automatic pipeline welding technology is in the development stage, and some problems in jointing, such as unfused roots, unfused side walls, and complex grooves, have not yet been completely solved: Type 1 slopes are often used for automatic welding of large-diameter and thick-walled pipelines. Supporting facilities such as pipe or composite grooves and pipe end groove shaping machines are not yet mature, so it is very meaningful to study automatic welding technology for large-diameter, thick-walled pipes.-shaped grooves.
The total length of the Zhongwei-Jingbian connection line of the Second West-East Gas Pipeline is about 345km. The steel pipe strength grade Qing Construction Engineering Corporation introduced a CRC fully automatic welding machine, which was used on the 21.0m wall thickness pipe in the 1B section of the tie line.
Welding methods, equipment, materials
The welding method uses STT root welding + CRC-F260 automatic welding machine for hot welding, filling, and covering. Welding equipment: Lincoln STT welding machine, Lincoln DC-400, CRC-F260 automatic welding machine. Shielding gas: STT root welding shielding gas 100%C02, fully automatic welding shielding gas 80% Ar + 20%C02.
Composite grooves or profile grooves are commonly used in automatic welding, and profile grooves can also be used in pipelines with small wall thicknesses. Their common feature is that the gap in the groove is small. The wall thickness of the pipeline of the Second West-East Gas Pipeline is 21.0mm, and the upper width of the Y-shaped groove is about 22m. This width is close to the swing limit of the CRC-P260 welding gun. This type of groove is a huge challenge for automatic welding. The welding process parameters of the automatic welding test were determined based on experience.
The above parameters were used to conduct automatic welding tests. During the test welding, it was found that automatic welds are prone to defects such as lack of fusion between layers, lack of side wall fusion, dense pores, and excess height in the overhead welding part.
During the test welding process, when the current was 210-235A, the voltage was 21-23V, the wire feeding speed was 420^480in/min, and the welding speed was 1215in/min, it was found that almost no layer appeared on the F1, F2, and F3 welds. There is no fusion between spaces, no fusion at grooves, and dense pores. The analysis shows that the groove width of F1, F2, F3, and three welds is small and the gas protection is sufficient, so no nitrogen holes will be generated; the small groove width makes the welding gun swing small and the swing frequency high. Under the condition of a certain wire feeding speed, the mother material and filler metal are fully fused, so the probability of confusion is small; the weld reinforcement in the overhead welding part is not large. When the current is 200-250A, the voltage is 18-22V, the wire feeding speed is 400500in/min, and the welding speed is 1216in/min, during the test welding, it was found that the vertical welding positions of F4, F5, and F6 had interlayer infusion and grooves. It is not fused, but there are still no pores, and there is not much reinforcement in the overhead welding part. The welding seam without interlayer fusion and groove fusion occurs when the welding current is less than 220A, the voltage is 21V, the wire feed speed is less than 450 in/min, the welding speed is greater than 15in/min, and the welding gun swing frequency is less than 90 times/mino to increase the wire feed. Speed, current, and voltage (adjust the extension length of the welding wire), increase the swing amplitude of the welding gun try to select a faster swing frequency of the welding gun, and control the welding speed of the vertical welding part. After the F4, F5, and F6 inspections, no lack of fusion between the layers was found. The groove is not fused. When the current is 220-250A, the voltage is 20-22V, the wire feeding speed is 450500in/min, and the welding speed is 1416in/min, the cover weld is not found to be unfused, but the excess height of the cover weld in the overhead welding position exceeds the standard. Analysis shows that the width of the cover weld is about 18^22mm, which is close to the maximum swing range of the CRC-P260 welding gun. The wide weld seam, the large swing amplitude of the welding gun, and the fast swing frequency make the molten pool exist for a long time and the molten pool will be exposed when the gun is moving. The pool has a stirring effect, and the deposited metal in the overhead welding position will sag under the action of gravity, electromagnetic force, etc., which will lead to the weld reinforcement in the overhead welding position exceeding the standard.
To ensure a good cover forming effect, the cover welding should select a smaller welding speed and reduce the welding gun swing frequency as much as possible to make the cover weld thin and wide, thereby reducing the molten pool existence time and achieving a reduction of The purpose of raising the position of Yu Gao. Based on the test welding results and analysis, the STT root welding + CRC fully automatic filling and capping process parameters of the tie line of the Second West-East Gas Pipeline were finally determined. Weld according to the welding parameters in Table 3. The weld has been inspected and found to have no defects such as pores, cracks, and lack of fusion. The surface of the weld is in good shape and the macroscopic metallography is good. The mechanical properties of the welds have been tested by the Welding Technology Center of the China Petroleum and Natural Gas Pipeline Research Institute, and all indicators meet the construction requirements for the tie-line connection of the Second West-East Gas Pipeline Pipeline. The successful application of STT root welding + CRC-P260 automatic welding on large-diameter, thick-walled (V-groove) pipes fully reflects the characteristics of the high-quality, efficient, and low labor intensity of automatic welding technology.
The above parameters were used for automatic welding tests. During the test welding, it was found that automatic welds are prone to defects such as lack of fusion between layers, lack of side wall fusion, dense pores, and excess height in the overhead welding part.
During the test welding process, when the current was 210~235A, the voltage was 21~23V, the wire feeding speed was 420^480in/min, and the welding speed was 12215in/mir, it was found that there was almost no welding on the F1, F2, and F3 welds. There is no fusion between layers, no fusion of grooves and dense pores. The analysis shows that the groove width of F1, F2, F3, and three welds is small and the gas protection is sufficient, so no nitrogen holes will be generated; the small groove width makes the welding gun swing small and the swing frequency high. Under the condition of a certain wire feeding speed, the mother material and filler metal are fully fused, so the probability of confusion is small; the weld reinforcement in the overhead welding part is not large. When the current is 200-250A, the voltage is 18-22V, the wire feeding speed is 400-500in/min, and the welding speed is 12~16in/min, during the test welding, it was found that the vertical welding positions of F4, F5, and F6 showed interlayer infusion and The groove is not fused, but there are still no pores
Post time: Jan-18-2024