A narrow gap full position TIG automatic welding process

Abstract

The present application belongs to welding process, and particularly relates to a narrow-gap all-position TIG automatic welding process. The narrow-gap all-position TIG automatic welding process comprises the following steps: 1) performing backing welding on a root bevel and a bottom of the bevel; 2) performing filling welding on a lower bevel and a groove, wherein the filling welding is single-layer multi-pass welding; and 3) performing covering welding on a top of the groove, wherein the covering welding adopts linear welding or oscillating welding. The present application has the following beneficial effects compared with the prior art: the groove of the narrow-gap automatic welding process is narrow, the filling amount of the welding deposited metal is small, and the welding cost is relatively low. The weld is lossless, and the pass rate of the physical and chemical detection is relatively high.

Description

Technical Field

[0001] This invention pertains to welding processes, specifically to an automated TIG welding process using narrow-gap all-position welding. Background Technology

[0002] P91 pipes are widely used in industries such as petrochemicals and nuclear power, primarily in the main steam pipelines of power plants, where the demand for welding is enormous. Currently, large-diameter, medium-thick-walled P91 pipes are mostly welded manually, which results in poor working conditions, high work intensity, and a low weld qualification rate. Full-position automated welding is rare.

[0003] Currently, the commonly used method for welding large-diameter, medium-thick-walled P91 pipes is manual tungsten inert gas (TIG) welding for the root pass followed by manual shielded metal arc (SMA) welding for the fill and cover passes. This combined TIG and SMA welding process results in a wider bevel, a larger filler metal volume, and consumes 2-3 times more material than narrow-gap automatic welding. However, the TIG and SMA welding process also has a lower weld qualification rate. (See manual TIG and SMA welding bevel example.) Figure 1 . Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a narrow-gap, all-position TIG automatic welding process that improves welding efficiency and reduces the amount of filler material consumed.

[0005] The specific technical solution adopted in this invention is as follows: a narrow-gap, all-position TIG automatic welding process, comprising the following steps:

[0006] 1) Perform root welding on the blunt edge at the root and the bottom of the blunt edge;

[0007] 2) Fill welding is performed on the lower blunt edge and bevel, wherein the fill welding is a single-layer multi-pass weld;

[0008] 3) And perform capping welding on the top of the bevel, using linear weld beads or oscillating weld beads.

[0009] In the above-described narrow-gap all-position TIG automatic welding process, in step 1), the voltage peak value of the welding electrical appliance is set to be 9.5V to 11.3V, the base current value is set to be 55A to 75A, the peak current value is set to be 150A to 170A, the base wire feed speed is set to be 200 to 300mm / min, the peak wire feed speed is set to be 200 to 400mm / min, the welding speed is set to be 45 to 55mm / min, and the wire diameter is φ1.0mm.

[0010] In the above-described narrow-gap all-position TIG automatic welding process, in step 2), the peak voltage range of the welding electrical appliance is set to 11.6–13.4V, the base current range is 60A–170A, the peak current range is 160–280A, the base wire feed speed is 200–650 mm / min, the peak wire feed speed is 200–900 mm / min, the welding speed is 49–59 mm / min, and the wire diameter is φ1.0 mm.

[0011] In the above-described narrow-gap all-position TIG automatic welding process, in step 2), the filler weld bead adopts a single-layer multi-pass welding method, and different numbers of filler layers are selected according to the weld width: 2 filler layers when the weld width is <11mm, and 3 filler layers when the weld width is ≥11mm.

[0012] In the above-described narrow-gap all-position TIG automatic welding process, in step 3), the peak voltage range of the welding electrical appliance is set to 12.1–13.8V, the base current range is 130A–150A, the peak current range is 220–260A, the base wire feed speed is 350–450 mm / min, the peak wire feed speed is 500–700 mm / min, the welding speed is 49–59 mm / min, and the wire diameter is φ1.0 mm.

[0013] The above-described narrow-gap all-position TIG automatic welding process requires heat treatment both before and after welding.

[0014] As described above, in a narrow-gap all-position TIG automatic welding process, preheating is required before welding. The recommended preheating temperature is 200-250℃.

[0015] As described above, in a narrow-gap, all-position TIG automatic welding process, the martensitic transformation occurs after welding when the workpiece temperature drops to 80℃~100℃ and is held for 1h~2h.

[0016] As described above, in a narrow-gap, all-position TIG automatic welding process, post-weld heat treatment is performed immediately after the martensitic transformation. The post-weld heat treatment process is shown in the table below:

[0017]

[0018] The heating and cooling rates for welding heat treatment are 6250 / δ, in °C / h, where δ is the thickness of the weldment in mm, and not greater than 300 °C / h. When the wall thickness is greater than 100 mm, the heating and cooling rates are controlled at 60 °C / h. The heating and cooling rates are not controlled below 300 °C.

[0019] Compared with the prior art, the present invention has the following advantages: the narrow gap automatic welding process has a narrow bevel, a small amount of weld metal filling, and relatively low welding cost. The weld is non-destructive and has a relatively high pass rate in physical and chemical testing. Attached Figure Description

[0020] Figure 1 Manual argon-electric welding beveling

[0021] Figure 2 Bevel configuration diagram Detailed Implementation

[0022] A pre-welding bevel is formed at the opposite ends of the pipe base material. The bevel includes a lower blunt edge defined by a bevel angle (α) and a root blunt edge protruding from the bottom of the lower blunt edge. The junction of the root blunt edge and the bevel is a rounded corner (β). The root blunt edge height (H1) ranges from 1.8mm to 2.2mm, the root blunt edge width (W1) ranges from 2.8mm to 3.2mm, the radius of the rounded corner (β) at the junction ranges from 0.8mm to 1.2mm, the top width (W) of the upper bevel ranges from 10mm to 22mm, the bevel angle (α) ranges from 5° to 7°, the assembly gap (W2) ranges from 0 to 1.0mm, and the width of the inner bore (W3) of the pipe ranges from 20mm to 30mm. A schematic diagram of the bevel form is shown below. Figure 2 .

[0023] The welding method includes the following steps:

[0024] 1) Perform root pass welding on the blunt edge at the root and the bottom of the blunt edge:

[0025] The invention is characterized in that, in the root pass welding step, the voltage peak value of the welding appliance is set to be 9.5V to 11.3V, the base current value is set to be 55A to 75A, the peak current value is set to be 150A to 170A, the base wire feed speed of the welding wire is set to be 200 to 300mm / min, the peak wire feed speed of the welding wire is set to be 200 to 400mm / min, the welding speed is set to be 45 to 55mm / min, and the welding wire diameter is set to be φ1.0mm.

[0026] 2) Fill welding is performed on the lower blunt edge and bevel, wherein the fill welding is a single-layer multi-pass weld:

[0027] The invention is characterized in that, in the filler welding step, the voltage peak value of the welding appliance is set to be 11.6–13.4V, the base current value is set to be 60A–170A, the peak current value is set to be 160–280A, the base wire feed speed of the welding wire is set to be 200–650mm / min, the peak wire feed speed of the welding wire is set to be 200–900mm / min, the welding speed is set to be 49–59mm / min, and the welding wire diameter is set to be φ1.0mm.

[0028] The filler weld uses a single-layer multi-pass welding method. The number of filler layers is selected according to the weld width: 2 filler layers when the weld width is <11mm, and 3 filler layers when the weld width is ≥11mm.

[0029] 3) And perform capping welding on the top of the bevel, using linear weld beads or oscillating weld beads:

[0030] The invention is characterized in that, in the cover welding step, the voltage peak value of the welding appliance is set to be 12.1-13.8V, the base current value is set to be 130A-150A, the peak current value is set to be 220-260A, the base wire feeding speed of the welding wire is set to be 350-450mm / min, the peak wire feeding speed of the welding wire is set to be 500-700mm / min, the welding speed is set to be 49-59mm / min, and the welding wire diameter is set to be φ1.0mm.

[0031] The heat treatment method includes the following steps:

[0032] 1) Preheating before welding: Preheating is required before welding. The recommended preheating temperature is 200-250℃.

[0033] 2) Martensitic transformation: After welding, the temperature of the weldment is reduced to 80℃~100℃ and held for 1h~2h.

[0034] 3) Post-weld heat treatment: Post-weld heat treatment should be performed immediately after the martensitic transformation is completed. Recommended post-weld heat treatment processes are shown in the table below:

[0035]

[0036] The heating and cooling rates for welding heat treatment are 6250 / δ (in °C / h, where δ is the thickness of the weldment in mm), and not greater than 300 °C / h. When the wall thickness is greater than 100 mm, the heating and cooling rates are controlled at 60 °C / h. The heating and cooling rates are not controlled below 300 °C.

[0037] The physical and chemical tests must meet the following requirements:

[0038]

[0039] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments.

[0040] Welding process tests were conducted on P91 material φ559×53.98mm pipes. ER62-B9 welding wire φ1.0mm was used as the welding material. The bevel dimensions and form are as follows: Figure 2 As shown.

[0041] Table 1 lists the main specification parameters for narrow-gap all-position automatic welding processes.

[0042] Parameter Description: When performing the root pass welding, the selected welding parameters are relatively small, as long as the weld fusion is guaranteed and both sides are well formed. The welding parameters are: peak current 160A, base current 65A; the peak welding voltage is 11.0V; the peak wire feed speed can be selected within the range of 200–400 mm / min, the base wire feed speed can be selected within the range of 200–300 mm / min, and the welding speed is 64 mm / min. For shielding gas flow rate, the front side is 60–70 L / min, and for back side shielding, the shielding gas flow rate can be selected within the range of 5–30 L / min, depending on the shielding requirements for both the front and back sides of the weld.

[0043] To ensure good fusion of the sidewalls, the filler welds are all single-layer multi-pass welds, and the base and peak current and voltage need to be increased during the welding process.

[0044] 1) When welding to the fourth layer, the welding parameters are: peak welding current reaches 260A, base welding current is 140A; peak welding voltage reaches 12.1V; peak wire feed speed is 700mm / min, base wire feed speed is 600mm / min; welding speed is 68mm / min.

[0045] 2) When welding to the seventeenth layer, the welding parameters are: the peak value of the welding current reaches 280A and the base value of the welding current is 180A; the peak value of the welding voltage reaches 13.1V; the peak value of the wire feed speed is 750mm / min and the base value is 550mm / min; the welding speed is 68mm / min.

[0046] 3) When welding to the 26th layer, the welding parameters are as follows: the peak value of the welding current reaches 285A and the base value of the welding current is 185A; the peak value of the welding voltage reaches 13.4V; the peak value of the wire feed speed is 750mm / min and the base value is 550mm / min; the welding speed is 68mm / min.

[0047] 4) The 29th layer is the cover pass weld. The welding parameters are as follows: peak welding current is 260A, base welding current is 160A; peak welding voltage is 12.7V; peak wire feed speed is 600mm / min, base wire feed speed is 400mm / min; welding speed is 65mm / min.

[0048] Before the 25th layer, the weld cross-sectional width is less than 11mm, and it is a single layer with two passes; for the 25th layer and subsequent welds, the weld cross-sectional width is greater than or equal to 11mm, and it is a single layer with three passes.

[0049] In order to ensure good fusion of the sidewalls during the filling and capping of welds, the welding process parameters should be adjusted appropriately according to the fusion condition of the weld metal pool and the sidewalls.

[0050] Table 1 Welding process parameters

[0051]

[0052]

[0053]

[0054] After the post-weld heat treatment, the weld joint was subjected to non-destructive and physical-chemical tests. All non-destructive tests were qualified and no defects were found. The results of the physical-chemical tests are shown in the table below:

[0055]

Claims

1. A narrow-gap, all-position TIG automatic welding process, characterized in that, Includes the following steps: 1) Perform root welding on the blunt edge at the root and the bottom of the blunt edge; 2) Fill welding is performed on the lower blunt edge and bevel, wherein the fill welding is a single-layer multi-pass weld; 3) And perform capping welding on the top of the bevel, using linear weld beads or oscillating weld beads; In 1), the voltage peak value of the welding appliance is set to be 9.5V~11.3V, the current base value is set to be 55A~75A, the current peak value is set to be 150~170A, the basic wire feeding speed of the welding wire is set to be 200~300mm / min, the peak wire feeding speed of the welding wire is set to be 200~400mm / min, the welding speed is set to be 45~55mm / min, and the welding wire diameter is set to φ1.0mm. In 2), the voltage peak value of the welding appliance is set to be 11.6~13.4V, the current base value is set to be 60A~170A, the current peak value is set to be 160~280A, the basic wire feeding speed of the welding wire is set to be 200~650mm / min, the peak wire feeding speed of the welding wire is set to be 200~900mm / min, the welding speed is set to be 49~59mm / min, and the welding wire diameter is set to be φ1.0mm. In 2), the filler weld is made using a single-layer multi-pass welding method. The number of filler layers is selected according to the weld width: 2 passes when the weld width is <11mm, and 3 passes when the weld width is ≥11mm. In 3), the voltage peak value of the welding appliance is set to be 12.1~13.8V, the current base value is set to be 130A~150A, the current peak value is set to be 220~260A, the basic wire feeding speed of the welding wire is set to be 350~450mm / min, the peak wire feeding speed of the welding wire is set to be 500~700mm / min, the welding speed is set to be 49~59mm / min, and the welding wire diameter is set to be φ1.0mm. Heat treatment is required both before and after welding. Preheating before welding: The preheating temperature is 200~250℃; Martensitic transformation: After welding, the temperature of the weldment is reduced to 80℃~100℃ and held for 1h~2h; Post-weld heat treatment: Post-weld heat treatment shall be performed immediately after the martensitic transformation is completed. The heating and cooling rates for welding heat treatment are 6250 / δ, in °C / h, where δ is the thickness of the weldment in mm, and shall not exceed 300 °C / h. The heating and cooling rates are not controlled below 300 °C. When the thickness of the weldment is greater than 100 mm, the heating and cooling rates are controlled at 60 °C / h, and the heating and cooling rates are not controlled below 300 °C.

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