A method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipes

Abstract

This invention provides a method for controlling the alloy composition of stainless steel submerged arc welds on bimetallic composite pipes. The method includes selecting the composite pipe and determining the welding process; determining the weld base melting area A1, the wire deposition filling area A2, the alloy element content Bi of the cladding stainless steel (or the alloy element content of the cladding submerged arc weld), and the alloy element content Di of the deposited welding wire; determining the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire; determining the relationship between the cladding areas of the first, second, third, and fourth welding wires and the cladding area of ​​the cladding weld wire; and designing the welding specifications for single-pass submerged arc welding of the cladding stainless steel four-wire cladding layer. This method solves the problem of low Cr and Ni alloy element content in the cladding stainless steel weld of bimetallic composite pipes after dilution when using submerged arc welding, which affects the corrosion resistance of the cladding stainless steel weld.

Description

Technical Field

[0001] This invention relates to the field of bimetallic composite pipe welding, and in particular to a method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipes. Background Technology

[0002] Because the two materials in a bimetallic composite pipe have different chemical compositions, the weld metal composition (referring to the content of a certain alloying element in the stainless steel, hereinafter the same) of the cladding stainless steel weld is easily diluted during the welding process, affecting the corrosion resistance of the cladding stainless steel weld. To avoid dilution of the cladding stainless steel weld metal composition during the welding process, resulting in a low content, one method is to design and weld a transition layer at the interface between the cladding and the base layer of the bimetallic composite pipe, and then use welding wire corresponding to the cladding stainless steel plate to weld the cladding stainless steel. Another method is to perform electroslag surfacing welding on the corresponding welding strip of the cladding stainless steel plate after the base layer welding is completed. A third method is to use submerged arc welding with a stainless steel welding wire that has a higher alloy content (Cr, Ni, etc.) than the cladding stainless steel. The advantages of the first and second methods for welding bimetallic composite pipes are a lower dilution rate of the cladding stainless steel weld metal composition, but the disadvantage is low welding efficiency, and the need to add or modify welding equipment on carbon steel welded pipe production lines. The advantage of the third method is high welding efficiency, and welding can be completed using existing carbon steel welded pipe production line equipment, but the disadvantage is a high dilution rate of the cladding stainless steel weld metal composition.

[0003] Chinese patent document CN 104942414 A describes a submerged arc welding process for bimetallic composite plates, and Chinese patent document CN113909648A describes a welding method for a straight seam bimetallic composite pipe. The process involves submerged arc welding of a 3mm cladding layer of 316L stainless steel in a bimetallic composite plate (pipe). A 309MoL stainless steel submerged arc welding wire with a higher Cr and Ni content than the 316L cladding stainless steel is used, matched with corresponding welding process parameters to weld the cladding stainless steel to compensate for the dilution of Cr and Ni content in the submerged arc weld of the cladding stainless steel. Chinese patent document CN 113798641 A describes a chemical composition design method for submerged arc welding wire of 3mm cladding stainless steel in bimetallic composite plates, specifying the required chemical composition for submerged arc welding of 3mm cladding stainless steel (316L, LC2205) to compensate for the dilution of Cr and Ni content in the submerged arc weld of the cladding stainless steel. The three patent documents mentioned above all pertain to bimetallic submerged arc welding (SAW) processes where the base layer is welded first, followed by the cladding layer. Currently, there are no commercially available SAW wires specifically designed for welding the stainless steel cladding layer of bimetallic composite pipes. When welding commonly used bimetallic composite plates with stainless steel cladding layers using similar methods, difficulties arise in matching the SAW wire to the cladding layer. A new method is needed to utilize currently available stainless steel SAW wires to match the corresponding welding process parameters for welding the cladding layer, thereby compensating for the dilution of alloying elements such as Cr and Ni in the weld. Therefore, we propose a method for controlling the weld alloy composition of bimetallic composite pipes with stainless steel SAW to solve the aforementioned problems. Summary of the Invention

[0004] This invention provides a method for controlling the alloy composition of stainless steel submerged arc welds in bimetallic composite pipes. It addresses the issue of high dilution rates of Cr and Ni alloy elements in the submerged arc weld of the cladding stainless steel layer during the submerged arc welding process of welding the base layer first and then the cladding layer in bimetallic composite pipes. The method employs welding process parameters corresponding to different grades of stainless steel submerged arc welding wire currently available on the market to weld the cladding stainless steel layer, thereby compensating for the dilution of Cr and Ni alloy elements in the cladding stainless steel submerged arc weld. This solves the problem of low Cr and Ni alloy element content in the cladding stainless steel weld of bimetallic composite pipes after dilution when using submerged arc welding, which affects the corrosion resistance of the cladding stainless steel weld.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipe, comprising the following steps: S1, selecting composite pipe: bimetallic composite pipe with a base wall thickness of 5-25mm and a cladding wall thickness of 3mm;

[0006] S2. Determine the welding process: Use submerged arc welding process to weld the base layer first and then the cladding layer;

[0007] S3. Determine the fusion area of ​​the weld base layer (A1), the welding wire deposition area (A2), and the alloy element content of the cladding stainless steel layer (B). i The alloy element content D of the weld wire i ;

[0008] S4. Determine the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire.

[0009] S5. Determine the relationship between the cladding area of ​​the first, second, third, and fourth welding wires in the cladding layer weld and the cladding area of ​​the welding wire in the cladding layer weld;

[0010] S6. Design the welding specifications for four-wire single-pass submerged arc welding of multi-layer stainless steel.

[0011] In the preferred embodiment, in S4, since the Cr and Ni alloy element content of the bimetallic composite pipe cladding layer is much greater than that of the bimetallic composite pipe base layer, when the Cr and Ni alloy element content of the welding wire deposited filling zone, the base layer melting zone, and the cladding stainless steel cladding layer are basically the same, the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire is as follows:

[0012] B i =D i *A2 / (A1+A2)=(D i1 *A 21 +D i2 *A 22 +D i3 *A 23 +D i4 *A 24 ) / (A1+A2) (1);

[0013] A 21 For the area of ​​a single weld filler, A 22 For the two-wire fusion filling area, A 23 For the three-wire welding filling area, A 24 D represents the area filled by the four-wire welding process. i1 For the content of alloying elements, D i2 The content of alloying elements in the two wires, D i3 The content of alloying elements in the three wires, D i4 The content of the four alloying elements is represented by ; i represents alloying elements such as Cr and Ni.

[0014] In the preferred embodiment, in S5, the cladding areas of the first, second, third, and fourth welding wires of the bimetallic composite pipe cladding weld and the cladding area of ​​the welding wire of the cladding weld are respectively determined by the following formulas:

[0015]

[0016]

[0017]

[0018]

[0019]

[0020] Where I1, I2, I3, and I4 are the welding currents for wires one, two, three, and four, respectively, in amperes; V1, V2, V3, and V4 are the arc voltages for wires one, two, three, and four, respectively, in volts; and v is the welding speed, in mm / min.

[0021] In the preferred embodiment, the penetration depth of the base weld is controlled at (t-1)±0.5mm (t is the base weld wall thickness in mm), the penetration depth of the cladding weld is controlled at 6±0.5mm, and the cladding weld melting base area A1 is controlled at 22±2mm. 2 The cladding area of ​​the welding wire in the cladding layer of the weld is controlled to be 46±2mm. 2 .

[0022] In the preferred scheme, in S6, the welding material matching and welding specifications are designed based on the principle that the Cr and Ni alloy element content of the cladding submerged arc weld seam is consistent with that of the cladding stainless steel. Welding is carried out using existing stainless steel submerged arc welding wires of different grades. The Cr and Ni alloy element content in the cladding wire is used to compensate for the Cr and Ni alloy element content in the base melting zone, so as to achieve the goal that the Cr and Ni alloy element content of the wire deposition filling zone, the base melting zone and the cladding stainless steel are basically consistent.

[0023] In the preferred embodiment, in S6, the welding specifications for single-pass submerged arc welding of clad stainless steel with four wires are as follows: welding current of 750-850A and arc voltage of 36±2V for one wire, welding current of 550-650A and arc voltage of 38±2V for two wires, welding current of 500-650A and arc voltage of 40±2V for three wires, welding current of 450-650A and arc voltage of 42±2V for four wires, and welding speed of 1.6±0.1m / min.

[0024] The beneficial effects of this invention are as follows: 1. In the submerged arc welding process of first welding the base layer and then welding the cladding layer of bimetallic composite pipes, the dilution rate of Cr and Ni alloy elements in the submerged arc weld of the cladding stainless steel is too high. This invention uses the welding process parameters corresponding to the different grades of stainless steel submerged arc welding wires currently available on the market to weld the cladding stainless steel to compensate for the dilution of Cr, Ni and other alloy elements in the submerged arc weld of the cladding stainless steel. This solves the problem that the content of Cr and Ni alloy elements in the cladding stainless steel weld of bimetallic composite pipes is too low after dilution when using the submerged arc welding process, which affects the corrosion resistance of the cladding stainless steel weld of bimetallic composite pipes.

[0025] 2. The submerged arc welding of the stainless steel cladding layer of the bimetallic composite pipe using the present invention does not require the addition or modification of welding equipment. The submerged arc welding of the stainless steel cladding layer of the bimetallic composite pipe can be completed using the existing carbon steel welded pipe production line welding equipment.

[0026] 3. This invention is beneficial to the promotion and application of the submerged arc welding process for bimetallic composite pipes with cladding stainless steel, which has the advantage of high welding efficiency. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0028] Figure 1 This is a schematic diagram of the weld seam of the bimetallic composite pipe of the present invention;

[0029] Figure 2 This describes the macroscopic morphology of the weld seam in the bimetallic composite pipe of the present invention. Detailed Implementation

[0030] Example 1:

[0031] like Figure 1-2 A method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipe includes the following steps: S1, Selecting a composite pipe: a bimetallic composite pipe with a base layer wall thickness of 5-25 mm and a cladding layer wall thickness of 3 mm;

[0032] S2. Determine the welding process: Use submerged arc welding process to weld the base layer first and then the cladding layer;

[0033] S3. Determine the fusion area of ​​the weld base layer (A1), the welding wire deposition area (A2), and the alloy element content of the cladding stainless steel layer (B). i The alloy element content D of the weld wire i ;

[0034] S4. Determine the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire.

[0035] S5. Determine the relationship between the cladding area of ​​the first, second, third, and fourth welding wires in the cladding layer weld and the cladding area of ​​the welding wire in the cladding layer weld;

[0036] S6. Design welding specifications for single-pass submerged arc welding of cladding stainless steel. This invention addresses the issue of high dilution rates of Cr and Ni alloy elements in the submerged arc welding weld of cladding stainless steel when welding the base layer first and then the cladding layer in a bimetallic composite pipe. It utilizes welding process parameters corresponding to different grades of stainless steel submerged arc welding wire currently available on the market to compensate for the dilution of Cr and Ni alloy elements in the cladding stainless steel weld. This solves the problem of low Cr and Ni alloy element content in the cladding stainless steel weld of bimetallic composite pipes after dilution, which affects the corrosion resistance of the cladding stainless steel weld.

[0037] The submerged arc welding of the stainless steel cladding layer of the bimetallic composite pipe using the present invention does not require the addition or modification of welding equipment; the submerged arc welding of the stainless steel cladding layer of the bimetallic composite pipe can be completed using the existing welding equipment of the carbon steel welded pipe production line.

[0038] This invention facilitates the promotion and application of a submerged arc welding process for bimetallic composite pipes with cladding stainless steel, which boasts high welding efficiency.

[0039] In the preferred embodiment, in S4, since the Cr and Ni alloy element content of the bimetallic composite pipe cladding layer is much greater than that of the bimetallic composite pipe base layer, when the Cr and Ni alloy element content of the welding wire deposited filling zone, the base layer melting zone, and the cladding stainless steel cladding layer are basically the same, the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire is as follows:

[0040] B i =D i *A2 / (A1+A2)=(D i1 *A 21 +D i2 *A 22 +D i3 *A 23 +D i4 *A 24 ) / (A1+A2) (1);

[0041] A 21 For the area of ​​a single weld filler, A 22 For the two-wire fusion filling area, A 23 For the three-wire welding filling area, A 24 D represents the area filled by the four-wire welding process. i1 For the content of alloying elements, D i2 The content of alloying elements in the two wires, D i3 The content of alloying elements in the three wires, D i4 The content of the four alloying elements is represented by ; i represents alloying elements such as Cr and Ni.

[0042] In the preferred embodiment, in S5, the cladding areas of the first, second, third, and fourth layers of the cladding weld and the cladding area of ​​the cladding weld are respectively determined by the following formulas:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] Where I1, I2, I3, and I4 are the welding currents for wires one, two, three, and four, respectively, in amperes; V1, V2, V3, and V4 are the arc voltages for wires one, two, three, and four, respectively, in volts; and v is the welding speed, in mm / min.

[0049] In the preferred embodiment, the penetration depth of the base weld is controlled at (t-1)±0.5mm (t is the base weld wall thickness in mm), the penetration depth of the cladding weld is controlled at 6±0.5mm, and the cladding weld melting base area A1 is controlled at 22±2mm. 2 The cladding area of ​​the welding wire in the cladding layer of the weld is controlled to be 46±2mm. 2 .

[0050] In the preferred scheme, in S6, the welding material matching and welding specifications are designed based on the principle that the Cr and Ni alloy element content of the cladding submerged arc weld seam is consistent with that of the cladding stainless steel. Welding is carried out using existing stainless steel submerged arc welding wires of different grades. The Cr and Ni alloy element content in the cladding wire is used to compensate for the Cr and Ni alloy element content in the base melting zone, so as to achieve the goal that the Cr and Ni alloy element content of the wire deposition filling zone, the base melting zone and the cladding stainless steel are basically consistent.

[0051] In the preferred embodiment, in S6, the welding specifications for single-pass submerged arc welding of clad stainless steel with four wires are as follows: welding current of 750-850A and arc voltage of 36±2V for one wire, welding current of 550-650A and arc voltage of 38±2V for two wires, welding current of 500-650A and arc voltage of 40±2V for three wires, welding current of 450-650A and arc voltage of 42±2V for four wires, and welding speed of 1.6±0.1m / min.

[0052] Example 2:

[0053] Further explanation based on Example 1: The cladding stainless steel of the bimetallic composite pipe is 304 with a wall thickness of 3mm. The 304 stainless steel cladding has a Cr alloy element content of 19±1% ​​and a Ni alloy element content of 9.25±1.25%. The steps for controlling the weld alloy composition of the submerged arc welded bimetallic composite pipe are as follows:

[0054] For bimetallic composite pipes with a 3mm thick cladding layer, a submerged arc welding process is adopted, where the base layer is welded first and then the cladding layer is welded. The cladding stainless steel submerged arc weld consists of three parts: the base layer melting zone, the cladding layer melting zone, and the wire deposition filling zone.

[0055] With A1 as the base layer melting area and A2 as the welding wire deposition filling area (A 21 For the area of ​​a single weld filler, A 22 For the two-wire fusion filling area, A23 For the three-wire welding filling area, A 24 (for the four-wire welding filling area), B i For the alloy element content of clad stainless steel, D i The alloy element content (D) of the weld wire i1 For the content of alloying elements, D i2 The content of alloying elements in the two wires, D i3 The content of alloying elements in the three wires, D i4 (where i represents the alloy element content of the four wires), and i represents alloy elements such as Cr and Ni. Since the Cr and Ni alloy element content of the cladding layer of the bimetallic composite pipe is much greater than that of the base layer, the relationship between the Cr and Ni alloy element content of the cladding layer submerged arc weld and the alloy element content of the cladding welding wire when the Cr and Ni alloy element content of the welding wire in the welding wire deposition filling zone, the base layer melting zone and the cladding stainless steel are basically the same is given by equation (1):

[0056] B i =D i *A2 / (A1+A2)=(D i1 *A 21 +D i2 *A 22 +D i3 *A 23 +D i4 *A 24 ) / (A1+A2) (1)

[0057] The cladding area of ​​the first, second, third, and fourth welding wires in the cladding layer and the cladding area of ​​the welding wire in the cladding layer are determined by the relationships (2), (3), (4), (5), and (6).

[0058]

[0059]

[0060]

[0061]

[0062]

[0063] Where I1, I2, I3, and I4 are the welding currents for wires one, two, three, and four, respectively, in amperes; V1, V2, V3, and V4 are the arc voltages for wires one, two, three, and four, respectively, in volts; and v is the welding speed, in mm / min.

[0064] The penetration depth of the base layer weld is controlled at (t-1)±0.5mm (t is the thickness of the base layer wall, in mm), the penetration depth of the cladding layer weld is controlled at 6±0.5mm, the cladding layer area A1 of the cladding layer weld is controlled at 22±2mm2, and the cladding area of ​​the welding wire of the cladding layer weld is controlled at 44±2mm2.

[0065] The welding specifications for the first wire ensure the penetration depth of the cladding weld and the melting area of ​​the base layer. The welding specifications for the first, second, third, and fourth wires comprehensively control the weld wire deposition area. Welding wires with appropriate Cr and Ni alloy element content are matched for the first, second, third, and fourth wires to ensure both penetration of the inner and outer welds of the bimetallic composite pipe and to reasonably control the Cr and Ni alloy element content of the cladding weld within the range of the cladding stainless steel's chemical composition. The welding wire grades matched for the first, second, third, and fourth wires are 312, 310, 312, and 310, respectively, with a diameter of 4mm. The Cr alloy element content of 312 welding wire is 30±2 (%) and the Ni alloy element content is 9.25±1.25 (%). The Cr alloy element content of 310 welding wire is 26.5±1.5 (%) and the Ni alloy element content is 21±1 (%). The welding current for one wire is 800±50A and the arc voltage is 36±2V; the welding current for two wires is 600±50A and the arc voltage is 38±2V; the welding current for three wires is 550±50A and the arc voltage is 40±2V; the welding current for four wires is 500±50A and the arc voltage is 42±2V; and the welding speed is 1.6±0.1m / min.

[0066] The weld filler area A of each wire is calculated based on the median values ​​of the Cr and Ni alloy element content of the welding wires matched with wires one, two, three, and four, and the median values ​​of the welding specifications for wires one, two, three, and four. 21 =15.8mm2, two-wire fusion filling area A 22 =10.7mm 2 Three-wire welding filling area A 23 =9.4mm 2 Four-wire welding filling area A 24 =8.2mm 2 The welding wire deposition area A2 = 44.2 mm 2 Meanwhile, A1 = 22mm 2 (Median value) The Cr alloy element content of 312 welding wire is 30% (median value) and the Ni alloy element content is 9.25% (median value). The Cr alloy element content of 310 welding wire is 26.5% (median value) and the Ni alloy element content is 21% (median value). The calculated Cr and Ni alloy element contents of the cladding submerged arc weld are 19.0% and 9.5% respectively, both within the range of Cr and Ni alloy element contents of the cladding 304 stainless steel of the bimetallic composite pipe. The Cr and Ni alloy element contents of the cladding 304 stainless steel of the bimetallic composite pipe are well controlled.

[0067] Example 3:

[0068] Further explanation based on Examples 1 and 2: The cladding stainless steel of the bimetallic composite pipe is 316 with a wall thickness of 3mm. The Cr alloying element content of the 316 cladding stainless steel is 17±1% and the Ni alloying element content is 12±2%. The steps for controlling the weld alloy composition of the submerged arc welded bimetallic composite pipe are as follows:

[0069] For bimetallic composite pipes with a 3mm thick cladding layer, a submerged arc welding process is adopted, where the base layer is welded first and then the cladding layer is welded. The cladding stainless steel submerged arc weld consists of three parts: the base layer melting zone, the cladding layer melting zone, and the wire deposition filling zone.

[0070] With A1 as the base layer melting area and A2 as the welding wire deposition filling area (A 21 For the area of ​​a single weld filler, A 22 For the two-wire fusion filling area, A 23 For the three-wire welding filling area, A 24 (for the four-wire welding filling area), B i For the alloy element content of clad stainless steel, D i The alloy element content (D) of the weld wire i1 For the content of alloying elements, D i2 The content of alloying elements in the two wires, D i3 The content of alloying elements in the three wires, D i4 (where i represents the alloy element content of the four wires), and i represents alloy elements such as Cr and Ni. Since the Cr and Ni alloy element content of the cladding layer of the bimetallic composite pipe is much greater than that of the base layer, the relationship between the Cr and Ni alloy element content of the cladding layer submerged arc weld and the alloy element content of the cladding welding wire when the Cr and Ni alloy element content of the welding wire in the welding wire deposition filling zone, the base layer melting zone and the cladding stainless steel are basically the same is given by equation (1):

[0071] B i =D i *A2 / (A1+A2)=(D i1 *A 21 +D i2 *A 22 +D i3 *A 23 +D i4 *A 24 ) / (A1+A2) (1)

[0072] The cladding area of ​​the first, second, third, and fourth welding wires in the cladding layer and the cladding area of ​​the welding wire in the cladding layer are determined by the relationships (2), (3), (4), (5), and (6).

[0073]

[0074]

[0075]

[0076]

[0077]

[0078] Where I1, I2, I3, and I4 are the welding currents for wires one, two, three, and four, respectively, in amperes; V1, V2, V3, and V4 are the arc voltages for wires one, two, three, and four, respectively, in volts; and v is the welding speed, in mm / min.

[0079] The penetration depth of the base layer weld is controlled at (t-1)±0.5mm (t is the base layer wall thickness in mm), the penetration depth of the cladding weld is controlled at 6±0.5mm, and the molten base layer area A1 of the cladding weld is controlled at 22±2mm. 2 The cladding area of ​​the welding wire in the cladding layer of the weld is controlled to be 46±2mm. 2 .

[0080] The welding specifications for the first wire ensure the penetration depth of the cladding weld and the melting area of ​​the base layer. The welding specifications for the first, second, third, and fourth wires comprehensively control the filler area of ​​the weld wires. Welding wires with appropriate Cr and Ni alloying element content are matched for the first, second, third, and fourth wires to ensure both penetration of the inner and outer welds of the bimetallic composite pipe and to reasonably control the Cr and Ni alloying element content of the cladding weld within the range of the cladding stainless steel's chemical composition. The welding wire grades matched for the first, second, third, and fourth wires are 310, 309Mo, 309Mo, and 310, respectively, with a diameter of 4mm. The Cr content of 310 welding wire is 26.5±1.5% and the Ni content is 21±1%. The Cr content of 309Mo welding wire is 24±1% and the Ni content is 13±1%. The welding current for one wire is 800±50A and the arc voltage is 36±2V; for two wires, the welding current is 600±50A and the arc voltage is 38±2V; for three wires, the welding current is 600±50A and the arc voltage is 40±2V; for four wires, the welding current is 600±50A and the arc voltage is 42±2V; and the welding speed is 1.6±0.1m / min.

[0081] The weld filler area A of each wire is calculated based on the median values ​​of the Cr and Ni alloy element content of the welding wires matched with wires one, two, three, and four, and the median values ​​of the welding specifications for wires one, two, three, and four. 21 =15.8mm2, two-wire fusion filling area A 22 =10.7mm 2 Three-wire welding filling area A 23 =10.6mm 2 Four-wire welding filling area A24 =10.4mm 2 The welding wire deposition area A2 = 47.5 mm 2 Meanwhile, A1 = 22mm 2 (Median value) The Cr alloy element content of 310 welding wire is 26.5% (median value) and the Ni alloy element content is 21% (median value). The Cr alloy element content of 309Mo welding wire is 24% (median value) and the Ni alloy element content is 13% (median value). The calculated Cr and Ni alloy element contents of the cladding submerged arc weld are 17.3% and 11.9% respectively, both within the range of Cr and Ni alloy element contents of the cladding 316 stainless steel of the bimetallic composite pipe. The Cr and Ni alloy element contents of the cladding 316 stainless steel of the bimetallic composite pipe are well controlled.

[0082] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for controlling the weld metal composition of submerged arc welded stainless steel bimetallic composite pipes, characterized in that: Includes the following steps: S1. Select composite pipe: bimetallic composite pipe with a base layer wall thickness of 5~25mm and a cladding layer wall thickness of 3mm; S2. Determine the welding process: Use submerged arc welding process to weld the base layer first and then the cladding layer; S3. Determine the fusion area of ​​the weld base layer (A1), the welding wire deposition area (A2), and the alloy element content of the cladding stainless steel layer (B). i The alloy element content D of the weld wire i ; S4. Determine the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire. S5. Determine the relationship between the cladding area of ​​the first, second, third, and fourth welding wires in the cladding layer weld and the cladding area of ​​the welding wire in the cladding layer weld; S6. Design of welding specifications for four-wire single-pass submerged arc welding of multi-layer stainless steel. In S4, since the Cr and Ni alloy element content of the bimetallic composite pipe cladding layer is much greater than that of the bimetallic composite pipe base layer, when the Cr and Ni alloy element content of the welding wire deposited filling zone, the base layer melting zone and the cladding stainless steel cladding layer are basically the same, the relationship between the Cr and Ni alloy element content of the cladding submerged arc weld and the alloy element content of the cladding welding wire is as follows: B i =D i *A2 / (A1+A2)=(D i1 *A 21 +D i2 *A 22 +D i3 *A 23 +D i4 *A 24 ) / (A1+A2)(1); A 21 For the area of ​​a single weld filler, A 22 For the two-wire fusion filling area, A 23 For the three-wire welding filling area, A 24 D represents the area filled by the four-wire welding process. i1 For the content of alloying elements, D i2 For the alloy element content of the two wires, D i3 For the alloy element content of the three wires, D i4 The content of alloying elements in the four wires; i represents the alloying elements Cr and Ni respectively; In S5, the relationships between the cladding areas of the first, second, third, and fourth layers of the cladding weld and the cladding area of ​​the cladding weld are as follows: ；（2）； （3）； （4）； （5）； （6）； Where I1, I2, I3, and I4 are the welding currents for wires one, two, three, and four, respectively, in amperes; V1, V2, V3, and V4 are the arc voltages for wires one, two, three, and four, respectively, in volts; and v is the welding speed, in mm / min.

2. The method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipes according to claim 1, characterized in that: The penetration depth of the base layer weld is controlled at (t-1) ± 0.5 mm, where t is the base layer wall thickness in mm. The penetration depth of the cladding layer weld is controlled at 6 ± 0.5 mm, and the molten base layer area A1 of the cladding layer weld is controlled at 22 ± 2 mm². 2 The cladding area of ​​the welding wire in the cladding layer of the weld is controlled to be 46±2mm. 2 .

3. The method for controlling the alloy composition of stainless steel submerged arc welded bimetallic composite pipes according to claim 1, characterized in that: in S6, the welding material matching and welding specifications are designed based on the principle that the Cr and Ni alloy element content of the submerged arc welded cladding layer is consistent with the Cr and Ni alloy element content of the cladding stainless steel. Welding is carried out using existing stainless steel submerged arc welding wires of different grades. The Cr and Ni alloy element content in the cladding wire is used to compensate for the Cr and Ni alloy element content in the base layer melting zone, so as to achieve the goal that the Cr and Ni alloy element content in the wire deposition filling zone, the base layer melting zone and the cladding stainless steel are basically consistent.

4. The method for controlling the weld metal composition of stainless steel submerged arc welded bimetallic composite pipe according to claim 1, characterized in that: in S6, the welding specifications for single-pass submerged arc welding of cladding stainless steel four-wire are as follows: welding current of 750~850A and arc voltage of 36±2V for one wire, welding current of 550~650A and arc voltage of 38±2V for two wires, welding current of 500~650A and arc voltage of 40±2V for three wires, welding current of 450~650A and arc voltage of 42±2V for four wires, and welding speed of 1.6±0.1m / min.

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