Bottom sealing welding process curve based on narrow-gap U-shaped groove, application and product

Abstract

The invention belongs to the field of subsea pipeline welding, and particularly discloses a bottom sealing welding process curve based on a narrow-gap U-shaped groove, application and a product, the bottom sealing welding process curve is used for welding the narrow-gap U-shaped groove, and on the basis of a CMT reference curve, at least one current pulse is introduced before and after the short-circuit stage respectively, so that the narrow-gap U-shaped groove is welded. Therefore, the root fusion width is increased, the root recess is avoided, the peak current and the cycle time are increased to increase the welding heat input, and the peak current rising rate and the peak current falling rate are reduced to prolong the peak current acting time. According to the method, the welding heat input and the root fusion width can be increased, the excellent single-face welding and double-face forming effect is achieved under the conditions of zero-gap assembly and no liner, the problem of weld defects is solved, and the service performance of the acid marine pipeline is effectively improved.

Description

Technical Field

[0001] The present application belongs to the field of sea pipe welding, and more specifically, to a bottom welding process curve, application and product based on a narrow gap U-shaped groove. Background Art

[0002] The geological conditions in the South my country Sea are complex and harsh. The content of acidic media such as H2S / CO2 in oil and gas is high. The exploitation of high-sulfur oil and gas is an important part of the development of marine oil and gas resources. Carbon steel oil and gas submarine pipelines (Middle East, Thailand and other projects) face the strong coupling of multiple factors such as low temperature, strong corrosion of hydrogen sulfide and fatigue load. The welding technology of strong acid-resistant carbon steel submarine pipelines is an important guarantee for their long-life service safety.

[0003] In the traditional process of laying submarine pipes, in order to improve the forming quality of root welding, copper liners are often used to assist in achieving high-quality forming of the root. However, although the copper liner improves the forming effect, a large amount of copper will penetrate into the weld. It is well known that copper has better corrosion resistance than iron. Copper infiltration into the pipeline will form a galvanic pair. Copper will accelerate the corrosion and dissolution of the pipeline (Fe) due to its high corrosion potential, seriously deteriorating the service life of the pipeline in acidic media. Therefore, it is urgent to develop a single-sided welding and double-sided forming bottom welding process without copper liners and with excellent root forming.

[0004] At present, the bottom welding processes for single-sided welding and double-sided forming mainly include surface tension transition technology (STT) and cold metal transition technology (CMT). When performing bottom welding of the pipeline, the STT technology must maintain a certain gap between the pipelines, the process is difficult to control, and the cost of STT equipment is relatively high. CMT technology has the advantages of small heat input and stable and reliable welding process. It can achieve full-position welding of pipelines under zero gap conditions, but it also faces the problem of poor adaptability to misalignment due to the narrow weld bead caused by small heat input. In addition, in the overhead welding area, due to the gravity of the molten pool metal, the root depression problem is very likely to occur. Root depression will weaken the strength of the pipeline connection, produce stress concentration, and reduce the reliability of the welded joint.

[0005] In addition, the H2S stress corrosion resistance of acidic marine pipelines is one of its main service indicators, which is closely related to the hardness of the joints, and the maximum hardness of the joints is usually required to be ≤248HV. Using high heat input welding is usually the most effective way to reduce the hardness of the joints. However, in the existing bottom welding process, high heat input usually corresponds to thicker welds, resulting in insufficient heat transfer to the root, causing the hardness of the root weld to exceed the standard; if the process parameters of low heat input are used to reduce the thickness of the weld, it is easy to cause incomplete penetration defects, and low heat input is easy to increase the cooling rate of the molten pool, promote the formation of martensite, and increase the hardness of the root weld instead of decreasing. Summary of the invention

[0006] In view of the defects of the prior art, the present application provides a bottom welding process curve, application and product based on a narrow gap U-shaped groove, aiming to solve the problems that the heat of the existing acid marine pipeline bottom welding cannot be transferred to the root, the root of the weld is concave, and the hardness of the bottom weld exceeds the standard, resulting in unqualified SSC (stress corrosion cracking) performance.

[0007] According to one aspect of the present application, a backing welding process curve based on a narrow gap U-shaped groove is provided, and the backing welding process curve is used for welding a narrow gap U-shaped groove, and on the basis of the CMT reference curve, at least one current pulse is introduced before and after the short-circuit stage to increase the root melt width and avoid root depression, while increasing the peak current and cycle time to increase welding heat input, and reducing the peak current rise rate and the peak current fall rate to extend the peak current action time.

[0008] Through the above technical scheme conceived by the present application, compared with the prior art, the present application can increase the welding heat input and the root weld width by introducing current pulses and optimizing multiple parameters, and can achieve excellent single-sided welding and double-sided forming effects under zero gap assembly conditions, thereby improving the SSC performance of the sour marine pipeline.

[0009] As a further preferred embodiment, the blunt edge thickness b of the narrow gap U-shaped groove is 1.45±0.1 mm, the single-side angle α of the groove is 3±0.5°, and the distance a between the top of the transition arc and the blunt edge is 2.95±0.1 mm.

[0010] As a further preference, compared with the CMT reference curve, the bottom welding process curve increases the peak current by 30% to 50%.

[0011] As a further preferred embodiment, compared with the CMT reference curve, the bottom cover welding process curve increases the cycle time by 300% to 500%.

[0012] As a further preferred embodiment, compared with the CMT reference curve, the bottom welding process curve reduces the peak current rising rate by 30% to 50%.

[0013] As a further preferred embodiment, compared with the CMT reference curve, the bottom welding process curve reduces the peak current drop rate by 20% to 40%.

[0014] As a further preference, two current pulses are introduced before and after the short-circuit phase respectively.

[0015] As a further preference, the duration of the introduced single current pulse is 5.5 ms to 7.5 ms, and the pulse peak current is 220A to 300A.

[0016] According to another aspect of the present application, a bottom sealing welding method for an acidic marine pipeline is provided, wherein the groove of the pipeline to be welded is first designed as a narrow gap U-shaped groove, and then the bottom sealing welding process curve is used for welding.

[0017] According to another aspect of the present application, there is provided a sour ocean pipeline manufactured by the above-mentioned backing welding method.

[0018] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art: 1. This application optimizes the backing welding process curve, which can increase the welding heat input and root molten width, and can achieve excellent single-sided welding and double-sided forming effects in the case of zero gap assembly and no backing. Even in the overhead welding area, a root weld with a certain excess height can be obtained, which solves the problem of weld defects, greatly reduces the assembly difficulty, improves the adaptability of the backing welding misalignment, and can make it easier for energy to reach the root, ensure that the molten pool is fully cooled and solidified, reduce the backing weld hardness, and improve the service performance of the acidic marine pipeline; 2. In particular, the present application optimizes the size of the U-shaped groove, making the bottom wider and the top narrower than the existing groove, thereby reducing the thickness of the bottom weld bead, making it easier for the arc energy to reach the root, and reducing the cooling rate of the molten pool metal, thereby reducing the hardness of the bottom weld bead while avoiding the incomplete penetration defect, and also avoiding the side wall incomplete fusion defect caused by insufficient fluidity of the molten pool metal during welding; 3. In addition, the present application optimizes the specific parameters of the back cover welding process curve, which can further improve the service performance of the sour ocean pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of a narrow gap U-shaped groove in the bottom cover welding process curve provided by the present invention; Figure 2 is the current waveform of the CMT reference curve used in Comparative Example 1 of the present invention; Figure 3 This is a root weld bead formation diagram of an acidic marine pipeline obtained in Comparative Example 1 of the present invention; Figure 4 is a weld structure diagram of an acidic marine pipeline obtained in Comparative Example 1 of the present invention; Figure 5 This is the weld hardness test result of the acidic marine pipeline obtained in Comparative Example 1 of the present invention; Figure 6 This is the SSC test result of the weld of the sour ocean pipeline obtained in Comparative Example 1 of the present invention; Figure 7 is the current waveform of the backing welding process curve used in Example 1 of the present invention; Figure 8This is a root weld bead formation diagram of an acidic marine pipeline obtained in Example 1 of the present invention; Fig. 9 is a weld formation diagram of the acidic ocean pipeline obtained in Example 1 of the present invention; Fig.10 is the weld hardness test result of the sour marine pipeline obtained in Example 1 of the present invention; Fig.11 This is the SSC test result of the weld of the sour ocean pipeline obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] According to one aspect of the present application, a backing welding process curve based on a narrow gap U-shaped groove is provided, which is used for welding the narrow gap U-shaped groove, and on the basis of the CMT reference curve, at least one current pulse is introduced before and after the short-circuit stage, respectively. The pulse current introduced before the short-circuit stage is used to increase the welding heat input and heat coverage range, promote the increase of the root molten width, and improve the adaptability of the backing welding misalignment; the pulse current introduced after the short-circuit stage is used to prolong the arc pressure action time, promote the molten pool metal to flow to the root, solve the root depression problem caused by the gravity drop of the molten pool metal, especially in the overhead welding state, and obtain a root weld with a certain excess height; at the same time, it is also necessary to increase the peak current and cycle time to increase the welding heat input, and reduce the peak current rise rate and the peak current drop rate to prolong the peak current action time, so that the increased heat input is easier to reach the root, while increasing the root molten width and excess height, reducing the molten pool metal cooling rate, thereby achieving the purpose of reducing the hardness of the backing weld, thereby improving the H2S stress corrosion resistance of the welded acidic marine pipeline.

[0022] The present application optimizes the backing welding process curve, which can increase the welding heat input and the root melt width, and can achieve excellent single-sided welding and double-sided forming effects under the conditions of zero gap assembly and no precipitation, thereby obtaining an acidic marine pipeline with high resistance to H2S stress corrosion.

[0023] Further, if Figure 1As shown, the blunt edge thickness b of the narrow gap U-shaped groove is 1.45±0.1mm, the single-side angle α of the groove is 3±0.5°, and the distance a between the top of the transition arc and the blunt edge is 2.95±0.1mm. In a preferred embodiment of the present application, the transition arc radius R is 3.2mm, and a suitable transition arc radius can be selected in practical applications. The present application optimizes the parameters of the narrow gap U-shaped groove, which is wider at the bottom and narrower at the top than the narrow gap U-shaped groove in the prior art. The wide bottom space design can reduce the thickness of the bottom weld, make it easier for the arc energy to reach the root, and reduce the cooling rate of the molten pool metal. While avoiding the incomplete penetration defect, the hardness of the bottom weld is reduced; the narrow upper groove design can avoid the side wall unfused defects caused by insufficient fluidity of the molten pool metal during welding.

[0024] Furthermore, compared with the CMT reference curve, the back cover welding process curve has the peak current (I b ) increases by 30% to 50%, the cycle time (T) increases by 300% to 500%, the peak current rise rate (d_boostup) decreases by 30% to 50%, and the peak current drop rate (d_boostup) decreases by 20% to 40%. When the peak current and cycle are too large, the heat input is too large, which is easy to cause the bottom welding to leak; when the peak current and cycle are too small, it is easy to cause the bottom welding to not be penetrated, and the heat input is small, which is easy to cause high hardness; when the peak current rise rate is too large, the welding current reaches the peak value in a very short time, which may cause the welding arc to be unstable and the droplet transition to be poor. When the peak current is too small, the welding current takes a long time to reach the peak value, and it cannot provide enough energy to melt through the workpiece, affecting the quality of the weld; when the peak current drop rate is too large, the weld cools quickly, resulting in high weld hardness, affecting the service performance. When the peak current drop rate is too small, the weld is overheated, resulting in coarse grains, affecting the weld performance.

[0025] Furthermore, the number of current pulses introduced before and after the short-circuit stage does not need to be consistent, and an appropriate number of current pulses can be introduced according to actual conditions. Preferably, two current pulses are introduced before and after the short-circuit stage, respectively. The duration of the introduced single current pulse is 5.5ms to 7.5ms, and the pulse peak current is 220A to 300A. When the pulse current and duration are too large, the heat input increases, which can easily lead to weld leakage and coarse grain problems, affecting weld formation and performance; when the pulse current and duration are too small, the heat input is insufficient, and it is difficult for heat to reach the root, resulting in high hardness at the root, affecting the service performance of the acidic sea pipe.

[0026] According to another aspect of the present application, a back-sealing welding process for an acidic marine pipeline is provided, specifically, the groove of the pipeline to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the above-mentioned back-sealing welding process curve to obtain the acidic marine pipeline.

[0027] The present application reduces the layer thickness of the bottom weld by designing a wide bottom space of a narrow gap U-shaped groove. On this basis, the peak current and cycle are increased by the bottom welding process curve, the peak current rise rate and the current drop rate are reduced, and two current pulses are introduced before and after the short-circuit stage. This can make it easier for the increased heat input to reach the root, while increasing the root molten width and excess height, reducing the cooling rate of the molten pool metal, thereby achieving the purpose of reducing the hardness of the bottom weld.

[0028] According to another aspect of the present application, a sour marine pipeline manufactured using the above-mentioned backing welding process is provided. The use of a narrow gap U-shaped groove and a backing welding process curve can achieve zero-defect welding of the sour marine pipeline, and the maximum hardness of the joint is less than 248HV10, and the stress corrosion cracking (SSC) test is qualified, meeting the service requirements of the sour marine pipeline.

[0029] The technical solution provided by this application is further described below based on specific embodiments.

[0030] Example 1 The groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the backing welding process curve to obtain the acidic marine pipeline, wherein: The blunt edge thickness b of the narrow gap U-shaped groove is 1.45 mm, the single-side angle α of the groove is 3°, the transition arc radius R is 3.2 mm, and the distance a between the top of the transition arc and the blunt edge is 2.95 mm.

[0031] The peak current of the CMT reference curve is 270A, the cycle is 5.5ms, the current rise rate is 220A / ms, and the current drop rate is 130A / ms. The back welding process curve is based on the CMT reference curve, and the peak current (I b ) increased by 33.3%, the cycle time (T) increased by 370%, the peak current rise rate (d_boostup) was reduced by 40%, and the peak current drop rate (d_boostup) was reduced by 30%. In addition, two current pulses with a duration of 7ms were introduced before and after the short-circuit stage, and the pulse peak current was 270A.

[0032] Example 2 The groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the backing welding process curve to obtain the acidic marine pipeline, wherein: The blunt edge thickness b of the narrow gap U-shaped groove is 1.35 mm, the single-side angle α of the groove is 2.5°, the transition arc radius R is 3.2 mm, and the distance a between the top of the transition arc and the blunt edge is 2.85 mm.

[0033] The peak current of the CMT reference curve is 270A, the cycle is 5.5ms, the current rise rate is 220A / ms, and the current drop rate is 130A / ms. The back welding process curve is based on the CMT reference curve, and the peak current (I b ) is increased by 30%, the cycle time (T) is increased by 300%, the peak current rise rate (d_boostup) is reduced by 30%, and the peak current drop rate (d_boostup) is reduced by 20%. In addition, two current pulses with a duration of 5.5ms are introduced before and after the short-circuit stage, and the pulse peak current is 220A.

[0034] Example 3 The groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the backing welding process curve to obtain the acidic marine pipeline, wherein: The thickness b of the blunt edge of the narrow gap U-shaped groove is 1.55 mm, the single-side angle α of the groove is 3.5°, the radius R of the transition arc is 3.2 mm, and the distance a between the top of the transition arc and the blunt edge is 3.05 mm.

[0035] The peak current of the CMT reference curve is 270A, the cycle is 5.5ms, the current rise rate is 220A / ms, and the current drop rate is 130A / ms. The back welding process curve is based on the CMT reference curve, and the peak current (I b ) is increased by 50%, the cycle time (T) is increased by 500%, the peak current rise rate (d_boostup) is reduced by 50%, and the peak current drop rate (d_boostup) is reduced by 40%. In addition, two current pulses with a duration of 7.5ms are introduced before and after the short-circuit stage, and the pulse peak current is 300A.

[0036] Example 4 The groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the backing welding process curve to obtain the acidic marine pipeline, wherein: The blunt edge thickness b of the narrow gap U-shaped groove is 1.45 mm, the single-side angle α of the groove is 3°, the transition arc radius R is 3.2 mm, and the distance a between the top of the transition arc and the blunt edge is 2.95 mm.

[0037] The peak current of the CMT reference curve is 270A, the cycle is 5.5ms, the current rise rate is 220A / ms, and the current drop rate is 130A / ms. The back welding process curve is based on the CMT reference curve, and the peak current (I b ) is increased by 40%, the cycle time (T) is increased by 400%, the peak current rise rate (d_boostup) is reduced by 40%, and the peak current drop rate (d_boostup) is reduced by 30%. In addition, two current pulses with a duration of 6.5ms are introduced before and after the short-circuit stage, and the pulse peak current is 260A.

[0038] Comparative Example 1 The groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then the narrow gap U-shaped groove is welded using the CMT reference curve in Example 1 to obtain the acidic marine pipeline, wherein the narrow gap U-shaped groove is the same as in Example 1.

[0039] The welds obtained in Example 1 and Comparative Example 1 were subjected to hardness tests, with the test positions being 2 mm below the top parent material, the middle of the weld, and 2 mm above the bottom parent material. The test force was 10 kN, the holding time was 15 s, the test spacing of the heat affected zone was 1 mm, and the test spacing between the parent material and the weld center was 2 mm. The welds were subjected to stress corrosion cracking (SSC) tests, the test duration was 30 days, the H2S concentration was greater than 2300 mg / L, the test stress was not less than 80% of the actual yield strength (AYS), and the test temperature was 24 ± 3 °C.

[0040] like Figure 3 As shown, the bottom welding of comparative example 1 shows obvious concavity in the overhead welding area; Figure 4 As shown in the figure, due to the rapid cooling rate, the weld structure is coarse martensite, resulting in the hardness of the backing weld significantly exceeding 248HV10. Figure 5 As shown. Moreover, after 30 days of SSC test, the weld cracked. Figure 6 shown.

[0041] The backing welding process curve of Example 1 increases the peak current and cycle, increases the backing welding heat input and energy, achieves uniform penetration of the backing welding, and increases the arc thrust, which can promote the transfer of the molten droplets; by reducing the current rising rate in the acceleration stage and the current falling rate after the acceleration stage, the arc is prompted to continue to impact the molten pool for a longer time in the current and falling stages, so that more molten pool metal is squeezed to the root of the weld and spreads out under continuous action. The root weld formation effect is as follows Figure 8 As shown in the figure: the molten pool metal is squeezed out to the root of the weld to form a surplus height, and the transition with the base material is uniform and smooth. Fig. 9 As shown, the weld is well formed, the layer thickness is uniform, and there are no defects such as lack of fusion, bottom depression, pores and cracks.

[0042] The wide bottom space design of the narrow gap U-shaped groove can reduce the layer thickness of the bottom weld. On this basis, the bottom welding process curve can increase the peak current and cycle, reduce the peak current rise rate and current drop rate, and introduce two current pulses before and after the short circuit stage, which can make the increased heat input easier to reach the root. While increasing the root molten width and excess height, the cooling rate of the molten pool metal is reduced, and the weld is fully melted, cooled and solidified, thereby achieving the purpose of reducing the hardness of the bottom weld and improving the service performance of the acid sea pipe. Fig.10 and Fig.11 As shown, the hardness of the welds is less than 248HV10, and there is no cracking after 30 days of SSC testing.

[0043] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. The bottom welding process curve based on narrow gap U-shaped groove is characterized by: The bottom welding process curve is used for welding narrow gap U-shaped grooves, and on the basis of the CMT reference curve, at least one current pulse is introduced before and after the short circuit stage to increase the root weld width and avoid root depression, while increasing the peak current and cycle time to increase welding heat input, and reducing the peak current rise rate and peak current drop rate to extend the peak current action time.

2. The back cover welding process curve according to claim 1, characterized in that: The thickness b of the blunt edge of the narrow gap U-shaped groove is 1.45±0.1 mm, the single-side angle α of the groove is 3±0.5°, and the distance a between the top of the transition arc and the blunt edge is 2.95±0.1 mm.

3. The back cover welding process curve according to claim 1, characterized in that: Compared with the CMT reference curve, the bottom welding process curve increases the peak current by 30% to 50%.

4. The back cover welding process curve according to claim 1, characterized in that: Compared to the CMT benchmark curve, the bottom cover welding process curve increases the cycle time by 300% to 500%.

5. The back cover welding process curve according to claim 1, characterized in that: Compared with the CMT reference curve, the bottom welding process curve reduces the peak current rising rate by 30% to 50%.

6. The back cover welding process curve according to claim 1, characterized in that: Compared with the CMT reference curve, the bottom welding process curve reduces the peak current drop rate by 20% to 40%.

7. The back cover welding process curve according to claim 1, characterized in that: Two current pulses are introduced before and after the short-circuit phase.

8. The back cover welding process curve according to any one of claims 1 to 7, characterized in that: The duration of the introduced single current pulse is 5.5ms to 7.5ms, and the pulse peak current is 220A to 300A.

9. A bottom sealing welding method for an acidic marine pipeline, characterized in that: First, the groove of the pipe to be welded is designed as a narrow gap U-shaped groove, and then welding is performed using the bottom sealing welding process curve as described in any one of claims 1 to 8.

10. A sour ocean pipeline manufactured by the backing welding method according to claim 9.

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