X60MOS steel grade submarine longitudinal submerged arc welding steel pipe and manufacturing method thereof

Abstract

The invention discloses an X60MOS steel-grade submarine longitudinal submerged arc welding steel pipe and a manufacturing method thereof. The base metal steel plate comprises, by mass, 0.01%-0.05% of C, 1.10%-1.40% of Mn, 0.10%-0.40% of Si, smaller than or equal to 0.020% of P, smaller than or equal to 0.003% of S, smaller than or equal to 0.08% of Mo, smaller than or equal to 0.25% of Ni, 0.15%-0.30% of Cr, smaller than or equal to 0.30% of Cu, smaller than or equal to 0.05% of V, 0.03%-0.06% of Nb, smaller than or equal to 0.020% of Ti, 0.020%-0.030% of Al, smaller than or equal to 0.01% of N, smaller than or equal to 0.0005% of B, 0.060%-0.110% of V + Nb + Ti and the balance Fe. The steel pipe has the beneficial effects that the steel pipe has the performances of corrosion resistance, low temperature resistance and the like by optimizing base metal steel plate components and welding process parameters and designing the groove size, and the requirements of seabed oil and gas conveying steel pipes are met.

Description

Technical Field

[0001] The invention relates to a straight seam welded steel pipe, in particular to an X60MOS steel grade submarine straight seam submerged arc welded steel pipe and a manufacturing method thereof, belonging to the technical field of steel pipe forming and manufacturing. Background Art

[0002] Unconventional oil and gas resources account for about 80% of oil and gas resources, and unconventional oil and gas resources are almost unexploited, and will be the focus of future development. Unconventional oil and gas resources are generally distributed in areas with harsh geographical environments such as the seabed, low temperature, remoteness, and earthquake fault zones. In addition, many oil and gas components contain corrosive gases such as H2S. According to the specific service conditions of oil and gas pipelines, the transmission steel pipes are required to have comprehensive properties such as low temperature resistance, large deformation resistance, and corrosion resistance when buried on the seabed, which puts forward higher requirements for pipeline construction, pipe material selection, and steel pipe manufacturing.

[0003] X60MOS steel grade submarine straight seam submerged arc welded steel pipe is used for oil and gas transportation steel pipe buried in the seabed. At present, most of the oil and gas transportation steel pipes with special properties such as high-strength pipes, submarine pipes, acid-resistant pipes, low-temperature pipes, and high-strain pipes on the market are high-end welded pipes with only a single performance. These steel pipes cannot meet the comprehensive performance requirements of being buried in the seabed and having corrosion resistance, low temperature resistance, etc. Summary of the invention

[0004] In order to overcome the deficiency that the existing oil and gas transmission steel pipes cannot meet the comprehensive performance requirements of corrosion resistance, low temperature resistance, etc. when buried on the seabed, the present invention provides an X60MOS steel grade submarine straight seam submerged arc welded steel pipe and a manufacturing method thereof.

[0005] The technical solution adopted by the present invention to solve the technical problem is: an X60MOS steel grade submarine straight seam submerged arc welded steel pipe, wherein the components and mass percentages of the parent steel plate are: C 0.01%-0.05%, Mn 1.10%-1.40%, Si 0.10%-0.40%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr 0.15%-0.30%, Cu≤0.30%, V≤0.05%, Nb 0.03%-0.06%, Ti≤0.020%, Al 0.020%-0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.060%-0.110%, and the balance is Fe.

[0006] Preferably, the components and mass percentages of the parent steel plate are: C 0.02% to 0.04%, Mn 1.20% to 1.30%, Si 0.20% to 0.30%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr0.20% to 0.25%, Cu≤0.30%, V≤0.05%, Nb 0.04% to 0.05%, Ti≤0.020%, Al 0.020% to 0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.070% to 0.100%, and the balance is Fe.

[0007] The components and mass percentages of the steel pipe weld are: C 0.01%-0.05%, Mn 1.20%-1.50%, Si 0.20%-0.50%, P≤0.020%, S≤0.005%, Mo 0.10%-0.20%, Ni0.05%-0.25%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

[0008] Preferably, the components and mass percentages of the steel pipe weld are: C 0.02% to 0.04%, Mn 1.30% to 1.40%, Si 0.30% to 0.40%, P≤0.020%, S≤0.005%, Mo 0.10% to 0.20%, Ni 0.10% to 0.20%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

[0009] The tensile strength of the steel pipe is: 415MPa≤Rt0.5≤565MPa, 520MPa≤Rm≤760MPa, Rt0.5 / Rm≤0.93, Af≥18%, weld joint Rm≥520MPa; CVN (tube body / weld / hot zone) (-48°C): average value ≥45J, single value ≥38J; DWTT (-38°C) ≥85%; hardness: tube body ≤230HV10, weld ≤250HV10; weld CTOD (-38°C) ≥0.15mm; HIC test: in line with ISO 15156-2 standard, no cracks; SSCC test: in line with ISO 7539-2 standard, no cracks.

[0010] The welding crack sensitivity index Pcm of the base steel plate is ≤0.15.

[0011] A method for manufacturing the X60MOS steel grade submarine straight seam submerged arc welded steel pipe comprises the following steps: edge milling, pre-bending, JCO forming, pre-welding, internal welding, external welding, first ultrasonic inspection, first X-ray inspection, mechanical diameter expansion, water pressure test, chamfering, groove processing, second ultrasonic inspection, second X-ray inspection, pipe end magnetic particle inspection and appearance quality inspection. In the edge milling process, the upper groove height is 8.5-9.0 mm and the blunt edge thickness is 5.5-6.5 mm.

[0012] The internal welding and the external welding adopt four-wire submerged arc automatic welding, the first wire adopts direct current reverse connection, and the second to fourth wires adopt alternating current.

[0013] In the internal welding step, the welding process parameters are as follows:

[0014] The first wire current is 1000~1100A, and the voltage is 32~36V;

[0015] The second wire current is 900-1000A, and the voltage is 35-40V;

[0016] The third wire current is 700-800A, and the voltage is 35-40V;

[0017] The fourth wire current is 600-700A and the voltage is 40-44V;

[0018] The welding speed is 150-180cm / min.

[0019] In the external welding step, the welding process parameters are as follows:

[0020] The first wire current is 1100~1200A, and the voltage is 32~36V;

[0021] The second wire current is 900-1000A, and the voltage is 35-40V;

[0022] The third wire current is 700-800A, and the voltage is 35-40V;

[0023] The fourth wire current is 600-700A and the voltage is 40-44V;

[0024] The welding speed is 150-180cm / min.

[0025] The beneficial effects of the present invention are as follows: by optimizing the components of the base steel plate, the base steel plate has better low-temperature impact toughness and low-temperature DWTT performance; the groove size is reasonably designed to effectively solve the problem of coarse grains in the secondary thermal cycle of welding, which leads to poor toughness in the hot zone, and ensure the low-temperature impact toughness of the hot zone; the welding process parameters are optimized to enable the weld to obtain a suitable penetration depth and good performance; the steel pipe has comprehensive properties such as corrosion resistance, low temperature resistance, and large deformation resistance, which meets the requirements for steel pipes buried on the seabed to transport oil and gas. DETAILED DESCRIPTION

[0026] The present invention is further described below by way of examples. However, those skilled in the art should be aware that the present invention is not limited to the specific embodiments listed, and all embodiments that conform to the spirit of the present invention should be included within the protection scope of the present invention.

[0027] The invention discloses an X60MOS steel grade submarine straight seam submerged arc welded steel pipe and a manufacturing method thereof, wherein the components and mass percentages of a parent steel plate of the steel pipe are as follows: C 0.01%-0.05%, Mn 1.10%-1.40%, Si 0.10%-0.40%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr 0.15%-0.30%, Cu≤0.30%, V≤0.05%, Nb 0.03%-0.06%, Ti≤0.020%, Al 0.020%-0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.060%-0.110%, and the balance is Fe.

[0028] Preferably, the components and mass percentages of the parent steel plate are: C 0.02% to 0.04%, Mn 1.20% to 1.30%, Si 0.20% to 0.30%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr0.20% to 0.25%, Cu≤0.30%, V≤0.05%, Nb 0.04% to 0.05%, Ti≤0.020%, Al 0.020% to 0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.070% to 0.100%, and the balance is Fe.

[0029] The welding crack sensitivity index Pcm of the base steel plate is ≤0.15.

[0030] The present invention adjusts the components of the base steel plate and their mass percentage content to make the X60MOS steel grade steel plate have good low-temperature DWTT (drop weight tear test) performance. The shear area rate of the steel plate in the drop weight tear test at -38°C is 81% to 92%, and the average value reaches more than 89%.

[0031] The components and mass percentages of the steel pipe weld are: C 0.01%-0.05%, Mn 1.20%-1.50%, Si 0.20%-0.50%, P≤0.020%, S≤0.005%, Mo 0.10%-0.20%, Ni0.05%-0.25%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

[0032] Preferably, the components and mass percentages of the steel pipe weld are: C 0.02% to 0.04%, Mn 1.30% to 1.40%, Si 0.30% to 0.40%, P≤0.020%, S≤0.005%, Mo 0.10% to 0.20%, Ni 0.10% to 0.20%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

[0033] The tensile strength of the X60MOS steel grade submarine low-temperature acid-resistant straight seam submerged arc welded steel pipe is: 415MPa≤Rt0.5≤565MPa, 520MPa≤Rm≤760MPa, Rt0.5 / Rm≤0.93, Af≥18%, and Rm of the welded joint is ≥520MPa; Charpy impact CVN (tube body / weld / hot zone) (-48°C): average value ≥45J, single value ≥38J; drop weight tear test DWTT (-38°C) ≥85%; hardness: tube body ≤230HV10, weld ≤250HV10; weld crack tip opening displacement CTOD (-38°C) ≥0.15mm; hydrogen induced cracking HIC test: in line with ISO 15156-2 standard, no cracks; sulfide stress cracking SSCC test: in line with ISO 7539-2 standard, no cracks.

[0034] The manufacturing method of the X60MOS steel grade submarine straight seam submerged arc welded steel pipe comprises the following steps: edge milling, pre-bending, JCO forming, pre-welding, internal welding, external welding, first ultrasonic inspection, first X-ray inspection, mechanical diameter expansion, water pressure test, chamfering, groove processing, second ultrasonic inspection, second X-ray inspection, pipe end magnetic particle inspection and appearance quality inspection; in the edge milling process, the upper groove height of the parent steel plate is 8.5-9.0 mm, and the blunt edge thickness is 5.5-6.5 mm, so that the secondary heat cycle area moves down or disappears, ensuring that the welding process can be fully penetrated and the weld quality is ensured.

[0035] The internal welding and the external welding are both carried out by four-wire submerged arc automatic welding. The four welding wires are arranged in sequence along the weld seam, and Mn-Mo-Ti-B series welding wires are selected. The first wire adopts reverse direct current, and the second to fourth wires adopt alternating current.

[0036] When determining the welding parameters for the internal and external welding, the role of each wire in the four-wire welding is fully considered. At the same time, the difference in heat input of the internal and external welding, the impact on the impact performance of the heat-affected zone of the steel pipe welding, and the impact of the wall thickness on the impact performance of the heat-affected zone are considered to determine the appropriate welding parameters and heat input for the internal and external welding to perform welding, which solves the problem of severe reduction in strength and toughness caused by the secondary thermal cycle of welding, and makes the weld and hot zone have excellent low-temperature impact toughness. Among them,

[0037] In the internal welding step, the welding process parameters are as follows:

[0038] The first wire current is 1000~1100A, and the voltage is 32~36V;

[0039] The second wire current is 900-1000A, and the voltage is 35-40V;

[0040] The third wire current is 700-800A, and the voltage is 35-40V;

[0041] The fourth wire current is 600-700A and the voltage is 40-44V;

[0042] The welding speed is 150-180cm / min.

[0043] In the external welding step, the welding process parameters are as follows:

[0044] The first wire current is 1100~1200A, and the voltage is 32~36V;

[0045] The second wire current is 900-1000A, and the voltage is 35-40V;

[0046] The third wire current is 700-800A, and the voltage is 35-40V;

[0047] The fourth wire current is 600-700A and the voltage is 40-44V;

[0048] The welding speed is 150-180cm / min.

[0049] The JCO forming process is as follows: using a JCO forming machine to punch half of the pre-bent steel plate multiple times to form a "J" shape, and then punching the other half multiple times to form a "C" shape, and finally pressing the middle of the steel plate once to form an open "O" shape.

[0050] In the examples, the Charpy impact test is performed according to ASTM A370-2012; and the DWTT test is performed according to SY / T6476-2007.

[0051] Embodiment 1

[0052] X60MOS steel grade steel plate, width 2006mm, thickness 22.2mm.

[0053] The components and mass percentages of the X60MOS steel grade steel plate are: C 0.02%, Mn 1.20%, Si0.20%, P0.025%, S 0.002%, Mo 0.07%, Ni 0.20%, Cr 0.18%, Cu 0.25%, V 0.04%, Nb0.04%, Ti 0.018%, Al 0.028%, N 0.009%, B0.0004%, V+Nb+Ti0.100%, and the balance is Fe; the welding crack sensitivity index Pcm=0.12%.

[0054] The DWTT performance of X60MOS steel grade steel plate was tested, and the test results are shown in Table 1.

[0055] Table 1 DWTT test results of X60MOS steel grade steel plate in Example 1

[0056]

[0057] It can be seen from Table 1 that the average shear area rate of the X60MOS steel grade steel plate in this embodiment reached more than 90%, and the shear area rate of each sample reached more than 82%, which meets the requirements of the steel pipe base material for the low temperature and acid corrosion resistance environment on the seabed.

[0058] Embodiment 2

[0059] X60MOS steel grade steel plate, width 2006mm, thickness 22.2mm.

[0060] The components and mass percentages of the X60MOS steel grade steel plate are: C 0.03%, Mn 1.30%, Si0.30%, P0.015%, S 0.002%, Mo 0.06%, Ni 0.18%, Cr 0.25%, Cu 0.20%, V 0.03%, Nb 0.04%, Ti 0.015%, Al 0.022%, N 0.01%, B 0.0003%, V+Nb+Ti0.080%, and the balance is Fe; Pcm=0.15%.

[0061] The DWTT performance of X60MOS steel grade steel plate was tested, and the test results are shown in Table 2.

[0062] Table 2 DWTT test results of X60MOS steel grade steel plate in Example 2

[0063]

[0064]

[0065] It can be seen from Table 2 that the average shear area rate of the X60MOS steel grade steel plate in this embodiment reached more than 89%, and the shear area rate of each sample reached more than 86%, which meets the requirements of the steel pipe base material for the low temperature and acid corrosion resistance environment on the seabed.

[0066] Embodiment 3

[0067] X60MOS steel grade steel plate, width 2006mm, thickness 22.2mm.

[0068] The components and mass percentages of the X60MOS steel grade steel plate are: C 0.04%, Mn 1.35%, Si0.28%, P0.010%, S 0.001%, Mo 0.065%, Ni 0.15%, Cr 0.22%, Cu 0.18%, V 0.02%, Nb0.038%, Ti 0.016%, Al 0.024%, N 0.01%, B 0.0002%, V+Nb+Ti0.070%, and the balance is Fe; Pcm=0.147%.

[0069] The DWTT performance of X60MOS steel grade steel plate was tested, and the test results are shown in Table 3.

[0070] Table 3 DWTT test results of X60MOS steel grade steel plate in Example 3

[0071]

[0072] It can be seen from Table 6 that the average shear area rate of the X60MOS steel grade steel plate in this embodiment reached more than 86%, and the shear area rate of each sample reached more than 71%, which meets the requirements of the steel pipe base material for the low temperature and acid corrosion resistance environment on the seabed.

[0073] Embodiment 4

[0074] The X60MOS steel grade steel plates provided in Examples 1 to 3 are selected, and the manufacturing method of the present invention is adopted to produce submarine straight seam submerged arc welded steel pipes, the steel pipes having a diameter of φ813 and a wall thickness of 22.2 mm.

[0075] The X60MOS steel grade steel plates provided in the first to third embodiments are formed after milling, pre-bending, JCO forming, pre-welding, internal welding, external welding, first ultrasonic inspection, first X-ray inspection, mechanical expansion, water pressure test, chamfering, groove processing, second ultrasonic inspection, second X-ray inspection, magnetic particle inspection of pipe ends and appearance quality inspection. Among them,

[0076] In the milling step, the upper and lower bevel angles are both 35°, the upper bevel height is 8.5-9.0 mm, and the blunt edge thickness is 5.5-6.5 mm.

[0077] In the JCO forming step: use the JCO forming machine to punch half of the pre-bent steel plate multiple times to form a "J" shape, then punch the other half multiple times to form a "C" shape, and finally press the middle of the steel plate once to form an open "O" shape.

[0078] In the internal welding step: four-wire submerged arc automatic welding is used to weld the inner welding groove of the steel pipe, the welding wire used is Mn-Mo-Ti-B series welding wire, and the welding process parameters are: the first wire current is 1050A, and the voltage is 34V; the second wire current is 950A, and the voltage is 38V; the third wire current is 750A, and the voltage is 40V; the fourth wire current is 650A, and the voltage is 42V; the welding speed is 165cm / min.

[0079] In the external welding step: four-wire submerged arc automatic welding is used to weld the welding groove on the outside of the steel pipe. The welding wire used is Mn-Mo-Ti-B series welding wire. The welding process parameters are: the first wire current is 1150A, and the voltage is 34V; the second wire current is 950A, and the voltage is 38V; the third wire current is 750A, and the voltage is 40V; the fourth wire current is 650A, and the voltage is 42V; the welding speed is 165cm / min.

[0080] The chemical composition and mass percentage of the obtained steel pipe weld are: C 0.01%-0.05%, Mn 1.20%-1.50%, Si 0.20%-0.50%, P≤0.020%, S≤0.005%, Mo 0.10%-0.20%, Ni 0.05%-0.25%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

[0081] The Charpy impact properties of the weld and hot zone of the steel pipe processed by the X60MOS steel grade steel plate provided in Examples 1 to 3 were tested, and the test results are shown in Table 4.

[0082] Table 4 Charpy impact test results of steel pipe weld and hot zone

[0083]

[0084] It can be seen from Table 4 that the average values ​​of the Charpy impact energy of the weld and hot zone of the X60MOS steel grade straight seam submerged arc welded pipe manufactured by the technical solution of the present invention are higher than 123J and 146J respectively, and the low temperature resistance is good, meeting the requirements for low temperature toughness of the steel pipe in the low temperature and acid corrosion resistance environment of the seabed.

[0085] The HIC, SSCC, and CTOD properties of the steel pipe welds processed by the X60MOS steel grade steel plates provided in Examples 1 to 3 were tested, wherein no cracks were found in the weld HIC and SSCC tests, and the weld CTOD test results are shown in Table 5.

[0086] Table 5 CTOD test results of steel pipe welds

[0087]

[0088] It can be seen from Table 5 that the CTOD performance of the weld of the X60MOS steel grade straight seam submerged arc welded pipe manufactured using the technical solution of the present invention is good, and meets the crack opening displacement performance requirements for the steel pipe in the submarine low temperature and acid corrosion resistant environment.

[0089] Embodiment 5

[0090] The performance test was carried out on the submarine straight seam submerged arc welded steel pipe with a diameter of φ813 and a wall thickness of 22.2 mm produced by the technical solution of the present invention. The test results are shown in Table 6.

[0091] Table 6 Test results of submarine straight seam submerged arc welded steel pipe

[0092]

[0093]

[0094] The X60MOS steel grade submarine straight seam submerged arc welded steel pipe and the manufacturing method thereof of the present invention control the components and contents of the steel pipe base material so that the steel plate has good low-temperature impact toughness and low-temperature DWTT performance; reasonably design the groove size to solve the problem that the toughness of the hot zone is poor due to coarse grains in the secondary thermal cycle of welding, and the low-temperature impact toughness of the hot zone is guaranteed; set the process parameters such as the current, voltage, angle, wire spacing and welding speed of each wire in the welding process so that the weld obtains a suitable penetration depth and good performance; the weld finally obtains a structure mainly composed of acicular ferrite and has good strength and toughness, and solves the problem that the strength and toughness of the steel pipe are reduced due to local heating during the welding process.

[0095] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the claims of this patent.

Claims

1. An X60MOS steel grade submarine straight seam submerged arc welded steel pipe, characterized by: The components and mass percentages of the base steel plate are: C 0.01%-0.05%, Mn 1.10%-1.40%, Si 0.10%-0.40%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr 0.15%-0.30%, Cu≤0.30%, V≤0.05%, Nb 0.03%-0.06%, Ti≤0.020%, Al 0.020%-0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.060%-0.110%, and the balance is Fe.

2. According to claim 1, the X60MOS steel grade submarine straight seam submerged arc welded steel pipe is characterized in that: The components and mass percentages of the parent steel plate are: C 0.02%-0.04%, Mn 1.20%-1.30%, Si 0.20%-0.30%, P≤0.020%, S≤0.003%, Mo≤0.08%, Ni≤0.25%, Cr0.20%-0.25%, Cu≤0.30%, V≤0.05%, Nb 0.04%-0.05%, Ti≤0.020%, Al 0.020%-0.030%, N≤0.01%, B≤0.0005%, V+Nb+Ti 0.070%-0.100%, and the balance is Fe.

3. The X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 1 is characterized in that: The components and mass percentages of the steel pipe weld are: C 0.01%-0.05%, Mn 1.20%-1.50%, Si 0.20%-0.50%, P≤0.020%, S≤0.005%, Mo 0.10%-0.20%, Ni 0.05%-0.25%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

4. The X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 3 is characterized in that: The components and mass percentages of the steel pipe weld are: C 0.02%-0.04%, Mn 1.30%-1.40%, Si0.30%-0.40%, P≤0.020%, S≤0.005%, Mo 0.10%-0.20%, Ni 0.10%-0.20%, Cr≤0.20%, Cu≤0.20%, V≤0.05%, Nb≤0.04%, Ti≤0.020%, Al≤0.020%, N≤0.030%, B≤0.0025%, and the balance is Fe.

5. The X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 4 is characterized in that: The tensile strength of the steel pipe is: 415MPa≤Rt0.5≤565MPa, 520MPa≤Rm≤760MPa, Rt0.5 / Rm≤0.93, Af≥18%, weld joint Rm≥520MPa; CVN (tube body / weld / hot zone) (-48℃): average value ≥45J, single value ≥38J; DWTT (-38℃) ≥85%; hardness: tube body ≤230HV10, weld ≤250HV10; weld CTOD (-38℃) ≥0.15mm; HIC test: in line with ISO15156-2 standard, no cracks; SSCC test: in line with ISO 7539-2 standard, no cracks.

6. The X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 1 or 2, characterized in that: The welding crack sensitivity index Pcm of the base steel plate is ≤0.

15.

7. A method for manufacturing the X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 1, comprising the following steps: Milling, pre-bending, JCO forming, pre-welding, internal welding, external welding, first ultrasonic inspection, first X-ray inspection, mechanical expansion, water pressure test, chamfering, groove processing, second ultrasonic inspection, second X-ray inspection, magnetic particle inspection of pipe end and appearance quality inspection, characterized in that: in the milling process, the upper groove height is 8.5-9.0mm and the blunt edge thickness is 5.5-6.5mm.

8. The X60MOS steel grade submarine straight seam submerged arc welded steel pipe according to claim 7 is characterized in that: The internal welding and the external welding adopt four-wire submerged arc automatic welding, the first wire adopts direct current reverse connection, and the second to fourth wires adopt alternating current.

9. The manufacturing method according to claim 8, characterized in that: In the internal welding step, the welding process parameters are as follows: The first wire current is 1000~1100A, and the voltage is 32~36V; The second wire current is 900-1000A, and the voltage is 35-40V; The third wire current is 700-800A, and the voltage is 35-40V; The fourth wire current is 600-700A and the voltage is 40-44V; The welding speed is 150-180cm / min.

10. The manufacturing method according to claim 9, characterized in that: In the external welding step, the welding process parameters are as follows: The first wire current is 1100~1200A, and the voltage is 32~36V; The second wire current is 900-1000A, and the voltage is 35-40V; The third wire current is 700-800A, and the voltage is 35-40V; The fourth wire current is 600-700A and the voltage is 40-44V; The welding speed is 150-180cm / min.

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