A method for forming a high manganese steel plate head for LNG storage tank

Abstract

A method for forming a high manganese steel plate head for an LNG tank. When the radius of curvature of the high manganese steel plate head is R=200mm-2000mm, warm forming or hot forming is used for the head. During warm forming, a drum machine is used for preliminary pre-pressing after unloading, and the pre-pressed head is heated to a heating temperature of 500℃-600℃ in a furnace, or an online heating spinning machine is used for spinning without heating in a furnace. During hot forming, the head plate and the mother material test plate are put into the furnace at the same time. After heating in the furnace, the temperature out of the furnace is controlled at 800℃-850℃. The insulation time in the furnace is less than 0.5 hours, and the head is quickly air-cooled after hot pressing. The present invention can solve the technical difficulties in the processing and forming of small-diameter heads of high manganese steel. The high manganese steel processed according to this method has good performance and good product appearance quality. It is a key technology for the application of high manganese steel in LNG tanks, with feasible process, independent and controllable technology, and reliable quality.

Description

Technical Field

[0001] The invention belongs to the field of construction and design of marine LNG storage tanks, and in particular relates to a method for forming a high-manganese steel plate head of an LNG storage tank. Background Art

[0002] Clean energy is the guarantee for sustainable development of today's society. In recent years, the production and trade of global liquefied natural gas (LNG) has become increasingly active and is becoming a new hotspot in the world's oil and gas industry. For this reason, a large number of LNG storage tanks need to be built at home and abroad to store and transport LNG. Traditional LNG storage tank construction materials use expensive Invar alloys, 9Ni steel, aluminum alloys and austenitic stainless steel. In recent years, high manganese austenitic steel has attracted much attention due to its low price and excellent plasticity and toughness. High manganese austenitic low-temperature steel has good low-temperature resistance and wear resistance, and is very suitable for storing liquefied natural gas. High manganese steel is low in price and has almost become an ideal material for LNG fuel storage tanks. Its application in LNG low-temperature fuel tanks has become an inevitable trend.

[0003] High manganese steel forming and processing is one of the key construction technologies for LNG tanks, and its research provides technical guarantee for the success of high manganese steel LNG tanks. By solving the process problems in the construction of high manganese steel, identifying the potential risks in industrialization, and formulating solutions, the reliability of the forming structures such as the head and shell of the high manganese steel LNG tank on the actual ship is guaranteed.

[0004] According to the characteristics of high manganese steel materials, it is very difficult to change the state of hot-formed or cold-formed parts through heat treatment after processing, and improper cold-forming pressing will produce a large number of surface cracks. In order to meet the construction specifications of LNG storage tanks, fiber elongation exceeding 5% needs to be heat treated, and the performance must be qualified after heat treatment. It is necessary to formulate a reasonable forming process, conduct process tests, and determine the process based on the test results until the performance test meets the requirements of the "Guidelines for the Application of High Manganese Austenitic Low-Temperature Steel" and solidify the forming process. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for forming a high manganese steel plate head for an LNG tank, aiming to achieve the purpose that the head made of high manganese steel plate meets various specifications of the LNG tank. The technical solution adopted is:

[0006] A method for forming a high manganese steel plate head for an LNG tank, when the curvature radius R of the high manganese steel plate head is 200mm-2000mm, warm forming or hot forming is used to process the head, and the specific operation is as follows:

[0007] During warm forming processing, plasma, laser and high-pressure water jet cutting are used.

[0008] After unloading, a drum beating machine is used for preliminary pre-pressing and forming. When beating, the high-manganese steel plate is placed on the lower tire of the drum beating machine to ensure that the edge of the high-manganese steel plate can move freely. The drumming depth is 1 / 10, 1 / 5, 1 / 4, and 1 / 3 of the final forming depth respectively. The drumming is carried out in order from the middle to the surrounding areas.

[0009] The pre-pressed head is put into the furnace and heated to a heating temperature of 500℃-600℃. The temperature of the furnace is 200℃-400℃ during heating. The temperature is increased by 100℃ per hour to 500℃-600℃. The temperature is kept warm for 30 minutes. The head is molded or spun by an oil press, a hydraulic press or a spinning machine to finally form a butterfly, an elliptical or a spherical shape with an inner diameter of 400mm-4000mm. Alternatively, the prefabricated head is spun by an online heating spinning machine without heating in the furnace. The head is heated and spun at the same time. The heating temperature is 500℃-600℃ to a final inner diameter of 400mm-4000mm.

[0010] The warm pressed heads are subjected to 100% PT or MT inspection on appearance, and those without any defects are qualified.

[0011] During hot forming processing, plasma, laser and high-pressure water jet cutting are used to cut the materials, and at the same time, hot-pressed furnace-following mother material test plates are cut out.

[0012] The head plate and the base material test plate are put into the furnace at the same time. After heating in the furnace, the temperature out of the furnace is controlled at 800℃-850℃. The insulation time in the furnace is less than 0.5 hour. After hot pressing, it is quickly air-cooled.

[0013] After the head is hot pressed and formed, if there is any deformation or dimensional deviation, it needs to be heated again to 500℃-600℃ to adjust the shape to the qualified size. When heating again, the mother material test plate is put into the furnace for heating together.

[0014] Carry out mechanical property test on the parent material test plate of the furnace, and carry out 100% PT or MT inspection on the appearance of the hot pressed head. The product without any defects is qualified.

[0015] The above-mentioned method for forming a head of a high manganese steel plate for an LNG tank, further, has a plate thickness of 8mm-40mm.

[0016] The above-mentioned LNG tank high manganese steel plate head forming method further, during the warm forming process, the high manganese steel plate is heated before the initial pressing and preforming, using a heating temperature of 500℃-600℃, the furnace temperature during heating is 200℃-400℃, and the temperature is increased by 100℃ per hour to 500℃-600℃, and kept warm for 30 minutes.

[0017] The above-mentioned method for forming a high manganese steel plate head for an LNG storage tank further adopts hot forming to process the head when the curvature radius R of the high manganese steel plate head is 200mm-500mm; and adopts warm forming or hot forming to process the head when the curvature radius R of the high manganese steel plate head is 500mm-2000mm.

[0018] The above-mentioned method for forming a high manganese steel plate head for an LNG tank further adopts hot forming to process the head when the curvature radius of the high manganese steel plate head is less than 500 mm and the plate thickness is greater than 20 mm.

[0019] The above-mentioned method for forming a high manganese steel plate head for an LNG storage tank, further, the head is a butterfly-shaped or elliptical head pressed by whole plate molding, or a spherical head pressed by whole plate.

[0020] The research on the process method of hot forming of high manganese steel plate heads for LNG tanks fills this technical blank in China. Since the use of high manganese steel for the construction of LNG tanks at home and abroad is in the initial research stage, our company has carried out a lot of research and testing on this type of high manganese steel heads, which can solve the technical difficulties in the processing and forming of small-diameter heads of high manganese steel. The high manganese steel processed according to this process has good performance and good product appearance quality. It is a key technology for the application of high manganese steel in LNG tanks, with feasible process, independent and controllable technology and reliable quality. DETAILED DESCRIPTION

[0021] According to the design of commonly used LNG tanks, the curvature radius of the head diameter of high manganese steel is generally from R = 200mm to R = 7500mm, and the plate thickness range is generally 8mm-40mm. For heads with a diameter of more than 2000mm, cold forming is generally possible. However, the main pressure-bearing head parts such as the gas dome or liquid dome of the LNG tank have a radius ranging from R = 200mm to R = 2000mm, and their processing often requires warm forming or hot forming, especially when the radius is less than 500mm and the thickness is greater than 20mm, and cold forming is difficult, and hot forming (heating above 750℃) or warm forming (heating below 600℃) is required. Warm forming or hot forming can adopt the following process solutions to solve the forming of heads below R2000, which can not only ensure the forming effect, but also ensure the performance and surface quality of the steel plate after forming, especially the tensile performance. The performance indicators after forming can reach the mechanical properties of the plate in Table 1.

[0022] Table 1 Example 1

[0023] Warm forming is used to make an elliptical high manganese steel plate head with a thickness of 20mm and an inner diameter of 1400mm. The specific operations are as follows:

[0024] Steel plate cutting should be done according to the size of the steel plate. Plasma, laser, and high-pressure water jet cutting can be used. Flame cutting should not be used.

[0025] For pre-pressing of the head, because the high manganese steel plate has high strength and large rebound, a drumming machine is generally used for preliminary pressing and pre-forming to facilitate subsequent pressing and forming. When drumming, the high manganese steel plate is placed on the lower tire of the drumming machine to ensure that the edge of the high manganese steel plate can move freely. The drumming depth is 1 / 10, 1 / 5, 1 / 4, and 1 / 3 of the final forming depth respectively. The drumming is carried out in the order from the middle to the surrounding. In order to increase the pressing amount and prevent cracks from cold forming, the high manganese steel plate can be heated before pre-pressing. The heating temperature is 500℃-600℃. The furnace temperature is 200℃-400℃ during heating. It is heated to 500℃-600℃ at a rate of 100℃ per hour and kept warm for 30 minutes. The maximum heating temperature should not exceed 600℃. Heating can prevent the formation of cold cracks in the forming process to the greatest extent and ensure the appearance quality.

[0026] For the final pressing of the head, the prefabricated head is put back into the furnace and heated to a heating temperature of 500℃-600℃. It is first heated to 500℃-600℃ in the furnace, and the temperature of the furnace is 200℃-400℃. It is heated to 500℃-600℃ at a rate of 100℃ per hour, and kept warm for 30 minutes. The head is molded or spun by an oil press, a hydraulic press or a spinning machine to form an ellipse with a final inner diameter of 1400mm. It can also be spun by an online heating spinning machine without heating in the furnace. The head is heated and spun at the same time. The heating temperature should not exceed 600℃.

[0027] After the head is pressed and formed, the appearance must be 100% PT or MT tested, and it is qualified if there is no defect. Example 2

[0028] The spherical high manganese steel plate head with a thickness of 20mm and an inner diameter of 500mm is made by hot forming. The specific operations are as follows:

[0029] Cut the steel plate according to the size of the steel plate. Plasma, laser, and high-pressure water jet cutting can be used. Flame cutting is not suitable. At the same time, hot-pressed furnace parent material test plates are cut out.

[0030] The head with a radius of 500mm that is difficult to form by cold pressing needs to be hot pressed. Before hot pressing, the head plate and the mother material test plate are put into the furnace at the same time. After heating in the furnace, the temperature out of the furnace is controlled at 800℃-850℃. The insulation time in the furnace is less than 0.5 hour, and it is quickly air-cooled after hot pressing.

[0031] If the head is deformed or has dimensional deviation after pressing, it needs to be reheated to 500℃-600℃ to adjust the shape until the size is qualified. When reheating, the mother material test plate should be heated in the furnace together.

[0032] The mechanical properties of the test plate of the parent material in the furnace were tested and passed. The following Table 2 shows the performance indicators of the 20mm thick butterfly head with a radius of 500mm and the hot pressing temperature is controlled at 850℃, which meets the qualified performance of the parent material.

[0033] After the head is pressed and formed, the appearance must be 100% PT or MT tested, and it is qualified if there is no defect.

[0034] Table 2

[0035] The above takes the hot pressing process of a 20 mm thick steel plate as an example, but the actual application is not limited to 20 mm thick plates. Hot pressing is suitable for the same type of pressing and forming process of high manganese steel materials.

[0036] According to the forming or heat treatment mechanism of conventional steel plates, the hot forming process destroys the supplied heat treatment state or the supplied mechanical properties and requires heat treatment to restore the performance. However, according to this technical route, high manganese steel does not need heat treatment after warm pressing or hot pressing, or can be heat treated according to the rolling process. Practice has found that the performance of carbon steel cannot be restored to the original performance of the steel mill according to the hot rolling process or after its austenite characteristic solid solution, especially the yield Rp0.2 is lower than 400MPa.

[0037] This patent provides a process for forming high manganese steel plates for LNG tanks, which can solve the above-mentioned technical problems of low performance of conventional hot forming, difficult cold forming and easy cracking and poor appearance quality. It can ensure the strength and other performance indicators of the high manganese steel head material after forming.

[0038] The invention can be used in high manganese steel to manufacture LNG tank heads and other similar high manganese steel plate head pressing and forming conditions.

Claims

1. A method for forming a high manganese steel plate head for an LNG tank, characterized in that: When the curvature radius of the high manganese steel plate head is R=200mm-2000mm, warm forming or hot forming is used to process the head. The specific operations are as follows: During warm forming, plasma, laser, and high-pressure water jet cutting are used; After unloading, use a drumming machine for preliminary pre-pressing and forming. When drumming, place the high-manganese steel plate on the lower tire of the drumming machine to ensure that the edge of the high-manganese steel plate can move freely. The drumming depth is 1 / 10, 1 / 5, 1 / 4, and 1 / 3 of the final forming depth respectively. The drumming is carried out from the middle to the surrounding areas. The preformed head is put into a furnace and heated to a heating temperature of 500°C-600°C. The temperature of the furnace is 200°C-400°C during heating. The temperature is increased by 100°C per hour to 500°C-600°C. The temperature is kept at this temperature for 30 minutes. A hydraulic press, a hydraulic press or a spinning machine is used for molding or spinning, and finally a butterfly shape, an elliptical shape or a sphere with an inner diameter of 400mm-4000mm is formed. Alternatively, the preformed head is spun by an online heating spinning machine without heating in a furnace. The head is heated and spun at the same time as it is spun. The heating temperature is 500°C-600°C, and the inner diameter is finally 400mm-4000mm. The warm pressed heads are subjected to 100% PT or MT inspection for appearance, and those without any defects are qualified; During hot forming, plasma, laser and high-pressure water jet cutting are used to cut the material, and hot-pressed furnace-following mother material test plates are cut at the same time; The head plate and the base material test plate are put into the furnace at the same time. After heating in the furnace, the temperature out of the furnace is controlled at 800℃-850℃. The heat preservation time in the furnace is less than 0.5 hours. After hot pressing, it is quickly air-cooled. After hot pressing and forming, if there is any deformation or dimensional deviation, it needs to be heated again to 500℃-600℃ to adjust the shape until the size is qualified. When heating again, the mother material test plate should be heated in the furnace together; Carry out mechanical property test on the parent material test plate of the furnace, and carry out 100% PT or MT inspection on the appearance of the hot pressed head. The product without any defects is qualified.

2. The method for forming a high manganese steel plate head for an LNG tank according to claim 1, characterized in that: The thickness of the board is 8mm-40mm.

3. The method for forming a high manganese steel plate head for an LNG tank according to claim 1, characterized in that: During warm forming, the high manganese steel plate is heated before the initial pressing and preforming, with a heating temperature of 500℃-600℃. The furnace temperature is 200℃-400℃, and the temperature is increased by 100℃ per hour to 500℃-600℃, and kept warm for 30 minutes.

4. The method for forming a high manganese steel plate head for an LNG tank according to claim 1, characterized in that: When the curvature radius R of the high manganese steel plate head is 200mm-500mm, hot forming is used to process the head; when the curvature radius R of the high manganese steel plate head is 500mm-2000mm, warm forming or hot forming is used to process the head.

5. The method for forming a high manganese steel plate head for an LNG tank according to claim 1, characterized in that: When the curvature radius of the high manganese steel plate head is less than 500mm and the plate thickness is greater than 20mm, hot forming is used to process the head.

6. The method for forming a high manganese steel plate head for an LNG tank according to claim 1, characterized in that: The head is a butterfly-shaped or elliptical head pressed by the whole plate, or a spherical head pressed by the whole plate.