Production method of L245 steel grade for oil and gas pipeline

Abstract

The invention relates to the technical field of rolling processes of hot-rolled pipeline steel plates, and particularly discloses a production method of L245 steel for oil and gas pipelines, which is characterized in that the mass percentages of components in heated and smelted molten iron are respectively limited according to different thickness specifications of produced steel coils; a cold blank heating mode is adopted in the hot rolling process, whether a steel blank is a cold blank or a hot blank is judged according to the charging temperature of the steel blank, the heating temperature, the in-furnace time and the soaking section heating time are controlled, and the heating temperature is set according to different thickness specifications of produced steel coils; a finish rolling inlet reference temperature, a finish rolling temperature and a coiling temperature are respectively set according to different thickness specifications of produced steel coils, and front-section cooling is adopted in a cooling strategy; the descaling box of the roughing mill group is normally put into use, and the descaling box of the finishing mill group is normally put into use; on the premise of keeping the low cost of the L245 steel, the strength is slightly higher than the standard requirement, and the impact energy at-20 DEG C is greatly improved; the H2S corrosion resistance is high, the welding adaptability is good, and the process universality is high.

Description

Technical Field

[0001] This invention relates to the field of hot-rolled pipeline steel plate rolling technology, specifically to a production method of L245 steel for oil and gas pipelines. Background Technology

[0002] L245 steel is a low-carbon microalloyed steel widely used in oil and gas pipeline engineering. Its typical mechanical properties are: yield strength ≥245MPa, tensile strength 415~565MPa, and impact energy at -20℃ ≥27J.

[0003] The traditional L245 steel rolling process has the following problems: 1. Weak resistance to H2S corrosion: In acidic oil and gas environments containing H2S, L245 steel is prone to hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC), which limits its application in sulfur-containing oil fields.

[0004] 2. Insufficient low-temperature toughness: When the ambient temperature during transportation is below -20℃ (such as in cold regions), the impact strength of L245 steel may not meet the standard requirements.

[0005] 3. Limited weldability: The high carbon equivalent leads to higher hardness in the heat-affected zone of the weld, which makes it prone to cold cracking.

[0006] Therefore, it is necessary to design a production method for L245 steel used in oil and gas pipelines to solve the problems of poor corrosion resistance, insufficient toughness, and poor weldability of existing L245 steel. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a production method for L245 steel for oil and gas pipelines.

[0008] The technical solution adopted by this invention to solve its technical problem is: a production method of L245 steel for oil and gas pipelines, comprising the following steps: S1. The thickness specifications of the produced steel coils are different, and the mass percentage of the components in the molten iron is limited accordingly. S2. The hot rolling process adopts the cold billet heating method. The billet is judged as cold billet or hot billet according to the furnace charging temperature. The heating temperature, furnace time and soaking zone heating time are controlled. The heating temperature is set according to the different thickness specifications of the steel coils produced. S3. For steel coils of different thicknesses, separate reference temperatures for the finishing mill inlet, the final rolling temperature, and the coiling temperature are set, and the cooling strategy for all of them adopts front-end cooling. S4. For steel coils with different thickness and width specifications, the convexity value range is set to 10-80µm. S5. Descaling control: The descaling box of the roughing mill is in normal operation, and the R1 and R2 descaling of the roughing mill are each performed once. The descaling box of the finishing mill is in normal operation. S6. After the coiled steel coils are placed in the warehouse, they are kept in a sheltered place to cool slowly. Then they are bundled, labeled and finished before being put into the warehouse.

[0009] Specifically, the steel coil thickness in step S1 is 3.0-12.0 mm, and the mass percentage composition of the molten iron is C: 0.14-0.17%, Si: 0.13-0.27%, Mn: 0.55-0.75%, P≤0.020%, S≤0.010%, Als: 0.010-0.035%, Ti: 0.005-0.025%, N≤0.0060%, with the remainder being iron and residual elements. The thickness of the steel coil is 12.01-28.0 mm. The mass percentage composition of the molten iron is C: 0.14-0.17%, Si: 0.13-0.27%, Mn: 0.60-0.80%, P≤0.020%, S≤0.010%, ALs: 0.010-0.035%, Nb: 0.005-0.015%, Ti: 0.005-0.025%, N≤0.0060%, with the remainder being iron and residual elements.

[0010] Specifically, the residual elements include Cu≤0.30%, Ni≤0.30%, Cr≤0.30%, Mo≤0.15%, and B≤0.0010%.

[0011] Specifically, in step S2, the thickness of the steel coil is 3.0-10.30 mm, the first heating temperature is 1240±30℃, the soaking temperature is 1230±30℃, and the target reference temperature for tapping is 1200±30℃. The thickness of the steel coil is 10.31-19.0 mm, the first heating temperature is 1240±30℃, the soaking temperature is 1220±30℃, and the target reference temperature for tapping is 1190±30℃. The thickness of the steel coil is 19.01-28.0mm, the first heating temperature is 1230±30℃, the soaking temperature is 1210±30℃, and the target reference temperature for exiting the furnace is 1180±30℃.

[0012] Specifically, in step S1, when the billet loading temperature is <400℃, it is a cold billet, the billet is in the furnace for 150-240 minutes, and the heating time in the soaking zone is ≥24 minutes. When the billet loading temperature is ≥400℃, it is a hot billet. The billet time in the furnace is ≤240 minutes, and the heating time in the soaking zone is ≥18 minutes.

[0013] Specifically, in step S3, the thickness of the steel coil is 3.0-10.30 mm, the reference temperature for the finishing mill entrance is 1030±20℃, the final rolling temperature is 860±20℃, and the coiling temperature is 620±20℃. The thickness of the steel coil is 10.31-19.0 mm, the reference temperature for the finishing mill entrance is 1010±20℃, the finishing mill temperature is 850±20℃, and the coiling temperature is 610±20℃. The thickness of the steel coil is 19.01-28.0mm, the reference temperature for the finishing mill entrance is 1000±20℃, the final rolling temperature is 840±20℃, and the coiling temperature is 600±20℃.

[0014] Specifically, the steel coil in step S4 has a thickness of 3.0-8.0 mm, a width of 1300-1600 mm, and a convexity of 35±25 µm. The steel coils have a thickness of 3.0-8.0 mm, a width of 1601-1900 mm, and a crown value of 35±25 µm. The steel coils have a thickness of 3.0-8.0 mm, a width of 1901-2100 mm, and a crown value of 40±25 µm. The thickness of the steel coil is 8.01-12.0 mm, the width is 1300-1600 mm, and the crown value is 40±25 µm; The thickness of the steel coil is 8.01-12.0 mm, the width is 1601-1900 mm, and the crown is 40±25 µm. The thickness of the steel coil is 8.01-12.0 mm, the width is 1901-2100 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1300-1600 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1601-1900 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1901-2100 mm, and the crown is 50±25 µm. The thickness of the steel coil is 19.01-28.0 mm, the width is 1300-1600 mm, and the crown value is 50±25 µm; The thickness of the steel coil is 19.01-28.0 mm, the width is 1601-1900 mm, and the crown is 50±25 µm. The steel coils have a thickness of 19.01-28.0 mm, a width of 1901-2100 mm, and a crown value of 55±25 µm.

[0015] Specifically, in step S5, the number of descaling passes for roughing mills R1 and R2 is selected and adjusted by the operator based on the inlet temperature of the finishing mill.

[0016] The present invention has the following beneficial effects: The production method of L245 steel for oil and gas pipelines designed in this invention maintains the low cost of L245 steel (alloy cost is reduced by 15~20% compared with traditional formula), while the strength is slightly higher than the standard requirements, the impact energy at -20℃ is greatly improved, and it can adapt to the environment at -40℃.

[0017] The production method of L245 steel for oil and gas pipelines designed in this invention has strong resistance to H2S corrosion. Through the synergistic effect of Ni, Cu, Mo and Nb elements, the HIC / SSCC performance meets the standards of acidic oilfields.

[0018] The production method for L245 steel used in oil and gas pipelines designed in this invention has good welding adaptability, with a welding HAZ impact energy ≥50J (-10℃), requiring no preheating or only a low preheating temperature (≤50℃); the process has high universality, and the hot rolling and cooling process parameters are compatible with conventional pipeline steel production lines, making it easy to promote industrialization. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Example 1

[0020] The production method of L245M-1 steel grade (coil thickness specifications of 3.0-12.0mm) includes the following steps: 1. The thickness specifications of the steel coils produced are determined by different mass percentages of the components in the molten iron during heating and smelting. The mass percentages of the components in the molten iron are as follows: C: 0.15%, Si: 0.2%, Mn: 0.6%, P≤0.015%, S≤0.005%, Als: 0.015%, Ti: 0.01%, N≤0.0040%, with the remainder being iron and residual elements; residual elements include Cu≤0.30%, Ni≤0.30%, Cr≤0.30%, Mo≤0.15%, and B≤0.0010%.

[0021] The determination is based on gaseous N, and the maintenance of spectral N is not used as a criterion. The carbon equivalent CEV is calculated as C+Mn / +(Cr+Mo+V) / 5+(Cu+Ni) / 15.

[0022] 2. The hot rolling process adopts the cold billet heating method. The billet is judged as cold billet or hot billet based on the furnace charging temperature. The heating temperature, furnace time and soaking zone heating time are controlled. The heating temperature is set according to the different thickness specifications of the steel coils produced.

[0023] The thickness of the steel coil is 3.0-10.30mm, the first heating temperature is 1210℃, the soaking temperature is 1200℃, and the target reference temperature for tapping is 1170℃.

[0024] The steel coil thickness is 10.31-12.0mm, the first heating temperature is 1210℃, the soaking temperature is 1190℃, and the target reference temperature for tapping is 1160℃.

[0025] When the billet loading temperature is <400℃, it is a cold billet. The billet stays in the furnace for 150 minutes, and the soaking zone heating time is 24 minutes.

[0026] When the billet loading temperature is ≥400℃, it is a hot billet. The billet is in the furnace for 240 minutes, and the soaking zone heating time is 18 minutes.

[0027] 3. For steel coils of different thicknesses, separate reference temperatures for the finishing mill inlet, the final rolling temperature, and the coiling temperature are set, and the cooling strategy for all of them adopts front-end cooling.

[0028] The thickness of the steel coil is 3.0-10.30 mm, the reference temperature for the finishing rolling entrance is 1010℃, the final rolling temperature is 840℃, and the coiling temperature is 600℃.

[0029] The thickness of the steel coil is 10.31-12.0 mm, the reference temperature for the finishing rolling entrance is 1000℃, the final rolling temperature is 830℃, and the coiling temperature is 600℃.

[0030] 4. For steel coils with different thickness and width specifications, the crown value range is set to 10-80µm. The intermediate billet thickness is set according to the hot rolling mill model.

[0031] The steel coils have a thickness of 3.0-8.0 mm, a width of 1300-1600 mm, and a crown of 10 µm.

[0032] The steel coils have a thickness of 3.0-8.0 mm, a width of 1601-1900 mm, and a crown value of 20 m.

[0033] The steel coils have a thickness of 3.0-8.0 mm, a width of 1901-2100 mm, and a crown of 40 µm.

[0034] The steel coils have a thickness of 8.01-12.0 mm, a width of 1300-1600 mm, and a crown of 40 µm.

[0035] The steel coils have a thickness of 8.01-12.0 mm, a width of 1601-1900 mm, and a crown of 40 µm.

[0036] 5. Descaling Control: The descaling box of the roughing mill is in normal operation, with one descaling pass each for R1 and R2 of the roughing mill, and the descaling box of the finishing mill is in normal operation. The number of descaling passes for R1 and R2 of the roughing mill is selected and adjusted by the operator based on the inlet temperature of the finishing mill.

[0037] 6. After being coiled, the steel coils are placed in the warehouse and allowed to cool slowly in a sheltered environment. Then, they are bundled, labeled, and finished before being stored in the warehouse.

[0038] Overall performance: While maintaining the low cost of L245 steel (alloy cost is reduced by 15~20% compared to traditional formula), the strength is slightly higher than the standard requirements, the impact energy at -20℃ is greatly improved, and it can adapt to the environment at -40℃.

[0039] Strong resistance to H2S corrosion: Through the synergistic effect of Ni / Cu / Mo / Nb, the performance of HIC / SSCC reaches the standard of acidic oilfield.

[0040] Good welding adaptability: welding HAZ impact energy ≥50J (-10℃), no preheating required or only low preheating temperature (≤50℃).

[0041] High process versatility: The hot rolling and cooling process parameters are compatible with conventional pipeline steel production lines, making it easy to promote industrialization. Example 2

[0042] The production method of L245M-2 steel (coil thickness specifications of 12.01-28.0mm) includes the following steps: 1. The thickness specifications of the steel coils produced are determined by the different mass percentages of the components in the molten iron during heating and smelting. The mass percentages of the components in the molten iron are as follows: C: 0.15%, Si: 0.2%, Mn: 0.65%, P≤0.015%, S≤0.005%, Als: 0.015%, Nb: 0.008%, Ti: 0.01%, N≤0.0040%, with the remainder being iron and residual elements; residual elements include Cu≤0.30%, Ni≤0.30%, Cr≤0.30%, Mo≤0.15%, and B≤0.0010%.

[0043] The determination is based on gaseous N, and the maintenance of spectral N is not used as a criterion. The carbon equivalent CEV is calculated as C+Mn / +(Cr+Mo+V) / 5+(Cu+Ni) / 15.

[0044] 2. The hot rolling process adopts the cold billet heating method. The billet is judged as cold billet or hot billet based on the furnace charging temperature. The heating temperature, furnace time and soaking zone heating time are controlled. The heating temperature is set according to the different thickness specifications of the steel coils produced.

[0045] The thickness of the steel coil is 12.01-19.0mm, the first heating temperature is 1270℃, the soaking temperature is 1250℃, and the target reference temperature for tapping is 1200℃.

[0046] The steel coil thickness is 19.01-28.0mm, the first heating temperature is 1260℃, the soaking temperature is 1240℃, and the target reference temperature for exiting the furnace is 1200℃.

[0047] When the billet loading temperature is <400℃, it is a cold billet. The billet stays in the furnace for 150 minutes, and the soaking zone heating time is 24 minutes.

[0048] When the billet loading temperature is ≥400℃, it is a hot billet. The billet is in the furnace for 240 minutes, and the soaking zone heating time is 18 minutes.

[0049] 3. For steel coils of different thicknesses, separate reference temperatures for the finishing mill inlet, the final rolling temperature, and the coiling temperature are set, and the cooling strategy for all of them adopts front-end cooling.

[0050] The thickness of the steel coil is 12.01-19.0mm, the reference temperature for the finishing rolling entrance is 1030℃, the final rolling temperature is 870℃, and the coiling temperature is 630℃.

[0051] The thickness of the steel coil is 19.01-28.0mm, the reference temperature for the finishing rolling entrance is 1020℃, the final rolling temperature is 860℃, and the coiling temperature is 620℃.

[0052] 4. For steel coils with different thickness and width specifications, the crown value range is set to 10-80µm. The intermediate billet thickness is set according to the hot rolling mill model.

[0053] The steel coils have a thickness of 12.01-19.0 mm, a width of 1300-1600 mm, and a crown of 45 µm.

[0054] The steel coils have a thickness of 12.01-19.0 mm, a width of 1601-1900 mm, and a crown of 45 µm.

[0055] The steel coils have a thickness of 12.01-19.0 mm, a width of 1901-2100 mm, and a crown of 50 µm.

[0056] The steel coils have a thickness of 19.01-28.0 mm, a width of 1300-1600 mm, and a crown of 50 µm.

[0057] The steel coils have a thickness of 19.01-28.0 mm, a width of 1601-1900 mm, and a crown of 50 µm.

[0058] The steel coils have a thickness of 19.01-28.0 mm, a width of 1901-2100 mm, and a crown of 55 µm.

[0059] 5. Descaling Control: The descaling box of the roughing mill is in normal operation, with one descaling pass each for R1 and R2 of the roughing mill, and the descaling box of the finishing mill is in normal operation. The number of descaling passes for R1 and R2 of the roughing mill is selected and adjusted by the operator based on the inlet temperature of the finishing mill.

[0060] 6. After being coiled, the steel coils are placed in the warehouse and allowed to cool slowly in a sheltered environment. Then, they are bundled, labeled, and finished before being stored in the warehouse.

[0061] Overall performance: While maintaining the low cost of L245 steel (alloy cost is reduced by 15~20% compared to traditional formula), the strength is slightly higher than the standard requirements, the impact energy at -20℃ is greatly improved, and it can adapt to the environment at -40℃.

[0062] Strong resistance to H2S corrosion: Through the synergistic effect of Ni / Cu / Mo / Nb, the performance of HIC / SSCC reaches the standard of acidic oilfield.

[0063] Good welding adaptability: welding HAZ impact energy ≥50J (-10℃), no preheating required or only low preheating temperature (≤50℃).

[0064] High process versatility: The hot rolling and cooling process parameters are compatible with conventional pipeline steel production lines, making it easy to promote industrialization.

[0065] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0066] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for producing L245 steel for oil and gas pipelines, characterized in that, Includes the following steps: S1. The thickness specifications of the produced steel coils are different, and the mass percentage of the components in the molten iron is limited accordingly. S2. The hot rolling process adopts the cold billet heating method. The billet is judged as cold billet or hot billet according to the furnace charging temperature. The heating temperature, furnace time and soaking zone heating time are controlled. The heating temperature is set according to the different thickness specifications of the steel coils produced. S3. For steel coils of different thicknesses, separate reference temperatures for the finishing mill inlet, the final rolling temperature, and the coiling temperature are set, and the cooling strategy for all of them adopts front-end cooling. S4. For steel coils with different thickness and width specifications, the convexity value range is set to 10-80µm. S5. Descaling control: The descaling box of the roughing mill is in normal operation, and the R1 and R2 descaling of the roughing mill are each performed once. The descaling box of the finishing mill is in normal operation. S6. After the coiled steel coils are placed in the warehouse, they are kept in a sheltered place to cool slowly. Then they are bundled, labeled and finished before being put into the warehouse.

2. The production method of L245 steel for oil and gas pipelines according to claim 1, characterized in that, The steel coil in step S1 has a thickness of 3.0-12.0 mm, and the molten iron contains the following composition by mass percentage: C: 0.14-0.17%, Si: 0.13-0.27%, Mn: 0.55-0.75%, P≤0.020%, S≤0.010%, Als: 0.010-0.035%, Ti: 0.005-0.025%, N≤0.0060%, with the remainder being iron and residual elements. The thickness of the steel coil is 12.01-28.0 mm. The mass percentage composition of the molten iron is C: 0.14-0.17%, Si: 0.13-0.27%, Mn: 0.60-0.80%, P≤0.020%, S≤0.010%, ALs: 0.010-0.035%, Nb: 0.005-0.015%, Ti: 0.005-0.025%, N≤0.0060%, with the remainder being iron and residual elements.

3. The production method of L245 steel for oil and gas pipelines according to claim 2, characterized in that, The residual elements include Cu≤0.30%, Ni≤0.30%, Cr≤0.30%, Mo≤0.15%, and B≤0.0010%.

4. The production method of L245 steel for oil and gas pipelines according to claim 1, characterized in that, The thickness of the steel coil in step S2 is 3.0-10.30 mm, the first heating temperature is 1240±30℃, the soaking temperature is 1230±30℃, and the target reference temperature for tapping is 1200±30℃. The thickness of the steel coil is 10.31-19.0 mm, the first heating temperature is 1240±30℃, the soaking temperature is 1220±30℃, and the target reference temperature for tapping is 1190±30℃. The thickness of the steel coil is 19.01-28.0mm, the first heating temperature is 1230±30℃, the soaking temperature is 1210±30℃, and the target reference temperature for exiting the furnace is 1180±30℃.

5. The production method of L245 steel for oil and gas pipelines according to claim 4, characterized in that, In step S1, the billet loading temperature is <400℃ and it is a cold billet. The billet is in the furnace for 150-240 minutes and the heating time in the soaking zone is ≥24 minutes. When the billet loading temperature is ≥400℃, it is a hot billet. The billet time in the furnace is ≤240 minutes, and the heating time in the soaking zone is ≥18 minutes.

6. The production method of L245 steel for oil and gas pipelines according to claim 1, characterized in that, The thickness of the steel coil in step S3 is 3.0-10.30 mm, the reference temperature for the finishing mill entrance is 1030±20℃, the final rolling temperature is 860±20℃, and the coiling temperature is 620±20℃. The thickness of the steel coil is 10.31-19.0 mm, the reference temperature for the finishing mill entrance is 1010±20℃, the finishing mill temperature is 850±20℃, and the coiling temperature is 610±20℃. The thickness of the steel coil is 19.01-28.0mm, the reference temperature for the finishing mill entrance is 1000±20℃, the final rolling temperature is 840±20℃, and the coiling temperature is 600±20℃.

7. The production method of L245 steel for oil and gas pipelines according to claim 1, characterized in that, The steel coil in step S4 has a thickness of 3.0-8.0 mm, a width of 1300-1600 mm, and a crown value of 35±25 µm. The steel coils have a thickness of 3.0-8.0 mm, a width of 1601-1900 mm, and a crown value of 35±25 µm. The steel coils have a thickness of 3.0-8.0 mm, a width of 1901-2100 mm, and a crown value of 40±25 µm. The thickness of the steel coil is 8.01-12.0 mm, the width is 1300-1600 mm, and the crown value is 40±25 µm; The thickness of the steel coil is 8.01-12.0 mm, the width is 1601-1900 mm, and the crown is 40±25 µm. The thickness of the steel coil is 8.01-12.0 mm, the width is 1901-2100 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1300-1600 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1601-1900 mm, and the crown is 45±25 µm. The thickness of the steel coil is 12.01-19.0 mm, the width is 1901-2100 mm, and the crown is 50±25 µm. The thickness of the steel coil is 19.01-28.0 mm, the width is 1300-1600 mm, and the crown value is 50±25 µm; The thickness of the steel coil is 19.01-28.0 mm, the width is 1601-1900 mm, and the crown is 50±25 µm. The steel coils have a thickness of 19.01-28.0 mm, a width of 1901-2100 mm, and a crown value of 55±25 µm.

8. The production method of L245 steel for oil and gas pipelines according to claim 1, characterized in that, In step S5, the number of descaling passes for roughing mills R1 and R2 is selected and adjusted by the operator based on the inlet temperature of the finishing mill.