Metal strip

Abstract

Provided is a metal strip for a pipe with which the weight of a pipe can be reduced while maintaining the strength of a joint portion that tends to be structurally the weakest. A metal strip L is formed by rolling. The thickness of each of a head end portion 1a and a tail end portion 1b, which are longitudinal end portions 1, is greater than the thickness of an intermediate portion excluding the longitudinal end portions 1. The metal strips are connected to each other in series by welding, and a pipe is made by performing a pipe-forming operation.

Claims

1. A metal strip, comprising: two longitudinal end portions, a longitudinal intermediate portion between the two longitudinal end portions, and two inclined portions connecting respective ones of the two longitudinal end portions to the longitudinal intermediate portion, each of the two longitudinal end portions having a thickness greater than a thickness of the longitudinal intermediate portion, each of the two inclined portions having a thickness that continuously and monotonically decreases from the respective one of the two longitudinal end portions to the longitudinal intermediate portion, the thickness of at least one of two longitudinal end portions continuously and monotonically decreases from an end surface thereof toward the inclined portion connected thereto, and a rate of change at which the thickness of the at least one of the two longitudinal end portions continuously and monotonically decreases along the longitudinal direction is smaller than a rate of change at which the thickness of the respective one of the two inclined portions decreases.

2. The metal strip according to claim 1, wherein the metal strip has a thickness along the longitudinal direction such that a ratio ((AB)/A) is 7% or more and 50% or less, where A is a maximum thickness of the longitudinal end portions and B is a minimum thickness of the longitudinal intermediate portion.

3. The metal strip according to claim 1, wherein a rate of change in the thickness of each of the inclined portions along the longitudinal direction is 0.001 [mm/m] or more and 0.1 [mm/m] or less.

4. The metal strip according to claim 1, wherein the metal strip is formed by hot rolling.

5. A metal strip, comprising: two longitudinal end portions, a longitudinal intermediate portion between the two longitudinal end portions, and two inclined portions connecting respective ones of the two longitudinal end portions to the longitudinal intermediate portion, one of the two longitudinal end portions having a maximum thickness greater than a maximum thickness of the other of the two longitudinal end portions, each of the two longitudinal end portions having a maximum thickness greater than a thickness of the longitudinal intermediate portion where the longitudinal intermediate portion is connected to a respective one of the two longitudinal end portions, and the intermediate portion having a thickness that decreases at a constant gradient from the one of the two longitudinal end portions with the greater maximum thickness to the other of the two longitudinal end portions.

6. The metal strip according to claim 5, wherein the metal strip has a thickness along the longitudinal direction such that a ratio ((AB)/A) is 7% or more and 50% or less, where A is a maximum thickness of the two longitudinal end portions and B is a minimum thickness of the longitudinal intermediate portion.

7. The metal strip according to claim 5, wherein a rate of change in the thickness of each of the inclined portions along the longitudinal direction is 0.001 [mm/m] or more and 0.1 [mm/m] or less.

8. The metal strip according to claim 5, wherein the metal strip is formed by hot rolling.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic perspective view illustrating a metal strip according to an embodiment of the present invention.

(2) FIG. 2 is a schematic side view of a metal strip according to a modification.

(3) FIG. 3 is a schematic side view of a metal strip according to a modification.

(4) FIGS. 4(a) and 4(b) are each a schematic side view of a plurality of metal strips that are connected to each other, FIG. 4(a) showing a case where metal strips according to the present invention are used, and FIG. 4(b) showing a case where metal strips according to a comparative example are used.

(5) FIG. 5 is a schematic side view of a metal strip according to a modification.

(6) FIG. 6 is a side view of a metal strip used for describing EXAMPLE.

DESCRIPTION OF EMBODIMENTS

(7) Next, an embodiment of the present invention will be described with reference to the drawings.

(8) FIG. 1 is a schematic perspective view illustrating an example of a metal strip according to the present embodiment. In each of the figures, the dimension in the longitudinal direction (rolling direction) is considerably reduced.

(9) (Structure of Metal Strip)

(10) In the following description, steel will be used as an example of the material of a metal strip. However, the material of a metal strip according to the present invention is not limited to steel, and may be any metal material that can be hot-rolled, such as aluminum or copper.

(11) As illustrated in FIG. 1, a metal strip L according to the present embodiment includes a head end portion 1a and a tail end portion 1b, which are longitudinal end portions 1; a longitudinal middle portion 2, which is located between the longitudinal end portions 1; and two inclined portions 3 connecting the longitudinal end portions 1a and 1b to the longitudinal middle portion 2. The metal strip L is hot-rolled so as to have a desired thickness in profile. Then, the metal strip L is coiled by a coiler to form a coil. As necessary, pickling treatment may be performed on the coil after rolling. The length of the metal strip L is, for example, in the range of 50 m to 2500 m.

(12) The metal strip L is manufactured by rolling so as to have a predetermined thickness in the range of, for example, 1.0 mm to 30.0 mm. In the present embodiment, the thickness of each of the longitudinal end portions 1 is set to be greater than the thickness of the longitudinal middle portion 2 and the thicknesses of the inclined portions 3. The longitudinal middle portion 2 and the inclined portions 3 correspond to an intermediate portion excluding the longitudinal end portions 1.

(13) The metal strip L according to the present embodiment is a hot-rolled steel sheet manufactured by rolling as described above so that the thickness of the longitudinal middle portion 2 is uniform or substantially uniform along the longitudinal direction and so that the thicknesses of the inclined portions 3 gradually decrease from the longitudinal end portions toward ends of the longitudinal middle portion 2. Pickling treatment may be performed after hot rolling.

(14) The thicknesses of the longitudinal end portions 1 of the metal strip L and the thickness of the longitudinal middle portion 2 of the metal strip L are set so that the ratio ((AB)/A) is 7% or more and 50% or less, where A is the maximum thickness of the longitudinal end portions 1, and B is the thickness of the longitudinal middle portion 2. In the present specification, the ratio ((AB)/A) will be referred to as a thickness deviation. In FIG. 1, A is the thickness of the longitudinal end portions 1, because the thickness of the longitudinal end portions 1 is uniform. In a case where the thicknesses of the longitudinal end portions 1 change as in FIG. 2, A is the maximum thickness of the longitudinal end portions 1 (the thicknesses at the end surfaces in FIG. 2).

(15) As illustrated in FIG. 3, it is not necessary that the maximum thicknesses of the head end portion 1a and the tail end portion 1b in the longitudinal direction be the same. The maximum thickness of each of the longitudinal end portions 1a and 1b is set so as to satisfy the condition described above.

(16) The longitudinal middle portion 2 forms the body of the metal strip L, that is, the body of a pipe body to be made from the metal strip L. Therefore, the thickness of the longitudinal middle portion 2 is determined on the basis of the material of the metal strip L, the diameter of the pipe body to be made and the like so that a strength required for an intended use can be obtained. Subsequently, for example, by using the strength of the longitudinal middle portion 2 as a benchmark, the maximum thickness of the longitudinal end portions may be determined so that the joint strength at the longitudinal end portions, which will serve as joint portions, becomes close to the strength of the longitudinal middle portion 2, in particular, the strength of a part of the longitudinal middle portion 2 near the longitudinal end portions.

(17) Here, since the strength of a structure can be evaluated, for example, by the moment of inertia of area, an increase in the strength is proportional to the square of the thickness.

(18) The thickness deviation is set to be 7% or more and 50% or less for the following reasons. The lower limit of thickness deviation is set to be 7% or greater, because the effect of weight reduction is small and the effect of increasing the joint strength at connection portions is small if the thickness deviation is less than 7%. The upper limit of thickness deviation is set to be 50% from the view point of preventing occurrence of buckling, because the difference between the strength of the longitudinal middle portion 2 and the joint strength at the connection portions becomes large if the thickness deviation is greater than 50%, although it may be contribute to weight reduction. It is preferable that the thickness deviation be 10% or more and 30% or less. Preferably, variation in the strength along the longitudinal direction is suppressed.

(19) Variation in the thickness of the inclined portion 3 along the longitudinal direction is set to be in the range of 0.001 [mm/m] or more and 0.1 [mm/m] or less.

(20) The upper limit of the variation of the inclined portion 3 is set to be 0.1 [mm/m] for the following reason. As the variation along the longitudinal direction increases, the variation in the strength along the longitudinal direction increases, and the risk of occurrence of buckling increases. From this viewpoint, the risk of occurrence of buckling can be suppressed if the variation is 0.1 [mm/m] or less.

(21) The lower limit of the variation is set to be 0.001 [mm/m] because, as the variation decreases, the length of the longitudinal middle portion 2, which forms the body of the metal strip L and the body of a pipe body to be made from the metal strip L, decreases, and thereby the effect of weight reduction is reduced. Therefore, the lower limit is set to be 0.001 [mm/m] or greater.

(22) Even when the end portions of a metal strip are formed so as to be thick in hot rolling, if the thickened end portions are removed by pickling, slitting, or the like, such a metal strip is not a metal strip according to the present invention. A metal strip according to the present invention has longitudinal end portions that are thick when the metal strip is used as a product.

(23) (Regarding Pipe Body and Pipe)

(24) The metal strip L itself may be used as a steel strip, or a steel strip having an appropriate width may be made by slitting the metal strip L.

(25) The steel strip is formed into a pipe body. Then, a long pipe is made by successively connecting a plurality of pipe bodies by butt-welding the ends of the pipe bodies to each other.

(26) Alternatively, a long pipe may be manufactured by forming a pipe body while successively joining the steel strips by welding. Any existing method may be used to make a long pipe. For example, a pipe is continuously manufactured by roll forming as follows: while uncoiling a coiled steel strip, the steel strip is successively rolled to be formed into a U-shape and further into an O-shape; and ends of the steel strip in the width direction are continuously welded so as to close the O-shape. In this case, a long pipe is manufactured by successively welding a tail end portion of a preceding coil to a head end portion of the next coil.

(27) (Advantages)

(28) FIG. 4(a) is a schematic side view of a case where steel strips each having the aforementioned thickness profile are successively welded on the basis of the present embodiment. FIG. 4(b) illustrates a comparative example in a case where steel strips, which have end portions having a thickness that is the same as that of the steel strips in FIG. 4(A) and that is uniform along the longitudinal direction, are successively joined to each other by welding.

(29) When a pipe body is made by forming a steel strip into an O-shape, the diameter of the pipe body is determined by the width of the steel strip and the thickness of the pipe is determined by the thickness of the steel strip. As can be seen from comparison between FIGS. 4(a) and 4(b), with the present embodiment (see FIG. 4(a)), a strength the same as that of the comparative example can be maintained at joint portions between the pipe bodies, while weight reduction can be achieved because the bodies of the pipe bodies (the longitudinal middle portions 2) are thin. In the steel strip according to the present embodiment, the thickness of the longitudinal middle portion 2 may be set to be an appropriate thickness with which a strength required for a pipe to be made from the steel strip can be obtained.

(30) When forming a long pipe such as an oil-well cleaning pipe, by connecting the steel strips so that the thicknesses of the longitudinal middle portions 2 successively become smaller, the thickness of the pipe can be made smaller toward one end, that is, the weight of the pipe can be made smaller toward the end. Also in this case, by making the thicknesses of the longitudinal end portions 1 be the same, even when the thicknesses of the longitudinal middle portions 2 differ from each other, the steel strips can be butt-welded to each other so as to have no steps or so as to have only small steps therebetween. Note that, according to the present embodiment, it is not necessary to make the diameter of the pipe smaller toward one end even when making a long pipe such as an oil-well cleaning pipe, because the weight of each of the pipe bodies can be reduced. In other words, the shapes of metal strips, which will become the pipe bodies, may be the same.

(31) Thus, weight reduction of the entire pipe can be achieved, while suppressing variation in the strength of the pipe along the longitudinal direction, including the strengths of welded joint portions.

MODIFICATIONS

(32) In the embodiment, a case where the thickness of the longitudinal middle portion 2 is uniform or substantially uniform along the longitudinal direction is used as an example. However, it is not necessary that the thickness of the longitudinal middle portion 2 be uniform along the longitudinal direction. For example, as illustrated in FIG. 5, the longitudinal middle portion 2 may have a thickness that decreases at a constant gradient from the head end toward the tail end. In the case where the thickness of the longitudinal middle portion 2 along the longitudinal direction changes, it is preferable that variation in the thickness along the longitudinal direction be 0.1 [mm/m] or less. This is in order to suppress buckling, which may occur due to an increase in variation in the strength along the longitudinal direction, as described above.

(33) In the embodiment, a case where a long pipe is made from the metal strips L is used as an example. Alternatively, a long structural element, such as a long beam, may be made by welding ends of a plurality of steel strips. Also in this case, the weight of the structural element can be reduced while maintaining the strength of welded portions which are structurally the weakest, because the thicknesses of portions excluding the welded portions are small. However, the present invention is particularly effective when it is applied to a long pipe. The long pipe is not limited to an oil-well cleaning pipe. The long pipe may be used as a beam or a column.

Example 1

(34) Referring to FIG. 6, examples of the embodiment will be described.

(35) Metal strips A to I having the following dimensions were made from a material in accordance with API 5ST (corresponding to a hot steel sheet having a tensile strength of 600 to 700 MPa). The length X of each metal strip was 100 m, and the width of each metal strip was 1000 mm.

(36) Each of the metal strips according to the present embodiment was made under the following conditions. A steel having the following composition was hot-rolled to form a metal strip, while setting the finishing temperature to be in the range of 820 to 920 C. and setting the coiling temperature to be in the range of 550 to 620 C.

(37) The composition of the steel was, in mass %, C: 0.13%, Si: 0.2%, Mn: 0.7%, P: 0.02% or less, S: 0.005% or less, Sol.Al: 0.01-0.07%, Cr: 0.5%, Cu: 0.2%, Ni: 0.2%, Mo: 0.1%, Nb: 0.02%, Ti: 0.01%, N: 0.005% or less, and the balance being Fe and inevitable impurities.

(38) metal strip A

(39) longitudinal end portions length x1: 1.0 m thickness t1: 5.18 mm

(40) longitudinal middle portion length x2: 78 m thickness t2: 4.45 mm

(41) inclined portion 3 length x3: 10 m
metal strip B

(42) longitudinal end portions length x1: 1.0 m thickness t1: 5.18 mm

(43) longitudinal middle portion length x2: 78 m thickness t2: 4.93 mm

(44) inclined portion 3 length x3: 10 m
metal strip C

(45) longitudinal end portions length x1: 1.0 m thickness t1: 5.18 mm

(46) longitudinal middle portion length x2: 84 m thickness t2: 4.45 mm

(47) inclined portion 3 length x3: 7 m
metal strip G

(48) longitudinal end portions length x1: 0.0 m thickness t1: 5.18 mm

(49) longitudinal middle portion length x2: 80 m thickness t2: 4.45 mm

(50) inclined portion 3 length x3: 10 m
metal strip H

(51) longitudinal end portions length x1: 0.0 m thickness t1: 5.18 mm

(52) longitudinal middle portion length x2: 80 m thickness t2: 4.93 mm

(53) inclined portion 3 length x3: 10 m
metal strip I

(54) longitudinal end portions length x1: 0.0 m thickness t1: 5.18 mm

(55) longitudinal middle portion 2 length x2: 86 m thickness t2: 4.45 mm

(56) inclined portion 3 length x3: 7 m

(57) In addition, metal strips D, E, and F for comparative examples, each having a uniform thickness along the longitudinal direction, were made from a material the same as above. The thicknesses of the metal strips were as follows. metal strip D: 4.45 mm metal strip E: 4.93 mm metal strip F: 5.18 mm

(58) For the metal strips A and G, (5.184.45)/5.18=0.14, that is, the thickness deviation along the longitudinal direction is 14%. Variation of the inclined portion 3 along the longitudinal direction is (5.184.45)/10=0.073 [mm/m].

(59) For the metal strips B and H, (5.184.93)/5.18=0.048, that is, the thickness deviation along the longitudinal direction is 4.8%. Variation of the inclined portion 3 along the longitudinal direction is (5.184.93)/10=0.025 mm/m.

(60) For the metal strips C and I, (5.184.45)/5.18=0.14, that is, the thickness deviation along the longitudinal direction is 14%. Variation of the inclined portion 3 along the longitudinal direction is (5.184.45)/7=0.104 mm/m.

(61) For each the metal strips A to I, the same four metal strips were connected to each other in series by welding.

(62) Then, the welded joint portion and portion where the thickness varied were cut into a specimen, and a tensile test was performed on each of the specimens. The specimens were prepared in accordance with JIS No. 5, and the test was performed with a testing method in accordance with JISZ2201.

(63) In general, there is a correlation between the tensile strength and the fatigue strength of a material. Therefore, a tensile strength ratio can be regarded as a fatigue strength ratio.

(64) Table 1 shows the results.

(65) TABLE-US-00001 TABLE 1 Tensile Strength Ratio Weight Reduction (where F is 1.0) Ratio (%) A, G 1.0 12 B, H 1.0 4 C, I 0.9 13 D 0.8 14 E 0.9 5 F 1.0 0

(66) As can be seen from Table 1, in the cases where the metal strips A and G according to the present invention are used, weight reduction of 12% as compared the metal strips F can be achieved, while maintaining a tensile strength ratio the same as that of the metal strips F.

(67) In contrast, in the cases where the metal strips B and H are used, weight reduction rate is smaller than that of the metal strips A and G, although a tensile strength ratio the same as that of the metal strips F can be maintained.

(68) In the cases where the metal strips C and I are used, the tensile strength ratio is lower, that is, the fatigue strength ratio is lower than that of the metal strips A, G, and F, although the weight reduction rate about the same as that of the metal strips A and G can be achieved.

(69) As can be seen from the results for the metal strips D, E, and F, as the thickness of the entirety of the metal strip decreases, the tensile strength ratio, that is, the fatigue strength ratio decreases, while the weight reduction ratio increases. In other words, in general, there is a trade-off between the tensile strength ratio (fatigue strength ratio) and the weight reduction ratio. In contrast, with the metal strips A and G according to the present invention, a significant weight reduction can be achieved without decreasing the tensile strength ratio (fatigue strength ratio).

(70) As heretofore described, by making a long pipe from the metal strips L, which satisfy the range of the present invention, the lifetime of the pipe can be increased while achieving weight reduction.

REFERENCE SIGNS LIST

(71) 1 longitudinal end portion 1a head end portion 1b tail end portion 2 longitudinal middle portion 3 inclined portion L metal strip