JPS6260592B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spiral steel pipe in which three or more layers are laminated.

Conventionally, spiral steel pipes are made using pipe-making machines using steel strips, but they are only made of a single layer.
There were restrictions on manufacturing and economics for large-diameter pipes, high-pressure pipes, and special-purpose pipes.

In other words, since spiral steel pipes are made from hot-rolled steel strips, the thickness that can be manufactured is up to 25.4mm, and when it comes to large-diameter pipes, high-pressure piping, etc.
Even though the pipe needs to have a thickness of 25.4 mm, the original material is not available and it is impossible to manufacture it. Furthermore, when transporting low-temperature objects such as LNG or corrosive fluids, expensive stainless steel strips are currently used.

On the other hand, if existing steel strips are laminated in multiple layers to make a spiral pipe, it is possible to manufacture a pipe with a large thickness, but when making a laminated pipe with three or more layers, it is not always possible to inspect the welded part of the middle layer. There are drawbacks to not being able to fully implement it. In addition, if a corrosion-resistant, low-temperature material such as stainless steel strip is used for the innermost layer, and carbon steel is used for the second and subsequent layers, welding of the second layer carbon steel strip takes into account weld penetration into the innermost layer. Therefore, it is necessary to use a welding rod made of the same expensive material as the innermost layer, and welding may be difficult in some cases.

The present invention aims to solve the above-mentioned problems and to provide a method for manufacturing a spiral tube having three or more layers, which has sufficient strength and is highly economical. In other words, for spiral pipes with three or more layers, the joint ends of the innermost and outermost steel strips must be welded together,
In addition, it is a necessary and sufficient condition that the pipe be welded over a thickness of 1/2 or more of the pipe thickness.

Now, as shown in Figures 5 and 6, in a pressure vessel that receives internal pressure (P), circumferential force (Ft) and axial force (Fz) act due to internal pressure (P), and each Circumferential stress (σt) and axial stress (σz) are generated.

Here, the circumferential force (Ft) is defined as the resultant force of the internal pressure (P) acting on the inner wall of the pipe acting in a direction perpendicular to the cut plane, assuming that the container is cut at an arbitrary cross section in the longitudinal direction. , attempts to separate the container into two parts along the cut surface. This resultant force is maximum in the circumferential direction when the cross section includes the diameter, so the maximum circumferential force (Ft) at the B-B and C-C sections is Ft=D・l・P=2・r・l・P, and the circumferential stress (σt) is σt=Ft/A ₁ (because A ₁ =2・t・l) =2・r・l・P/2・t・l=r・P/ t −(1). Note that t=t ₁ +t ₂ +t ₃ .

Next, with the virtual cross section M-N as a boundary, both ends (lids) of the container serve as pressure receiving surfaces for internal pressure (P), and a tensile force is applied in the vertical direction. In other words, it is the axial force (Fz). This axial force (Fz) is Fz=π・r ²・P, and the axial stress (σz) is σz=Fz/A ₂ (because A ₂ = 2・π・r・t) = π・r・P/2・π・r・t=r・P/2t −(2). In addition, t=t ₁ + t ₂ + t ₃ From the above equations (1) and (2), the tube thickness t is as follows: σt=r・P/t→t=r・P/σt −(3) σz=r・P /2t→t=r・P/2σz −(4). In the design of the pressure vessel, the pipe thickness is determined by taking into account the destruction caused by the internal pressure (P) as follows: σt=σa σz=σa σa: Design allowable stress of the vessel material. This is explained in (3) above.
Equation (4) shows that in terms of strength, it is possible to cope with the internal pressure (P) and the axial stress (σz) with a pipe thickness that is 1/2 of the circumferential stress (σt). Therefore, the internal pressure acting on the pipe can be coped with by the circumferential strength of the entire pipe thickness and the axial strength by 1/2 of the total pipe thickness.

Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1a and 1b, 1 indicates a spiral multilayer tube. That is, Fig. 1a shows a pipe completed by laminating multiple layers of steel strips in a spiral shape.
Figure b shows the cross-sectional state in detail.

Fig. 2 shows a cross section including the pipe axis of a pipe laminated in three layers, in which 2 is the outermost layer, 3 is the middle layer, 4 is the innermost layer, 5 is the welded joint of the outermost layer, and 6 is the welded joint of the outermost layer.
7 indicates a welded joint in the innermost layer, and 7 indicates opposing ends of the steel strip in the intermediate layer.

Further, FIG. 3 shows a spiral multilayer pipe laminated in four layers, 8 in the same figure shows the middle layer, and 9 shows the opposing surface of the unwelded steel strip of the middle layer.

As can be seen from FIGS. 2 and 3, the outermost layer 2 and the innermost layer 3 are welded in a spiral manner, and are thoroughly inspected and repaired if necessary. but,
Since the intermediate layers 7, 8, and 9 are simply wrapped with steel strips and are not welded, there is no need for inspection and, of course, there is no need for any welding repairs.

The manufacturing process of the spiral multilayer pipe according to the present invention is as follows:
First, as in the production of conventional spiral tubes, the innermost layer is formed and welded from the inner and outer surfaces to form a pipe, and then the intermediate layer is wound on the adjacent stage. In the case of a three-layer pipe, the outermost layer may be wrapped in the next stage, and the lower layer may be considered as a backing metal and one-sided welding may be performed with penetration, or it may be welded without penetration into the lower layer. In the case of multilayer pipes with three or more layers, the same process can be used to stack them, but in either case, as explained earlier, the sum of the thicknesses of the welded layers must be at least 1/2 of the total pipe thickness. It requires becoming.

Therefore, for extremely thick cylindrical shells such as high-pressure vessel shells, 1/2 of the above-mentioned total pipe thickness is required.
Since the laminate plates corresponding to the above plate thickness must be welded together, the intermediate layer must also be welded together as appropriate, but in this case, sufficient inspection and necessary repairs should be carried out as described above. After that, the outer layer can be further wrapped. However, in a layer to be welded together, when it is melted into a lower layer, it is necessary to shift the phase of the start of winding so that the weld line between the layer to be welded and the layer immediately below it does not coincide.

In addition, each laminated layer does not need to be made of the same material; for example, if corrosion resistance is required, the innermost layer may be made of stainless steel, and the outer layer may be made of carbon steel, and the seam of the layer adjacent to the innermost layer may be made of stainless steel. If the joints of the subsequent layers are welded without welding, the welding material may be the same as that of the outer layer.

FIG. 4 is an example in which a flange is attached to the end of a spiral multilayer pipe to connect it to other piping.
Reference numeral 10 indicates a flange, and 11 indicates a joint weld between the flange and the pipe. As can be seen from the figure, since the spiral multilayer pipe is welded to the flange over its entire thickness, the axial force is distributed from the flange to each welded layer, and the unwelded intermediate layer is axially No force is applied, and only circumferential forces need to be withstood. This is true for any end structure other than flanges.

As detailed above, according to the present invention, it is possible to provide an economical steel pipe that has a wide range of applications, has sufficient strength performance, and can omit some welding, making a great contribution to the industry. However, there is.

[Brief explanation of the drawing]

FIG. 1a is an overall schematic diagram showing an embodiment according to the present invention, FIG. 1b is a diagram showing some details of FIG. 1a, and FIG. 2 is a partial sectional view of a three-layer laminated pipe according to the present invention. , Fig. 3 is a partial cross-sectional view of a pipe laminated in four layers according to the present invention, Fig. 4 is a partial cross-sectional view showing a state in which a flange is connected to the pipe according to the present invention, and Fig. 5 is a partial cross-sectional view showing the state in which a flange is connected to the pipe according to the present invention. A vertical cross-sectional view of the container, FIG. 6 being a cross-sectional view perpendicular to its axis. 2...outermost layer, 3...middle layer, 4...innermost layer,
5... Welded joint on the outermost layer, 6... Welded joint on the innermost layer, 7... Opposing ends of the intermediate layer.

Claims (1)

[Claims] 1. In a method of manufacturing a multilayer pipe by spirally winding three or more layers of metal strips, the sum of the thicknesses of the innermost and outermost layers of the metal strips forming the multilayer pipe is less than 1/2 of the total pipe thickness. If the thickness is too large, all the spiral joints of the innermost and outermost layers will be welded, and if the sum of the thicknesses of the innermost and outermost layers is less than 1/2 of the total pipe thickness, welding will be performed. It is characterized by welding all of the innermost and outermost layers and a part of the middle layer in a spiral shape so that the sum of the thicknesses of the layers is 1/2 or more of the total pipe thickness or less than the total pipe thickness. Method for manufacturing spiral multilayer pipes.