JPH0796132B2 - Bending method of thick-walled pipe - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of bending a thick-walled pipe into an arc shape.

(Prior Art) For sour oil pipes, it is desirable to use thick-walled clad pipes whose outer layer is made of high-strength carbon steel and whose inner layer is made of a highly corrosion-resistant, high-nickel alloy.

The inner layer material is typically so-called 60 nickel, IN625 containing about 60% nickel is used, and the outer layer and the inner layer are integrally formed by centrifugal casting.

In order to form the above-mentioned clad tube into a bend tube, as shown in FIG. 1, a straight clad tube (4) is supported by a guide (1) consisting of a group of rollers so as to be able to be drawn out in the axial direction, and the end of the guide (1) is formed. A high-frequency heating device (2) is installed in the vicinity, and the tip of the cladding tube (4) is connected to the free end (3) of the rotating arm (3).
Clamp to 1).

While locally heating the cladding tube (4) by the high frequency heating device (2), the arm (3) is rotationally driven to draw out the cladding tube (4) in an arc shape and bend the tube in an arc shape.

Close to the downstream side of the heating device (2), the cooling water nozzle (6)
Is installed, the pipes that bend in an arc shape and pass through are sequentially cooled to prevent deformation of the arc pipes.

The heating temperature is 900 to 1000 ° C. Under these conditions, neither cracks nor wrinkles are found in the inner layer (42) and the outer layer (41).

A so-called 40-nickel clad tube having a nickel content of less than 40% nickel and having IN825 as an inner layer material containing about 40% nickel is also used for sour oil well piping.

The cladding tube (4) using the above IN825 as the inner layer material is
When bent into an arc under the same conditions as in the case of 25, there is almost no problem if the radius of curvature is about 3 times the pipe diameter. However, if the radius of curvature is increased to about twice the pipe diameter, as shown in FIG. 3, there is no problem on the side of the pipe that receives the compressive stress (hereinafter, the abdominal side) where the curvature is large, but the curvature that receives the tensile stress is not a problem. A large number of cracks (5) were generated in the circumferential direction of the tube on the surface of the inner layer on the small side (hereinafter, dorsal side), and the product was damaged. This is because the toughness of the material is insufficient with respect to the tensile force acting on the inner layer (42) on the back side during processing.

Common sense is that if the heating temperature for the clad tube (4) is raised to further soften the clad tube (4), the occurrence of cracks should be prevented, but when actually done,
Cracks could not be prevented.

It is considered that this is because when the heating temperature is increased, the softening degree of the clad tube is increased to facilitate bending, but the tensile strength is decreased.

Contrary to common sense, the present invention clarifies a method for bending a pipe in which cracking does not occur on the inner surface by lowering the heating temperature.

(Means for Solving the Problem) According to the present invention, a thick-walled pipe is held by a guide (1) so as to be movable in the axial direction, and a heating device (2) is provided near the end of the guide (1). Inner layer (42) in the method of bending the pipe in an arc shape by drawing it in an arc shape while heating locally
Is characterized in that a thick-walled tube formed of a high nickel alloy containing 38 to 46 (wt%) of Ni is drawn out in an arc shape while heating the surface of the inner layer to 750 to 850 ° C.

(Operation and effect) In the bending process of a pipe, it is common knowledge that the higher the heating temperature, the higher the softening degree of the pipe, the less strain on the pipe, and the easier the working.

As in the present invention, the heating temperature for the thick-walled tube is set to 900-1
If the temperature is lower than 000 ° C, the elongation of the tube becomes lower than that at the conventional heating temperature and the processing becomes difficult. When the heating temperature was intentionally lowered to 750 to 850 ° C during bending of the pipe, it was found that no cracks were formed on the inner and outer surfaces of the pipe.

At 750 ° C or lower, no plastic deformation occurs, and at 850 ° C or higher, cracks are generated on the inner surface of the pipe as in the conventional case.

Example In the example, the outer layer (41) is high carbon steel and the inner layer (42) is IN82.
The bending process of the centrifugally cast clad pipe (4) of 5 will be described, but it goes without saying that the entire pipe can be bent to form the IN825.

The outer layer (41) and the inner layer (42) of the cladding tube (4) will be described in detail. The components of the outer layer (41) are C0.10 and Si in weight%.
0.20, Mn0.93, P0.017, S0.009, Ni0.51, Cr0.06, Mo0.
18, V0.07, balance Fe.

The inner layer (42) in the examples is stabilized with niobium in order to improve the corrosion resistance and the weldability, and the component is wt%,
C0.05 or less, Si1.0 or less, Mn1.0 or less, P0.03 or less, S0.03
Below, Ni38-46, Cr19.5-23.5, Mo2.5-3.5, Cu1.5-
3.0, Nb0.6 to 1.2, balance Fe.

The bending apparatus is a known high-frequency bending apparatus, and is provided in the vicinity of the end of the guide (1) including a guide (1) including a roller group (11) that supports the clad tube (4) so as to be movable in the axial direction. A high frequency heating device (2) for heating the clad pipe (4), a cooling water nozzle (6) provided immediately after the high frequency heating device (2) and the tip of the clad pipe (4) are clamped into an arc shape. It is composed of a rotating arm (3) to be pulled out. The rotation center (32) of the arm (3) is located on an imaginary line L orthogonal to the axis of the straight cladding tube (4) from the outlet (21) of the high frequency heating device (2).

However, in bending the pipe, it is common knowledge that the higher the heating temperature is, the better the elongation of the pipe becomes, so that the pipe is not overloaded and the working becomes easy. The heating temperature for (4) was set to 750 to 850 ° C, which is lower than the conventional temperature of 900 to 1000 ° C. In this heating temperature range, as shown in FIG. 2, the elongation of the tube is in the conventional heating temperature range.
It is lower than that at 900-1000 ℃.

In addition to the condition that cracks did not occur in the inner and outer layers during bending of the pipe, a low temperature range of 750 to 850 ℃ was used.

Plastic deformation does not occur at 750 ° C or lower, and tensile strength decreases remarkably at 850 ° C or higher.
Cracks occurred in 1).

The following table shows an outer diameter of 173 mm in which the inner and outer layers are composed of the above-mentioned components,
The data is obtained by bending a centrifugally cast clad tube with an inner diameter of 117 mm (outer layer thickness: 25 mm, inner layer thickness: 3 mm) under different conditions.

800 ° C on the side with a large radius of curvature on the inner surface of the clad tube (4)
When high-frequency bending is performed in, it is possible to form without bending until bending with a curvature of 2DR.

The present invention is not limited to the configuration of the above embodiment,
Various modifications are possible within the scope described in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a bending apparatus and method, FIG. 2 is a sectional view of a bend pipe, and FIG. 3 is a graph showing a relationship between heating temperature of a cladding pipe and tensile strength and elongation. is there. (1) ... Guide, (11) ... Roller (2) ... High frequency heating device, (3) ... Arm (4) ... Clad tube

Claims (2)

[Claims] 1. A thick-walled pipe is held by a guide (1) so as to be movable in the axial direction, and a heating device (2) is provided near the end of the guide (1) to locally heat the thick-walled pipe. Inner layer (42) in the method of pulling out in an arc shape and bending the pipe into an arc shape
Is characterized in that a thick-walled tube made of a high nickel alloy containing 38 to 46 (wt%) Ni is drawn out in an arc shape while heating so that the inner layer surface becomes 750 to 850 ° C. Bending method for thick-walled pipe. 2. The method for bending a thick-walled pipe according to claim 1, wherein the inner layer (42) contains Nb 0.6 to 1.2 (% by weight).