JP6740993B2 - Inner resin lining thin-walled steel pipe and method for manufacturing the same - Google Patents

Description

The present invention relates to an inner surface resin lined thin-walled steel pipe mainly used for water pipes and a method for manufacturing the same.

As a steel pipe for waterworks and the like, a carbon steel pipe for piping specified in JIS G 3452 (hereinafter, also referred to as "JIS specified steel pipe") is used. The pipe end of the carbon steel pipe for pipes is provided with a threaded portion having a screw (male thread) formed on the outer surface of the pipe, and a carbon pipe for adjoining pipes is connected through a pipe joint having a screw (female thread) formed on the inner surface. Joined with steel pipe. For the screw, a JIS B 0202 parallel pipe screw (hereinafter also referred to as "JIS standard parallel screw") or a JIS B 0203 pipe taper screw (hereinafter also referred to as "JIS standard taper screw") is used. (Hereinafter, both will be collectively referred to as "JIS prescribed screw").

As compared with such a carbon steel pipe for piping specified in JIS G 3452, a steel pipe (thin steel pipe) having the same outer diameter but a reduced thickness (wall thickness) is proposed as a lightweight steel pipe. It's coming.

At that time, in order to form a screw (male thread) on the outer surface of the steel pipe, a cutting screw that forms a screw thread by cutting the steel pipe with a blade called a checker has been the mainstream for many years, but the thickness of the steel pipe at the thread portion is reduced. Is inevitable, especially when applied to thin-walled steel pipes, the wall thickness at the bottom of the thread root becomes extremely thin, making it difficult to cut, and the strength of the threaded joint decreases, resulting in a significant decrease in seismic resistance. There was a problem that it did.

On the other hand, in recent years, a rolling screw in which a roller (rolling tool) having a thread formed on the outer surface of a rolling roller is pressed against a steel pipe to form the thread by plastic working is becoming widespread. Unlike the cutting screw, the rolling screw secures the thickness of the steel pipe at the root of the thread, so the strength of the threaded joint is high, and even when applied to thin-walled steel pipe, it can have sufficient earthquake resistance. There is an advantage that.

As shown in FIG. 1( a ), the method for forming the rolling screw as described above includes gradually rotating the steel pipe from the end of the steel pipe to a space between rolling rollers (rolling tools, for example, 5). So-called "step rolling", in which three rolling rollers (rolling tools) that normally rotate are simultaneously moved toward the steel pipe, as shown in FIG. 1(b). There is "group rolling".

Regarding such a rolled screw, in Patent Document 1, a core is inserted into a thin-walled steel pipe whose thickness is reduced to 70% to 50% with respect to the thickness specified in JIS B 0202, and A method of obtaining a thread profile is disclosed. In the case of a thin-walled steel pipe, in step rolling, the thread does not rise in the shape defined in JIS B 0202 or JIS B 0203, which causes a thread failure, but according to Patent Document 1, the problem is It is said that the problem can be solved by inserting it.

On the other hand, in order to prevent corrosion of the inner surface of the steel pipe, an inner resin-lined steel pipe in which a resin lining (for example, a lining of polyethylene powder or polyolefin powder) is applied to the inner surface of a carbon steel pipe for piping is widely used (for example, , Patent Documents 2 and 3).

Even for such an inner surface resin-lined steel pipe, in order to reduce the weight, a thin-walled steel pipe (inner-side resin-lined thin-walled steel pipe) having a thickness smaller than that of JIS G 3452 is required.

Japanese Patent No. 3488345 Patent No. 5928328 Japanese Patent No. 5353297

However, when an attempt is made to manufacture an inner surface resin-lined thin-walled steel pipe thinner than the JIS-specified steel pipe as described above, the following problems occur.

First, when a JIS standard screw is formed on the outer surface of the steel pipe end of the thin-walled steel pipe by rolling, the rigidity of the steel pipe decreases as the thickness of the steel pipe decreases, so a rolling tool was pressed against the outer surface of the steel pipe. At that time, the steel pipe is crushed, or the deformation in the same direction as the pushing of the rolling tool becomes large, and the reaction force against the rolling tool decreases. As a result, the deformation and filling (plastic flow) of the material into the recess provided on the outer circumference of the rolling tool due to the formation of the thread becomes small, and there is a problem that the prescribed thread shape cannot be formed. If the prescribed thread shape cannot be formed, the fluid passing through the pipe will leak from the joint, and the seismic strength of the joint will decrease.

To solve this problem, in the case of an inner resin lined thin-walled steel pipe, the method of inserting a core into the end of the steel pipe to obtain a prescribed thread shape cannot be applied, as in Patent Document 1 described above. When the core is inserted, at least the inner surface of the steel pipe comes into contact with the core with high surface pressure, and in some cases, the resin slides on the inner surface of the steel pipe due to damage and peeling due to rolling and sliding, which significantly reduces corrosion resistance. Because. Even if the resin lining on the inner surface of the steel pipe as described above is allowed to be damaged or peeled off and the inner surface of the steel pipe is repaired after the rolling screw is formed, the surface energy of the resin lining (for example, polyethylene) itself is low. It is difficult for the material to adhere or adhere, and the repair cannot be performed, or the repair material is peeled off and the repair effect cannot be obtained, so that it becomes difficult to exhibit corrosion resistance.

Further, as a problem that becomes noticeable when forming a rolled screw of a thin-walled steel pipe, as shown in FIG. 2, unevenness is formed on the inner surface of the steel pipe of the threaded portion after the rolling process in the same phase as the spiral thread of the outer surface of the steel pipe. What happens is that it happens.

When such unevenness of the inner surface of the steel pipe becomes large, the resin lining on the inner surface of the steel pipe cannot follow the uneven deformation and is partially peeled off, resulting in a decrease in corrosion resistance. I can't say it. This phenomenon is even more likely to occur when the thickness of the thin steel pipe is less than 87.5% of the thickness specified in JIS B 0202.

Even if the resin lining on the inner surface of the steel pipe does not peel off, if there is unevenness on the inner surface of the steel pipe as described above, the O-ring provided for the purpose of stopping water at the joint between the steel pipe and the pipe joint is deformed by the unevenness on the inner surface of the steel pipe. However, the sealing is incomplete, and the corrosion resistance of the joint is reduced. Fig. 3 shows the cross section of the joint of a typical polyethylene powder lined steel pipe. In the case of the O-ring shown in Fig. 3, assuming that the inner surface of the threaded portion is uneven, the O-ring will definitely affect its effect. Receive. If the inner surface of the pipe formed in the same phase as the helical thread formed on the outer surface of the steel pipe has large irregularities, the O-ring will go over at least one protrusion, and the water-stopping effect can easily be reduced. Be inferred.

Therefore, it is necessary to reduce the amount of unevenness on the inner surface of the steel pipe of the threaded portion to the extent that the resin lining on the inner surface of the steel pipe does not peel off and the water blocking function of the O-ring is not impaired.

The present invention has been made in view of the above circumstances, and an inner surface resin provided with a good threaded portion (the thread shape of the outer surface of the steel pipe is a JIS prescribed shape, and the unevenness of the inner surface of the steel pipe is small) An object of the present invention is to provide a thin-walled steel pipe and a manufacturing method thereof.

The present inventors conducted the following studies in order to solve the above problems.

First, when the wall thickness of the steel pipe is made thinner than that of the JIS standard, a screw having a JIS standard shape can be formed on the outer surface of the steel pipe by rolling without using a core as in Patent Document 1, Considered the range.

Next, on the premise of the thickness range, for the unevenness of the inner surface of the steel pipe at the threaded portion, determine the range in which the resin lining on the inner surface of the steel pipe does not peel off and the water stop function of the O-ring is not impaired, and the range is determined. A method for suppressing the unevenness on the inner surface of the steel pipe was examined.

The present invention is based on the findings (details will be described in the section of [Modes for carrying out the invention] described later) obtained by such studies, and has the following features.

[1] A carbon steel pipe for piping specified in JIS G 3452 has the same outer diameter, a thickness of less than 100% and 78% or more, a resin pipe lining on the inner surface of the steel pipe, and a steel pipe end portion, An inner surface resin comprising a threaded portion having a thread according to JIS B 0202 or JIS B 0203 on the outer surface of the steel pipe, and the unevenness of the inner surface of the steel pipe of the threaded portion is 200.0 μm or less at a maximum height Rz. Lining thin-walled steel pipe.

[2] The inner surface as described in [1] above, which has the same outer diameter and a thickness of less than 87.5% and 78% or more with respect to the carbon steel pipe for piping specified in JIS G 3452. Resin-lined thin-walled steel pipe.

[3] A method for manufacturing an inner surface resin-lined thin-walled steel pipe according to [1] or [2], which comprises a thin-walled steel pipe manufacturing step for manufacturing a thin-walled steel pipe, and an inner surface for forming a resin lining on the inner surface of the thin-walled steel pipe. A method for manufacturing an inner resin-lined thin-walled steel pipe, comprising: a resin lining step; and a screw forming step of forming a screw on an outer surface of a steel pipe end portion of the thin-walled steel pipe having a resin lining on the inner surface.

[4] The thread forming step is a thread forming step for forming a thread by rolling, and in the thread forming step, at least one of the following (A), (B), and (C) is performed. The method for producing an inner surface resin lined thin-walled steel pipe according to the above [3], which is performed.
(A) Step rolling is used, and a lubricant having a friction coefficient of 0.08 or less is used.
(B) Using step rolling, the rotation speed of the rolling tool is set to 70 rpm or less.
(C) Using the rolled rolling.

ADVANTAGE OF THE INVENTION According to this invention, the inner surface resin lining thin-walled steel pipe provided with a favorable screw part (The screw shape of the steel pipe outer surface is a shape of JIS regulation, and the unevenness|corrugation amount of the steel pipe inner surface is small) can be obtained.

As a result, compared with the conventional inner surface resin lined steel pipe, it is possible to reduce the weight of the steel pipe while having the same joint seismic strength, and it is possible to improve workability and workability of the pipe. Furthermore, by reducing the additional load on the structure, it is possible to give a margin to the seismic strength of the entire structure. Further, in the processing of the screw portion, the use of the core can be omitted, so that the total cost of the screw processing equipment can be reduced and the production efficiency can be improved by shortening the processing time.

It is a figure which shows a step rolling and a shift rolling. It is a figure which shows the unevenness|corrugation of the steel pipe inner surface of a screw part. It is a figure which shows the joining part of a steel pipe and a pipe joint. It is a figure which shows the influence of the wall thickness which acts on a rolling screw shape. It is a figure which shows the influence of the lubricant (friction coefficient) which affects the inner surface unevenness|corrugation amount of a screw part. It is a figure which shows the influence of the rotation speed of a rolling tool which affects the inner surface unevenness|corrugation amount of a screw part. It is a figure which shows the influence of the rolling processing method which acts on the inner surface unevenness|corrugation amount of a screw part. It is a figure which shows the influence of the rolling processing method which acts on the inner surface unevenness|corrugation amount of a screw part. It is a figure which shows the stress state in step rolling (finite element method analysis). It is a figure which shows the stress state at the time of rolling and rolling (finite element method analysis).

As mentioned above, the description will focus on the process of the present invention.

In the present invention, the thinning of the JIS standard steel pipe (carbon steel pipe for piping) was attempted. However, in the following, among the JIS standard steel pipes, the nominal diameter 25A (outer diameter 34 mm, wall thickness A typical example will be described in the case of studying thinning based on a steel pipe having a thickness of 3.2 mm).

By the way, in the present invention, the thickness of the JIS-specified steel pipe is the “thickness” in Table 4 of JIS G 3452:2014, and the “thickness tolerance” at that time is (+0%, -12.5%).

First, when the wall thickness is made thinner than the JIS standard steel pipe, the range of the thickness of the steel pipe in which the JIS standard screw can be formed by rolling on the outer surface of the steel pipe end without using the core as in Patent Document 1 is examined. did.

Specifically, a steel pipe having a nominal diameter of 25 A (outer diameter 34 mm, wall thickness 3.2 mm) is used as a reference steel pipe, and the outer diameter is set to 34 mm, which is the same as the reference steel pipe, with respect to the thickness ts (3.2 mm) of the reference steel pipe. To reduce the thickness t (that is, reduce the thickness ratio t/ts). The screw was a taper screw specified by JIS, and the screw was formed by step rolling, which requires a small device. Cutting oil was used as the lubricant, and the rotation speed of the rolling tool was 88 rpm. No core was used.

FIG. 4 shows an example of the cross-sectional shape of the threaded portion when the thickness ratio is reduced. 4A shows a thickness ratio of 100% (t/ts=1.0), FIG. 4B shows a thickness ratio of 78% (t/ts=0.78), and FIG. The thickness ratio is 66% (t/ts=0.66).

As shown in FIG. 4, when the thickness ratio is 78% (t/ts=0.78), the screw ratio specified by JIS is the same as the thickness ratio of 100% (t/ts=1.0). Are formed. On the other hand, in the case where the thickness ratio is 66% (t/ts=0.66), the screw specified by JIS cannot be formed.

From these results, if the thickness of the steel pipe is less than 100% and 78% or more of the thickness of the JIS-compliant steel pipe, the JIS-compliant screw is attached to the outer surface of the steel pipe end without using the core as in Patent Document 1. It was judged that they could be formed by rolling.

Next, assuming that thickness range (less than 100% and 78% or more of the thickness of the JIS-compliant steel pipe), the resin lining on the steel pipe inner surface is peeled off for the amount of unevenness of the steel pipe inner surface of the threaded portion. The range was investigated without causing the O-ring to impair the water blocking function. The unevenness of the inner surface of the steel pipe was evaluated by the maximum height Rz (JIS B 0601:2001) with the entire threaded portion as a reference length.

As a result, it was determined that when the unevenness amount Rz of the inner surface of the steel pipe of the threaded portion was 200.0 μm or less, the resin lining on the inner surface of the steel pipe did not peel off and the water-stopping function of the O-ring was not impaired (for details, See below).

Then, the method of suppressing the unevenness amount Rz of the inner surface of the steel pipe of the threaded portion to 200.0 μm or less was examined.

At that time, as the thin-walled steel pipe, a steel pipe (outer diameter 34 mm, thickness 2.5 mm) having a thickness ratio of 78% with respect to the reference steel pipe (nominal diameter 25 A (outer diameter 34 mm, thickness 3.2 mm)) is used. I was there. The screw was a taper screw defined by JIS, and the screw was formed by step rolling.

As a result, basically, plastic flow of the material that exceeds the amount required to form the JIS-standard screw thread shape on the outer surface of the steel pipe, that is, excessive filling and flowing of material into the rolling tool side is suppressed. I found that the point was to do.

FIG. 5 shows an example of the relationship between the lubricant used and the uneven shape of the inner surface of the threaded portion. FIG. 5A shows the case where cutting oil (friction coefficient 0.1 to 0.3) is used, and FIG. 5B shows the case where solid lubricant (friction coefficient 0.04 to 0.06) is used. .. The rolling speed of the rolling tool was 505 rpm.

As shown in FIG. 5, compared with the case of using the cutting oil (friction coefficient 0.1 to 0.3), the inner surface of the steel pipe when the solid lubricant (friction coefficient 0.04 to 0.06) is used It can be seen that the unevenness amount Rz is reduced from 300.0 μm to 120.0 μm.

By reducing the amount of unevenness on the inner surface of the steel pipe, the difference in deformation amount between the concave portion and the convex portion of the steel pipe having the initial inner diameter of about 29.0 mm (initial inner radius of about 14.5 mm), that is, the difference in strain Δ0. 18 mm/14.5 mm=0.0012, which is a 1.2% difference in strain. In general, since the strain difference of 1% with respect to the resin is sufficiently large, it can be said that the local reduction of the strain difference of 1.2% at the uneven portion of the inner surface of the steel pipe is very effective in preventing the peeling of the inner lining of the steel pipe.

Similarly, regarding the amount of deformation of the O-ring, in the case of the O-ring having a wire diameter of 3.5 mm, the crushing margin for exhibiting the function is 0.46±0.14 mm, which is smaller than that of the O-ring shown in FIG. When the inner surface unevenness amount Rz is 300.0 μm, it can be understood that there is a concern that the water blocking effect will not be exhibited if there is a diameter difference that exceeds the allowable deviation of the crushing margin. On the other hand, when the friction is reduced, it can be said that the crushing margin is within the allowable range.

From these results, by using a lubricant with a friction coefficient of 0.08 or less, excessive filling and inflow of material to the rolling tool side can be suppressed (that is, the tendency that the outer surface of the screw part rises is reduced. Then, it was determined that the unevenness amount Rz on the inner surface of the steel pipe can be set to 200.0 μm or less, and the thread rolling can be performed without any particular problems in the covering function and the O-ring function of the inner surface resin-lined steel pipe. .. However, the friction coefficient of the lubricant is preferably 0.03 or more in consideration of slipping of the rolling tool.

FIG. 6 shows an example of the relationship between the rotation speed of the rolling tool and the uneven shape of the inner surface of the threaded portion. 6A shows the case where the rolling speed of the rolling tool is 505 rpm, and FIG. 6B shows the case where the rotational speed of the rolling tool is 88 rpm. Cutting oil was used as the lubricant.

As shown in FIG. 6, when the rotation speed of the rolling tool is set to 88 rpm as compared with the case where the rotation speed of the rolling tool is set to 505 rpm, the unevenness amount Rz of the inner surface of the steel pipe is changed from 340.0 μm to 230.0 μm. You can see that it is reduced.

From these results and the like, by controlling the rotation speed of the rolling tool to 70 rpm or less, it is possible to suppress the excessive filling and inflow of the material into the rolling tool side and reduce the unevenness amount Rz of the inner surface of the steel pipe to 200.0 μm or less. It was determined that the thread rolling can be performed without any particular problems in the coating function and the O-ring function of the inner surface resin lined steel pipe. However, in view of productivity, it is preferable to set the rotation speed of the rolling tool to 40 rpm or more.

FIG. 7 and FIG. 8 show an example of the relationship between the rolling process method, the appearance of the steel pipe after rolling (concavo-convex state of the inner surface), and the concavo-convex shape of the inner surface of the screw part. FIGS. 7A and 8A show the case where the thread formation is performed by step rolling, and FIGS. 7B and 8B show the case where the screw formation is performed by the offset rolling. Cutting oil was used as the lubricant, and the rotation speed of the rolling tool was 88 rpm for step rolling and 200 rpm for shift rolling. Incidentally, the step rolling of FIGS. 7A and 8A is the same as that of FIG. 6B described above.

As shown in FIGS. 7A and 8A, when threads were formed by step rolling, unevenness was generated on the inner surface of the steel pipe (unevenness amount Rz=230.0 μm). On the other hand, as shown in FIGS. 7(b) and 8(b), when the thread formation was performed by the offset rolling, no unevenness was generated on the inner surface of the steel pipe (unevenness amount Rz=0.0 μm ).

This is found from the forming simulation analysis using the finite element method. In step rolling, as shown in FIG. 9, the inner surface of the steel pipe at the portion in contact with the rolling tool during rolling is shown. The stress in the pipe axis direction in Fig. 2 becomes compressed, and the corrugations in the pipe axis direction, and consequently the unevenness on the inner surface of the steel pipe, tend to be formed easily. On the other hand, in the case of offset rolling, as shown in FIG. 10, it is understood that tensile stress acts in the pipe axis direction at the contact portion with the rolling tool, and the occurrence of the above waveform is suppressed. As a result, unevenness on the inner surface of the steel pipe is reduced or the occurrence thereof is suppressed. Therefore, it is construed that the application of group rolling is desirable.

From these results, it is possible to reduce the unevenness amount Rz of the inner surface of the steel pipe to 200.0 μm or less by forming the screw by slip rolling, and there is no particular problem in the covering function and the O-ring function of the inner surface resin lined steel pipe, It was determined that rolling could be performed.

The above is the case where the JIS standard taper screw is formed by rolling the standard 25 mm diameter steel pipe (outer diameter 34 mm, wall thickness 3.2 mm) among the JIS standard steel pipes. The same can be said when the standard steel pipe is used as the standard steel pipe or when the JIS standard parallel thread is formed by rolling.

Here, as described above, when the unevenness amount Rz on the inner surface of the steel pipe in the threaded portion is 200.0 μm or less, it is determined that the resin lining on the inner surface of the steel pipe does not peel off and the water blocking function of the O-ring is not impaired. I will describe the points I did.

First, regarding "the resin lining on the inner surface of the steel pipe does not peel off", when the nominal diameter 25A or more having a thread pitch of 2.3091 mm is used as the reference steel pipe to reduce the thickness, the unevenness amount Rz is 250.0 μm or less. It was judged that the unevenness amount Rz was 200.0 μm or less when thinning the nominal diameters of 15A and 20A having the thread pitch of 1.8143 mm as the reference steel pipe.

Here, the physical meaning that the amount of unevenness Rz is the above value (250 μm or less, 200.0 μm or less) means that the length of the steel pipe in the case where unevenness occurs in the threaded portion from the situation where there is no unevenness before the thread formation. This means that the elongation in the direction does not exceed 3%. The implication that the amount of elongation of the threaded portion does not exceed 3% is that the amount of elongation of the steel pipe due to the diameter reduction of the steel pipe end that occurs due to the rolling forming of the taper screw is about 7%, and It is intended that an elongation of about 10% (this is the upper limit, and the smaller the better, of course) is that it does not act on the inner surface lining (for example, polyethylene). It is calculated in consideration of the remaining critical strain of about 10%.

On the other hand, strictly speaking, as to "the water-stopping function of the O-ring is not impaired", it depends on the wire diameter of the O-ring used and the amount of unevenness at the position on the inner surface of the steel pipe that is in contact with the O-ring. Although it cannot be said, it basically means that the amount of unevenness is within the allowable range of the crushing margin of the O-ring. Specifically, as an example, when an O-ring with a wire diameter of 2.4 mm is used, the crushing margin reference value is 0.37 mm±0.10 mm when calculated based on the JIS standard, and it is in contact with the O-ring. It is necessary that the unevenness amount Rz of the inner surface of the steel pipe at the position to be set is 200.0 μm or less. By the way, if the inner surface of the steel pipe is flat and has no irregularities, the O-rings will contact without any gaps, but if the inner surface of the steel pipe has irregularities, the O-ring will not come into contact with the inner surface of the steel pipe.

From the above, it was judged that if the unevenness amount Rz on the inner surface of the steel pipe of the threaded portion is 200.0 μm or less, the resin lining on the inner surface of the steel pipe does not peel off and the water blocking function of the O-ring is not impaired.

Then, based on the above-described examination results, as an inner surface resin-lined thin-walled steel pipe, the outer diameter is the same and the thickness is less than 100% and 78% or more as compared with the JIS-specified steel pipe, and the resin lining is formed on the inner surface of the steel pipe. And an inner surface resin lined thin-walled steel pipe having a threaded portion having a JIS standard screw (rolled screw) on the outer surface of the steel pipe at the end of the steel pipe, and the unevenness amount Rz of the inner surface of the steel pipe at the threaded portion is 200.0 μm or less. Was conceived.

Then, the method of manufacturing the inner surface resin lining thin-walled steel pipe, using a steel plate having the same plate thickness as the thickness of the thin-walled steel pipe to be manufactured, a thin-walled steel pipe manufacturing step of manufacturing a thin-walled steel pipe by the forge welding method or the electric resistance welding method, and An inner surface resin lining step of forming a resin lining on the inner surface of the thin-walled steel pipe, and a rolling screw forming step of forming a rolling screw on the outer surface of the steel pipe end of the thin-walled steel pipe having a resin lining on the inner surface are provided. In, at least one of the following (A), (B), and (C) may be performed.

(A) Using step rolling, a lubricant having a friction coefficient of 0.08 or less (preferably 0.03 or more) is used.

(B) Using step rolling, the rotation speed of the rolling tool is 70 rpm or less (preferably 40 rpm or more).

(C) Using the rolled rolling.

By doing so, it is possible to obtain an inner resin-lined thin-walled steel pipe having a good threaded portion (the outer surface of the steel pipe has a shape defined by JIS and the amount of irregularities on the inner surface of the steel pipe is small).

As a result, compared with the conventional inner surface resin-lined steel pipe, it is possible to reduce the weight of the steel pipe and to have an equivalent joint seismic strength, and improve workability and workability of the pipe. Further, since the load on the structure can be reduced, it is possible to give a margin to the seismic strength of the entire structure. Further, it is possible to omit the use of the core in the processing of the screw portion, and it is possible to improve the production efficiency by reducing the total cost of the screw processing equipment and the processing time.

In particular, the inner surface resin lining having a wall thickness of less than 87.5% and 78% or more of the thickness of the JIS-compliant steel pipe has a large unevenness on the inner surface of the steel pipe at the threaded portion, and the resin lining on the inner surface of the steel pipe becomes large. Easily peels off or impairs the water blocking function of the O-ring, but as described above, it becomes possible to form a good threaded portion, and the effect of weight reduction is great, so that the above-mentioned effect is remarkable. ..

Claims (4)

With respect to the carbon steel pipe for piping specified in JIS G 3452, the outer diameter is the same, and the thickness is less than 100% and 78% or more,
Has a resin lining on the inner surface of the steel pipe,
The steel pipe end portion is provided with a threaded portion having a screw having a shape based on JIS B 0202 or JIS B 0203 on the outer surface of the steel pipe,
An inner surface resin-lined thin-walled steel pipe, wherein the amount of irregularities on the inner surface of the steel pipe of the threaded portion is 200.0 μm or less at the maximum height Rz. An inner surface resin-lined thin-walled steel pipe according to claim 1, wherein the outer diameter is the same as the carbon steel pipe for piping specified in JIS G 3452 and the thickness is less than 87.5% and 78% or more. .. A method for producing a thin-walled steel pipe with an inner resin lining according to claim 1 or 2,
A thin-walled steel pipe manufacturing process for manufacturing a thin-walled steel pipe,
An inner surface resin lining step of forming a resin lining on the inner surface of the thin steel pipe,
And a screw forming step of forming a screw on an outer surface of a steel pipe end portion of a thin-walled steel pipe having a resin lining on an inner surface thereof. The screw forming step is a rolling screw forming step of forming a screw by rolling.
The method for producing an inner surface resin lined thin-walled steel pipe according to claim 3, wherein at least one of the following (A), (B), and (C) is performed in the thread forming step.
(A) Step rolling is used, and a lubricant having a friction coefficient of 0.08 or less is used.
(B) Using step rolling, the rotation speed of the rolling tool is set to 70 rpm or less.
(C) Using the rolled rolling.