JPS594205B2 - Kinzoku pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal pipe in which the creep strength of the welded portion is enhanced.

Conventionally, when producing pipes that are subjected to internal pressure during use by hot extrusion, it is considered important to make the thickness of the pipe uniform, and this point has been given some consideration.

This idea is based on the idea that if the thickness in the circumferential direction differs depending on the location, then when internal pressure is applied, the hoop stress will vary depending on the location, and the hoop stress at the thinnest part will be maximum, and stress will be concentrated in that part, leading to premature It is based on the fact that destruction occurs.

This idea is correct when the internal pressure is large and the hoop stress is close to the breaking stress of the pipe, or when thinking about gradually increasing the internal pressure to break the metal pipe, but when the internal pressure is small and the resulting hoop stress is This is not sufficient if the pipe deforms in a creep manner within a few minutes of the breaking stress.

In general, metal pipes made by hot extrusion usually have welds in the length direction, and impurities in the molten metal or Alloying elements tend to segregate easily, and oxides on the billet surface tend to collect in the welded areas of pipes made by hot extruding heated billets.

Although this tendency has been considerably alleviated recently due to advances in extrusion technology, it cannot essentially be eliminated.

Therefore, since these welded parts are alloy-strengthened or dispersion-strengthened, if the thickness of the pipe is uniform, the internal pressure will be gradually increased to cause the pipe to break. It will be strong.

However, the stress acting on the metal pipe is a fraction of its breaking stress, and the hot water temperature used is the melting point of the metal (absolute hot water temperature display).
When the temperature is about 100% or higher, the pipe deforms in a creep manner through a mechanism mainly based on atomic diffusion.

In such cases, impurities or oxides in the welded portion are likely to become a starting point for cracks during the creep deformation process.

Therefore, in extreme cases, the welded part may hardly elongate and may even seemingly break brittle.

As a result, the elongation at break of the entire pipe becomes small, and practical requirements are not met.

The reason for this is that although it has a welded part that is likely to become a weak point due to creep deformation, if the circumferential thickness of the pipe is made uniform in the same way as a metal pipe without a welded part, then the circumferential This is based on the idea that the amount of creep deformation is the same in each direction.

Based on this knowledge, the inventors of the present invention conducted various experiments and conducted intensive studies, and as a result, the thickness of the welded part, which is likely to be a weak point in terms of creep deformation, was set to be thicker than other circumferential parts, and the thickness of the welded part in that part The inventors have discovered that the elongation at break of the entire pipe can be significantly improved by reducing the amount of deformation, leading to the present invention.

That is, the present invention provides a metal pipe having a welded portion in the longitudinal direction by hot extrusion, in which the thickness of the welded portion is increased by 10% or less than the original thickness of the pipe to improve the creep strength of the welded portion. This relates to a metal pipe characterized by reinforced.

In other words, the hot extruded pipe of the present invention strengthens the weld without causing any practical problems, and even when used in conditions where atomic diffusion is the main deformation process in creep deformation, metal The welded portion of the pipe does not become a weak point, and therefore the creep rupture elongation of the metal pipe can be significantly improved.

Now, to explain this in detail with a drawing, in the drawing Y-Y
There are two welded parts on the line, and the thickness y of these welded parts is, for example, 10% or less thicker than the thickness X on the X-y line.

The thickness near the Y-r line gradually becomes thinner as it moves away from the Y-r line in the circumferential direction, and approaches the original thickness X of the pipe.

At that time, the extent to which the wall thickness should be made thicker than X from the Y-Y line depends on the relative relationship between X and y. Ideally, the range should be wide, but in reality it is desirable to define it from the viewpoint of bending rigidity, etc. as described below.

In other words, the bending stiffness in the x-x' force direction and the bending stiffness in the Y-7 direction must be made in such a way that the bending stiffness in the Y-7 direction will not cause problems during subsequent handling of the pipe or when some processing is performed on the pipe. The width in the circumferential direction of the thick portion that is thicker than or X is determined as appropriate.

An example of processing the pipe after the above-mentioned hot extrusion is corrugation processing to impart flexibility to the aluminum pipe.

In this case, brass=1.10. If the wall thickness is larger than X in the range of A circumference from the Y-Y' line to the left and right, the pipe can be corrugated without becoming elliptical, and no problems will occur during subsequent handling. This was confirmed as a result of an experiment.

Examples will be given below to further clarify the effects of the present invention.

Example 1 Using 0.4% Sn-0.2% 5b-pb gold alloy, average outer diameter 601nTx x = 3.5 mm-, y =
A 3.7 mrn pipe was conventionally extruded using a Hanson-Robertson continuous lead machine.

For comparison, a pipe with an average outer diameter of 60mm and a thickness of 3.5mm (uniform) was similarly extruded from a lead alloy having the same composition (Comparative Example 1).

Each of the pipes produced in this way was cut to a length of 1.5 m, one end was sealed, and a valve was attached to the other end to apply internal pressure, and 10 such test pieces were made for each sample. .

2. While heating these test pieces to 50°C. oKg/2
Table 1 shows the results of examining the elongation and crack position at fracture by applying an internal pressure of .

From this result, the pipe of the present invention had no fracture at the welded portion and was able to significantly increase the elongation at fracture.

Example 2 A billet made of two types of aluminum metal (JIS H2102) was used, the average outer diameter was 90 ynm, and X = 2.
A pipe of 2imxy = 2.4 tax was continuously extruded under hot conditions using a Schlemann extruder in a conventional manner.

For comparison, the average outer diameter is 90my using the same material of aluminum.
A pipe with x and q dimensions of 2.2 mm (uniform) was also extruded under the same conditions (proportionality 2).

The pipes thus produced were each cut into lengths of t and mm, one end of which was sealed, and a valve capable of applying internal pressure was attached to the other end.

Ten such test pieces were prepared for each sample.

These test pieces were heated to 200°C and 10kg/
Table 2 shows the results of examining the elongation and crack position at fracture under the internal pressure of the CD.

As a result, in the pipe of the present invention, there was no fracture at the welded portion, and the elongation at fracture was significantly improved.

Note that the pipe of Example 2 was subjected to the corrugation process that is applied to ordinary aluminum pipes, but the process was completed in exactly the same manner as in Comparative Example 2.

As described above, in the metal pipe of the present invention, the welded portion does not become a weak point in terms of creep strength, and as a result, the creep rupture elongation of the metal pipe can be significantly improved.

Therefore, if the present invention is applied to the metal coating of OF ketal subjected to internal hydraulic pressure, at least one of the causes of destruction of the coating can be eliminated, and the economical benefits thereof are very large.

[Brief explanation of drawings]

The drawing is a cross-sectional view showing an embodiment of the metal pipe of the present invention. X: Original thickness of the pipe, y: Thickness of the welded part.

Claims (1)

[Claims] 1. In a metal pipe that has a welded part in the longitudinal direction by hot extrusion, the thickness of the welded part is increased by 10% or less than the original thickness of the pipe to increase the creep strength of the Kamimachi welded part. A metal pipe featuring