JPS61186142A - Production of pipe joint - Google Patents

Abstract

PURPOSE:To increase the performance for ultrasonic reflectoscope and to make the production of compound-shaped pipe easy by welding other pipes after making the crystal grain size smaller by destroying with forging the crystal organization of the joint part of the pipe made by casting. CONSTITUTION:The end part 1a of the pipe 1 which becomes the joint to connect with other pipe 3 by welding is cast smaller than the aimed joint diameter size. A joint 2 is then formed by expanding >=1.5 times the diameter size of the end part 1a of the pipe 1 with its forging. The majority of the cast organization of the joint 2 part is destroyed to perform the removal of the directional quality of the crystal and the unification of the material, also to make the crystal grain size smaller. The ultrasonic reflectoscope inspection around the connection part is then performed by weld-connecting the other pipe 3 with the pipe joint 2. Even such a minute defect that cannot be detected by the ultrasonic reflectoscope inspection of the pipe made by casting be detected.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a method of manufacturing a pipe joint, and in particular, when a pipe joint is constructed by combining casting and forging, it is difficult to connect it to other pipes, etc. The present invention relates to a method of manufacturing a pipe joint suitable for improving the ultrasonic flaw detection performance of a joint portion.

"Prior Art and its Problems" Conventionally, in the piping of nuclear power plants, etc., the quality of joints connected by welding has to be confirmed through product inspection. In this case, a forged pipe joint made of stainless steel or the like has a relatively fine and homogeneous internal structure, and therefore can be inspected with high precision by ultrasonic flaw detection. On the other hand, when constructing by casting, it has the advantage that it is easy to manufacture pipes with complicated shapes, but on the other hand, crystal grain boundaries and resinous structures in the internal structure of the joint part are detected as similar defects in ultrasonic inspection. Since the method produces echoes and attenuates the ultrasonic waves, the accuracy of the test tends to be low, and for this reason, there is a problem that it cannot be applied to parts that require ultrasonic flaw detection.

``Objects of the present invention and means for achieving the same'' The present invention aims to improve the ultrasonic flaw detection performance of joints of pipes constructed by casting, and to expand the scope of application in nuclear power plants, etc. It is characterized by destroying the cast structure by forging and reducing its crystal grain size, and by combining the casting and the button to form a pipe joint, the crystal structure of the joint part is made finer. This reduces the reflection or attenuation of ultrasonic waves at grain boundaries.

“Embodiment” An embodiment of the present invention will be described below with reference to the drawings.

First, the end 1 that will be the joint that will be connected to another pipe by welding.
A pipe 1 as shown in FIG. 1 is produced by casting, in which a is intentionally smaller in diameter than the intended joint diameter. The degree to which this diameter is reduced is set to 2/3 or less of the required diameter of the joint in order to ensure a forging ratio of 1.5 times or more in the forging process to be described later.

Next, the end portion 1a of the pipe 1 is forged to increase its diameter by 1.5 times or more to form a joint 2 having the desired dimensions as shown in FIG. Most of the cast structure of the two parts is destroyed to remove the crystal orientation and make the material uniform, and the grain size is reduced to a grain size number of 1.5 or more as specified in the ASTM-E45 standard. It is.

When another pipe 3 is connected by welding to the thus manufactured pipe joint 2 as shown by the chain line in FIG. Since the crystal grain size in this part is reduced to a grain size number of 1.5 or more, the reflection or attenuation phenomenon of ultrasonic waves at the grain boundaries in this part is reduced, making it less likely that the grain boundaries will be detected as defects. It is what it is. Therefore, it is possible to carry out highly accurate ultrasonic flaw detection and detect minute defects that could not be detected by conventional ultrasonic flaw detection of tubes constructed by casting.

In addition, in the forging process of the above embodiment, the diameter of the joint 2 portion was expanded by 1.5 times or more;
1. It is also possible to make the wall thickness of the part thick in advance and then forge it to 273 or less to form the desired wall thickness.
A training ratio of 5 times or more can be secured, and the grain size can be reduced to grain size number 1.
．． 5 or more, and the forging process in the present invention includes both of these processing methods. Also,
When manufacturing the pipe 1 by casting, as shown in FIG. 4, a cooling mold 5 having a large heat capacity is installed in the sand mold 4 so that these cavities 4a and 5a intersect.
If the resinous crystals 6 that grow from the surface are formed in intersecting directions inside, the direction of the crystals after the forging process can be made more random and the crystal grain size can be further reduced. If it is cast according to the law,
Impurities with relatively low specific gravity can be pushed out to further promote homogenization and refinement of grain size.

"Effects of the Invention" As explained above, according to the method for manufacturing a pipe joint of the present invention, casting and forging are combined to destroy the cast structure of the joint part and reduce its crystal grain size. When performing ultrasonic flaw detection inspection, it is possible to reduce the occurrence of ultrasonic reflection and attenuation phenomena at grain boundaries, improve ultrasonic flaw detection performance, and perform high-precision inspection. This has the effect that it can be expanded to a degree that cannot be applied to tubes constructed by conventional casting, and in that case, it is possible to easily manufacture tubes with complicated shapes by casting.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing a pipe constructed by casting in an embodiment to which the method of the present invention is applied, and FIG. 2 is a longitudinal cross-sectional view showing the state after forging the joint portion of the pipe in FIG.
FIG. 3 is a model diagram showing an example of a mold for manufacturing the pipe shown in FIG. 1 and a state of crystal formation when the mold is used. l...tube, 1a...end, 2...
・Joint, 3...other pipe, 4...sand mold,
5... Chilled metal, 6... Resin-like product.

Claims (1)

[Claims] 1. A method for manufacturing a pipe joint, characterized in that the crystal structure of the joint portion, which is formed by casting and is connected to another pipe or the like by welding, is destroyed by forging to reduce the crystal grain size of the joint portion.