JPH0381069A - Tube end seal welding method for corrosion resistant duplex tube - Google Patents

Abstract

PURPOSE:To prevent the occurrence of weld defects and weld metal cracking by forming a gap on an inner and outer tube boundary of tube ends and then, subjecting the interval between the tube end face of an outer tube and the outer peripheral surface of an inner tube to fillet welding with material of the same system as the inner tube. CONSTITUTION:The outer pipe 2 is fitter to the inner tube 3 on the duplex tube 1 and the inner tube 3 is exposed on the tube end. The outer peripheral surface 5 of the inner tube 3 is tack-welded with material of the same system as the inner tube 3 and the diameter of the exposed part of the inner pipe 3 is reduced by solidification and shrinkage of position beads 6 to form the gap 7 on the inner and outer tube boundary. The interval between the tube end face of the outer tube 2 and the outer peripheral surface 5 of the inner tube 3 is subjected to fillet welding with material of the same system as the inner tube 3 to form a fillet welded zone 8. By this method, the occurrence of the weld defects and weld metal cracking are prevented. Afterward, cladding by multilayer welding is performed to form a multilayer welded zone 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to corrosion-resistant double-pipe pipes used for line pipes for transporting oil or natural gas containing corrosive substances, or for piping in the chemical industry. The present invention relates to an end seal welding method.

[Conventional technology]

Corrosion-resistant double pipes, which reduce the amount of expensive corrosion-resistant alloys used and have increased strength, are used for line pipes, tubing, and piping in the chemical industry, and the fields of use are expanding more and more recently. Such corrosion-resistant double pipes include a thin-walled inner pipe made of a corrosion-resistant material and a thick-walled outer pipe made of carbon steel, which are fitted together using a heat expansion method, etc. It is effective as a composite material that has the characteristics of a high-strength material for the outer tube.

If the carbon steel of the outer tube is exposed at the end of a corrosion-resistant double pipe where the inner tube and outer tube are fitted, it may cause damage during line pipe installation, etc.
When circumferentially welding double pipes together, depending on the groove shape, the corrosion-resistant components of the weld may be diluted by the carbon steel, and the corrosion resistance of the inner surface of the double pipe may deteriorate at the weld. etc., when connecting a threaded pipe end and a coupling by screwing together, the carbon steel of the outer pipe will be exposed in the gap between the pipe end and the coupling, and the corrosion resistance will deteriorate. Seal welding is performed by overlaying a corrosion-resistant material on the pipe ends.If such seal welding is applied, circumferential joint welding between double pipes can be easily performed at the installation site.

Conventional tube end seal welding of double tubes involves exposing the inner tube at the tube end, and welding a corrosion-resistant material of the same type as the inner tube between the exposed outer peripheral surface of the inner tube and the tube end surface of the outer tube. This was done by performing fillet welding as a material and then performing multilayer overlay welding with filler metal.

[Problems to be Solved by the Invention] When the pipe ends of a double pipe in which an inner pipe and an outer pipe are fitted are seal-welded using the above-mentioned conventional technique, the following problems occur. Although the inner and outer tubes of a double tube are in contact, there is a small gap at the boundary depending on the surface roughness of both tubes, and the corrosion-resistant material for the inner tube is more common than the carbon steel for the outer tube. Since the coefficient of thermal expansion is large, the gap between the inner and outer tubes is narrowed due to thermal expansion during seal welding, and the air existing at the boundary is thermally expanded and pressurized, and is discharged into the molten metal during fillet welding. However, circular defects such as blowholes occur. Furthermore, depending on the dilution ratio of carbon steel and high alloy, for example, weld metal cracking may occur at the boundary due to solidification shrinkage stress and welding thermal stress of the deposited metal and base metal.

The present invention prevents welding defects from occurring when seal-welding the pipe ends of a corrosion-resistant double pipe in which a thin-walled inner pipe made of a corrosion-resistant material and a thick-walled outer pipe made of carbon steel are fitted together. The purpose is also to prevent weld metal cracking.

[Means and actions for solving problems]

The present invention exposes the inner tube at the tube end of a corrosion-resistant double tube in which a thin-walled inner tube made of a corrosion-resistant material and a thick-walled outer tube made of carbon steel are fitted together, and After welding the outer circumferential surface with the same material as the inner tube and forming a gap at the boundary between the inner and outer tubes at the end of the tube, weld the inner tube between the end surface of the outer tube and the outer circumferential surface of the inner tube. The gist of the present invention is a method for welding a pipe end seal for a corrosion-resistant double pipe, which is characterized by fillet welding using the same material as the pipe.

The double pipe to which the present invention is applied is a double pipe in which an outer pipe and an inner pipe are fitted together by a heat expansion method or the like. Fitting by the thermal expansion method is performed, for example, by inserting an inner tube into an outer tube that has been heated and expanded, and cooling the outer tube while applying water pressure to the inner tube. Corrosion-resistant materials for the inner tube include stainless steel,
High-alloy steel, super alloy, titanium, titanium alloy, copper-based alloy, etc. are the carbon steels for the outer tube, such as high-strength API 5
^XP-110 etc. are adopted, and the atmosphere and conditions inside and outside the tube,
The material is designed to have characteristics such as corrosion resistance and strength depending on the installation of double pipes or piping conditions.

The present invention will be specifically explained below with reference to the drawings.

FIG. 1 shows a partial axial cross section of the pipe end of a corrosion-resistant double pipe. The double pipe 1 has an outer pipe 2 and an inner pipe 3 fitted together, and the inner pipe 3 is first exposed at the end of the pipe as shown in (a). 4 is the tube end surface of the outer tube 2, and 5 is the outer circumferential surface of the inner tube 3, both of which are beveled by cutting with a cutting tool. Next, as shown in (b), the outer circumferential surface 5 of the inner tube 3 is welded using the same material as the inner tube 3, and the diameter of the exposed part of the inner tube 3 is reduced by the solidification and shrinkage of the attachment bead 6. A gap 7 is formed at the tube boundary. Next, as shown in (C), fillet welding is performed between the tube end surface 4 of the outer tube 2 and the outer circumferential surface 5 of the inner tube 3 using the same material as that of the inner tube 3 to form a fillet welded portion 8. During this formation process, air within the boundary between the inner and outer tubes expanded by welding heat is released from the front surface of the molten metal, which will form the corner weld 8, and is not discharged into the molten metal, thereby preventing welding defects from occurring. be done. Furthermore, the solidification shrinkage stress and welding thermal stress of the weld metal and base metal continue to be released until the gap 7 between the inner and outer tube boundaries is filled, and when cooling is completed, the shrinkage stress becomes small, preventing weld metal cracking. . Thereafter, multilayer welding is performed to form a multilayer welded portion 9.

〔Example〕

(1) Example of the present invention: outer diameter is 8+5/8 inch (219,
1mm), wall thickness is 11.0mm (7) API 5
The outer tube 2 is an L As a filler metal, a finishing bead 6 is formed by TIG welding as shown in FIG. 1(b) to form a gap 7 at the boundary between the inner and outer tubes, and then a fillet weld 8 is formed as shown in FIG. 1(c). And a multilayer welded portion 9 was formed.

(2) Conventional example: Same as the example of the present invention, but the finishing bead 6 was not formed at the end of the corrosion-resistant double pipe 1, and the same self-welded part 8 and multilayer welded part 9 as the example of the present invention were formed. .

Applicable standards for the soundness of the welded parts of the inventive example and the conventional example:
ASME Sec, V, Criteria: ASTM Se
c, ■Evaluated by radiographic examination using UW51.

The results are shown in Table 1. Δ indicates slightly poor, ○ indicates good, and ◎ indicates very good. Note that a circular defect is
Blowholes and similar rounded defects. The examples of the present invention were very good in all evaluation items.

Table 1 [Effects of the Invention] According to the present invention, welding is performed at the pipe end seal weld of a corrosion-resistant double pipe in which a thin-walled inner pipe made of a corrosion-resistant material and a thick-walled outer pipe made of carbon steel are fitted. Defects and weld metal cracks are prevented from occurring, and the integrity of the corrosion-resistant double pipe can be stably ensured. Furthermore, when using corrosion-resistant double pipes, when pipes are circumferentially welded together, welding work is facilitated and the soundness of the welded portion is stably ensured. therefore,
It has greatly contributed to improving the construction of corrosion-resistant double pipes, for which demand is expected to increase in the future, for line pipes and tubing that transport oil and natural gas containing corrosive substances, and for various chemical industries, etc., and has achieved industrial value. is enormous.

[Brief explanation of drawings]

FIGS. 1(a), 1(b), and 1(C) are diagrams for explaining the present invention. 1: double pipe, 2: outer pipe, 3: inner pipe, 4: pipe end surface of outer pipe,
5: outer peripheral surface of inner tube, 6: finishing bead. 7: Gap, 8: Corner weld, 9: Multilayer weld. Figure 1Figure 1

Claims (1)

[Claims] The inner tube is exposed at the tube end of a corrosion-resistant double tube in which a thin-walled inner tube made of a corrosion-resistant material and a thick-walled outer tube made of carbon steel are fitted, and the inner tube is exposed to the outer peripheral surface of the exposed inner tube. After welding is performed using the same type of material as the inner tube to form a gap at the boundary between the inner and outer tubes at the end of the tube, welding is performed between the end surface of the outer tube and the outer peripheral surface of the inner tube using the same type of material as the inner tube. A pipe end seal welding method for a corrosion-resistant double pipe, which is characterized by fillet welding using materials.