JPS5944957B2 - Dehydrogenation equipment for welding difficult-to-weld materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding dehydrogenation device for welding pipes such as cast steel pipes made of hydrogen-containing difficult-to-weld materials.

Furnace reaction tubes for the petrochemical industry and cast steel tubes for steel heat treatment-related equipment are made of cast steel tubes made of heat-resistant cast steel or other cast steel materials that are butted against each other and connected by welded joints.

However, cast steel pipes manufactured from heat-resistant and corrosion-resistant steel specified as ASTM [CK-20] contain 25% Cr, 20% Ni, O,
The main component is 2% C, but when a small amount of Nb is added to this, the solubility of hydrogen is particularly high, and some of the hydrogen dissolved in the metal material is dissolved when the molten metal condenses during casting. However, most of it remains in defects in the metal structure, causing gasification at grain boundaries during welding and causing intergranular cracking.

The conventional dehydrogenation treatment for metal materials involves melting and casting the material under normal conditions, cooling it to room temperature, and then holding the cast steel pipe at a temperature of 500 to 900°C during heat treatment to dehydrate it. It was something that practiced the basics.

However, in order to house the entire cast steel pipe in the furnace, the heat treatment furnace requires a corresponding degassing furnace, and the heating method and how to maintain the degree of vacuum in the furnace are difficult, and the pipe bends D after treatment. This caused many problems, which not only required a great deal of effort to straighten the curves, but also caused damage to the cast steel pipe when straightening the curves. In order to solve this problem, the inventors
I have fabricated the device shown in the figure and attempted dehydrogenation treatment. In this device, the grooves of tubes 1 and 2 made of difficult-to-weld materials are butted against each other, and the ends of the tubes are covered with airtight lids 6 and 7. A ventilation pipe 8 is passed through one lid 6 and an inert gas container 11 and a vacuum device 10 are connected through a valve 9, and the outer periphery of the groove is surrounded by a heating device 13. After communicating the inert gas container 11 into the pipes 1 and 2 and filling the pipes 1 and 2 with inert gas to form the first welding layer 12 on the bottom of the groove and sealing the gap between the grooves airtightly, Next, by operating the valve 9, a vacuum device 10 is communicated with the pipes 1 and 2 to reduce the pressure, and at the same time, the groove is heated by the heating device 13 to locally dehydrogenate the groove.
The welding of the second and subsequent layers was performed. This device was extremely effective in that it could locally dehydrogenate the vicinity of the groove without using a degassing furnace. During processing, the material was heated to high temperatures in the atmosphere, causing severe oxidation, which had a serious effect on welding of the second and subsequent layers.

Therefore, before starting the second layer, the outer surface of the first weld layer must be ground to remove the oxide layer, which has the disadvantage of requiring a long time for this grinding. The present invention can easily perform dehydrogenation treatment on pipes made of difficult-to-weld materials by limiting it to a local area of the weld joint, and does not oxidize the outer surface of the first weld layer during the dehydrogenation treatment process. Therefore, it is an object of the present invention to provide an apparatus that can immediately carry out the second and subsequent layers.

As shown in FIG. 1, the present invention is "CK-20" (containing Nb).
This is a device for forming a joint in which two cast steel pipes 1.2 made of a non-fermentable welding material such as 1. 4 is locally dehydrogenated, the outer part 5, 5 remote from the joint being a conventional cast steel tube with a high hydrogen solubility I on the cast side. Fig. 2 shows a dehydrogenation device for a receptacle joint according to the present invention, in which airtight covers 6 and 7 are applied to the base ends of two cast steel pipes 1 and 2, respectively. It passes through a vent pipe 8, and the outer end of the vent pipe 8 is connected via a three-way switching valve 9 to a vacuum device 10 and an inert gas container 11 such as argon gas.

On the outer periphery of the bevel, a sealed case 15 equipped with an injection port 16 is removably arranged around the tubes 1 and 2, and a heating wire, high-frequency heating, gas burner heating is installed inside or outside the sealed case 15. A known heating device 13, such as the one shown in FIG.

The hermetic case 15 can be of any shape that can be attached to and removed from the groove, for example, a cylindrical case that is inserted into the tubes 1 and 2 from the tip, or a half-split cylinder that is divided into semicircular shapes. The tubes 1 and 2 can be attached by approaching them from the front and back and sandwiching them on the grooved part.

When welding, first, the two cast pipes 1 and 2 made of a metal welding material are gripped by chucks 17 and butted against each other, and the inert gas container 11 is inserted into the pipes 1 and 2 by operating the valve 9. The pipe hole is filled with an inert gas such as argon gas by connecting the chucks 17, 17 to a rotating device (not shown).
While simultaneously rotating the grooves 3 and 3, apply TIG welding using argon gas from the outside of the grooves 3 and 3.
Bevel 3, while keeping the inside and outside of 3 in an argon gas atmosphere.
A first contact layer 12 is formed which airtightly closes the space between the two.

Next, the valve 9 is switched to allow the vacuum device 10 to communicate with the pipes 1 and 2 through the ventilation pipe 8, and the pipe holes blocked by the airtight lids 6 and 7 are evacuated and the pressure is reduced.

Since the grooves 3.3 are airtightly connected by the first capping layer 12, it is possible to easily create a high vacuum of about 10 -3 t0rr in the tube hole. While reducing the pressure inside the pipe, a sealing case 15 is attached to the groove, and the upper part of the first contact layer 12 is closed.
The injection port 16 is filled with an inert gas such as argon gas to prevent oxidation of the surface of the first welding layer 12, and at the same time, the heating device 13 heats the groove 4 near the groove by 500°C. ~
Heat to a high temperature of 900℃.

The sealed case 15 does not necessarily have to be in close contact with the surfaces of the tubes 1 and 2; even if there is some gap, the pressure of the inert gas flowing in from the inlet 16 can be raised slightly above atmospheric pressure. By doing so, the sealed case 15 can be filled with an inert gas and the first containment layer 12 can be prevented from being oxidized. Local dehydrogenation treatment in the vicinity of the groove is carried out by maintaining the vacuum inside the tube and the heating in the vicinity of the groove for a predetermined period of time. After the dehydrogenation process is completed, the sealed case 15 and the heating device 13 are moved to the side or removed, and the chuck 1 is removed.
7, the tubes 1 and 2 are simultaneously rotated again, and the second and subsequent weld layers 14 are formed to fill the gap between the grooves by a welding method such as automatic TIG welding, manual TIG welding, or covered arc welding. Then, the rear joint is completed.

An example of butting and connecting steel pipes according to the present invention is shown below.

Base material: Dimensions of two Nb-containing "CK-20" tubes: Outer diameter: 1501 mm, wall thickness: 15 mm, length: 3 m The grooves of the base metals were butted together, and the base metals were heated in argon gas. Manual TIG using a manual TIG connecting rod with a diameter of 24 mm and approximately the same components.
A first welding layer was formed by welding.

Next, the pressure inside the tube is reduced to a high vacuum of about 10-3 t0rr in 5 minutes, and at the same time, argon gas is injected into the sealed case.
By heating the outer surface of the tube to 700-800°C and holding it for 30 minutes, the hydrogen content near the joint was reduced to 11.4p.
pm to 2.2 ppm. Using a manual TIG connection rod with a diameter of 3.211 and having approximately the same composition as the base material,
Perform IG contact to form a second contact layer after the second layer,
Completed the receptacle joint. As a result of radiographic inspection and cross-sectional die check of the joint, it was found to be defect-free and JISI class? A joint was obtained, no bending 9 of the cast steel pipe occurred, and no straightening was necessary. It goes without saying that the present invention can also be applied to cast steel pipes or forged pipes manufactured by centrifugal casting or pouring. In the present invention, as described above, since both ends of the tube hole of the rear joint are covered with airtight covers 6 and 7, the first ? When forming the contact layer 12, an inert gas is filled into the tube hole, and the first layer 12 is filled with an inert gas. After the contact layer is formed, the inside of the pipe hole can be made into a high vacuum, and the heating device 13 only heats the local area near the groove, and there is no need to use a degassing furnace, so the operation is simple. Dehydrogenation and dehydrogenation can be completed in a short time.

In addition, compared to the conventional case where the entire cast steel pipe is housed in a degassing furnace and heated, the work is simpler, and the cast steel pipe does not bend. Advantageously, the problem of material damage is eliminated. In particular, the present invention has the first feature on the bottom of the groove.
After the contact layer 12 is formed and the gap between the grooves is sealed airtight, the groove is covered with a sealing case 15 and sealed with an inert gas.
Even when heated to a high temperature by the heating device 13 and subjected to dehydrogenation treatment, the surface of the first welding layer 12 does not oxidize, and extensive welding of the second layer and subsequent layers can be started immediately, eliminating the trouble of conventional oxide layer removal. Isn't it okay to omit it, but is it of high strength? Demonstrates the excellent effects that joints can provide.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a rear joint dehydrogenated by the apparatus of the present invention, FIG. 2 is a partially sectional front view of each joint dehydrogenation apparatus according to the present invention, and FIG. 3 FIG. 2 is a partially sectional front view of another dehydrogenation device. 1, 2...Cast steel pipe, 3...Bevel, 4.
...Near the joint part, 5...Outside part, 6, 7
...Tight lid, 8...Vent pipe, 9...
...Valve, 10... Vacuum device, 11...
Inert gas container, 12...First contact layer, 13.
... Heating device, 15 ... Sealed case, 1
6... Inlet.

Claims (1)

[Claims] 1 For two pipes with joint grooves butted against each other, seal covers are placed on both sides of the grooves to airtightly close the tube holes, and a vacuum device and an inert gas container are inserted into the ventilation holes that pass through the seal covers. 1. A dehydrogenation device for welding difficult-to-weld materials, characterized in that a sealed case surrounding the outer periphery of a groove portion and equipped with an inert gas inlet and a heating device are removably installed.