JP2005152955A - Welding method and welding system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding method and welding system by which film qualities of a weld zone and heat affected zone where the corrosion is most likely to occur can be improved, the deterioration due to the corrosion of supply piping and the metal contamination of supply gas can be reduced, and a Cr<SB>2</SB>O<SB>3</SB>passivation film is excellent in non-catalyst property, so that a highly decomposable gas such as hydride can stably be supplied without being decomposed. <P>SOLUTION: In the method, welding is performed by using gaseous argon as a back shielding gas in a welding process and the 100% Cr<SB>2</SB>O<SB>3</SB>passivation film is formed again by switching the gaseous argon to gaseous argon containing about several 10 ppm oxygen in a heat treatment process, following which the back shielding gas is switched to the gaseous argon and the annealing treatment is performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a welding technique and a welding system for performing chromium oxide passivation treatment during welding.

  Conventionally, a pair of pipes with a chromium passivation film formed on the inner surface are butted together, and welding is performed while flowing argon gas as a back shield gas inside the pipe, and then the back shield gas flowing into the pipe is changed to argon gas. A welding method and a welding system are known in which heat treatment is performed to such an extent that the welded portion is not melted by switching to an oxidizing argon gas to which an oxidizing gas is added (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 11-104881

By the way, in the welding method and the welding system configured as described above, since a uniform film quality is formed in the entire inside of the pipe, it is said that the film quality formation of the most easily corroded weld and heat affected zone is insufficient. There was a problem.
In order to solve the above-described problem, the present invention is capable of supplying a corrosive gas and a decomposable gas stably and safely by performing a high-quality Cr ₂ O ₃ passivation process on the weld bead simultaneously with welding. It is an object to provide a welding method and a welding system that can be used.
An object of this invention is to provide the welding method and welding system which can improve film quality.
An object of the present invention is to provide a welding method and a welding system capable of forming a 100% chromium oxide film without strictly controlling the processing conditions in the heat treatment step.

  In order to achieve the object, the welding method according to claim 1 performs at least a welding process, a cooling process, a heat treatment process, and an annealing process process in this order during one welding process when butt welding pipes. By controlling the back shield gas supplied during the process, a metal oxide film having a controlled film thickness is formed simultaneously with welding, and after switching the back shield gas to an inert gas during the continuous welding process, The gist is to perform the annealing process.

The gist of the welding method according to claim 2 is that the metal oxide film formed by butt welding of the pipe is 100% Cr ₂ O ₃ .

  The welding method according to claim 3, wherein an oxidizing gas or an oxygen gas mixed with a back shield gas used for butt welding of the pipe can be mixed at an arbitrary concentration and flow rate, and is inactive during a series of welding processes. The gist is to switch from a gas to a mixed gas and from a mixed gas to an inert gas at an arbitrary time.

5. The welding method according to claim 4, wherein the film thickness of the 100% Cr ₂ O ₃ passivation film formed by butt welding of the pipe controls the concentration of oxygen gas, the heat input temperature, and the heat input time. Therefore, the gist is to arbitrarily form the film with a film thickness of 1 to 100 nm.

  The gist of the welding method according to claim 5 is that the back shield gas in the annealing process during the welding is an inert gas, preferably an inert gas whose moisture concentration in the argon gas is controlled to 1 ppm or less. To do.

  The gist of the welding method according to claim 6 is that the pipe is a ferritic stainless steel pipe having a chromium content of 25% or more.

  The welding system according to claim 7, wherein the back shield gas supply system that is supplied when welding the pipes in a butt condition is an inert gas supply system that supplies an inert gas to the welding process, the cooling process, and the annealing process. The gist of the invention is that it comprises an oxidizing gas supply system for supplying an oxidizing atmosphere gas in the heat treatment step and an arc gas supply system for welding the pipe.

The welding system according to claim 8, wherein the butt welding of the pipe is performed in the order of a welding process, a cooling process, a heat treatment process, and an annealing process, and at the time of the welding process, the cooling process, and the annealing process, The gist is that an inert gas is used for the back shield gas by an inert gas supply system, and a mixed gas is used for the back shield gas supply system from the oxidizing gas supply system in the heat treatment step.

  The welding system according to claim 9 is provided with an adjustment mechanism that causes the pressure fluctuation of the pipe internal pressure when the back shield gas is switched to be less than 10% of a set pressure, and arbitrarily adjusts the concentration of the mixed gas. And

  The gist of the welding system according to claim 10 is that the rotational speed of the pipe in the heat treatment step is 10 rpm or more, preferably 15 rpm or more.

In the welding method and the welding system of the present invention, the structure as described above can improve the film quality of the welded part and the heat-affected zone that are most likely to be corroded. In addition, the Cr ₂ O ₃ passivated film is excellent in non-catalytic properties, so that it is possible to stably supply a gas such as a highly decomposable hydride without decomposing. it can.

  Next, embodiments of the welding method and the welding system of the present invention will be described with reference to the drawings.

  FIG. 1 is a system block diagram of the welding system of the present invention, and FIG. 2 is a block diagram of work processes of the welding system of the present invention.

  In FIG. 1, 1 and 2 are stainless steel pipes (hereinafter referred to as “piping”) that are welded in a butt-matched manner, 10 is a back shield gas supply system that is supplied when welding the pipes 1 and 2, and 20 is An argon gas supply system for supplying argon gas to the back shield gas supply system 10, and 30 is an arc gas supply system for welding.

  The back shield gas supply system 10 includes a gas supply valve 11, a fluid controller 12, a fluid controller 13, a valve 14, and a valve 15 in this order. Further, an exhaust system including a valve 16 and a flow rate adjusting valve 17 is branched from between the fluid controller 12 and the fluid controller 13. Further, a switching exhaust system having a switching valve 18 is branched from between the valve 14 and the valve 15.

  The argon gas supply system 20 is branched from a gas supply valve 21 and a downstream side of the gas supply valve 21, and is connected between the fluid controller 12 and the valve 16 and includes a fluid controller 22 and a valve 23. A first dilution system, a second dilution system connected between the valve 14 and the valve 15 and having a fluid controller 24 and a valve 25, and a fluid controller connected between the valve 15 and the pipe 1 26 and a welding gas supply system provided with a valve 27.

  The arc gas supply system 30 includes a gas supply valve 31, a flow rate control valve 32, a valve 33, and a welding head 34 in this order. A flow system having a valve 35 and a flow meter 36 is branched from between the flow control valve 32 and the valve 33.

  Next, a welding process using the welding system of the present invention will be described.

(Matching process)
In the butting process, the upstream pipe 1 is fixed to a pipe fixing cassette (both not shown) using a positioning jig, and then the positioning jig is removed to connect the upstream end face of the downstream pipe 2 to the upstream side. The downstream pipe is fixed to the pipe fixing cassette while abutting the downstream end face of the pipe 1.

(Welding process)
From this state, the welding head 34 is mounted on the pipe fixing cassette, the welding machine is started, and welding is performed.

  At this time, the arc gas is controlled by the flow rate adjusting valve 32 and the flow meter 36 with the valve 35 opened and the valve 33 closed, and then the valve 35 is closed and the valve 33 is switched to the open state. And arc gas.

Further, the normal welding gas is supplied by closing the switching valve 15 and opening the switching valve 27.
The concentration of the oxidizing gas is accurately controlled by the flow controllers 22 and 24 and is exhausted by closing the switching valve 15 and opening the switching valve 18 during the welding process.

(Cooling process)
The cooling step is a step of lowering the temperature of the bead portion by lowering the current value and the rotational speed. The back shield gas remains Ar, and the current value is reduced to less than half that during welding. Also, the rotational speed is reduced to 60-80% during welding. At this time, it is preferable to gradually decrease the rotational speed.

(Heat treatment process)
After the cooling process is completed, the gas supply valve 11 is opened, 100% oxygen is supplied to the fluid controller 12, controlled by the fluid controller 12 (1 cc / min), and then controlled by the fluid controller 22. The first stage dilution is performed with the argon (99 cc / min). At this time, the oxygen concentration is 1%.

  Thereafter, the oxygen diluted in the first stage is controlled by the fluid controller 13 (8 cc / min), and the second stage dilution is performed by the fluid controller 24 with the controlled argon (3992 cc / min).

  Thereby, the back shield gas (4000 cc / min) in which the oxygen concentration is arbitrarily controlled (10 ppm to 90 ppm or more) is obtained.

  At this time, when oxygen gas (8 cc / min) diluted in one stage flows through the fluid controller 13, the valve 16 and the flow rate adjusting valve 17 are used to suppress the increase in pressure on the primary side of the fluid controller 13. One-stage diluted oxygen gas other than the gas amount controlled by the controller 13 is exhausted.

The concentration of the oxidizing gas is accurately controlled by the flow rate controllers 22 and 24. By closing the switching valve 18, opening the switching valve 15, and closing the switching valve 27, the back shield gas is welded. Switch from argon gas to backshield gas containing oxidizing gas during chromium oxide passivation.
Further, the rotation speed of the pipes 1 and 2 in the heat treatment process is set to 10 rpm or more, preferably 15 rpm or more, and the temperature difference in the circumferential direction of the weld bead part and the heat affected part when the heat treatment is performed is optimized. It can process at the heat processing temperature.
In addition, as the method for introducing the oxidizing gas, the method of diluting the gas concentration in two stages has been shown.

(Annealing process)
When the heat treatment step is completed, the back shield gas is switched to Ar, and the welded portion is annealed. The annealing process is a process for improving the film quality, and is sometimes referred to as a film quality improvement process.

  At this time, the back shield gas is switched from the oxidizing gas in the heat treatment step to an inert gas (argon gas) similar to that during normal welding.

As a result of performing butt welding of a ferritic stainless steel pipe containing 25% or more of chromium using an automatic welding machine for a stainless steel pipe generally used and the gas supply system of the present application, and measuring a weld bead portion with ESCA, It was confirmed that a 100% Cr ₂ O ₃ passivation treatment film was formed with a film thickness of 10 nm or more.

  Butt welds of ferritic stainless steel pipes containing 25% or more of chromium using a commonly used automatic welding machine for stainless steel pipes and the gas supply system of the present application, and the weld bead portion is measured by ESCA. The composition ratio was measured. In the conventional welding technique, about 3% of Fe was detected in the vicinity of the surface, particularly the outermost surface, but it was confirmed that it was reduced to less than 1% when the welding method of the present application was used.

  A ferritic stainless steel pipe was butt welded using a commonly used automatic welder for stainless steel pipe and the gas supply system of the present application, and the welded pipe was subjected to a corrosion test with HCl. As a result of ESCA measurement on weld bead and heat-affected zone, it was confirmed that Cl element was only physically adsorbed on the outermost surface and was not detected in the depth direction and was not corroded. It was done.

  By the way, the internal pressure fluctuation at the time of gas switching in the gas supply system of the present application is less than 10% of the set pressure. It was confirmed that no occurred. Moreover, as a result of conducting a tensile test of the welded part, it was also confirmed that it has a strength that sufficiently satisfies the JIS standard.

Thus, welding is performed using argon gas as the back shield gas in the welding process, and 100% Cr ₂ O ₃ passive state is obtained by switching from argon gas to argon gas containing several tens of ppm of oxygen in the heat treatment process. After re-forming the chemical treatment film, the back shield gas was switched to argon gas and annealed, so that even under welding conditions in which about 3% of iron oxide was contained in the vicinity of the surface, 100% Cr ₂ O ₃ It becomes possible to improve the film quality of the passivation film.

1 is a system block diagram of a welding system, showing a welding method and a welding system according to an embodiment of the present invention.

Similarly, it is a block diagram of a work process.

Explanation of symbols

1 ... Piping (upstream side)
2 ... Piping (downstream)
10 ... Back shield gas supply system 20 ... Argon gas supply system 30 ... Arc gas supply system

Claims (10)

  At least one welding process, cooling process, heat treatment process, and annealing process process are performed in this order during one welding process when butt-welding pipes, and the back shield gas supplied during each process is controlled simultaneously with welding. A welding method comprising: forming a metal oxide film with a controlled film thickness; and performing the annealing treatment step after switching the back shield gas to an inert gas during the continuous welding step. The welding method according to claim 1, wherein the metal oxide film formed by butt welding of the pipe is 100% Cr ₂ O ₃ .   The oxidizing gas or oxygen gas mixed with the back shield gas used for the butt welding of the pipe can be mixed at an arbitrary concentration and flow rate. The welding method according to claim 1 or 2, wherein the gas is switched to gas at an arbitrary time. The film thickness of the 100% Cr ₂ O ₃ passivation film formed by butt welding of the pipe can be arbitrarily set to a film thickness of 1 to 100 nm by controlling the oxygen gas concentration, heat input temperature, and heat input time. The welding method according to any one of claims 1 to 3, wherein the welding method is formed.   5. The back shield gas in the annealing treatment step during welding is an inert gas, preferably an inert gas whose moisture concentration in argon gas is controlled to 1 ppm or less. The welding method as described in any one.   The welding method according to any one of claims 1 to 5, wherein the pipe is a ferritic stainless steel pipe having a chromium content of 25% or more. The back shield gas supply system that is supplied when welding the pipes in the butt state includes an inert gas supply system that supplies an inert gas to the welding process, the cooling process, and the annealing process, and an oxidizing atmosphere gas in the heat treatment process. A welding system comprising: an oxidizing gas supply system to be supplied; and an arc gas supply system for welding the pipe.   Butt welding of the pipe is performed in the order of a welding process, a cooling process, a heat treatment process, and an annealing process, and the back shield gas is supplied by the inert gas supply system during the welding process, the cooling process, and the annealing process. The welding system according to claim 7, wherein an inert gas is used, and a mixed gas is used in the back shield gas supply system from the oxidizing gas supply system in the heat treatment step.   9. The concentration of the mixed gas is optionally adjusted by providing an adjustment mechanism that causes the pressure fluctuation of the pipe internal pressure when the back shield gas is switched to be less than 10% of a set pressure. The described welding system. The welding method according to any one of claims 7 to 9, wherein a rotation speed of the pipe in the heat treatment step is set to 10 rpm or more, preferably 15 rpm or more.

Images