JP2010159870A - Zirconium (zr) bellows - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a zirconium (Zr) thin-walled pipe resisting severe shape processing to provide a novel highly corrosion-resistant zirconium bellows formed by hydraulic/roll forming. <P>SOLUTION: When increase in a content of oxygen and nitrogen in weld metal and thermally affected areas is regulated to be 100 ppm or less in a pipe forming process of the zirconium thin-walled welded pipe to be used for forming the zirconium thin bellows, the zirconium bellows can be formed by hydraulic forming or roll forming. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high-corrosion-resistant zirconium (Zr) metal hydroformed or roll-formed bellows that absorbs the displacement of piping and pressure vessels through which corrosive fluid flows, such as in chemical plants and pharmaceutical manufacturers.

Conventional technologies and issues

  As corrosion resistant metals, stainless steel and titanium have excellent formability, and both metal bellows have been used in piping systems for decades. Furthermore, in order to improve the fatigue characteristics of the titanium bellows, JP-A-5-318110 discloses a method for controlling the thickness of a welded joint and a vacuum heat treatment method using a getter. Japanese Patent Application Laid-Open No. 9-14549 discloses that the ratio of the thickness of the peak portion of the bellows to the thickness of the valley portion is controlled in order to improve the fatigue characteristics of the stainless steel bellows.

  The expansion pipe joints used in reducing liquids and gases, which are disadvantages of corrosion resistance of titanium and stainless steel, used in various fields of the chemical industry are generally composed of fluororesin bellows. . The fluororesin deteriorates and deteriorates over time and has a problem in the bellows life. Further, since the fluororesin bellows has lower resistance to high temperature and high pressure than metal, there is a problem that usage conditions are limited. Accordingly, there is a demand for a metal bellows having higher temperature and higher pressure.

  Zirconium metal has corrosion resistance comparable to that of fluororesin against reducing liquids and gases, which are disadvantages of corrosion resistance of titanium and stainless steel. Since April 1996, our company has been supplying disc-shaped zirconium bellows to customers.

  However, there is no U-shaped zirconium bellows that can save much more material than the disc-shaped bellows and has better displacement absorption performance. The cause is that a pipe that can withstand a severe molding process is required for the hydraulic forming or roll forming of the U-shaped bellows. Usually, a forming pipe is formed by bending and welding a plate. Zirconium (Zr) material has higher affinity between oxygen and nitrogen than titanium. In the case of ordinary TIG welding, plasma welding, and laser welding methods, the ductility decreases due to the solid solution of oxygen and nitrogen into the weld metal and heat affected range of the zirconium material, and severe hydroforming or It cannot withstand roll forming. Therefore, it has been impossible to produce a U-shaped zirconium (Zr) bellows by hydraulic molding or roll molding.

  The present invention provides a thin pipe made of zirconium that can withstand severe forming processing, and provides a hydroformed or roll-formed bellows of zirconium (Zr) material having excellent corrosion resistance, which has been impossible to manufacture until now. With the goal.

  In order to achieve the above object, the present invention is a pipe forming method for suppressing an increase in the content of oxygen plus nitrogen in a weld metal and a heat-affected range part to 100 ppm or less in a longitudinal welding process of a thin pipe for bellows molding, A welded thin pipe made of zirconium (Zr) that can withstand hydraulic forming or roll forming is manufactured.

  In the longitudinal welding process of the thin-walled pipe, the method of suppressing the increase in the content of oxygen and nitrogen in the weld metal and the heat affected zone is a method of rapidly cooling the weld and the heat affected zone.

  As a method for welding the thin-walled pipe, TIG welding, plasma welding, laser welding, electron beam welding, or the like is applied.

  In TIG welding, plasma welding, and laser welding, the purity of the argon gas used as the shielding gas is not 100% even if sufficient sealing is performed with an after shield, a back shield, or the like. Even in electron beam welding performed in a vacuum, it is impossible to avoid the slight mixing of oxygen and nitrogen in the atmosphere. Since zirconium is a metal more active than titanium, it reacts easily with oxygen and nitrogen at 300 ° C. or higher in the atmosphere, and embrittles even if it absorbs a small amount of oxygen and nitrogen. As a result of various investigations on the weld metal generated in the bellows forming process and cracks in the heat-affected range, the present invention has the following types of cracks: cracks generated at the boundary between the heat-affected range and the weld metal, and weld metal parts. There are two types of cracks that have occurred. It was found that three-quarters occurred at the boundary between the heat affected zone and the weld metal, and one-quarter occurred at the weld metal. As the inventor's knowledge, for the zirconium welded pipe, the thickest part of the surface oxide film is the boundary between the heat-affected area and the base material, so the main cause of cracking is not due to cracking of the surface oxide film It was estimated that there was no solid solution of oxygen and nitrogen inside the substrate.

  In view of this, the present invention provides a zirconium thin-walled pipe that can withstand severe molding by shortening the time at high temperatures and suppressing solid solution of oxygen and nitrogen by rapidly cooling the weld zone and the heat affected zone. Tube. It has been possible to provide a hydroformed or roll-formed bellows of a zirconium (Zr) material having excellent corrosion resistance, which has been impossible to produce until now.

  Using Zirconium Zr702 (ASTM R60702), a material having a plate thickness of 0.8 mm, pipes for bellows forming were formed by the TIG welding method as examples of the present invention and comparative examples. A bellows molding test was performed by a hydraulic molding method using four 150A pipes piped as comparative examples and one 150A pipe piped as an example of the present invention.

  Table 1 shows the contents of oxygen and nitrogen in the base metal provided in the mill sheet from the material manufacturer, the results of IGA analysis of oxygen and nitrogen concentrations in the weld zone and the heat-affected area in the conventional TIG welding method of the comparative example, IGA analysis results of oxygen and nitrogen concentrations in the TIG welded part of the invention example and the heat affected range are described.

  In the case of hydroforming in Table 2, when the cracks of Comparative Examples 1 to 4 occur, the elongation ratio of the weld metal part and the heat-affected zone, the weld metal part of the bellows and the heat-affected zone part of the present invention example successfully formed The growth rate of

Disc-shaped bellows shape and U-shaped bellows shape

Claims (2)

  Zirconium (Zr) thin-walled (plate thickness 0.5-3.2 mm) U-shaped bellows manufactured by hydraulic forming or roll forming.   In the process of forming a zirconium thin welded pipe used to form the zirconium thin bellows, an increase in the content of weld metal and oxygen plus nitrogen in the heat-affected range is suppressed to 100 ppm or less. Bellows to do.

Images