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¶ Home - Press - Development of Rolling Technique for Stainless Steel Seamless Pipe with Plug Mill Process

In recent years, demand for stainless steel seamless pipes has risen in response to the increasing number of oil and gas wells in highly corrosive environments. In particular, there are reports1 that if the running cost is considered, 13 percent chromium martensitic stainless steel for oil and gas wells is more economical than the combination of carbon steel OCTG and inhibitors, which are used in corrosive environments. Consequently, demand for stainless seamless pipe has shown a remarkable increase. However, the hot workability of stainless steel is lower than that of carbon steel, and as a result, these materials show high rates of internal and external surface imperfections and short life of rolling tools, which includes plug and guide shoe, when the conventional Mannesmann plug mill process is used.

To solve these problems, someone has developed new rolling techniques of stainless steel seamless pipes using the Mannesmann plug mill process. These new manufacturing techniques consist of developing a drive roller shoe system for piercer and automatic plug exchanger for the piercer and elongator. As a result, remarkable improvements in product quality, productivity and rolling tool cost have been achieved. This article will describe manufacturing techniques of stainless steel seamless pipes using the Mannesmann plug mill process.

MANUFACTURING PROCESS OF MEDIUM DIAMETER SEAMLESS PIPE The manufacturing process of medium diameter stainless steel seamless pipe is shown in Figure 1 and is summarized as follows. Long billet is cut into the required length at the billet cutting line, which is not shown in the figure. After the heating process, each cut-out billet is pierced by a Mannesmann piercer and becomes a hollow bloom, which is expanded in diameter by an elongator. The hollow is rolled to the required thickness by a plug mill, and the internal surface is reeled. Finally, the outside diameter of the pipe is fixed by a sizing mill.

PROBLEMS OF STAINLESS
STEEL ROLLING
During hot seamless rolling by the Mannesmann plug mill process, the cross-helical rolling mill is used for piercing and elongating. The fixed guide shoes have conventionally been applied to the cross-helical rolling mill to control the outside diameter of the hollow bloom and prevent vibration of the hollow bloom. The sliding friction between the fixed shoe and the hot hollow bloom causes scoring and local galling of the shoe, which can cause various problems, such as:
1.External surface imperfections of the pipe
2.Low productivity due to frequent tool repair and change