Gasket and pipe joint

Details Gasket and pipe joint Gasket and pipe joint

1999-02-22

2001-08-14

Browne, Lynne H. (Department: 3629)

Pipe joints or couplings

Particular interface

C285S917000, C277S541000

Reexamination Certificate

active

06273477

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a gasket and a pipe joint comprising the gasket.
Pipe joints are widely used, for example, in fluid control devices for use in fabricating semiconductors. Such pipe joints comprise a pair of tubular joint members, an annular gasket interposed between opposed end faces of the two joint members, and threaded means for joining the two joint members. With pipe joints of the type described, it is common practice to prepare the tubular joint members and the gasket from the same stainless steel (e.g., SUS316L). When checked for Vickers hardness, the joint members had a hardness of about 310 to about 390 Hv at the surface and about 260 to about 320 Hv at a portion thereof 100 micrometers away from the surface, and the gasket had a hardness of about 300 to about 330 Hv at the surface and about 260 to about 290 Hv in its interior.
Since pipe joints are repeatedly disassembled and reassembled for the maintenance and inspection of the fluid control device, the conventional pipe joint wherein the tubular joint members and gasket are made of the same stainless steel has the problem that the joint members which are difficult to replace unlike the gasket develop flaws, failing to assure the joint of fluid tightness. Although it is possible to change the material for the gasket from stainless steel to nickel or copper which is softer, another problem is then encountered in that the material reacts with the gas for use in fabricating semiconductors. For example, Ni reacts with CO at room temperature, producing Ni carbonyl [Ni(CO)
4
] gas, resulting in impaired fluid tightness due to the corrosion of Ni or reducing the purity of the gas to be used for manufacturing semiconductors.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gasket which Is unlikely to react with a gas such as CO, also obviating the likelihood that the tubular joint member, which is difficult to replace unlike the gasket, will be flawed, and a pipe joint comprising the gasket.
The present invention provides a gasket prepared from a stainless steel comprising, in ratio by weight, 12.90 to 15.00% of Ni, 16.50 to 18.00% of Cr, 2.00 to 3.00% of Mo, up to 0.02% of C, up to 0.30% of Si, up to 0.40% of Mn, up to 0.03% of P, up to 0.003% of S, up to 0.25% of Cu and up to 0.01% of Al, the gasket having a surface with a Vickers hardness of 90 to 160.
The preset invention provides a pipe joint comprising a pair of tubular joint members, an annular gasket interposed between opposed end faces of the two joint members, and threaded means for joining the two joint members, the pipe joint being characterized in that each of the joint members is prepared from a stainless steel having a surface with a Vickers hardness of at least 300, the gasket being prepared from a stainless steel comprising, in ratio by weight, 12.90 to 15.00% of Ni, 16.50 to 18.00% of Cr, 2.00 to 3.00% of Mo, up to 0.02% of C, up to 0.30% of Si, up to 0.40% of Mn, up to 0.03% of P, up to 0.003% of S, up to 0.25% of Cu and up to 0.01% of Al, the gasket having a surface with a Vickers hardness of 90 to 160.
When the Vickers hardness of the surface of the gasket is smaller than 90, the gasket fails to have a sufficient strength, whereas if the hardness exceeds 160, there is an increased likelihood that the gasket will mar or flaw the joint member made from a stainless steel having a surface with a Vickers hardness of at least 300 (usually up to 400). The gasket surface is more preferably 100 to 140 Hv in Vickers hardness.
According to the present invention, each tubular joint member, which is difficult to replace unlike the gasket, is precluded from being marred or flawed, and the gasket and the tubular joint member will not react with CO or like gas since both are made from stainless steel, consequently eliminating another problem of entailing impaired fluid tightness or lowering the purity of the gas for use in fabricating semiconductors.


REFERENCES:
patent: 4660868 (1987-04-01), Totani
patent: 5118141 (1992-06-01), Miyashita
patent: 5458156 (1995-10-01), Okubo et al.
patent: 5575245 (1996-11-01), Watanabe
patent: 5678803 (1997-10-01), Shinohara
patent: 0 758 067 (1997-02-01), None
Patent Abstract of Japan, Publication No. 07278758, Oct. 24, 1995.
Patent Abstract of Japan, Publication No. 09279315, Oct. 28, 1997.

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