PIPE JOINT

Abstract

Provided herein is a pipe joint of a relatively small joint diameter for use under ultrahigh pressure conditions. The pipe joint includes first and second joint members having mutually communicating fluid passages; and a gasket interposed between abutting end surfaces of the first and second joint members. The first and second joint members have ring-shaped seal projections formed at the abutting end surfaces thereof. The pipe joint satisfies a coefficient F of 0.4 or less in the following formula (1).

F=(D.sub.3.sup.2D.sub.1.sup.2)/(D.sub.4.sup.2D.sub.2.sup.2), Formula (1):

where D.sub.1 represents the inner diameter of the first and second joint members, D.sub.2 represents the inner diameter of the gasket, D.sub.3 represents the diameter of the seal projections, and D.sub.4 represents the outer diameter of the gasket.

Claims

1. A pipe joint comprising: first and second joint members having mutually communicating fluid passages; and a gasket interposed between abutting end surfaces of the first and second joint members, the first and second joint members having ring-shaped seal projections formed at the abutting end surfaces thereof, wherein the pipe joint satisfies a coefficient F of 0.4 or less in the following formula (1),
F=(D.sub.3.sup.2D.sub.1.sup.2)/(D.sub.4.sup.2D.sub.2.sup.2), Formula (1): where D.sub.1 represents the inner diameter of the first and second joint members, D.sub.2 represents the inner diameter of the gasket, D.sub.3 represents the diameter of the seal projections, and D.sub.4 represents the outer diameter of the gasket.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a longitudinal sectional view representing an embodiment of a pipe point of the invention.

[0018] FIG. 2 is a schematic diagram of a model simulating the stress and strain occurring in the pipe joint of FIG. 1 under applied internal pressure.

[0019] FIG. 3 is a graph representing a relationship between coefficient F, and the pressure P at which a gasket starts to come off.

[0020] FIG. 4 is a graph representing a relationship between coefficient F, and the pressure P at which the contact between a gasket and a joint member becomes loose.

[0021] FIG. 5 is a graph representing a relationship between coefficient F, and the gasket displacement at which the contact between a gasket and a joint member becomes loose.

DESCRIPTION OF EMBODIMENTS

[0022] A preferred illustrative embodiment of the present invention is described below in detail, with reference to the accompanying drawings. It is to be noted that the parameters, including the dimensions, materials, shapes, and relative positions of the constituent components described in the embodiment below are merely illustrative, and are not intended to limit the scope of the invention, unless otherwise specifically stated.

[0023] A pipe joint includes first tubular joint member (1) and a second tubular joint member (2) having mutually communicating fluid passages; a circular ring-shaped gasket (3) interposed between the right end surface of the first joint member (1) and the left end surface of the second joint member (2); and a retainer (5) that holds the circular ring-shaped gasket (3) while being held by the first joint member (1). The second joint member (2) is fixed to the first joint member (1) with a nut (4) screwed to the first joint member (1) from the second joint member (2) side. The pipe joint also includes circular ring-shaped seal projections (7) and (8) radially formed at the abutting end surfaces of the joint members (1) and (2), and overtightening preventing ring-shaped projections (9) and (10) formed around the seal projections (7) and (8).

[0024] The both ends of the gasket (3) are flat surfaces perpendicular to the axial direction. The outer circumferential surface of the gasket (3) has a stopper (3b) composed of an outer flange.

[0025] The joint members (1) and (2), and the gasket (3) are made of SUS316L.

[0026] An inward flange (11) is formed at a right end portion of the nut (4), and the nut (4) is fitted around the second joint member (2) at the flange (11). The nut (4) has an internal thread (12) formed on the inner circumferential surface of its left end portion, and the internal thread (12) is mated with an external thread (14) formed on the right end portion of the first joint member (1). An outward flange (13) is formed on the outer circumference at the left end of the second joint member (2), and a thrust ball bearing (6) for preventing corotation is interposed between the outward flange (13) and the inward flange (11) of the nut (4).

[0027] The overtightening preventing ring-shaped projections (9) and (10) project further toward the gasket (3) in horizontal direction than the circular ring-shaped seal projections (7) and (8), so that the projections (9) and (10) press the retainer (5) from both sides when the joint members are tightened with a force that exceeds the proper torque.

[0028] The gap between the retainer (5) and the overtightening preventing projections (9) and (10) reaches zero as the nut (4) is tightened with a tool such as a spanner after it is fitted in place by hand, and further tightening of the nut (4) is met with greatly increasing resistance to prevent overtightening.

[0029] The inner circumference (1a) of the first joint member (1), the inner circumference (2a) of the second joint member (2), and the inner circumference (3a) of the gasket form a fluid passage.

[0030] When the inner diameter of the first and second joint members is D.sub.1, the inner diameter of the gasket is D.sub.2, the diameter of the seal projections is D.sub.3, and the outer diameter of the gasket is D.sub.4, it is preferable that the coefficient F=(D.sub.3.sup.2D.sub.1.sup.2)/(D.sub.4.sup.2D.sub.2.sup.2) be 0.4 or less. The coefficient F is more preferably 0.3 or less.

[0031] Here, D.sub.3 is the diameter of the ring as measured at the center of the highest portion of the circular ring-shaped seal projections (7) and (8), and D.sub.4 is the outer diameter of the circular ring-shaped gasket (3), excluding the stopper (3b).

[0032] With a coefficient F of 0.4 or less, the gasket tends to deform less. A coefficient F of 0.3 or less is even more preferred because the gasket deforms even less with such a coefficient F.

[0033] FIG. 2 is a schematic diagram representing a model simulating the stress and strain occurring in the pipe joint under applied internal pressure. The basic configuration analyzed had the gasket (3) between the first pipe joint (1) and the second pipe joint (2). D.sub.1 is the inner diameter at the circumference (1a, 2a), D.sub.2 is the inner diameter at the circumference (3a), D.sub.3 is the diameter of the circular ring-shaped seal projection (7, 8), and D.sub.4 is the outer diameter of the gasket (3) excluding the stopper (3b).

TEST EXAMPLE 1

[0034] A finite element analysis was conducted using members made of stainless steel. Table 1 below shows values of D.sub.1 to D.sub.4, coefficients F derived from these values of D.sub.1 to D.sub.4, and pressures P at which the gasket (3) starts to come loose. FIG. 3 is a graph representing a relationship between F and P. The broken line represents an approximate straight line.

TABLE-US-00001 TABLE 1 Pressure P at which gasket Analysis D.sub.1 D.sub.2 D.sub.3 D.sub.4 Coefficient starts to come No. (mm) (mm) (mm) (mm) F loose (MPa) Analysis 1 4.35 7.57 9.00 10.90 1.0093 153.72 Analysis 2 3.30 4.40 5.80 10.2 0.2686 264.96 Analysis 3 5.50 6.00 9.00 14.10 0.3117 205.20

[0035] As can be seen from FIG. 3, the coefficient F is linearly related to the pressure P at which the gasket starts to come off, showing that the coefficient F is indeed appropriate.

TEST EXAMPLE 2

[0036] A finite element analysis was conducted using members made of stainless steel. Table 2 below shows values of D.sub.1 to D.sub.4, coefficients F derived from these values of D.sub.1 to D.sub.4, and pressures P at which the contact between the gasket (3) and the joint members (1) and (2) becomes loose. FIG. 4 is a graph representing a relationship between F and P. The broken line represents an approximate straight line.

TABLE-US-00002 TABLE 2 Pressure P at which contact Analysis D.sub.1 D.sub.2 D.sub.3 D.sub.4 Coefficient starts to become No. (mm) (mm) (mm) (mm) F loose (MPa) Analysis 4 6.00 6.00 12.00 14.10 0.6633 153.00 Analysis 5 6.00 6.00 11.00 14.10 0.5221 165.00 Analysis 6 6.00 6.00 10.00 14.10 0.3931 174.00 Analysis 7 6.00 6.00 9.00 14.10 0.2764 180.00 Analysis 8 6.00 6.00 8.50 14.10 0.2227 186.00

[0037] As can be seen from FIG. 4, strong linearity is maintained between coefficient F and the pressure P at which the contact starts to become loose, as in FIG. 3, though the approximate straight line is less steep than in FIG. 3 because the test analyzes the pressure at which the gasket and the joint members start to lose contact. It can be understood from this result that the coefficient F is appropriate.

TEST EXAMPLE 3

[0038] A finite element analysis was conducted under the same conditions used in Test Example 2. Table 3 below shows values of D.sub.1 to D.sub.4, and coefficients F derived from these values of D.sub.1 to D.sub.4, along with the displacements in the inner and outer diameters of the gasket, and the displacement in the circular ring-shaped seal projections (7) and (8) by the gasket as measured when the contact between the gasket (3) and the joint members (1) and (2) was lost. FIG. 5 is a graph representing a relationship between F and displacement. The unit of displacement is millimeter.

TABLE-US-00003 TABLE 3 Displacement in Displacement in Displacement of Analysis D.sub.1 D.sub.2 D.sub.3 D.sub.4 Coefficient inner diameter outer diameter ring-shaped No. (mm) (mm) (mm) (mm) F of gasket of gasket seal projection Analysis 9 6.00 6.00 12.00 14.10 0.6633 0.180 0.232 0.175 Analysis 10 6.00 6.00 11.00 14.10 0.5221 0.295 0.290 0.245 Analysis 11 6.00 6.00 10.00 14.10 0.3931 0.278 0.265 0.241 Analysis 12 6.00 6.00 9.00 14.10 0.2764 0.177 0.181 0.176 Analysis 13 6.00 6.00 8.50 14.10 0.2227 0.159 0.160 0.176

[0039] In FIG. 5, the displacement in the inner diameter of the gasket is represented by solid line, the displacement in the outer diameter of the gasket is represented by broken line, and the displacement in the position of the circular ring-shaped seal projection of the gasket is represented by dotted line. Ina range of coefficient Fbetween 0.66 and 0.52, all of these displacements increase as the coefficient F decreases. In a range of coefficient F between 0.52 and 0.40, all of the displacements are almost constant, regardless of the coefficient F. In a range of coefficient F between 0.40 and 0.27, all of the displacements decrease as the coefficient F decreases. The displacements are the smallest, and remain constant in a range of coefficient F of 0.27 or less.

[0040] Because smaller displacements are more advantageous in terms of improving pressure tightness, the coefficient F is preferably in a range of 0.4 or less, in which the displacements are smaller. More preferably, the coefficient F is in a range of 0.3 or less, in which the displacements have the smallest values, and remain constant.

INDUSTRIAL APPLICABILITY

[0041] A pipe joint can be provided that is compact, and is optimally shaped for use in a pipe intended for use under ultrahigh pressure.

REFERENCE SIGNS LIST

[0042] 1: First joint member [0043] 2: Second joint member [0044] 3: Gasket [0045] 7: Circular ring-shaped seal projection [0046] 8: Circular ring-shaped seal projection