WO1998015769A1

WO1998015769A1 - Low erosive wear elbow joint design

Info

Publication number: WO1998015769A1
Application number: PCT/US1997/015335
Authority: WO
Inventors: Charles Ortloff; Ting Hong Chung (Ken)
Original assignee: Fmc Corporation
Priority date: 1996-10-07
Filing date: 1997-09-02
Publication date: 1998-04-16
Also published as: AU4243497A

Abstract

In combination with an elbow joint (22) comprising a conduit (24) having an internal bore (32), an inlet (26), an outlet (28) and an elbow (30) forming an angle between the inlet and the outlet, the improvement comprising a perturbation (34) formed in the bore (32) within the elbow (30).

Description

Low Erosive Wear Elbow Joint Design Background of the Invention

1. Field of the Invention

The present invention relates to elbow joints used in piping systems for conveying fluids or other materials. More particularly, the invention relates to an elbow joint which comprises a perturbated elbow bore design for reducing the degree of erosive wear in the elbow joint.

2. Description of Related Art

Elbow joints are commonly used to change the direction of material being conveyed through a piping system. They comprise a length of conduit having an inlet adapted to be connected to the piping system, an outlet adapted to be connected to the piping system and an elbow which forms an angle of typically 90° between the inlet and the outlet. In certain applications, such as well fractionating operations, the piping system is used to convey relatively abrasive materials. Consequently the elbow joints are subject to substantial erosive wear from the material. Summary of the Invention

It has been found through experimentation and numerical analysis that the degree of wear can be reduced by enlarging or creating a perturbation in bore of the elbow. The resulting concavity in the elbow bore is believed to reduce the velocity of the material due to the corresponding increase in volume in the elbow and also alter the flow and particle trajectories in a manner which limits the high energy, low angle impacts between the material and the bore that are the primary cause for wear in elbow joints. Accordingly, the present invention is directed to an elbow joint which comprises a length of conduit having an inlet and an outlet separated by an elbow forming an angle between the inlet and the outlet. The elbow joint comprises a radius measured from its longitudinal axis; and for purposes of this invention the radius collinear with the symmetry axis of the elbow joint at an azimuthal angle of 180° is referred to as the outer radius. According to the present invention, the outer radius is increased according to a predetermined relationship to form a perturbation in the elbow. Fairing techniques are then used to transition from the increased outer radius to the radii at azimuthal angles of ±90°. The resulting concavity or "stomach" created in the bore of the elbow will reduce the degree of erosive wear typically experienced in standard elbow joints.

These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is a side elevation view of a prior art elbow joint;

Figure 1A is a cross-sectional view of the elbow joint depicted in Figure 1 taken along the line A-A;

Figure 2 is a cross-sectional view of one embodiment of an elbow joint according to the present invention; and Figure 2A is a cross-sectional view of the elbow joint of Figure 2 taken along the line B-B. Detailed Description of the Preferred Embodiments

Referring to Figures 1 and 1A, a prior art elbow joint 10 is shown to comprise a length of conduit 12 having an inlet section 14 and an outlet section 16 joined by an elbow 18 which forms an angle, in this case 90°, between inlet 14 and outlet 16. Conduit 12 comprises a bore 20 having a generally circular cross section, and elbow joint 10 has a longitudinal centerline L which, for purposes of this description, follows the angle of elbow 18 from inlet 14 to outlet 16. Inlet 14 and outlet 16 may be provided with suitable means (not shown) to enable elbow joint 10 to be connected to a piping system (not shown).

The angle φ of elbow 18 is measured between a plane P1 perpendicular to the centerline L at the juncture of inlet 14 and elbow 18 and a plane P2 perpendicular to centerline L at the juncture of outlet 16 and elbow 18. In the prior art elbow joint depicted in Figure 1 , φ = 90°. The angle φ' is the angle measured clockwise, as viewed in Figure 1 , from the bisector of the angle φ. The radius r of elbow joint 10 is defined as the distance between centerline L and bore 20. In addition, for purposes of this description, the radius of elbow 18 at an azimuth angle α of 180° is defined as the outer radius R. The azimuth angle α is the angle in the cross section of conduit 12 from a point T closest to the intersection of planes P1 and P2 and another point on conduit 20, as depicted in Figure 1A. The above-defined quantities are related to the Cartesian quantities x_v x₂ and x₃, as is understood by one of ordinary skill in the art, and these quantities can be programmed into a numerically controlled machine for manufacturing elbow joint 10. Referring to Figures 2 and 2A, an embodiment of the elbow joint of the present invention, which is indicated by reference number 22, is similar to elbow joint 10 in that it comprises a conduit 24 having an inlet section 26, an outlet section 28 and an elbow 30 forming an angle between inlet 26 and outlet 28. Conduit 24 comprises a bore 32 having a generally circular cross section in the areas of inlet section 26 and outlet section 28, and elbow joint 22 has a longitudinal centerline L which follows the angle of elbow 30 from inlet 26 to outlet 28. Furthermore, inlet 26 and outlet 28 may be provided with suitable means (not shown) to enable elbow joint 22 to be connected to a piping system (not shown). In accordance with the present invention, bore 32 is enlarged in the area of elbow 30 to form a perturbation or concavity 34 in elbow 30. This is accomplished by enlarging outer radius R by an amount D, which in practice can be any amount but in a preferred embodiment is related to the angle φ of elbow 30. Thus, for example, when the angle φ of elbow 30 is 90°, D may be determined by one of the following formulas:

D = e-cosφ', where -45° < φ < 45°; (1)

D = e'-cos²φ\ where -45° < φ < 45°; (2)

D = A - e"-s², (3) where A is an amplitude constant, s is the distance measured from the φ' = 0 axis and the quantities e, e' and e" are pre-selected eccentricity amplitudes. The amplitude constant A is selected in conjunction with the eccentricity amplitude e" such that D will be its greatest at the outer radius where s=0 and will be 0 when s is a predetermined distance from the φ' = 0 axis. The eccentricity amplitudes are determined by trial and error, the objective being to achieve a perturbation which results in an acceptable degree of wear reduction in the elbow joint but at the same time is not unacceptably large. For example, Figure 2 depicts a 2-inch diameter elbow joint wherein the outer radius R has been enlarged by an amount D determined by equation (1) and wherein eccentricity amplitude e was selected to be 0.06 foot.

It should be pointed out that the value D is added to the outer radius R, which has previously been defined as existing only where the azimuth angle α = 180°. In accordance with the preferred embodiment of the invention, the radius r of conduit 24 in the area of perturbation 34 is gradually reduced using three-dimensional fairing techniques, which are known to those skilled in the art, until the radius is equal to the radius of inlet 26 and outlet 28 at azimuth angle α = ±90°. This results in a concavity within bore 32 which transitions smoothly between inlet 26 and outlet 28.

This concavity increases the volume within elbow 30, which reduces the velocity of the material flowing through elbow joint 22. In addition, perturbation 34 alters the flow and particle trajectories in a manner which limits the high energy, low angle impacts between the material and bore 32 that are the primary cause for wear in elbow joints. As a result, elbow joint 22 will experience a lower rate of erosive wear.

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.

Claims

What is Claimed is:

1. In combination with an elbow joint comprising a conduit having an internal bore, an inlet, an outlet and an elbow forming an angle between the inlet and the outlet, the improvement comprising: a perturbation formed in the bore within the elbow.

2. The elbow joint of claim 1 , wherein the conduit comprises a longitudinal centerline and a radius measured from the centerline to the bore, wherein the elbow comprises an outer radius defined at an azimuth angle of 180°, and wherein the outer radius is greater than the radius, whereby the difference between the outer radius and the radius forms the perturbation.

3. The elbow joint of claim 2, wherein the difference between the outer radius and the radius is dependent on the angle of the elbow.