BACKGROUND OF THE INVENTION Double containment pipe fittings have been known and used in the past. Typical of these fittings are those found in the following U.S. Patents: 4,903,719; 4,915,121; 5,141,261; 5,141,260; and 4,886,305.

While these fittings have been useful in a number of applications, there still is room for improvement and the present invention provides an improved double containment fitting which relies upon the geometry of the pipe segments to present inner and outer spaces for fluid flow.

SUMMARY OF THE INVENTION The present invention is directed to a double containment pipe fitting which can be of metal or plastic and which has an inner and outer pipe. The inner pipe has a polygonal cross section to present a number of edges which extend parallel with the longitudinal axis of the pipe and these edges engage the inner surface of the outer pipe to present the double containment feature, namely the central portion of the inner pipe being one fluid flow path and the spaces between the flat outer sides of the inner pipe facing the inner surface of the outer pipe forming the second path for the assembly or the fitting. The fitting can be such that a cross section of the inner pipe can be triangular, square, rectangular or polygonal. Thus, considerable latitude is

or can be achieved with the teachings of the present invention.

The present invention provides an improved double containment pipe fitting which has an inner tube and an outer tube with the inner tube having corners or edges which space the inner tube from the outer tube to present the double containment feature at the inner and outer surfaces of the inner tube.

Other features and advantages of the present invention will become apparent as the following specification progresses, reference being had to the accompanying drawings for an illustration of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical section through a first embodiment of the assembly of the present invention; Fig. 2 is an end elevational view of the assembly of Fig. 1; Fig. 3 is an isometric view of the inner pipe member of the assembly of Fig. 1; Fig. 4 is an isometric view of one segment of the outer pipe member of the assembly of Fig. 1; and Figs. 5, 6 and 7 are side elevational views showing reducing elbow, tee and crossing embodiments of the assembly of Fig. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A first embodiment of the fluid pipe assembly of the present invention is broadly denoted by the numeral 10 and is shown in Figs. 1 and 2. Assembly 10 includes a pair of tubular pipes 12 and 14, pipe 12 being within pipe 14 and forming an el for the flow of fluid through the pipe 12 along a path, for instance, denoted by the arrows 15 in Fig. 1. Pipe 12 can be of any suitable material, such as metal or plastic and typically is of stainless steel so as to render it especially

suitable for use in conveying toxic liquids over a predetermined path. Other fluids, such as gases and other liquids, can be transported through the assembly 10 and specifically through el shaped pipe 12 in either direction.

The pipe 12 has two mutually perpendicular segments 12a and 12b which are in fluid communication with each other at the central portion of the assembly 10. The pipe 12 has a polygonal cross section (see Fig. 3) so as to present four flat sides 12c which extend from a shoulder 12d to the central location 12f at the central part of the tube 12. The remaining part 12g of segment 12b extends from shoulder 12d to the outer end face 12e of the tube segment 12b and this portion 12g is circular as shown in Figs. 2 and 3. The junctions between the flat sides 12c of pipe 12 present edges 12j which are parallel with each other and which are adapted to slidably engage the interior cylindrical surface 14c of tube 14. This engagement of the edges 12j with surface 14c is shown in Figs. 2 and 4. The side edges 12j of pipe 12 in effect center pipe 12 in pipe 14 when the assembly is complete. While four edges 12j have been shown and described, it is clear that there could be two or three points of contact, such as edges 12j, or more than four points of contact, such as edges 12j, for centering purposes.

To construct assembly 10, pipe 12a is first made in accordance with the teachings of Fig. 3. Then, pipe segments 14a and 14b are made in accordance with the teachings of Fig. 4.

Pipe 14a and 14b are slidably assembled and centered over edges 12j on legs 12a and 12b of member 12 until the angularly cut ends 14a of pipe segments 14a and 14b abut ends 14d. They are then connected and sealed together with a weld 16 which when complete accurately locates, locks, and centers member 12 within member 14.

When so connected, the assembly 10 is formed and the

edges 12j of pipe 12 will sealingly engage the inner surfaces of respective segments 14a and 14b. Moreover, the central axis of pipe 12a is coincident with the central axis of pipe 14a. Similarly, the central axis of pipe 12b is coincident with the central axis of pipe segment 14b. The spaces denoted by the numeral 18 are not necessarily sealed from each other. There could be fluid communication between adjacent spaces 18 if desired. However, there is fluid isolation of spaces 18 from the interior of pipe 12. Thus, the assembly 10 can be used for conveying fluids, especially toxic fluids, through pipe 12 while the pipe remains out of fluid communication with tube 14.

In use, the assembly 10 is coupled at its outer end faces 12e such as by welding to a similar, circular end pipe or tube of the same diameter. End faces 14f are also welded to pipes of the same diameter.

Figs. 5, 6 and 7 show different configurations for the pipe assembly of the present invention. In each case, where there is an outlet, there is a pipe extension broadly denoted by the numeral 25 so that the assembly can be coupled to another pipe such as by welding or the like. Also in each case of the embodiments of Figs. 5-7, there are a plurality of edges which extend parallel to the leg in which the edges are received. Thus, the cross section of the inner tube in each of the embodiments of Figs. 5-7 is polygonal in that there is a pipe having a triangular cross section, a square cross section, a rectangular cross section or another polygonal cross section with more than four edges at the junctions between the flat sides of the leg.

Other modifications and variations can be made to the disclosed embodiment without departing from the subject of the invention as defined by the following claims. For example, structure other than edges 12j can be used to generally center pipe 12 within pipe 14.

Sides 12c could be other than flat, such as convex.