Improved Method of Forming a Socket Weld

Technical Field

The invention relates to a method of forming a socket weld connection between a tubular element such as a pipe, a nipple or a nozzle and a second element such as another pipe, a drum, a header or a tube sheet.

When welding a tubular element such as a pipe, nipple or nozzle to a second element such as another tube, a boiler drum or a header or a tube sheet of a heat exchanger, a socket weld is often used wherein the end of the tubular element is inserted into a recess, termed a socket, in the surface of the second element. To properly align the tubular element prior to welding, it is desirable to bring the end of the tubular element in contact with the seat of the socket. However, a structure of this type is considerably stressed when the weld is made and tensions are produced in the weld seam which may cause cracking of the seam when the weld contracts as it cools. For this reason, contact of the end of the pipe with socket set is usually avoided by backing-off the tubular element away from the socket set such that a gap of approximately one and one-half millimeters is maintained between the end of the tubular element and the socket seat. By doing this, the end of the tubular element is free to move axially downward as the weld contracts thereby relieving stresses in the weld seam which could otherwise cause cracking of the seam. Unfortunately, backing the tubular element away from the socket seat is a cumbersome operation which can also result in inaccurate positioning of the tubular element.

Background Art

The prior art, U.S. Patent No. 3,003,601, provided for a socket weld connection between a tubular element and a second elemen wherein a portion of the end of the tubular element was maintained in contact with the seat of a flat bottom socket in the surface of the second element during the welding process without causing crack¬ ing of the resultant weld seam. According to this prior art, the en face of the tubular element must be machined to provide a relatively thin rim extending from the end of the tubular element. The tubular element is inserted into the socket such that the relatively thin ri extending from the end of the tubular element contacts the flat seat of the socket, a gap thereby being established between the end of the tubular element and the socket seat into which the relatively thin rim is free to deform upon shrinking of the weld.

Disclosure of Invention

According to the present invention there is provided an improved method of forming a socket weld connection between a tubular element and a vessel, of the type wherein a recess having a diameter slightly greater than the diameter of the tubular element is bored into the surface of the vessel, the tubular element is inserted into the recess so as to contact the seat thereof and welding heat is applied externally around the circumference of the tubular element at the intersection of the tubular element with the surface of the vessel. The improvement comprises tapering the seat of the recess from its outer c rcumference inward at a downward angle with respect to the horizontal of at least 10°.

The improved method of the present invention possesses the advantage that the end face of the tubular element need not be machined to produce a relatively thin rim extending therefrom. Thus a very time consuming step is eliminated in favor of the simple operation of tapering the socket seat as the socket is bored into the second element.

Another advantage of the present invention is that the flat end face of the tubular element is permitted to contact the seat of the recess thereby ensuring accurate positioning of the tubular element within the recess, while at the same time providing a gap

between the end face of the tubular element and the seat of the recess so that the tubular element may deform upon shrinking of the structure after the weld has been made without causing excessive stresses and cracking within the weld connection. Contact between the end face of the tubular element and the seat of the socket is limited to a line contact along the outer circumference of the end of the tubular ele¬ ment. This limited contact has been shown to be sufficient to ensure accurate positioning of the tube, but not great enough to offer sufficient resistance to deformation to induce excessive stresses within the weld seam as the weld shrinks upon cooling.

Brief Description of the Drawing

These and further features and advantages of the invention become evident in the description of the following embodiment shown in the drawing attached wherein:

Figure 1 is a sectional side elevation view of a tube socket welded to another tube with a fillet weld in accordance with the method of the present invention; and

Figure 2 is a sectional side elevation view of a tubular element welded to a vessel with a single-J groove weld in accordance with the method of the present invention.

Best Mode for Carrying Out the Invention

Referring to the drawings, a tubular element 10 is shown welded to a second element 20, such as another tube as shown in

Figure 1 or a vessel such as a drum or header as shown in Figure 2. A recess is bored into the surface of the second element, and the end face 50 of the tubular element 10 is inserted therein. The recess may comprise a number of known shapes such as the simple annular socket 30 of Figure 1 or the more elaborate socket 32 of Figure 2 wherein a weld groove, such as a single-J pipe weld groove, is embodied in the socket itself. It is desirable to insert the tubular element 10 all the way into the recess 30, 32 until the end face 50 of tubular element 10 is ^' in contact with the seat 40 of the socket so that proper and accurate positioning of the tubular element can be assured.

In accordance with the invention, the seat 40 of the socket 30, 32 is tapered from its outer circumference inward at a downward

angle with respect to the horizontal of at least 10°. Although any taper of an angle greater than 10° ensures that sufficient space is available for the end face of the tubular element to deform without causing excessive stresses in the weld seam, it is preferred that the angle of the taper be limited to not more than 15° in order to avoid removing unnecessary large amounts of metal from the second element which could locally adversely affect the structural integrity of the second element.

In forming the weld, welding metal is deposited externally around the circumference of the tubular element 10 at the intersec¬ tion of the tubular element 10 with element 20 to form a weld seam 60 therebetween. As the weld seam 60 cools and contracts, the outer c cumferential portion of the end face 50 of the tubular element 10 is free to deform inward and downward into the gap between the end face 50 of the tubular element 10 and the tapered seat 40 of the socket. Because the tubular element 10 is free to deform, stresses do not develop within the weld seam 60 upon contraction and the weld seam 60 is not subject to cracking. The gap 45 between the end face 50 of the tubular element 10 and the tapered seat 40 of the socket is essential for allowing the desired deformation necessary to produce the socket weld connection of the present invention.