Abstract: A tube for a cracker unit in which ethylene is produced withstands, without oxidizing or losing its strength, the elevated temperatures required to effect cracking, yet retards coking. The tube has a shell formed from stainless steel or high nickel alloy and a liner formed from an iron-aluminum alloy. The liner retards the deposit of carbon and its build up known as coking. To form the tube, a high alloy ingot is bored to provide a bore that extends through its center. Then a weld overlay is applied to surface of the bore, with the overlay being derived from a weld metal containing at least 16% aluminum and the balance essentially iron. Thereafter, the ingot is heated to its hot working temperature and extruded through sets of opposed rollers, with the direction of advance being in the direction of the bore. The extruding transforms the ingot into a lined tube.

Abstract: A weldment, such as the wall of a pressure vessel, is formed from segments, each of which includes a steel substrate, a protective layer of tantalum which is exposed to the interior of the vessel and an intervening layer of copper which lies between and is bonded to the substrate and the protective layer. The substrate and the two layers which form the cladding are explosively bonded together and the bonding procedure may leave the protective layer with small domes or embossments and pockets of trapped gas behind the embossments. The two segments are welded together edge-to-edge at their substrates, with their protective and intervening layers aligned. If one were to follow the traditional procedure, one would place a tantalum batten strip over the protective layers along the opposed edges so as to cover the edges, and then weld the batten strip to the protective layer along the edges of the strip.

Abstract: A tube-type heat exchanger has two tubesheets, each provided with a multitude of bores, and tubes which extend between the tubesheets at their bores, their hollow interiors opening into the bores. Each tube at its ends is joined to the tubesheets along fillet welds which, being free from crevices, eliminate the build up of deposits and corrosion which commonly develop in the crevices of heat exchangers. To assemble the heat exchanger, each tube is passed through a bore in one of the tubesheets and advanced toward the other tubesheet, its leading end being inserted into a socket at the end of a bore in the other tubesheet. Then the leading end of the tube is welded to the tubesheet at which it is located. This leaves the trailing end of the tube in the bore of the tubesheet through which the tube was initially inserted, and that bore likewise terminates at a socket. The trailing end of the tube is machined down from within the bore until it extends no farther than the socket at the end of the bore.

Abstract: Segments of a clad pressure vessel are welded together along seams at which the cladding is removed to expose a steel backing, so that initially a groove opens out of the cladding toward the interior of the vessel at each seam. Batten strips cover the grooves, and each of those strips has a depressed center portion which fits into the groove for that strip to center the strip along its groove. The batten strip also has flanges which extend outwardly from the depressed portion to overlie the cladding, to which they are welded along their edges. Cover plates are welded over the ends of batten strips. Thus, the cladding, the batten strips and the cover plates totally isolate the steel backing of the pressure vessel from the interior of the vessel, so that the contents of the vessel will not corrode the backing.

Abstract: In order to join a tube to a tubesheet of a heat exchanger, the end of the tube is inserted into a socket at the end of a hole that passes through the tubesheet. The socket is large enough to receive the tube, but the hole is not, so the tube bottoms out in the socket and is thus located both radially and axially by the socket. A ring mold is fitted around the tube and moved against the tubesheet, so that its end fits into an annular groove that surrounds the socket in the back face of the tubesheet. The ring mold has a chamfered confining surface that surrounds the tube where the tube emerges from the socket. Once the ring mold is in place the portion of tube that is within the socket is welded autogenously to the tubesheet by rotating an electrode within the hole. The molten weld metal flows outwardly to the confining surface, but is prevented by that surface from flowing circumfentially, even when the welding is performed with the tube in a horizontal position.

Abstract: A layered head for a pressure vessel includes a frame which has the general contour of the head and is formed from a plurality of stiffeners, some of which extend circumferentially and others of which extend meridionally. The stiffeners create a grid and each opening of the grid is occupied by a plurality of plates which are curved to match the contour of the frame and are stacked upon one another in face-to-face contact. Moreover, the several plates in each grid opening are progressively larger in surface area, with the innermost plate having the smallest surface area and the outermost plate having the largest. The peripheral edges of the plates are located directly opposite the sides of the stiffeners, and to accommodate the variance in the surface areas of the plates, the sides of the stiffeners are stepped.

Abstract: A head for a pressure vessel has a contoured liner and successive wraps that overlie the liner and conform in contour to it. The liner has a machined outwardly presented surface, whereas the wrap immediately over it has a machined inwardly presented surface, and the liner and wrap are welded together with their opposed machined surfaces in face-to-face contact. The same holds true with the successive wraps so that two adjacent wraps are in face-to-face contact along their machined surfaces. A wrap may be heated prior to being placed over the liner or over another wrap so that upon cooling the wrap shrinks and places the underlying liner and wraps in a state of precompression. Both the liner and the various wraps may be formed from segments which are dished to the proper contour, then welded together into a rough liner or wrap, and finally machined along the appropriate surfaces. They may likewise be formed from single plates, forgings or castings.

Abstract: A layer head or shell for a pressure vessel is formed by building up successive wraps over a liner, each wrap consisting of a plurality of segments which fit together such that the wrap completely covers the liner or the wrap immediately under it. Each segment is curved to conform to the surface over which it is installed, and once in place a seal is provided along its periphery. Air is evacuated from the space between the wrap segment and the underlying surface so that air at atmospheric pressure will force the wrap segment down tightly against the underlying surface. During this time tack welds are made along the periphery of the wrap segment to join it to the underlying layer. Then the vacuum is released and a final or continuous weld is made along the periphery. As the weld cools it places the underlying layers in a state of precompression.

Abstract: A tube-type vessel, such as a heat exchanger, has tubes that extend away from a tubesheet provided with holes which axially align with the tubes and open into the tube interiors. The diameter of each hole in the tubesheet is less than the outside diameter of the tube with which it aligns, but is greater than the inside diameter of the tube, thereby producing an offset between the inside surface of the tube and the surface of the hole. The tubes are attached to the tubesheet by welds, and each weld forms a fillet between exterior surface of its tube and the back face of the tubesheet and further forms a smooth beveled transition between the inside surface of the tube and the surface of the hole. The fillets eliminate the crevices that surround the tubes in conventional structures, and as a consequence no material will build up around the tubes and collapse them. To unite the tubes with the tubesheet, the latter at each hole is provided with a socket into which the end of a tube is fitted.