Patent Number: 056235267
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 3 and 4 show a first embodiment of the invention. In this arrangement, straps 100 which are made of the same material as the shroud 14, for example stainless steel 304, are, in this embodiment, fastened to the shroud using so called "P-bolts" 102. While it is to be specifically noted that the invention is not limited to the use of these so called "P-bolts", this particular type of fastening technique is preferred in connection with this embodiment. With the illustrated straps, the H5 to H8 welds are spanned or covered. A plurality of straps 100, for example four or more straps, can be used; however, they need not necessarily be uniformly arranged at 90 degree intervals and the spacing is determined on a case-by-case basis depending on the reinforcement which is required and the space which is available. Prior to being submerged, each strap 100 is mounted on a delivery fixture and fitted with three (by way of example only) EDM heads (not shown) which are positioned at the sites where the "P-bolt" connections are required. Each of the straps is then lowered down through the annulus 104 defined between the shroud 14 and inner wall of the pressure vessel 16, using a so called "rigid pole" system. When each of the straps 100 is maneuvered into the desired position, the EDM tool heads cut the appropriately shaped holes through the wall of the shroud. The EDM heads are then remotely released and removed while the strap is maintained in position. The "P-bolts" 102 are then lowered into position, slid into the strap, threaded in and expanded. Each "P-bolt" 102 is then crimped to lock it in place. In the illustrated embodiment, the strap has an L-shape and the lower end or foot 100f fastened to a shroud support plate 30. The EDM process is carried out in a manner wherein the tooling loads are negligible and no chips are produced during each cut. The fines which are produced during the cutting operation are flushed out by water which is directed through the electrode by flushing pumps which take suction on the shroud and pass the water through filters. The filters in this instance are 0.8 micron and capture 99.9% of the fines in the water which is pumped through the area of the EDM electrodes. An alternative to the above "pre-mounting" technique resides in the strap being placed in position and the EDM cutting tools, which are supported at the ends of a delivery mast, then delivered into position in the annulus between the shroud and the pressure vessel using the above mentioned rigid pole system. Tool fixtures including alignment features and positioning clamps can be used to secure the mast and the tool head at the proper location for the respective cuts. It will be noted that the shroud 14, to which the strap according to the first embodiment of the invention is applied, has eight welds H1 to H8; and that the strap 100 illustrated in FIG. 3 is such as to span welds H5 to H8. This strap is able to withstand bend, and shear in addition to tension, and thus, when fastened to the shroud in the illustrated position, is able to securely support the shroud against bending and shearing forces as well as tension, and thus can be expected to increase the strength and resistance of the shroud to forces produced by seismic activity and the like for both horizontal and vertical welds. For further disclosure pertaining to the above mentioned "P-bolts", reference may be had to U.S. Pat. No. 5,065,490 issued to Wivagg et al. on Nov. 19, 1991. The disclosure of this patent is hereby incorporated by reference. It will be noted that FIG. 4 shows a variant of the first embodiment. That is to say, in this figure, an opening 106 is formed in the shroud 14 immediately above the top of the strap 100 and a flange section 100a is formed at the upper end of the illustrated strap 100. The flange 100a is arranged to project through the hole 106 into the interior of the shroud 14 where it can be connected to an internal tie rod or the like type of structure. FIGS. 5 and 6 show a second embodiment of the invention. This embodiment features a strap 100' which has an angled foot section 100f' and which is adapted for use with a shroud having a skirt portion 14a'. This embodiment is essentially similar to the first with this latter mentioned exception. FIG. 6 shows the strap of FIG. 5 in enlarged form. In this drawing the use of "P-bolt" type fasteners is shown. It will be noted that the length of the straps shown in FIGS. 3 to 6 is not limited to that shown in the drawings and can be of any suitable length. For example, it is clearly within the scope of the invention to make the straps long enough as to extend along a substantial portion of the height of the shroud and to span welds H4 to H8 for example. It will be further noted that the upper ends of the straps can be formed with outwardly extending flanges which are adapted to be connected to an external support structure such as a tie rod or the like, and thus cooperate with this additional structure in a manner which will extend the supportive effect of the straps over the full length of the shroud. Alternatively, a hole can be formed in the shroud which allows an inwardly extending flange to be fitted through the hole and to be connected to an internally disposed support structure. As will be appreciated, in the event that a hole is formed in the shroud for the purposes of allowing a flange or projection to pass through into the interior of the shroud, the hole and the projection member should have very similar dimensions so that a relatively snug fit is achieved and the amount of water which can flow through any remaining gaps is minimized to the maximum possible degree. Although the present invention has been described with reference to only two basic embodiments, it will be appreciated that a number of variations and modification are possible without departing from the scope of the invention and that the scope of the invention is determined only by the appended claims.