Patent Number: 054085098
Section: description

DETAILED DESCRIPTION OF THE INVENTION An automatic remote stud tensioning and stud insertion and removal system for nuclear pressure vessels is shown schematically in FIGS. 1-4. A nuclear reactor generally indicated at 200 has a dome 202 with a standard flange 204 that is secured by a plurality of studs and nuts in a usual manner. The flange is covered a plurality of flange cover sectors 206. Each of which, in the preferred embodiment, take approximately one-sixth of the circumference of the flange and each of which have two posts 208 upon which apparatus sectors 224 will be mounted as to be discussed below. Each flange cover sector has a series of wheels 210 which allow the device to be rotated so that the flange cover sectors can be brought to the reactor from one point as for example by means of a hoist 212 and then rotated around to completely cover the circumference of the flange and are then connected by bolts or any other convenient fastening means to form a unitary ring on the flange. A caddy, generally indicated at 216, includes a bottom portion 217 from which vertical posts 219 extend to support top rails 218. A gantry 220 is positioned on top of the caddy and it is powered by a motor 230 to move the gantry along the top rails 218 and motor 234 to raise and lower the apparatus sectors at the end of the gantry onto the flange. The caddy has supports 222 which allow it to be moved up to the location of the flange where the apparatus sectors 224, mounted between the side rails in the caddy, are to be delivered by the gantry to the flange cover sector. The flange cover sectors are rotated around the flange sequentially to receive the appropriate apparatus whether tensioners 226 or stud insertion and removal tools 228. The flange cover sectors are rotated about the flange typically by pin gear means. The pin gear motor is mounted on the caddy, and the pin gear extends therefrom. The pins of the pin gear are received in slots extending peripherally about the flange cover sectors. Movement of the pin gear thereby causes a corresponding movement of the flange cover sectors. By means of remotely controlled actuation, various motors 234, 230, and other motors not shown coact to move the appropriate apparatus sectors from caddy 216 onto the posts 208 of the flange cover sectors to support the appropriate apparatus whether they be stud insertion and removal tools 228 or stud tensioners 226 in the appropriate flange sector. After the appropriate apparatus whether it be stud tensioners or stud insertion and removal tools is positioned it is automatically actuated through the operating cycle by remote control as will be described hereinafter. Several operating cycles are necessary for the tools to operate on all studs on the flange. The apparatus sectors have tools positioned in such a manner as to operate on studs which are not contiguous. Therefore, after the tools on an apparatus sector operate on corresponding studs, the tools are raised by the ball screws or other convenient positioning means and the flange cover rotated an increment to enable the tools to operate on three other studs. The operation cycle is repeated until all of the studs on the flange have been processed by the appropriate tools as required. After the appropriate servicing is conducted to the studs holding the dome of the pressure vessel, the tensioners and the stud insertion and removal tools can be removed and then the caddy can be withdrawn to allow for opening of the dome and servicing of the reactor. The advantage of the system is clear in that it enables the reactor to be opened without any human intervention or with a minimum of human intervention by means of a remote control and operated tensioners and stud insertion and removal tools. Referring to FIGS. 5-15 dealing with the stud tensioner, a stud tensioner generally indicated at 100 has a lower housing 150 that rests on the flange of a pressure vessel over the nut 106 of a stud generally indicated at 105. The tensioner incorporates and operates in many similar ways to the integral tensioner shown in U.S. Pat. No. 4,535,656 which shows an integral stud tensioner, and also U.S. Pat. No. 3,995,828 which shows in detail indicator measuring means for measuring the elongation of studs. Both of these patents are incorporated herein by reference. The tensioner has an upper housing consisting of several units 140, within each unit there being disposed a piston 142. The pistons coact with each other, the lower pushing against the upper, to eventually push against the puller bar nut 118, which is fixed to the puller bar 198. The puller bar 198 is connected to the stud by means of a puller bar socket 144 which is intended to engage the threaded means at the top of the stud and to threadably engage the top of the puller bar. The puller bar socket is brought into engagement with the top of the stud by means of a puller bar socket drive 152 which has a gear formed at the upper portion drive which in turn mates with the pinion gear 156 of the puller drive motor 154 located on the side of the tensioner. Actuation of the motor rotates the puller bar drive motor pinion to rotate the socket drive 152 which will cause the puller bar socket to rotate and threadably engage the top of the stud. Once the puller bar, through its socket, is engaged and the hydraulic pumping system, generally indicated at 102, is actuated to provide hydraulic fluid through the hydraulic controls generally indicated at 104, hydraulic fluid will enter the top cylinder, pushing up top piston 142 and will then pass through the hydraulic connection 162 to pressurize the lower cylinder. As the cylinders move upward against the puller bar nut 118, the force will be exerted through the puller bar coupling to the top of the stud, elongating the stud and allowing the stud nut 106 to be relaxed so that the nut drive motor 148 driving motor pinion gear 158 can contact the nut drive gear 146 which engages the top of the nut drive to rotate the nut and back it off. There are several sensors in the system which coact with the hydraulic pumping system to automatically operate the stud tensioner. There is a nut sensor 110 which will indicate whether the stud nut has been backed off and to what extent. There are puller bar socket sensors 114 and 114A which senses the relative position of the puller bar socket and which can determine how far the puller bar has moved and whether the puller bar is in the proper position for operation. There are also overstroke and return piston sensors 115 and 115A which are positioned above the upper piston to indicate the relative activity of the piston. An elongation measuring system is provided in the apparatus which automatically and accurately measures the elongation of the stud produced by the tensioner. It consists of several coacting parts. First, in the stud itself there is a relaxed rod generally indicated at 176 mounted in a bore 178 running almost the length of the stud. The construction is shown in detail in FIG. 15. The rod is mounted or resting on a plug 180 positioned in the bottom of the stud and extends through a locating annulus 190 to an end 188 an enlarged end bore 196 at the top of the stud 174. Thus, the end 188 of the relaxed rod 176 is held in position ready to contact an indicator rod that will be mounted in the puller bar to be described. Because the rod is relaxed, it will not be stretched in the same manner as will the stud, and will therefore provide an accurate indication of the true stretch of the stud. The true stretch can be obtained by comparing the end position of the end of the stud 174 with the position of the end of the relaxed rod 188. The position of the end of the stud is determined by means of the linear variable differential transmitter generally indicated at 170, which is connected to an indicator rod 194 that in turn is mounted to a datum disk 172 positioned within a centering disk 166 located at the end of the puller bar. The centering disk 166 has a conical section which is intended to be aligned with the enlarged portion for the enlarged bore 196 of the stud. The end of the relaxed rod 188 therefore will be centered to meet the lower end of the indicator rod 194. To ensure that the indicator rod is positioned at the proper location with respect to the end of the relaxed rod 188, the datum disk 172 has a plurality of pins 182 which extend downward through the centering disk 166 and are urged downward by springs 184. They require compression of the springs in order to properly seat the pins on the top of the stud 174. Therefore because of the resilience offered by the springs, it is easy to determine whether there is any relative movement still available to the datum disk so that the position of the datum disk and therefore of the indicating rods can be easily and clearly established with respect to the top of the stud. The indicator rod 194 is free to slide in order to contact the top of the end of the relaxed rod 176 and therefore moves the indicator rod 194 to deflect and produce a change in the linear variable differential transmitter 170. This movement is sensed in coaction with the datum sleeve 192 that extends and is connected to the datum disk 172 and that rides outside of the guide sleeve 186 that extends upward and threadably connected to the linear variable differential transmitter 170. In effect the difference of the change in relative distance between the end of the indicator rod 194 and the guide sleeve 186 is measured by the linear variable differential transmitter. The end of indicator rod 194 forms a plunger 195 which extends upward into a bore 197 in the bottom of the linear variable differential transmitter 170, so that the threaded portion 199 of linear variable differential transmitter 170 which is connected to guide sleeve 192 will be relatively stationary with respect to the plunger 195 which will be moving within bore 197 and therefore will be sensed by the linear variable differential transmitter 170. The linear variable differential transmitter is connected to the hydraulic pumping system by appropriate circuitry and also connected to the hydraulic controls 104 to control the operation of the tensioner. Basically, the order of operation of the tensioner involves lowering the tensioner by means of a motor or any other suitable means by which the tensioner can be lifted with the apparatus sectors until the lower housing is positioned over the stud nut 106. The puller bar socket drive motor is then actuated to rotate the puller bar socket drive and therefore rotate the puller bar socket around the threaded portion at the upper end of the stud. Once firmly threadably engaged, as can be determined by sensor 114A the tension required for driving the puller bar drive motor, hydraulic pressure is applied to the pistons to tension the stud. When the linear variable differential transmitter or elongation measuring system, which can be generally referred to as 170, senses the appropriate degree of extension, sufficient to relax the stud nut 106, the nut drive motor can be actuated to rotate the nut drive gearing. This will back the nut away from the flange of the pressure vessel leaving the nut in a raised position and the stud relaxed. The automatic equipment used to lower the tensioner can then be actuated to lift off the tensioner and to move the tensioner out of position over the end of the stud to then make way for the stud drive tool to back out the stud if needed. Clearly the situation can be reversed if an when it is necessary to tension the stud and tighten the nut. In that case, the nut would first be backed down by the nut drive motor and puller bar and drive motor would be engaged to engage the puller bar to the stud, the pistons would then be actuated to tension the stud and then the nut would be further backed down with the stud in a tensioned condition. Then the puller bar drive motor would be backed off to disengage the puller bar socket from the stud and the tensioner would be removed from the vicinity of the stud. The stud insertion and removal tool shown in FIGS. 16-24 is indicated generally at 30 and comprises a stud insertion and removal tool base plate 32 connected by means of primary or outer tie rods 36 to a primary platform 34. The stud insertion and removal tool is shown and discussed in more detail in previously issued U.S. Pat. No. 4,548,103 issued Oct. 22, 1985 the entire contents of which are incorporated herein by reference. The stud insertion and removal tool assembly fits around a reactor pressure vessel stud 33 having a nut 31 positioned at its base. On the primary platform 34 is mounted a hydraulic pumping system, shown schematically in FIG. 24, for the entire unit 48 which is used for various functions to be herein described. A hydraulic lift cylinder 46 is mounted on the primary platform 34 and is connected to a tertiary or third drive platform 41. A drive actuating cylinder 42 mounted on the secondary drive platform 38 is connected through the third drive platform 41 and is used to actuate part of the stud gripping mechanism generally indicated at 50 which is mounted on one of the outer tie rods 36. The stud gripping mechanism 50 has a gripping motor 44 which is controlled by means of hydraulic controls 45 mounted on the primary platform 34. The secondary drive platform 38 is connected to the third drive platform and stabilizes the third drive platform 41 by a series of inner tie rods 40. It should be noted that the third drive platform 41 is larger than the secondary drive platform 38 so that the secondary drive platform 38 can fit above the third drive platform 41 and within the confines of the outer tie rods 36. The stud gripping mechanism 50 consists of basically a housing, generally indicated at 54, having a lower section 56 and an upper section 58. The gripping motor 44 is mounted on the upper section 58 and has a drive shaft 62 extending down into the lower section 56 to drive a drive gear 64. Drive gear 64 engages driven gear 65 which is part of drive sleeve 60 so as to turn the entire drive sleeve 60. Drive sleeve 60, shown in detail in FIG. 25, is connected to a gripping coupling 70 adapted to fit about and engage the thread of stud 33 at the upper end of the stud. Within the gripping coupling 70 is a gripping ring 66 made of aluminum, copper or other soft metal so that the entire stud gripping mechanism 50 can be lowered down and around the threads at the top of the stud 33 to engage the threads and align the threads of the gripping coupling 70 with the threads of the stud without damaging the threads of the stud. Above the gripping coupling 70 is a drive coupling 80 partially extending down into the stud gripping mechanism 50 and held by drive coupling retaining means 82 in the form of fingers which are connected to the third platform 41 and extend into an annular groove 74 in the outside of the drive coupling 80. The drive coupling 80 has a key 76 which extends outwardly from the outer wall of the drive coupling 80 through a slot 78 in the drive sleeve 60. This allows the drive coupling to be raised or lowered with respect to the drive sleeve 60 upon actuation of the drive actuating cylinder 42. The device operates as shown in FIGS. 19-23. When it is desired to remove or insert a stud, the nut for the stud must be in a backed off position. If the stud is to be removed, the stud insertion and removal tool 30 is placed over the stud by means of a motor, and the stud drive tool is lowered until the base plate 32 is firmly seated on top of the pressure vessel flange and the outer tie rods 36 surround the stud. The hydraulic cylinder 46 for the third drive platform is in a position so that there is no force acting downwardly or upwardly on the stud or the gripping mechanism. The hydraulic lift cylinder can be manipulated to raise and then lower the gripping mechanism until the gripping ring contacts the threads of the stud to properly align the gripping mechanism so that the threads of the gripping coupling 70 can then threadably engage the threads of the stud. The gripping motor 44 is then actuated to rotate the drive sleeve 60 via the drive gear 64 and driven gear 65 formed on the outside of the drive sleeve. The drive sleeve will thereby screw the gripping coupling onto the threads of the stud. The hydraulic cylinder 46 for the drive platform will compensate for the space and automatically move the platform down. Once the gripping coupling 70 has fully engaged the threads at the top of the stud, the stud can be backed off by actuating the drive actuating cylinder 42 to push the third drive platform 41 down towards the top of the stud so that the drive coupling 80 will engage with the driving means in the form of hex engaging means 72 formed at the top of the stud. The drive coupling 80 moves within the stud gripping mechanism because of the slot 78 in the drive sleeve and the key 76, which rides in the slot. Once the drive coupling is engaged with the engaging means, the entire system is locked in place and then once again gripping motor 44 driving external drive gear 64 on the drive sleeve 60 can be used to rotate the entire stud to back the stud off from the pressure vessel. To disengage the stud drive tool, the drive actuating cylinder is actuated to bring the drive coupling out of engagement with the hex engaging on top of the stud. The gripping coupling can then be rotated using the external driven gear on the drive sleeve to unthread the drive tool from the threads of the stud and then the stud driver can be hoisted away. While the drive coupling is rotating to back off the stud, it is supported at top by the coupling retaining fingers 82 which are located in the annular groove 74 and by a thrust bearing 68 positioned in the bottom of the lower section 56 of the housing. It will be understood that various changes in the details, materials, arrangements of parts and operating conditions which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principles and scope of the invention.