Power-driven screwing tool for pressure vessel heads

The heads of a pressure vessel are normally attached to the vessel body by studs and nuts arranged in a bolting circle. Each nut is engaged by a wrench, the handle of which is radially outwardly disposed relative to the bolting circle. The outer ends of all the wrench handles have elongated openings slidably engaged by pivot pins that pivotally connect the handles to the ends of turn-buckles, so that the wrenches may all work concurrently. Preferably, the wrenches are ratchet-type socket wrenches. Hydraulic cylinders are attached to some of the wrench handles and impart a back-and-forth movement to the latter for screwing the nuts at a precisely-measured and uniform torque and all simultaneously. The arrangement can be modified to suit different numbers of studs and/or diameters of the bolting circle.

FIELD OF THE INVENTION 
This invention relates to a screwing tool for pressure vessel head bolting. 
BACKGROUND OF THE INVENTION 
Pressure vessel heads are fastened to the vessel body with an intermediate 
gasket by studs and nuts arranged in a bolting circle. It is essential 
that each nut be screwed with precisely the same torque to ensure a 
perfectly-tight closing of the head. 
In the past, it was very difficult and time-consuming to obtain a 
leak-proof joint, even though a torque-metering wrench was used for 
screwing the nuts, because the latter were screwed one after the other, 
resulting in unequal flattening of the gasket around the head. This 
problem frequently occurs in nuclear pressure vessels, such as heat 
exchangers, wherein the gasket is metallic and must be replaced when 
unevenly flattened. 
OBJECTS OF THE INVENTION 
It is accordingly the main object of the present invention to provide a 
screwing tool of the character described, in which all the nuts of a 
pressure vessel head can be screwed simultaneously. 
It is another object of the invention to provide a tool of the character 
described, in which all the nuts can be screwed with a precisely-matched 
torque. 
Another object of the present invention is to provide a tool of the 
character described, which can be easily modified to suit the number of 
nuts and/or the diameter of the bolting circle. 
SUMMARY OF THE INVENTION 
Each pressure vessel head-fastening nut is engaged by a corresponding 
radially-extending wrench. All the wrenches are pivotally tied together at 
the outer ends of their handles along a tying circle concentric with the 
bolting circle formed by the nuts. Therefore, all the wrenches may rotate 
concurrently about the respective nut axis. Hydraulically-powered means 
cause simultaneous rotation of all the wrenches to screw or unscrew the 
nuts. Preferably, all the wrenches are maintained in a common plane by 
means of a support ring pivotally attached to their handles. Preferably 
also, spring means are assocated with each wrench to bias the latter into 
engagement with the nut. The parts of the whole arrangement are preferably 
detachable, so that the number of wrenches used can be varied together 
with their radial arrangement, so as to suit various numbers of bolts and 
nuts and/or various diameters of the bolting circle. The wrenches used are 
preferably ratchet-type socket wrenches.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1 and 2 show a pressure vessel body 8, to the end of which is secured 
the head 10 by means of studs 12 and nuts 14. The nuts 14 and studs 12 are 
arranged along a bolting circle and are equally spaced apart along said 
circle. 
In accordance with the invention, a plurality of wrenches are provided, 
that is as many wrenches as there are nuts 14 to be screwed or unscrewed. 
The wrenches are all similar and of the same construction. Each wrench may 
be a conventional ratchet-type box socket wrench, as shown at 16 in FIG. 
2, or other conventional ratchet-type wrenches, as shown at 17 and 17' in 
FIGS. 5 and 6. 
Referring to FIG. 2, the socket carried by the collar 18 at inner end of 
the straight handle 19 of the wrench is adapted to non-rotatably fit over 
the nut 14, with the handle 19 extending radially and outwardly of the 
bolting circle. According to the invention, the outer end of each handle 
19 is formed with an enlarged boss 20, having an elongated opening 21 
extending along the axis of the handle. 
A transverse pivot pin 22 extends through opening 21 for each wrench. Each 
pin 22 retains the outer annular ends of the stems of two pairs of 
turn-buckles 23 and 24. The turn-buckles 23 of one pair are arranged 
externally of the turn-buckles 24 of the other pair. Each pair of 
turn-buckles extend between and pivotally interconnects the outer ends of 
the handles 19 of two adjacent socket wrenches 16, 17 or 17'. This is 
clearly shown in FIGS. 1 and 4. Thus, all of the wrenches are pivotally 
and adjustably attached at their outer ends to one another by means of the 
turn-buckles 23 and 24 to form a tying circle. The retaining pins 22 have 
a head 25 and a cotter pin 26 for easy detachment of the turn-buckles from 
the associated wrench handles 19. The turn-buckles serve to adjust the 
distance between the outer ends of the wrenches, so as to avoid any play 
in the circular direction. The pins 22 are free to move radially within 
the elongated openings 21, but are biased towards the radially inner ends 
of said openings 21 by means of a leaf spring 27 forming a yoke, the outer 
ends of which are applied against the ends of the stems of the outer 
turn-buckles 23, with the center of the leaf spring fixed to the boss 20 
by means of a wing bolt 28. The handle 19 of each wrench is provided with 
a rounded stock pin 29 intermediate the ends of the handle and a wrench 
support ring 30 engages the pin 29 of all the wrenches radially outwardly 
of the same. This ring 30 is in the shape of a flat channel and the handle 
of each wrench is retained flat against said channel by means of a U-clamp 
31 having threaded ends on which nuts 32 are screwed. The U-clamps 31 
allow limited pivotal movement of the wrench handles with respect to the 
support ring 30. The support ring 30 maintains the arrangement of all the 
wrenches in a common plane. This plane is normal to the longitudinal axes 
of the studs 12. In order to positively maintain the socket carried by 
collar 18 in engagement with the respective nuts 14, it is preferable to 
provide a tension spring 33, which is hooked to the wrench handle at one 
end and to a bracket 34 at the other end for maintaining the spring under 
tension. In the example shown in FIG. 2, the bracket 34 is in the form of 
a key, which surrounds a nut 35 screwed on stud 12, the latter protruding 
from the flange 36 of the pressure vessel body 8. 
By applying a rotating force on the tying circle which connects the outer 
ends of the wrenches 16 in one or the other direction, simultaneous 
screwing or unscrewing of the nuts 14 is obtained. To achieve this, a 
hydraulically-powered system is used. A rigid frame 40 is secured in 
position, for instance on the floor 37 in the general plane of the 
pressure vessel head 10. The frame 40 is of square shape, and adjacent 
each corner thereof, there is mounted a cylinder-and-piston arrangement 41 
pivoted at 42 to a bracket secured to the inside of frame 40. The piston 
rod 43 of each cylinder arrangement 41 forms at its outer end a pivoted 
yoke 44 consisting of the bored transverse leg 45 of piston rod 43 and of 
two parallel arms 47 pivoted to leg 45 by pin 46 and on the ends of a pin 
22', which is longer than the remaining pins 22 but which otherwise have 
the same function, that is pivotally connect adjacent pairs of 
turn-buckles 23, 23, as shown in FIG. 4. In the example shown, there are 
four hydraulic cylinders 41 connected to the tying circle at spaced-apart 
points thereof and arranged tangentially to that tying circle. The 
cylinders 41 are hydraulically fed and are double-acting, so that the 
tying circle may be rotated clockwise or anti-clockwise. The hydraulic 
lines 48 for cylinders 41 are interconnected in parallel and are connected 
to a three-way valve 49, in turn fed by a manual hydraulic pump 50 
operated by a lever 51. The valve 49 has three positions and is operated 
by a control line 48; the three positions are: neutral, clockwise and 
anti-clockwise. The system may be provided with manometers to indicate the 
fluid pressure and, therefore, this is an indication of the precise torque 
applied by all the wrenches on the individual nuts. Obviously, the pump 
for supplying the hydraulic pressure to the various cylinders 41 could be 
motorized. 
The elongated openings 21 receiving the pivot pins 22, 22' at the tying 
circle allow for the rotation of the individual wrenches each about a 
center, namely: the axis of the nut 14, which is different from the center 
of rotation of the tying circle. By proper adjustment of the individual 
turn-buckles, it will be realized that all the wrenches can be rotated 
through a preceisely-equal angle and all simultaneously. Using the 
integral box-ratchet-type socket wrench 16 of FIG. 2, the device will be 
used with a maximum of efficiency for tightening of the nuts 14, in a few 
strokes. Wrench 16 is preferred, since the axis of handle 19 intersects 
nut 14. Two other ratchet-type socket wrenches can be used, as shown in 
FIGS. 5 and 6. They are less preferred, since their nut-engaging socket 53 
or 55, journalled in the inner end of the handle 19, are offset relative 
to handle 19. 
The pawl-and-ratchet system of wrenches 16, 17 or 17' applies torque to the 
socket in one direction only, thereby allowing free return movement of the 
handle. A two-way ratchet system can also be provided to allow unscrewing 
of the nuts by also exerting a reciprocating action on the tying circle. 
FIG. 7 schematically shows in full line a bolting circle 54 of a given 
diameter and along which all the nuts and studs of the pressure vessel 
head are disposed and showing the cylinder-and-piston arrangement 
connected to the wrenches 16, 17 or 17' at equally-spaced-apart points 
around the bolting circle. FIG. 7 shows that in the case of a bolting 
circle of a larger or smaller diameter, as indicated in dot-and-dash 
lines, it is necessary to outwardly displace the cylinder-and-piston 
arrangement, so that they will remain tangential to the tying circle. 
Also, it is necessary to replace the wrench-support ring 30 by another 
similar one, but of another appropriate diameter. Should the number of 
nuts to be screwed or unscrewed be more or less than that shown, the 
system can be easily modified, so as to decrease or increase the number of 
individual wrenches. 
The assembly of the present invention can also be used for studs arranged 
in a or several straight lines, such as a square, along a curve other than 
a circle.