The invention relates to a pipe coupling comprising a chain collar or clamp, said coupling being positioned between two parts of a circuit to be connected, such as two pipes or a pipe and a valve.
The invention more particularly relates to a coupling of the type comprising two end fittings which can be fixed to two parts of the circuit to be connected and an open collar constituted by a plurality of articulated elements with which are associated tensioning means, said elements cooperating with the end fittings in order to bring the latter into tightly sealed contact during the utilization of tensioning means.
A known coupling of this type is shown in FIG. 1. It has two conical end fittings 10 fixed to the ends of pipes, for example for welding, and a chain collar 20 constituted by a plurality of elements or links 22 articulated on one another via connecting elements 24. Collar 20 is open and has a screw-nut system 36 and a not shown hook located at its two opposite ends. The collar is closed by engaging the nut of the screw-nut system on the hook. Moreover, each of the links 22 defines two inner and facing frustum-shaped surfaces which engage on outer frustum-shaped surfaces formed on the end fittings in order to bring the latter towards one another when the collar is closed and then tightened by means of the screw-nut system 36. The bringing together of end fittings 10 compresses an annular gasket 19 in such a way that the sealing of the circuit is ensured.
Couplings of this type have numerous advantages compared with other known connection systems. Thus, these couplings are generally much less cumbersome than conventional couplings with bolted flanges for identical pipe diameters. Moreover, the fittings and tightening of the coupling can be carried out much more rapidly and easily than with traditional couplings. In addition, the tightening force can be significantly reduced by carefully choosing the inclination angle of the conical surfaces formed on the end fittings and on the collar links. In addition, when the coupling is used for connecting two apparatuses in a circuit, the distance separating said apparatuses can be very small, because the collar tensioning means are located in the plane of the latter, perpendicular to the pipe axis, whereas the bolts of conventional bolted flange couplings have to be introduced axially. Finally, the collar can be replaced or reused on other identical end fittings and there is no need for there to be any positioning before the welding of the end fittings onto the pipes.
Despite the numerous advantages of couplings with end fittings using so-called chain collars, this type of coupling is not used when fitting and removal have to be carried out remotely, for example by means of a manipulator. This is particularly the case when the two parts of the circuit to be connected are positioned behind a tightly sealed wall only permitting a limited radial access.
The failure to use such couplings under these special conditions is due to the fact that the fitting of the collar onto the end fittings necessitates at least two operations. These operations consist on the one hand of holding one of the ends of the collar and on the other of winding the collar around the end fittings so as to bring the two collar ends into the vicinity of one another in order to permit the closing and tightening of the collar by tensioning means. This problem is increased when the cross-section of the pipes to be connected increases. Thus, due to the clearances necessarily existing at the articulations between the different links of the collar, the fitting of the latter can be difficult when the collar is of a considerable length and in fact certain of the collar elements can be positioned obliquely on the end fittings.