Piecing Up

Apart from slip lining, the three techniques for rehabilitating large diameter mains with PE100 or PE100-RC liner pipe are die drawing, rolldown, and folding, and in these three cases the liner pipe termination fittings must not be installed until the liner pipe has completed its reversion. Piecing up should not start until no movement has occurred for at least twelve hours.

When full recovery has been achieved, final inspection carried out and the liner has been accepted by the client as being fully compliant, the liner pipe end can be cut to the appropriate length and an expander inserted to expand the liner to accept the fitting insert to enable jointing to a standard electrofusion coupling or mechanical fitting. The photograph below shows a hydraulic expanded in place in preparation for a Transgrip fitting.

 Where electrofusion couplings are to be used for the connection, alignment clamps must be used.

When installing gaskets or sealing rings, the components containing the seats for these gaskets or rings should be supported so that the seats are concentric. This is particularly important on large and therefore heavy fittings, and ensures that gaskets are not trapped and damaged, and that all the bolt tension is available for compressing the gasket or ring, and is not dissipated trying to pull the components into alignment.

A cost effective approach is an overlength make up piece. This will have one welded flange, a loose full end load flange adaptor for the other end, and a coupler with both angular capability and full end load resistance. By cutting the make up piece in a suitable position and using one, or in certain cases two couplers, it should be possible to cater for virtually any piecing up situation, with all necessary materials ready stored on site.

Alternatively an Electrofusion coupling together with a PECat and flange adapter can be used and this will create an end load capable coupling.

Because of the risks associated with fitting failures on large diameter mains, each piecing up operation should be designed and supervised by an engineer. 

 All fittings used should have adequate angular and end load capability, and adequate arrangements must be made for anchorage of the connections in accordance with local/national or Company codes of practice.

Live gas connections

Following successful testing, gas connections will usually be made live to reconnect the liner pipe to the existing gas network. These live gas operations will utilise different equipment dependent on the diameter, operating pressure and material of the pipe. Regulations and codes of practice for such activities will vary according to network owners and National requirements.

Typical Equipment used may be Wask Bagstop, Iris stop, Flow stop, Kleiss stopper systems, etc.