Methods of sealing annular space between inner and outer gas mains for tie-overs

Abstract

A method of tying over an individual customer service connection from a live outer gas main to an inner gas main inserted therein. The inner main is centered within the outer main and an annular region is defined upstream from the customer service connection which is to be tied over. An opening is formed in the side wall of the live outer main intermediate the ends of the annular region and a quantity of a high-density froth foam such as, for example, urethane foam, sufficient to fill the annular region is injected into it. The foam is allowed to harden to prevent gas from flowing downstream below the annular region to the service connection to be tied over. The outer main may then be cut away downstream from the annular region and the new customer service connection made through the side wall of the inner main exposed by cutting away the outer main. In the first embodiment of the method, a special centering tool contains a valve. This centering tool is used at the downstream end of the annular region and customer service connections below this downstream end are closed. At the beginning of the foam-injection step, the valve in the special centering tool is opened. As the foam fills the annular region, a static pressure chamber is formed downstream from the special centering tool. Filling of the annular region is indicated when foam flows outwardly through the valve in the centering tool. In a second embodiment of the method, the annular region is defined between a pair of line restrictors at the upstream and downstream ends of the annular region. Gas flow downstream past the line restrictors carries foam to the downstream end of the annular region, insuring that the annular region will be filled with foam.

Dependencies are inferred from the claim text.