In a recent study of all pipeline failures in a large petroleum producing areal, 55% of these failures were found to be caused by corrosion. Of these, internal corrosion caused 2.7 times the failures that external corrosion caused.
As well, approximately two thirds of all interval corrosion failures occurred in water lines. although they make up only one tenth of the total line length.
In the production of crude oil from the well to the refinery, large volumes of water (either produced water or Source water) must be reinjected into the formation for reservoir maintenance optimization.
As is commonly understood. and certainly verified by the earlier stated statistics, this combination of salt/fresh water causes serious internal corrosion implications on a steel pipeline - water is a fantastic electrolyte!
This paper will deal specifically with the evolution of "liners" to address this problem of internal corrosion of pipe.
In the context of this paper, we shall be dealing with a very simple concept - that being to keep the corrosive fluid away from the metallic pipe with a thick, continuous barrier, and be able to simply and without necessity of rigorous engineering interpretation, be able to periodically or continuously monitor the successful operation of that barrier.
There has been an evaluation of two earlier generations of in-situ liner procedures. The subject of this paper is the third, it is called the 'ITITE LINER'I, and is supplied and installed by United Pipeline Systems Inc.
The first generation of liner is commonly referred to as "slip-lining", in Which a nonmetallic pipe is "slipped" into a metallic pipeline. In this case, the non-metallic pipe is normally very much smaller in diameter than the metallic pipe. to allow easy entry, and this nonmetallic pipe is itself the pressure containing pipe as pressures of 150 psi or less, although certain non-metallics (eg: fibreglass) can be operated higher. The second generation of liners, which have been used, involves the insertion of high density polyethylene pipe into an existing metallic pipeline. the outside diameter of the polyethylene pipe being slightly less than the inside diameter of the metallic pipeline. Usually the initial annular space is 3%-7%, and with increase in pressure, the polyethylene radically expands, and contacts the metallic pipeline. As such, the metallic pipeline acts as the pressure bearing pipe.
As the pressure is decreased, the liner radiallycontracts, although over a period of time, the liner relaxes to an equilibrium diameter somewhere larger than its initial diameter.
In 1985 the third generation was investigated and testing began to develop a method by which a liner was installed tight inside the steel pressure containing pipe.
The TITE LINER being set permanently against the steel pipe wall is an important technical innovation, as there is no radial strain of the liner at any pressure.
The liner material used to date is high density polyethylene. As such, the fluid service into which the liner can be placed is dictated by the chemical resistance of the polyethylene.
