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In-situ Repair Method for Concrete Cylinder Pipe

IN-SITU REPAIR METHOD FOR CONCRETE CYLINDER PIPE

HISTORY

The IT3 System has recently been used to repair concrete cylinder pipe that has been used extensively in both industrial and municipal pipeline systems for many years. However, once the calcium hydroxide is leached out of the concrete by the interaction with constituents in the fluid - especially H2S, CO2, chloride and sulfate ions, and bacteria - the steel component sees an accelerated rate of corrosion failure.

Unisert Systems was contacted in 1979 to repair two extensively corroded concrete cylinder systems. The first was an 18" line for Shell in West Texas carrying brackish water, and the second, a 14" line owned by Texaco, Inc. in Aneth, Utah that transports river water. Used in injection systems, both had seen approximately 15 to 20 years' service. The corrosion in both systems had reached a level where catastrophic failures were occurring even at the average operating pressures of 150 and 260 psi with pressure fluctuations ranging from vacuum to 360 and 400 psi respectively.

SOLUTION

Since the original concrete cylinder pipelines were in such an advanced stage of deterioration, they could not be counted on to contribute the total hoop strength to the overall multiwall design. As a result, Unisert's design basis called for the layers of grout and reinforced plastic to contribute the major load carrying capabilities in the steel-cement-FRP multi-layer system.

Concrete cylinder pipe is joined with a bell and spigot connection and these are designed to a maximum degree of mitre. A specially designed pig was sent through the line in both installations to verify that this degree of mitre did not produce a bending radius that would microcrack the FRP during insertion.

Each project involved work in entirely different terrains - from flat, populated areas in Odessa, Texas, to the rocky hills of Utah. In West Texas a major design constraint was the staging areas, used to join the FRP liner on the surface, were in the midst of populated areas involving street crossing, and they provided limited access to the pipeline. Therefore, once joined, the liner segments had to be transported on rollers distances of up to 2 miles and at times when it would not interfere with traffic. For Texaco, the rocky terrain and, again, the distance between the staging areas and the insertion sites were constraints to be considered along with a greater severity of mitre angle.

RESULTS

Both systems were pressure tested successfully after installation and both have not experienced any problems or leaks. Shell's line has been in service for over a year and Texaco's, since late May. In West Texas the end connection utilized was the SF joint (flanged packer) and in Utah the SL joint (inline overwrap sleeve) was incorporated. Both connections were equally effective in accomplishing a seal preventing migration of fluids into the annular space, but the SL joint was found more efficient in terms of saving installation time.

Installation costs for the IT3 System were 70% to 80% of the replacement cost of a new-coated steel system. But most important, these two projects serve to document the use of Unisert's IT3 system as a repair alternative for concrete cylinder pipelines. The IT3 System provides a repair in continuous lengths from the inside rather than the outside of the carrier pipe. And, by its very nature, IT3 design provides: one, reinforcement in which the added layers of FRP/cement bear approximately 65% of the hoop load: two, excellent internal corrosion protection contributed by the plastic liner; and three, the ability as evidenced during fracture testing, to successfully bridge the large holes which can develop in the exterior case without danger of further system failures.

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