The rapid expansion in shale gas production is increasing the scope of produced water management services, including saltwater disposal (SWD). SWD systems can employ a variety of pipe-joining methods, including threaded, welded, flanged, and grooved, in addition to several non-metallic methods. For an independent oil and gas company operating in the Barnett shale play, the selection of grooved products for its saltwater disposal piping and pump assemblies proved reliable and maintenance friendly, two key factors in its SWD facility operations.
The challenge
Threaded piping has been the traditional pipe-joining method for small-diameter pipe in the upstream oil and gas industry, but this joining method is not ideal for SWD assemblies. On average, 50% to 60% of threaded pipe joints leak. These leaks and seepage are common due to varying tolerances between connections. Flanged assemblies also are not ideal because headers are expensive due to the make-on and make-up processes. They also have high maintenance costs.
Welding does not provide ease of access for the continuous maintenance required on SWD systems. In addition, the fabrication of welded fusion-bonded epoxy-coated systems increases installation time. Prior to assembly, the pipe must be fabricated and internal weld joints ground to create a smooth surface. The spools must be shipped out for coating and then joined in the field using flanges. If the system goes down and requires cutting and re-welding, there is no guarantee of a sound system. Welding internally plastic coated (IPC) pipe can harm the coating, affecting its corrosion resistance and potentially leading to a break in the system.
A publicly traded US-based independent oil and gas company with several hundred wells in the Barnett shale weighed all of these considerations when designing its saltwater disposal facilities. The operator moves about 100,000 b/d of produced water, so downtime requiring diversion to a commercial facility would be extremely costly. As a result, the operator sought a highly reliable and maintainable pipe-joining system. The company considered threaded, welded, fused polyethylene, PVC, and fiberglass. Having experienced scaling problems in the past with unlined black iron pipe, the operator decided on grooved IPC pipe for its above-ground applications.
Widely used in upstream production facilities and headers, grooved piping systems have been a mainstay in the oil and gas sector for decades. The joining method employs a coupling to mechanically join grooved-end pipe, fittings, and valves. A grooved joint comprises four elements: grooved pipe (or fitting/valve), a gasket, coupling housings, and nuts and bolts. The pipe groove is made by cold-forming or machining a groove into the end of a pipe. A pressure-responsive elastomer gasket is positioned around two abutted grooved-end components to create the seal. The coupling housings fully enclose the gasket, and the key sections of the housings engage the grooves. The bolts and nuts, which hold the housings together, are tightened with a socket wrench or impact wrench. In the installed state, the coupling housings encase the gasket and engage the groove around the circumference of the pipe to create a rigid leak-tight seal in a self-restrained pipe joint.
Applying the solution
The operator selected the Victaulic Style HP-70ES and Style 107H couplings, which enable quick installation and maintenance, minimize system downtime, eliminate leakage, and protect against problems in lined pipe. The Style HP-70ES withstands pressures up to 2,500 psi and is available in 2-in. to 12-in. sizes. The Style 107H rigid coupling is rated to 750 psi and is available in 2-in. to 8-in. sizes.
The operator’s continuous maintenance program at its SWD facilities calls for preventative maintenance – changing pump seals, inspecting impellers, repairing and replacing valves, and cleaning the system – on a near-daily basis. The grooved systems greatly simplified these tasks. The couplings create a union at every joint, which allows for two-bolt access to the system, easing maintenance and decreasing system downtime.
Accessing the system is as simple as loosening the nuts and bolts of a coupling and removing the housings and gasket. The disassembly of two contiguous couplings enables the removal of a valve, fitting, or section of pipe. Once the maintenance is complete, the couplings can be reused and reassembled on the joints. The speed and simplicity of assembly and disassembly led the operator to specify these products exclusively in high-maintenance areas.
The couplings also were beneficial and proved to be the only joining system that could ensure a downtime-free system in the IPC pipe.
The gaskets of the couplings feature an integral central leg that positions between the pipe ends, creating a continuous lined surface and providing pipe-end protection to prevent breakdowns in the pipe coatings. Heat is not required to assemble or disassemble the joints, so the coating is not affected during installation or maintenance.
With the occasional need to move the pipe around the facility, the operator found that the central leg of the gasket prevents the pipe ends from bumping together and affecting the coating. Another major factor important to the operator was the elimination of leakage. The couplings contain a pressure-responsive gasket that provides a triple-seal effect, creating a leak-tight joint. Gaskets are molded to fit over the pipe ends and seal between the grooves. They are slightly compressed as the coupling housing is tightened, and the internal cavity is energized by internal forces applying pressure downward on the sealing lips. The grooved systems have been used for several years at SWD facilities, and their proven reliability and ease of maintenance in produced water management is important as this need intensifies in accelerating shale development.
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