September 9, 2011
Hydrostatic testing of oil country tubular goods is done twice—once to test the weld seam, then again after the item is threaded and a coupling attached. Most hydrostatic testing systems test the entire length of the pipe both times, but a new unit, the box-end hydrostatic tester, tests just the threaded portion and the coupling, reducing the time and water needed for the second test.
Environmental concerns place stringent requirements on any piece of pipe manufactured to carry petroleum products, whether underground or underwater. In a nutshell, it simply can’t be allowed to leak. To ensure the integrity of oil country tubular goods (OCTG), manufacturers must vet each piece of pipe using a hydrostatic tester, or hydrotester. The test is straightforward: The pipe is capped at both ends and filled with water, then the water is pressurized to see if the pipe leaks.
Typically, after a length of pipe has passed that test, it moves on to the finishing floor, where it is threaded and a coupling is attached. Some manufacturers need to test the pipe again at that point, either to comply with local regulations or to meet their own standards. This ordinarily has been done by placing the entire pipe into the hydrotester a second time.
However, a quicker and more effective test pressurizes only what has been added to the pipe: the threads and the coupling. This is where the box-end hydrostatic pipe tester comes in.
The unit seals the coupling’s ID and OD to prevent leakage. The coupling is filled with water, which then is0 pressurized up to 20,000 pounds per square inch (PSI). Computerized sensors and high-resolution cameras are used to detect weak spots.
Testing just the threads and couplings is faster than testing a full length of pipe, and it uses far less water. Depending on the pipe’s length and diameter, a full-pipe hydrostatic test can use more than 400 gallons of water. Testing just the threads and coupler requires only one gallon.
In the box-end method, the pipe first is placed against an adjustable stop. Rotary arms pick up the pipe and place it onto V-rolls at the preset centerline height. They convey the pipe to the pinch clamp, which contains linear bearings, driven V-rolls, an encoder, and a timing device that self-centers and drives the pipe into the hydrostatic tooling.
The lower pipe saddles rise to secure the bottom of the pipe within the hydrotesting station. At the same time, an upper clamp secures the end of the coupling to prevent the pipe from moving during the test.
The test head engages the pipe, and a urethane seal in the interior of the pipe expands while a seal on the coupling’s OD collapses. This cavity is filled with water while the purge valve is open, allowing trapped air to escape. After the cavity is filled with water, the water-over-oil hydraulic pressure intensifier is activated, bringing the internal pressure up to a test set point. Leaks are monitored visually with high-resolution industrial cameras pointing at the bottom segment of the coupling-to-pipe joint and electronically with the PLC monitoring both the test pressure and the intensifier position.
The unit can operate in fully automatic, semiautomatic, and manual modes. All adjustments, from test pressure to fill pressure to test time, can be controlled at the touch of a button from the operator’s station, where alarm diagnostics and maintenance screens also provide for fast and accurate troubleshooting.
The unit can be integrated into a computer network, making test data from each pipe available to other areas of the finishing floor, including the drifting station, marking system, and bundler. Typical data collected includes pipe grade, OD and length, lot number, test pressure, test times, and test results.
The tester is designed to handle a variety of testing scenarios:
Manufacturers dealing with high pressures must make safety a prime concern. To that end, the unit has several safety features and devices. The test station is surrounded by a steel wall with blastproof windows, and access to it is controlled by a safety lock that must be opened with a key before anyone can enter.
The operator control panel is equipped with emergency stops. In addition, pressure transducers located at strategic locations determine faults or problems in the sequence. Information flows from the transducers to the PLC, which is programmed to prevent the test from proceeding if it detects a fault. In addition to enhancing operator safety, this prevents pipe damage.
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