Pennsauken, NJ, January 16, 2009 - To ensure the ongoing stability of offshore drilling platforms, the structural integrity of production risers, catenary risers, tendons and platform legs and braces are constantly monitored. Macro Sensors (www.macrosensors.com), specialists in the manufacture of LVDT-based linear position sensors and gaging probes, designed a pressure-balanced, oil-filled and double bellows-sealed LVDT assembly to enhance the reliability of multiple redundant LVDT-based extensometers mounted longitudinally around the circumference of the structural member to monitor structural integrity.
The LVDTs enabled measurement of the extension of the structural members to a fraction of a microstrain. For the huge loads on oil platforms, total movement being measured is typically less than 2mm. Because required measurement must be obtained in seawater depths down to 7500 ft., with external pressure of approximately 3800psi and where service life requirements are a minimum of 20 years, Macro Sensors designed its LVDT assembly from 316 SS and Inconel 625 for pressure and corrosion resistance. These materials enhance the high-reliability required of this instrument so that it will continue to operate for at least 10 years, even if the device is fully exposed to sea water.
Macro Sensors' LVDTs also resolved the problem of getting a useful signal back to the surface, even in great water depths, for monitoring, recording, and controlling thrusters and ballast transfer pumps. The extensometer housing can be outfitted with a variety of mechanical terminations to facilitate connection to the structural members.
To minimize the number of pressure-sealed connections, a 4-20ma loop-powered I/O was utilized, which the customer converted to a RS485 digital signal for transmission to the surface. The two-wire I/O also minimized any noise going to the digital converter that was contained in a high-pressure sealed bottle located nearby.
A major advantage of choosing an LVDT for this task is its extraordinary repeatability, regardless of offsets due to pressure and/or temperature. Offsets can be easily corrected in the data acquisition system on the platform above.
The LVDT extensometers performed favorably compared to results obtained from lower reliability alternative technologies such as resistance strain gages bonded to the same structural members.
For more information on Macro Sensors custom LVDTs, contact the factory at positionsensors@macrosensors.com or refer to the web site at www.macrosensors.com .
About Macro Sensors
Macro Sensors manufactures linear and rotary position sensors for linear position measurement and feedback in a variety of industrial applications including factory automation, motion control systems, metal fabricating, auto assembly as well as power plants, gas/steam turbines. Incorporated in 1994, the Company offers more than 200 years of cumulative design and manufacturing experience by its key staff in serving its OEM and end-user international customer base. On June 1, 2005, Macro Sensors was acquired by AST, manufacturer of state-of-the-art Micro-Electro- Mechanical- Structures (MEMS) based pressure sensors, transducers, and transmitters. Common applications of AST sensor products are in industrial OEM, hydraulic systems, fuel cells, medical gases, HVAC/R, refrigeration, oil & gas exploration/production, and off-road vehicles.
For more information on AST products and technology, visit the AST website at www.astsensors.com.
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