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11/02/2005
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A laser profiling machine has been developed that uses an optical encoder to accurately measure the profile of the inside of pipes. Dean Palmer reports
Fitting pipes together accurately is key to the construction of oil, gas and water pipes. Poor alignment or poor welds within pipes can result reduced lives for dynamic structures. To combat this, a measurement system has been produced that guarantees better quality production.
The profile measuring system was developed by the Optical Metrology Centre (OMC) based in Hertfordshire using sensor equipment from Micro-Epsilon. The 'OMC Pipe Profiler' was designed, built and tested to determine the dimension of pipe ends, but it can also be used to undertake a wide variety of measurements in similar industries.
OMC's system uses the optical triangulation technique to estimate the distance to the surface of the pipe without touching it. An optical encoder, Micro-Epsilon's optoNCDT 1400 sensor, provides the angle and distance data, which is then used to create a cross-sectional measurement. This combination is optimal for relatively close range measurements that have to be undertaken very quickly. The OMC profiler, for example, can acquire more than 1,000 measurements per second with an accuracy that is better than 0.05 mm.
Micro-Epsilon's non-contact optoelectronic displacement sensor was chosen for its compact size and accuracy, which enabled OMC to easily accommodate the sensor within the pipe profiling machine. Other triangulation lasers require a separate signal conditioner to process the data, whereas Micro-Epsilon's sensor incorporates all signal conditioning and processing inside the sensor head. A digital CCD array is used as the position-sensitive measuring element. Measuring ranges are from 5mm up to 200mm, output is 4-20mA, measuring rate is 1kHz, the resolution is 0.01% FSO and the sensor is rated to IP67. The sensor measures just 65mm by 50mm by 20mm and weighs 100g.
The sensor measures distances without contact against a wide variety of material surfaces, using the triangulation principle. A laser diode projects a visible light spot onto the surface of the target and the spot is imaged on a CCD-array by the receiver lens. In the integral controller the measured values are processed digitally and output as an analogue current signal or with an RS232 interface.
Dr Tim Clarke, director of OMC commented: "Our clients are very demanding in terms of the quality of our product and the information it supplies. Micro-Epsilon has been a good partner in the process of product development for this demanding market."
Analysis software was also key to the profiling system. The software enables the end user to fit pipes together based on the measurement data without actually having to move the pipes. The difference in the shape of any two pipes can be checked in this way allowing a 'go/no go' decision to be made. Often, pipes can be fitted together within tolerance if they are rotated so that bumps and hollows are lined up.
OMC is frequently asked to measure more than just pipe ends. Other application examples include 3-D pipe weld checking; optimal alignment of pipes; ovality measurements for bending trials; external ovality; longitudinal bending; corrosion; and Formula One racing models.
OMC and Technip won the 'Pipeline Industries Guild Offshore Technology' award 2004 for the application of the profiling instrument in pipe bending trials, enabling Technip to accurately understand the effect of ovality changes during the pipe reeling process.
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Author
Tom Shelley
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