Corrosion in Real TimeMarch 28, 2007 By: Melanie Martella, Sensors Sensors
Installations such as refineries, chemical plants, and other such beasts are peculiarly blessed with intricate networks of pipes, pressure vessels, or other structures that can suffer from corrosion. Normally, unplanned outages are avoided by dispatching personnel to visit the sites and take readings on the relative health of the parts in question. Alas, taking readings with conventional handheld instrumentation is often both difficult and time consuming, and depending on the equipment used and the person measuring, there can be quite a bit of variation among the measurements recorded.
THE CHALLENGE: Monitor corrosion in pipes
A natural gas plant had a 20 by 12 in. concentric reducer (a fitting that connects piping of different sizes) with a history of flow-enhanced rapid corrosion, as discovered by an annual ultrasonic scan. To understand exactly how quickly the corrosion was progressing during normal operations, the plant installed fiber-optic sensors from FOX-TEK on the outside surface of the reducer.
The sensors track the small deformations caused by the thinning of the pipe wall with up to 15 µm resolution. Data are analyzed using FOX-TEK's data management and analysis tool (DMAT), which automatically downloads data from the monitor. Custom models of the pipes and pressure vessels in the DMAT allow it to convert the raw sensor data to the desired parameters, e.g., wall loss, bending, temperature, and internal pressure.
Over the first 140 days of monitoring, the sensor system showed the actual corrosion rates to be much lower than expected. The sensor readings agreed with those made using ultrasonic testing.
The fiber-optic sensors allowed the plant to install sensors in difficult to access locations and in hazardous environments. The real-time monitoring increased safety and reliability and enabled the remote monitoring of wall loss.
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