How to verify the performance of corrosion monitoring sensors
Ultrasonic NDT inspection for oil and gas assets has been playing catch-up for quite a while until very recently. Evidence of this can be seen in pipes being in awkward positions for an inspector to access easily, or erecting scaffolds to access parts of the asset outside the shutdown-time intervals. Ionix UT monitoring solutions can be an excellent option for any inspector who is looking for reliable results within an extreme environment and can help them transition seamlessly between inspection and monitoring activities, read on to find out why.
Ionix Hybrid Solution
Ionix HotSense™ sensors are part of a hybrid solution that can be perfect for asset inspection as well as monitoring. The value of monitoring solutions is to build trends from a lot of data points collected over time from one location per sensor, so the inspector can see the data and where the wall thickness is heading into the future. It provides statistical confidence in running the asset between inspection intervals but does not replace inspection. At Ionix our sensors can be accessed through the measurement hub with a thickness gauge as if they are an inspection probe while still functioning as monitoring sensors.
The small and compact nature of the sensors means that they can be easily installed in tight spaces. It is also a high temperature performer in its ground roots with our HotSense™ transducers taking measurements from –55 °C up to +550 °C.
Monitoring and Inspection
Monitoring solutions typically use sensors that do not require re-calibration as they sit in one place all the time. These sensors are used for comparative measurements for the purpose to create trends of pipe or vessel wall thickness loss over time as opposed to a single one-off shot required typically in an inspection exercise. So even if there is a small error in thickness then the inspector will end up with a DC shift in the trend line, but the slope of the trend line remains the same which is the key deliverable of any monitoring solution. I.e., precision is more important than accuracy, as long as accuracy is within an acceptable limit.
The variations in thickness measurements are really small and often negligible compared to change in trend slopes, but they are a cause to call for verification from an inspector perspective. Inspectors are also familiar with a requirement to complete offset calibrations as part of their inspection procedures and they want to replicate this with monitoring transducers. The problem is that typical corrosion monitoring sensors are extremely precise. Removing the sensor to check them on a calibrated wall thickness block means that by the time they are put back in the original place they are not actually on the same spot, causing a jump in wall thickness values, rendering the trend line statistically inaccurate. This is why – as an end user – you are asked not to interfere with the location of the monitoring sensors unless it is absolutely necessary. Ionix have a way to verify that the monitoring sensors are working correctly without removing them from their installed place utilising the ultrasonic signals from the internal features of the probes.
How is it Done?
Firstly, the CALIPERAY automated monitoring system is optimized to work in echo-echo Mode-2 with the HotSense™ transducers. This removes the need for offset calibration when making measurements. Velocity compensation is also automatically applied from thermocouple measurements. This means all measurements received to the gateway and onwards to the user are accurate and precise.
Ionix can use the signature signals from internal features in the probes to provide a constant assurance that the sensor is working exactly as expected and allows it to be verified in situ using the signature signal response of the sensor, thereby satisfying both inspectors who have to comply with rigorous instrumentation conditions and corrosion/asset reliability managers who are interested in long term continuous flow of wall thickness data from key TML locations, in between those long intervals of inspection that span typically from turn around to turn around.
If you would like to know more about the benefits of HotSense™, please get in touch today.