The effects of interference radiation on radiometric measurements can be considerable and must therefore be controlled. As it is neither predictable when interference radiation will be present, nor how much the impact of a distant NDT testing on a nucleonic measurement is, customers need a reliable system that is automatically dealing with such events.
Berthold offers sophisticated products that manage interference radiation and provide the customer with a stable and reliable measurement that ensures a continuous process, avoids unscheduled shutdowns and therefore generate a real benefit for the customer. The features XIP (X-Ray Interference Protection) or RID (Radiation Interference Discrimination) are used for this. We help plant operators to get “RID” of problems caused by interference radiation and in doing so, we make sure they are always in control.
NDT, X-Ray and the consequential interference radiation
Interference radiation is a common issue for any radiation-based measurement, as in industrial complexes non-destructive testings (NDT) are performed basically on a daily schedule. These are typically weld or vessel integrity inspections. Usually radiation sources, like Iridium-192, with very strong source activities, will be used. Such interferences could cause a significant increase of count rate and therefore a misinterpretation of the level.
In the following, the handling of interference radiation in relation to radiometric measurements and their further development will be explained in more detail.
A) Informing the control room
In the past, when there were no systems for the detection of interference radiation, it was necessary for the control centre to be informed in good time about upcoming weld inspections. The weld inspection had to be carried out in close coordination with the control centre and the control was carried out manually, blindly so to speak, during this period. This gave rise to the following difficulties:
- It was not always ensured that the control room was informed about weld inspections.
- It was not uncommon for weld inspections to affect measurements that were thought to be out of their reach. The corresponding control centres were therefore not informed.
B) Separate X-ray detector
As weld inspections, particularly in chemical and petrochemical sector, became more and more common, the detection of interference radiation became more and more significant. The increased use of rod detectors, whose gamma-sensitive volume is significantly larger than that of point detectors and is therefore more easily influenced by interference radiation, increased the need for an automatic detection. For this purpose, X-ray detectors were used, which had the task of detecting an increase in radiation in the vicinity of the measurement and, in addition to the actual measurement, were placed in the vicinity of the measuring point. The idea was that the control room would be informed of an increased radiation level and detectors with a possibly outdated and fragile technology would be switched off. As a consequence, switching off the detectors meant that the measurement had to output a residual current. This method involved the following difficulties:
- For the X-Ray detector to measure the same interference radiation as the measurement detector itself
- In the case of an X-Ray alarm, the personnel in the control room must act immediately
- An additional detector ultimately increases the costs for each individual measuring point
C) XIP (X-ray Interference Protection)
Freezing the measured value in these cases would be of great help to the control room, since the level in the vessels only changes very slowly. The XIP function implemented by Berthold freezes the measured value when interference radiation occurs and signals this frozen state. In most cases, it is sufficient to continue with the frozen value and intervention by the control room is more than often not necessary at all.
D) RID (Radiation Interference Discrimination)
The LB 470 RID takes advantage of the fact that the radioactive isotopes used for weld inspection tests, such as iridium, selenium and X-rays, have a different radiation energy than the sources used by Berthold for the measurement itself. Berthold detectors use this energy difference to detect the interference radiation and to suppress it. This means that measurements can continue even under the influence of interference radiation.
Whitepaper “Radiation Interference Discrimination (RID)”
Berthold has published the whitepaper “Radiation Interference Discrimination (RID) – Managing Interference Radiation in Radiometric Level Measurements”, wherein the common sources of interference radiation are identified and effects on the nucleonic measurements are explained. The paper elaborates on how Berthold, with its highly sophisticated radiation interference detection (RID) feature, helps plant operators to maintain a reliable and repeatable measurement.
DuoSeries LB 470 with RID option
DuoSeries LB 470 is the radiometric level measurement from Berthold in true 2-wire technology, which is now also available with radiation interference detection (RID). The level measurement system with RID consists of a Co-60 measuring source and the UniSENS rod detector or the high sensitive SuperSENS detector along with a separate transmitter for display and operation. The detector mounted at the measuring point is connected to the transmitter via a two-wire cable.