Technology
CUI Spotter can monitor and detect corrosion under insulation.
The internal core wire corrodes faster than the pipeline because of its galvanic coupling with a more noble component.
Wherever water is present under the insulation, the internal core wire will corrode reaching a local interruption in a few months.
If you test CUI Spotter periodically with a Time Domain Reflectometry (TDR on Wikipedia) instrument, you can pinpoint interruptions and locate corrosion under insulation. After that, you can repair the sensor with a normal BNC connector. However, the local repair will not affect further measurements.
1. Monitor and detect corrosion under insulation with a coaxial cable
Looking at the sensor cross-section, there are four components:
- an outer braided electric insulator permeable to water
- an internal stainless steel braided sleeve permeable to water
- an inner braided electric insulator permeable to water
- an inner carbon steel metal wire
Carbon steel wire
Permeable braided insulation sleeve (outer and inner)
Braided stainless steel shielding
2. Galvanic corrosion helps us
When water enters the insulation, it wets a portion of the sensor. Here the stainless steel shielding and the carbon steel core wire will be in contact with the same electrolyte (water). After that, at one end of the cable, a short circuit (yellow line) will induce galvanic corrosion, accelerating the carbon steel core wire corrosion rate approximately three times compared to the carbon stile pipeline corrosion rate.
However, the effect will only increase the corrosion rate where water is present. In other words, the rest of the cable, which is dry will not corrode.
3. Time domain reflectometry is the key
Time domain reflectometry (TDR) is a well-established technology used to locate cable faults as interruptions, short circuits, etc. When connecting a TDR at the end of a coaxial cable voltage pulse travels in the cable with a known velocity.
When the pulse reaches an interruption in the cable, the change in impedance reflects the part of the signal back to the instrument. Subsequently, by measuring the time lapse between the two events, it is possible to calculate the interruption distance from the instrument:
- Pulse signal (voltage) sent through a conductor
- Pulse travel at a known velocity in the conductor
- Conductor interruptions reflect most of the pulse back
- Interruption position can be located at the exact distance from the measuring point (one of the cable ends)
In conclusion, using a TDR together with CUI Spotter, you can easily monitor and detect corrosion under insulation.
4. Monitor corrosion under insulation and detect problems far before leakages occur
Lab tests showed that with a 300 meters cable, the corrosion rate of the internal core wire will still be accelerated by factor three. This means that if the pipeline is corroding at 0.5 mm/year, CUI spotter internal wire will corrode at 1.5 mm/year.
When manufacturing the cable with a 0.7 mm internal core wire, the sensor response will be approximately 6 months.
Depending on the equipment corrosion allowance and coating expected performance, CUI Spotter can be tested every few years, thus allowing the detection of corrosion under insulation before leakage occurs.
