On a reactor or an autoclave the wall is consumed from inside, where no one can look during operation. Ultrasonic measurement quantifies the remaining thickness from outside, without opening or purging the circuit.
- ✓ Measurement from outside, with the plant in operation
- ✓ Echo-Echo mode to measure through the coating
- ✓ Grid file for mapping the inspection points
- ✓ History of the readings for calculating the corrosion rate
A pressure vessel loses thickness unevenly. Corrosion concentrates where the fluid stagnates, where turbulence is greater or where the internal lining has failed: the bottom, the areas near the nozzles, the interface line between the liquid and the vapour phase. The average value is of no use; what counts is the thinnest point.
That is why the inspection is organised as a mapping, not as an isolated reading. A grid of uniquely identified points is defined, it is followed again at every inspection and the values are compared with those of the previous campaigns. The difference between two campaigns, divided by the time elapsed, is the corrosion rate on which the calculated remaining life depends.
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Echo-Echo mode makes it possible to take the measurement without removing the surface insulation or the protective paint: the instrument ignores the coating layer and returns the thickness of the metal alone. It is an important operational difference, because it avoids having to restore the protection at every point measured.
Critical points of a pressure vessel
| Area | Reason for the inspection |
|---|---|
| Bottom and lower part of the shell | Stagnation of the fluid and build-up of deposits |
| Liquid/vapour interface line | Corrosive attack typically more severe |
| Around the nozzles | Local turbulence and geometric discontinuity |
| Dished ends and circumferential welds | Variations in thickness and heat-affected zones |
| Areas with internal lining | Local loss of protection not visible from outside |
From the reading to the inspection report
Instruments with a data logger organise the readings into grid files: each cell corresponds to a point of the mapping, and the operator moves through the grid without having to write anything down by hand. It is the quickest way not to lose the match between the figure read and the point where it was read.
Back at base the readings are transferred to DakMaster™, which compares them with the previous campaigns and generates the report to be attached to the vessel’s file. The stored A-Scan waveform remains available for reviewing doubtful readings afterwards.
Recommended instruments
| Instrument | Typical use |
|---|---|
| Dakota CMX10-DL | Top of the corrosion range: six modes, colour A-Scan, 16-point DAC |
| Dakota CMX3-DL | Corrosion with colour A-Scan and 4 GB data logger |
| Dakota MX2-DL | Extended mapping with B-Scan and waveform storage |
| Dual element transducers | Twin-crystal probes for corroded surfaces and high temperature |
Frequently asked questions
No. The measurement is taken from outside, resting the probe on the wall, so it does not require opening or purging the process circuit.
Not with instruments fitted with Echo-Echo mode, which exclude the coating layer and return the thickness of the metal alone. In Pulse-Echo mode the coating would instead be counted.
Yes, within the limits of the probe and couplant used. High-temperature transducers and gels exist: the combination has to be chosen according to the actual temperature of the wall.
Back to Chemical, Pharmaceutical and Food, or write to us from the Contacts page: describe the vessel and its operating conditions and we will point you to the right configuration.
Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
The information contained on this web page is provided for information purposes only. Although it has been compiled with the utmost care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.
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