Stainless steel resists, but it is not immune: erosion at elbows, localised attack where the fluid is most aggressive. On small-diameter piping the constraint is the curvature, and it is solved with the right probe.
- ✓ Small-diameter probes for sharply curved tubes
- ✓ Propagation velocity settable for each stainless alloy
- ✓ Scan mode to find the thinnest point quickly
- ✓ Measurement without interrupting the process or opening the line
In process lines the thinning is not spread evenly along the pipe. It concentrates at elbows, where the fluid changes direction and erosion is most intense, downstream of control valves, where turbulence is greater, and in the stretches where liquid stagnates when the plant is idle. That is where the inspection has to be concentrated.
The technical problem on these lines is the diameter. On a small-diameter tube the surface is sharply curved and a standard-diameter probe does not sit evenly: part of the energy does not enter the material and the reading becomes unstable. Small-diameter transducers are needed, sized to the actual radius of the tube.
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A second aspect concerns the material. Stainless alloys do not all have the same propagation velocity, and the coarse-grained structure of some austenitic steels scatters the ultrasonic beam. Calibration has to be carried out on a sample of the same alloy, and the reading validated on the A-Scan when the backwall echo comes back weak.
Where the inspection is concentrated
| Point on the line | Prevailing mechanism |
|---|---|
| Outer radius of elbows and bends | Erosion due to the change of direction of the fluid |
| Stretches downstream of valves | Turbulence and possible cavitation |
| Low points and stagnant stretches | Localised corrosive attack when the plant is idle |
| Diameter reductions | Local increase in the velocity of the fluid |
| Welds and heat-affected zones | Susceptibility to intergranular corrosion |
Probe, calibration and repeatability
The choice of probe starts from the diameter of the tube and its nominal thickness: the smaller and thinner the tube, the more a reduced-diameter transducer and a high frequency are needed. On sanitary and pharmaceutical lines, where the surface finish is excellent, the measurement turns out particularly stable.
Repeatability over time, on the other hand, depends on identifying the points. Physically marking the positions on the line and calling them up in the same order at every campaign is what makes the readings comparable and the thinning rate calculable.
Recommended instruments
| Instrument | Typical use |
|---|---|
| Dakota CMX1-DL | Corrosion measurement with six modes and a 4 GB data logger |
| Dakota CX8-DL | Line inspections with data logger and B-Scan |
| Dakota PMX2-DL | Thin tubes and high-resolution measurements |
| Dual element transducers | Small-diameter probes for sharply curved tubes |
Frequently asked questions
It depends on the probe used: the limit lies not with the instrument but with the transducer, which has to sit properly on the curved surface. Tell us the diameter and nominal thickness and we will propose the right probe.
Yes, bearing in mind that the coarse-grained structure of some alloys scatters the ultrasonic beam and weakens the backwall echo. In these cases the A-Scan is useful to validate the reading.
No. The measurement is taken from outside, and the presence of fluid inside does not prevent the wall thickness from being read.
Back to Chemical, Pharmaceutical and Food, or write to us from the Contacts page: tell us the diameter, alloy and nominal thickness of the lines to be inspected.
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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