In the Oil & Gas sector, thickness measurement is not there to describe a plant: it is there to decide whether the plant can stay in service. Dakota NDT instruments meet the requirements of API 570 and API 653 inspections, measure through the coating and archive the value for the calculation of the corrosion rate.
- ✓ Measurement through the coating with Echo-Echo ThruPaint™ mode
- ✓ Data logger up to 4 GB for campaigns covering hundreds of points
- ✓ A-Scan to validate the reading instead of trusting it
- ✓ Grid files for CML mapping and trending over time
- ✓ Monitoring of flange bolt tightening with the ultrasonic method
- ✓ NIST-traceable certificates for the defensibility of the data in an audit
In refineries and petrochemical plants the degradation mechanism is almost always the same: the wall thins from the inside, where no one sees it. A pipe that looks sound from the outside may have lost half of its design thickness, and the only possible measurement is the one taken from the outside, without stopping the process and without removing the insulation or the paint.
That is exactly the job of ultrasonic corrosion thickness gauges. The critical point is not obtaining a number — any instrument gives you that — but obtaining a reliable and defensible number: a reading taken on an epoxy coating without the correct mode overestimates the remaining wall thickness and hides the very flaw you were looking for. That is why the choice of instrument in this sector turns on three capabilities: measurement through the coating, A-Scan waveform to validate the echo, and structured archiving of the readings.
Need help choosing the right product?
The second requirement of the sector concerns bolted joints. On pressure flanges, torque tightening carries considerable uncertainty, because much of the applied torque is lost in friction; ultrasonic measurement of bolt elongation, by contrast, measures the actual load. The pages that follow go into the detail of each application case.
The application cases of the sector
| Application case | What is measured |
|---|---|
| Corrosion inspection on pipelines | Remaining wall thickness on pipelines in service, with and without coating |
| Thickness inspection of storage tanks | Shell, bottom and roof according to API 653 criteria |
| Insulated and coated piping | Metal thickness, ignoring paint and protective coating |
| Tightening of pressure flanges | Elongation and actual load of the studs, not the applied torque |
| CML mapping and corrosion trending | Coded measurement points repeated over time to calculate the rate |
Why measurement through the coating is decisive
In Pulse-Echo mode the instrument measures the time of flight of the echo from the first material it meets: if there is a layer of paint or coating over the metal, that layer enters the measurement and the thickness comes out greater than the real one.
- The Echo-Echo ThruPaint™ mode measures the distance between two successive echoes inside the metal, excluding the coating
- The CMX1-DL measures metal and coating separately, at the same time
- The A-Scan makes it possible to verify that the echoes used are the right ones
- On heavily corroded surfaces, adjustable gain is needed to recover a weak echo
That is why, in this sector, a Pulse-Echo-only instrument is not recommended for inspections on painted assets.
Dakota NDT instruments for the sector
| Instrument | When it is the right choice |
|---|---|
| Dakota CMX10-DL | Top of the corrosion range: six modes, colour A-Scan, flaw prove-up with DAC. For those who inspect every day |
| Dakota CMX2-DL | A-Scan and six measurement modes: the benchmark for API 570 and API 653 campaigns |
| Dakota CMX1-DL | Measures metal and coating together, with a 4 GB data logger. The entry point into the professional range |
| Dakota MX1-DL | Extended mappings: 999 × 52 grid files and over 225,000 readings that can be archived |
| Dakota ZX6-DL | Echo-Echo ThruPaint with data logger, when you need to measure over paint without A-Scan |
| Dakota BT1-DL | Checking the tightening of flange studs and bolts, in the field |
Reference standards
- API 570 — inspection, repair and rerating of in-service process piping
- API 653 — inspection, repair and reconstruction of vertical storage tanks
- EN 14127 — ultrasonic thickness measurement
- ASTM E797 — standard practice for thickness measurement by the contact method
- ASME PCC-1 — guidelines for the assembly of bolted flange joints
- EN 15317 — characterisation and verification of thickness measuring equipment
Frequently asked questions
Yes, provided you use an instrument with Echo-Echo mode. In Pulse-Echo the coating enters the measurement and the thickness is overestimated. The Echo-Echo ThruPaint mode measures between two echoes inside the metal and excludes the surface layer; the CMX1-DL also measures metal and coating separately.
The standard does not prescribe a type of display, but the A-Scan changes the quality of the work: it shows the waveform and makes it possible to recognise a reading distorted by a double bounce, by poor coupling or by very irregular corrosion. On assets in service, where a wrong reading has consequences, it is the function that makes the measurement verifiable.
The limit is not the instrument’s but the probe’s and the couplant’s. There are high-temperature transducers and gels that extend use well beyond ambient conditions; the contact must however be brief, and the sound velocity has to be corrected for temperature, because it varies with it.
The instrument archives the readings in grid files associated with the coded measurement points (CML). By repeating the campaign on the same points after an interval and downloading the data into DakMaster, you obtain the thickness variation between two inspections and from it the rate, from which the remaining life is derived according to the criteria of the applicable standard.
To find out which instrument meets the requirements of your inspection procedure, write to us stating the applicable standard, the type of asset and the presence of a coating.
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.
Some images on this website have been intentionally generated using Artificial Intelligence (AI). This is because, for many applications and projects, it is not possible to disclose photographs of the installation or of the actual system due to confidentiality agreements, confidentiality clauses and non-disclosure agreements (NDAs).