In marine and offshore work every surface is painted and every environment is aggressive. What is needed are instruments that measure the metal while ignoring the coating, stand up to use in the yard and archive thousands of readings for the periodic class surveys.
- ✓ Measurement on painted hull plating without removing the coating
- ✓ Grid files for the mappings required by class surveys
- ✓ B-Scan for the continuous wall profile along a path
- ✓ IP65 protection and extruded aluminium housing on the field models
- ✓ Probes dedicated to curved and corroded surfaces
- ✓ Inspection reports generated with DakMaster™
A hull loses thickness in two ways at once: electrochemical corrosion from the outside and attack by the cargo or the ballast from the inside. Neither is visible until it becomes severe, and the paint that protects the plate is also what prevents you from seeing it. The periodic surveys required by the classification societies are therefore based on extensive thickness measurement campaigns, on grids of points defined in advance and repeated at every survey.
The practical constraint is that those measurements have to be taken over the paint: blasting in order to measure means destroying the protection precisely where it is needed. A thickness gauge with Echo-Echo mode solves the problem at its root, because it measures the distance between two echoes inside the metal and the paint layer stays out of the count. On top of this comes the sheer volume of data: a campaign on a ship produces thousands of readings that must remain associated with the point at which they were taken.
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On offshore structures the structural component is added: welded nodes, jackets, tie rods and bolted joints subject to cyclic loads. Here thickness measurement is joined by weld flaw detection and tightening control. The pages that follow cover the four typical cases of the sector.
The application cases of the sector
| Application case | What is measured |
|---|---|
| Ship hull inspection | Remaining thickness of the hull plating on grids of points, measured over the paint |
| Underwater measurements on submerged structures | Hull bottom and structures below the waterline, with dedicated configurations |
| Offshore platforms and jackets | Tubular members, welded nodes and tightening of critical joints |
| Onboard tanks and bulkheads | Ballast tanks, cargo tanks and structural bulkheads |
Measuring in the yard: what really changes
In dry dock or on scaffolding the conditions are different from those of a laboratory, and the functions that matter are not the same.
- Scan mode: passing the probe over an area, the instrument holds the minimum value. It is the way to find the thinnest point without measuring a thousand of them
- Data logger with batching: the readings stay associated with the point, they do not end up in an undifferentiated list
- IP65 ruggedness: water, salt and knocks are the norm
- Battery life: a working day without changing batteries
Underwater measurement, by contrast, requires a specific configuration: tell us the depth and the operating method and we will check the feasibility case by case.
Dakota NDT instruments for the sector
| Instrument | When it is the right choice |
|---|---|
| Dakota MX2-DL | A-Scan and B-Scan with waveform archiving: extensive campaigns and inspections that have to be documented |
| Dakota MX1-DL | 999 × 52 grid files and over 225,000 readings: mapping an entire hull |
| Dakota CMX2-DL | Six measurement modes and 110 dB of gain: corroded plate and difficult surfaces |
| Dakota ZX6-DL | Echo-Echo ThruPaint and data logger, IP65: the yard instrument for painted surfaces |
| Dakota CX8-DL | B-Scan and a data logger holding 100,000 readings in 1,000 batches |
| Dakota FX70-DL | Inspection of structural welds and nodes, in the field |
Reference standards
- EN 14127 — ultrasonic thickness measurement
- ASTM E797 — thickness measurement by the contact method
- EN 15317 — verification and characterisation of thickness gauges
- EN ISO 17640 — ultrasonic testing of welded joints
- EN ISO 9712 — qualification and certification of NDT personnel
- Rules of the classification societies applicable to the vessel in question
Frequently asked questions
Yes, by using an instrument with Echo-Echo ThruPaint mode. By measuring between two echoes inside the metal, the coating is excluded from the result and there is no need to remove it. In Pulse-Echo mode only, by contrast, the paint would be counted as metal thickness and the reading would come out higher than the real one.
It depends on the model. The CX8-DL archives 100,000 readings in 1,000 batches, while the MX1-DL and MX2-DL have a 4 GB data logger with grid files up to 999 × 52 and over 225,000 readings. For a campaign on a ship it is worth going for the models with grid files, because they maintain the correspondence between reading and grid point.
Measurements on submerged structures require a specific configuration of instrument, probe and cable, which depends on the depth and on the operating method. There is no answer valid in general: contact us describing the job and we will confirm what can be achieved with the available range.
The B-Scan shows the profile of the wall along the path of the probe, instead of a single point value. On irregularly corroded plate it makes it possible to see the pattern of the thinning and to locate the deepest pit, which a point-by-point measurement can easily miss.
For a measurement campaign on a vessel or an offshore structure, write to us stating the type of structure, the presence of a coating and the number of points expected.
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).