How to Use Corrosion Mapping

corrosion on a material

Corrosion mapping is a quantitative way to inspect a material that has been reduced in thickness by oxidation or erosion. Since an ultrasonic path is directly reduced on a corroded part, a conventional UT beam can report one specific thickness at a time, while a phased array scan can produce an array of thicknesses.

For 3D scanners, since access to the internal surface is typically limited, combining a 3D scan (when available) with UT data creates a very powerful solution. Today, on-board instrument software provides all the necessary tools to produce effective corrosion mapping results with different levels of accuracy (resolution) depending on the technology used.

Corrosion Mapping


ExScan1000 is a simple, reliable, and user-friendly technology for easy tasks not requiring structural data storage or corrosion mapping. The operation of this device is simplified to the maximum. Simply connect the transducer to calibrate the device on the built-in calibration block and you can start measuring.

The instrument also supports one-point and two-point calibrations. When taking measurements, a gauge accuracy indicator is also displayed on the screen – the fuller it is, the more accurate the measurements. A standard gauge mode is used to identify general thinning caused by corrosion or erosion damage.

Automated Corrosion Mapping

Automated corrosion mapping systems can inspect 20 to 30 square meters per standard work day. The advantage of using automated imaging systems is that an image can quickly identify any significant reduction in wall thickness. These automated corrosion mapping scans can then be overlaid in equipment development drawings and accurately indicate the location of areas that have problems.

The images on this page show significant problems detected during field inspections. Automated corrosion mapping or ultrasonic material scans use a range of colors to represent the thickness range of the part being inspected. Typically, blue colors are used to represent nominal wall thickness while orange and red colors are used to indicate significant wall reduction.

Sonocon B and Sonocon BL

There is also a wide range of tasks, where it is necessary not only to measure the remaining thickness and to search for corrosion damage, but also to analyze the whole table of measurements, their statistical analysis, the database of measurements, and the formation of test reports. To complete these tasks, the Sonocon family of devices can be used: Sonocon B and Sonocon BL.

These devices have the same set of functions, differing only in their form factor. Sonocon B can be easily held in your hand and weighs only 2 lbs, although it is equipped with 800×480 pixels and 4.5 in screen. Sonocon BL has a 7.5-inch diagonal screen with the same resolution, a polyurethane-reinforced bumper housing and an extended keyboard.

Corrosion mapping by GPR

Ground Penetrating Radar (GPR) is a non-destructive technique that emits electromagnetic waves into the material, with the main objective of locating objects buried below the surface. Nowadays, its field of application is extended to a wide range of materials, including concrete. The emitted electromagnetic wave propagates through the host material, as it encounters an interface between different materials, after which it is reflected. The main types of GPR antennas used for civil engineering studies are air-coupled and ground-penetrating.

Previously, there was no decent method to undertake corrosion inspection and mapping in a concrete structure. Regular methods of corrosion mapping involved half-cell mapping or chain drag mapping, both of which require removal of the top of the slab and more intrusive work. GPR allows us to map corrosion activity quickly and accurately, and is completely non-intrusive.

We can scan structures through existing surface finishes and even be undertaken at traffic speeds. In the past, the use of GPR to analyze the presence of corrosion was inaccurate and used automatic data analysis. This automatic analysis did not take into account the complexities of the structure, often resulting in poor or erroneous results. GPR supports data analysis using the latest methods and visual analysis by trained personnel to evaluate the data to provide accurate results.

Inspection challenges

When it comes to thickness gauging, dual element probes with a roof angle have always been preferred when looking for corrosion. The same is true for progressive inspection of networks. The absence of interface echo will improve near-surface resolution, and beam convolution will improve sensitivity and signal to noise.

The wider availability of two axis scanners versus one axis has led to increased confidence in surface coverage. However, the associated restrictions of these two-axis scanners in terms of accessibility as well as their tedious deployment and lack of agility open up opportunities for improvement.

Benefits of corrosion mapping

    • Inspect a variety of assets and materials
    • Fast scan speed of up to 80 mm/second
    • High resolution image – 0.8 mm 50 mm sensor resolution
    • Scan width with 64 element array
    • Quickly adjust inspection angle on the fly for different diameter scans
    • Portable handheld equipment
    • Quickly inspect large areas
    • Limited coupling required (light water spray)
    • Maximum inspection depth of 80 mm in carbon steel
    • Reproducible inspection