The measurement of coatings on steel constructions is a demanding task that often demands immense physical effort from the user. A novel coating thickness gauge can assist in this regard.

Steel constructions such as bridges, pipelines or pylons are important tiers of infrastructure and corrosion is a significant risk and cost factor in these areas. Therefore, general conditions regulate the use of protective corrosion coatings on steel constructions as well as application and monitoring of the coating work. This reduces expenditures for corrosion protection during the life-time of a building and lowers any related risks, especially when dealing with the usual galvanizing of large steel constructions.

Free handling: measuring with the radio-based digital measuring probe QNix 8500 sat

Crucial steel constructions such as bridge railings, for instance, are protected with a Duplex coating system consisting of both, a galvanizing coating and, for example, an epoxy-based coating. Due to a synergetic effect, a Duplex coating allows for higher protection duration than that of the individual zinc layer and coating added together. To make use of this effect, the quality of the coating is just as important to the corrosion protection as is the coating material.

Coaters determine the quality of the coating on site

Two layers with a single measurement: possible thanks to the specific combined Fe and NFe measuring mode provided by the QNix 8500 coating thickness gauge.

Although the new procedures described in the ISO 12944 part 5 and the related ISO 19840 bring about some changes regarding the quality of a coating and may cause some misunderstanding between coaters and testers on site, its the proper adjustment and reliable operation of the devices that determine if the measurements taken are correct. However, to ensure the quality of a Duplex system – that is the thickness of the galvanizing and the epoxy-based coating on steel substrate – preferably both layers are measured.

Standards: Inspecting the coating thickness of steel structures

Since many steel constructions fulfill a vital function, the DIN EN ISO 12944 part 7 “Corrosion protection of steel structures using coating systems“ regulates the execution and inspection of coating work, including, under item 6.3, testing the thickness of dry coating using measuring procedures and methods according to EN ISO 2808. The updated EN ISO 12944:2007 part 5 as of January 2008, however, results in the most significant changes regarding coating thickness measurement of rough surfaces in the CEN (Comité Européen de Normalisation) member states.

Therefore, the magnetic measuring methods implemented by Automation Dr. Nix work in accordance with this standard. The methods are based on the measurement of magnetic flux and as described under item 5.5.6 together with Hall sensors and eddy-current measuring principles.

To achieve this, the state-of-the-art QNix 8500 coating thickness gauge provides a combined Fe and NFe measuring mode allowing for the galvanizing and the upper epoxy-based layer to be measured and saved conveniently in one single measurement. After referencing the gauge on uncoated steel using the NFe measuring mode and on the galvanized steel using the Fe measuring mode, the person testing can quickly check and document the individual coatings of the Duplex system of a piecework coating on site.

In the course of constructing large steel structures often repetitive measurements are required, for instance when the user places the probe incorrectly or with an angle. Such measurements require an unnecessary amount of time and money and must not account for more then 20 % of all measurements taken. A small, wireless, digital, radio-based coating thickness measuring probe is the perfect solution. The 30 grams light probe allows for almost free-handed measurement without any hindering cables ensuring reliable placement even under difficult conditions. The resulting independence directly improves reproducibility of probe placement thus ensuring perfect measuring accuracy.

Furthermore, the digitalization of the analogue measuring signals directly in the probe itself and the reliable wireless transmission of these digital measuring data with additional check sums guarantee the recognition of any interference during data transmission. If necessary the transmission is repeated automatically. Eventually, an audio signal from the gauge and flashing blue light at the probe confirm successful transmission.

The QNix 8500 coating thickness measuring system provides a wide range of analysis features

Individual and flexible: data analysis with a spread sheet program

Especially during the inspection of pylons or other high steel buildings where coating thickness can only be measured while climbing in extreme heights, this measuring probe offers a significant advantage: no cable hinders the user when climbing the mast and the data is stored reliably within the gauge.

For structured data collection, users can create batches with individual names within the gauge’s memory prior to inspection. These batches then can easily be selected during measurement on various control areas. In addition to the statistical processing of measurements using the gauge, the data can be analyzed conveniently using a PC. The flexibility of a spread sheet program allows for general statistical analysis such as quick determination of averaging and standard deviation as well as additional specific parameters for compliance with international standards.

To read the full report, published May and July 2010 in the German “Instandhaltung“ magazine, please visit: http://www.instandhaltung.de/stichwort/korrosionsschutz/