Measurement of Thick Coatings on Pipelines
On oil pipelines, propylene coatings serve a multitude of important purposes including corrosion prevention and insulation, but they are expensive. In order to ensure appropriate thickness for guaranteeing performance without wasting valuable material, the application process needs to be controlled carefully.
In the oil and gas industry, it is common to transport the liquid or gaseous goods through undersea pipelines. Insulation is not only necessary to avoid thermal losses, since the oil is mixed with hot steam to improve its fluid properties, but also to protect the pipe from the extreme temperatures (e.g. in the polar regions), high pressure and corrosive waters found at the bottom of the ocean: Any penetration of the coatings can eventually result in leakage and environmental disaster.
Therefore, for both corrosion prevention and insulation, the pipes are typically enclosed in one or more layers (often up to 100 mm thick in total) of polypropylene, a highly resilient thermoplastic polymer that can withstand the harsh deep-sea conditions. To ensure the layers are properly applied – sufficiently thick but without wastage or delamination – rigorous quality inspections must be performed using a highly accurate instrument that can measure coatings of such dimensions.
Figure 1: Coating thickness measurement on a pipeline segment with the FA100 probe connected to a DUALSCOPE® FMP100
Especially for these demanding requirements, FISCHER has developed the FA100 probe, which fully covers the thickness range of up to 100 mm. The FA100 can be connected to the handheld instruments of the FMP family, allowing mobile use wherever needed. The handy FMP gauges are available with either a touchscreen or – even more robust – conventional buttons.
Compared to ultrasonic instruments, the FA100 plus FMP combination provides more accurate results and easily handles multi-layer structures without negative influence, irrespective of coating material type. The results in Table 1 below demonstrate the consistency of 26 readings taken on a segment of insulated pipeline.
Coefficient of Variation
No. of Readings
No. of Blocks
Table 1: Results from pipeline inspection with probe FA100
Measuring the coating thickness is as simple as sliding the FA100 probe lengthways or sideways over the sample surface. In automatic measurement mode, the gauge screen shows a graphic representation of the coating thickness, which helps the user to assess coatings for evenness (concentricity/eccentricity). Final results are written to PDF via the powerful DataCenter software. Measurement area pictures and thickness annotations can be stored in application memories assigned to job sections, shifts or operators.
With the easy-to-operate handheld instruments of the FMP family, used in combination with FISCHER’s special probe for measuring thick layers, the FA100, pipeline coatings can be assessed precisely to ensure their quality and performance. For further information please contact your local FISCHER representative.
Porosity testing of enamel coatings on equipment used in the chemical and pharmaceutical industries
Because it is impervious to high temperatures and chemically reactive substances, vitreous enamel makes an excellent anti-corrosion barrier for the boilers and tanks used in the chemical and pharmaceutical industries. But this protection is only guaranteed if the coating is 100% continuous and has no pores, cracks, or other defects that could allow exchange between the equipment and its contents. This requires a reliable porosity test.
Steel tanks, pipes and mixers are often used in the manufacture of chemical and pharmaceutical products. To protect these parts from corrosion, they are coated with enamel 0.8-2.4 mm thick, depending on the requirements at hand. To ensure 100% protection, the enamel must be checked for gaps: To this end, the ISO 2746 standard test for enamelled articles for service under highly corrosive conditions specifies that the electrode of a high-voltage probe be moved slowly across the surface of the enamel. If the layer’s electrically insulating effect is interrupted (indicating a pore), the voltage drops suddenly. It is this voltage drop that is detected and signalled by the testing instrument.
Fig.1: Porosity test using the POROSCOPE® HV20 on a container in a chemical plant
The new POROSCOPE® HV20 is perfectly suited for the porosity testing of enamel coatings. The robust design of the probe head ensures longevity and meets all safety requirements for working with high voltage. Depending on the topology of the object to be tested, various electrodes are available for use, including flat brushes, sweepers or smaller whisks for testing inside of cavities.
Fig.2: Different electrodes are available for porosity testing
Porosity testing ideally takes place right after the enamelling process. The voltage applied is typically between 12 and 20 kV, depending on the thickness of the enamel layer. Based on the values laid out in the ISO 2746 standard, the correct voltage can be set directly on the probe head. Regular porosity evaluation during the fabrication of such pipes, tanks and mixers is the only way to verify the integrity of the enamel – a critical barrier that not only provides for corrosion protection of these components but also safeguards against contamination of their valuable contents.
The new POROSCOPE® HV20 is ideal for high voltage porosity testing of the vitreous and porcelain enamel coatings often used on equipment and infrastructure for the chemical and pharmaceutical industries. The adjustable range of 4-20 kV ensures that all common thicknesses can be reliably checked for defects such as cracks, pores and other weaknesses. For more information or a demonstration of the POROSCOPE® please contact your local FISCHER representative.