Determining the Surface Hardness of Paint Coatings – Pencil Testing vs. Instrumented Indentation Testing
Until recently, quick scratch testing with pencils to determine the hardness of paint coatings has been commonplace. However, the reliability and reproducibility of this method is questionable. Because of the stringent quality standards in the coating industry, it is necessary to be able to test the hardness of paint coatings reliably.
Screws, nuts, washers and bolts can be found everywhere holding our world together, but some of them lead a much harder life than others, especially those used in harsh environments like offshore installations. Because nobody ever wants to dismantle a wind turbine or oil rig just to replace the fasteners, special corrosion-resistant alloys of stainless steel are used for them. This enables the supplier to guarantee a much longer service life, but that, in turn, requires clear and rigorous supervision of the material composition.
Nails and other fasteners are coated to protect them against rust; the thickness of the zinc layer corresponds directly to how long they can resist corrosion. Extended warranties and constantly-changing regulations make it more important than ever for the fastener industry to assess whether the quality of the plating meets relevant standards.
For protection against the elements, exposed steel parts require an anti-corrosion coating such as hot-dip galvanization. To this end, a new directive for CE labelling of steel products and their corrosion protection will become effective in 2014. Product liability will be significantly tightened and manufacturers will be obligated to verify the thickness of the hot-dip galvanization.
Roofs are exposed to very harsh weather conditions over many years. To avoid corrosion and guarantee the longevity of steel sheet roofing, the coating of the steel must be of the highest quality. The coating structure is typically built up of three layers of lacquer over a basic zinc coating.
Paint for architectural coatings is not only used to give surfaces an attractive appearance, but also plays a very important role in protecting facades against external damage and corrosion. To avoid waiting years to see if the coating really protects the surface, simulating and measuring weathering influences is necessary.
To protect them against harsh weather conditions, exposed parts require a paint, lacquer or anodised coating of a certain thickness. Accurately inspecting the coating thickness is a challenge for the practitioner, espe¬cially on curved surfaces, because the geometry of the sample influences the measurement result.
Anticorrosion coatings on the interior of storage tanks are critical when storing many types of products, whether saltwater or freshwater, gasoline, ballast, foamy liquids, or diesel. Typically, regulations are in place to ensure that the right coating is used. Quality inspection of the coating is an essential part of compliance with the regulations.
Aluminum is often used for architecturally pleasing building façades and other structures exposed to weathering influences. Lightweight and fairly easy to work, it is also durable and requires little to no maintenance over the long term when effectively protected by an anodized coating. But to ensure the reliability of the corrosion protection, the sealing of the coating must be verified.
Ensuring the long-term protection of parts exposed to the extremely harsh conditions found in offshore environments requires intact anti-corrosion coatings. Any void, gap or pore in the coating can significantly shorten the lifetime of protected components. To control the quality of these crucial coatings, porosity testing is mandatory.
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.
Known for their resistance to oxidation and corrosion, Inconel alloys are often used in extreme environments subject to high heat and pressure. This is why Inconel coatings are often used in waste heat recovery boilers, which recycle the energy contained in hot exhausts given off by various manufacturing processes. However, to assure the functionality of the coating, a minimum thickness must be guaranteed, and thus, measured precisely.
The related costs of biofouling are so high that even expensive prevention technologies quickly pay for themselves: some sources put the savings in fuel consumption alone at 40%. Properly applied anti-fouling systems can significantly reduce a variety of operating costs, including downtime at dry dock. High-tech inspection instruments equipped to handle the wide variety of materials and thickness ranges typical of anti-fouling paints help ensure that the finished coatings can indeed fulfil their expected service lifetimes.
Micaceous iron oxide (MIO) coatings are called for wherever maximum corrosion protection is essential: Steel bridges, power poles, and even famous structures like the Eiffel Tower or Sydney Harbour Bridge are shielded against the elements with a layer of this specific type of paint. To ensure the coating actually lasts as long as foreseen by the manufacturer, a certain layer thickness must be applied and checked.
Ensuring the long-term protection of parts exposed to the extremely harsh conditions found in offshore environments requires specialised anti-corrosion coatings. For example, thermally sprayed aluminium (TSA) – used to protect stainless steel against corrosion even at high temperatures – can withstand marine influences for decades. However, to achieve such longevity, the TSA must have a certain coating thickness, making quality inspections mandatory.