Inspecting galvanised metal is a crucial stage. Hot-dip galvanising protects steel from corrosion for decades, but only if the zinc coating meets the relevant standards. How can a customer check this parameter themselves, quickly and with professional accuracy?

Let’s look at the physics of the process, the correct equipment and the rules for taking measurements.

What instrument should be used to take the measurement? (And why an automotive one won’t do)

The main mistake many customers make during inspection is using cheap automotive paint thickness gauges (designed to check car paintwork) or devices intended solely for thin-film electroplating.

What’s the problem?

Hot-dip galvanising is not simply a layer of paint on top. When metal is immersed in molten zinc, a complex iron-zinc alloy (a diffusion layer) is formed. Cheap devices and automotive sensors ‘get confused’: they detect the iron within the zinc coating itself and produce critically low or erratic results.

What should you use?

For professional and indisputable acceptance testing of steel structures in Ukraine, the quality standard is expert-level equipment from the market leader in non-destructive testing — NVF ‘Ultrakon’. The optimal choice is the TP-44M magnetic coating thickness gauge.

The most important rule: The TP-44M device must be fitted with an F2-type magnetic sensor. The F2 sensor is specifically designed for testing hot-dip galvanised coatings. The use of automotive ‘beepers’ or unsuitable sensors will result in incorrect readings. The TP-44M must be set to measure in micrometres (mkm).

At the Metal Invest Plant, the minimum average thickness of the hot-dip galvanised coating, in accordance with DSTU EN ISO 1461, is 85 mkm for steel over 6 mm thick, 70mkm for steel between 3 and 6 mm thick, and 55 µm for steel between 1.5 and 3 mm thick. The thicker the metal, the thicker the zinc layer required by the standard.

Hot-dip galvanising protects steel from corrosion for decades, but only if the thickness of the zinc coating complies with the standards. This article sets out the specifications in micrometres, explains what affects the thickness of the zinc coating, and provides a step-by-step guide on how to check the coating when accepting steel structures.

Zinc coating thickness specifications in accordance with DSTU EN ISO 1461

The standard specifies two parameters: local (minimum at any point) and average (based on a series of measurements on the product). The average thickness is used as a guide when accepting a batch.

Product and steel thickness	Minimum mean coating thickness, µm	Minimum local coating thickness, µm
Steel over 6 mm	85 (610 g/m²)	70 (505 g/m²)
Steel from 3 to 6 mm	70 (505 g/m²)	55 (395 g/m²)
Steel from 1.5 to 3 mm	55 (395 g/m²)	45 (325 g/m²)
Steel under 1.5 mm	45 (325 g/m²)	35 (250 g/m²)
Castings 6 mm and above	80 (575 g/m²)	70 (505 g/m²)
Castings under 6 mm	70 (505 g/m²)	60 (430 g/m²)

Table for products not treated by centrifugation (metal structures, supports, masts, sections); for metal fittings and small parts, a different table from the standard (centrifugation) applies.

To avoid confusion: in quick reference guides, the standard is often referred to by a single figure — this is the average coating thickness: 85 mkm for thick metal, 70 mkm for medium-thickness metal, and 55 mkm for thin metal.

What determines the thickness of hot-dip galvanising

Hot-dip galvanising is not simply a coat of paint on top. When the metal is immersed in molten zinc, an iron-zinc alloy (diffusion layer) forms on the metal; therefore, the thickness of the coating depends on:

• the thickness of the steel — the thicker the metal, the thicker the zinc coating. Profiles with thicknesses of 7 and 12 mm fall within the same range (over 6 mm), so the standard for them is the same;
• the chemical composition of the steel — reactive steel with a high silicon content is galvanised extremely quickly, and the zinc layer on it turns out thicker;
• the geometry of the product — proximity to edges, holes and welded joints alters the distribution of the coating.

Why ‘more zinc’ is not always better

Sometimes, a single welded structure combines components made from different grades of steel. If reaction steel is present, keeping the product in the molten zinc for extra time ‘to achieve the required thickness’ on the standard components is impractical and dangerous. On reactive steel, the zinc layer becomes excessive and brittle, creating a risk of reduced adhesion: the coating flakes and peels away from the metal upon even slight mechanical contact. The process engineer always seeks a balance to avoid damaging the product: the standard is the minimum required, not the goal of ‘the thicker, the better’.

How to measure the thickness of a zinc coating: which thickness gauge to choose

The thickness of a hot-dip galvanised coating is checked using a magnetic thickness gauge fitted with a sensor specifically designed for hot-dip galvanised coatings and calibrated in micrometres (mkm). Cheap automotive thickness gauges (for paint on car bodies) and devices designed for thin electroplating are not suitable for this purpose: hot-dip galvanised coatings contain an iron-zinc alloy, so the readings from such devices may be underestimated or unstable.

An example of a device for professional acceptance testing in Ukraine is the TP-44M magnetic coating thickness gauge from the ‘Ultrakon’ Research and Production Enterprise. For hot-dip galvanising, it is fitted with an F2-type magnetic sensor; without this, or with an unsuitable sensor, the readings will be inaccurate.

Cleanliness, contact pressure, edges: 4 rules for accurate measurement

Clean surface. The metal at the measurement point must be dry and free from dirt, grease and white tarnish (the result of natural zinc oxidation).

1. Clean surface. The metal at the measurement point must be dry and free from dirt, oil, grease and white deposits (products of natural zinc oxidation).
2. Perpendicular probe placement. Hold the probe perpendicular to the surface and press it firmly into place in one steady movement, without tilting. Do not slide the probe across the metal: place it, record the reading, then lift it.
3. Keep away from edges and welds. Avoid taking measurements near component edges, holes, corners and weld areas. Keep the probe at least 10–15 mm away from any edge.
4. Account for the geometry. When measuring a round pipe, position the probe so that its axis aligns with the pipe’s radius.

Methodology for the acceptance of galvanised steel structures based on significant surfaces

To ensure the inspection is objective, a representative sample is required:

1.  Distribute measurements evenly. For a long beam, column or support, take several measurements at the beginning, middle and end. If a component has several faces, take more measurements on the larger faces.
2. Follow the steel thickness range. Assess components within the same thickness range together. For example, measurements on 7 mm and 12 mm sections are combined into a single assessment (over 6 mm).
3. Check the average value. Take a series of 5–10 measurements across the significant surfaces of components within the same thickness range, and use the instrument’s automatic averaging function. Coating quality is assessed using the average, rather than a single reading.
4. Treat the structure as a single item. If a welded structure consists of components within the same steel thickness range, assess it as a whole; there is no need to measure every channel, angle or plate individually.

What is not measured: stiffeners, gussets, brackets

Small components — gussets, stiffeners, brackets — cannot be checked with a thickness gauge. Due to their complex geometry, proximity to edges and welded seams, they cause an ‘edge effect’ that distorts the sensor’s magnetic field, and even a precise instrument will display incorrect readings. Coating thickness is assessed only on the main significant surfaces.

The ‘next product’ rule: when a measurement shows a borderline value

If a measurement at a particular point on a single product yields a borderline result, do not rush to reject the batch. Hot-dip galvanising is a complex physico-chemical process, and the procedure requires you to take the next product from the same batch (with components within the same thickness range) and repeat the test. The quality of the batch is assessed based on the overall sample.

Frequently asked questions about the thickness of the zinc coating

What is the minimum thickness of hot-dip galvanising?

For steel over 6 mm thick — 85 µm (average) and 70 µm (local); for 3–6 mm thick — 70 and 55 µm; for 1.5–3 mm thick — 55 and 45 µm.

What is the difference between the average thickness and the local thickness?

The average thickness is the result of a series of measurements taken on the product; the local thickness is the minimum permissible value at a single point.

How many measurements need to be taken?

A series of 5–10 measurements across the significant surfaces of the component within a single thickness range, distributed proportionally across the surface areas of the faces.

Can the zinc thickness be measured on stiffening ribs and near welds?

No: the edge effect distorts the readings. Move at least 10–15 mm away from the edge.

What should be done if a measurement is at the limit of the specification?

Do not reject the batch immediately: take the next product from the same batch and repeat the check

Why can’t you simply add more zinc if the thickness is insufficient?

On reactive steel, additional holding time in the molten bath results in a brittle excess layer and the risk of the coating flaking off.

Hot-dip galvanising of steel structures in Cherkasy with quality control standards

‘Metal Invest’ carries out hot-dip galvanising on its own production line with a 14-metre bath, so we can protect even large steel structures without cutting them. Production capacity is up to 500 tonnes per month, with a full production cycle: from cutting and fabrication to galvanising. We also accept hardware and small metal structures for processing on our new galvanising line. 

Would you like to calculate the cost or clarify the coating thickness requirements for your product? Submit an enquiry at metalinvest.ua

Hot-dip galvanising is the industry standard for metal protection in Cherkasy, ensuring unrivalled durability for structures. In a world where corrosion causes damage to infrastructure every year, this method is becoming a fundamental investment for any responsible business.

Why is choosing hot-dip galvanising an investment in durability?

The main advantage of hot-dip galvanising lies in creating a reliable barrier between the steel and the corrosive environment. The key benefits of this method include:

• High corrosion resistance: The coating withstands decades of use even under the harshest conditions.
• Self-healing effect: When minor scratches appear, the zinc ‘seals’ them through electrochemical processes, preventing damage to the base steel.
• No need for frequent maintenance: Galvanised structures do not require annual painting, which significantly reduces operating costs over the structure’s lifetime.

Main areas of application for galvanised steel structures

Thanks to its reliability, galvanised steel has become indispensable in many B2B sectors. A general table of the types of structures that should be galvanised:

Sector	What We Galvanize	Why It Is Critically Important
Construction and Infrastructure	Bridges, support beams, overpasses	Protection against precipitation and salt
Agri-industrial sector	Grain silos, hangars, irrigation systems, farms	Resistance to corrosive environments (fertilisers, moisture)
Energy and Telecommunications	Power line pylons, mobile phone masts, towers	Work in hard-to-reach places where painting is not possible
Road Infrastructure	Crash barriers, lighting columns, signs, frames	Safety and a long service life free from corrosion

MetalInvest’s expert opinion: the importance of coating quality

Why do professional developers choose hot-dip galvanising? Applications in industrial construction

In modern construction, a structure’s service life is a key indicator of its quality. Using steel structures without proper anti-corrosion protection is a deliberate risk of hidden defects arising. Hot-dip galvanising is now the gold standard, enabling major repairs to be avoided for decades to come.

In the construction industry, we work with a wide range of structures where protection against moisture and external factors is critical:

• Load-bearing building frames: Columns, beams and trusses, which form the ‘skeleton’ of the structure. The zinc coating ensures the structural integrity of the framework, regardless of humidity levels.
• Bridge structures and flyovers: These structures are constantly exposed to precipitation, temperature fluctuations and, frequently, aggressive road de-icing agents (salts).
• Fencing systems and façades: Metal subsystems for curtain walls, fences and balustrades, which must retain their aesthetic appearance without any signs of corrosion.
• Staircases and fire escapes: Elements located outside the main building and most exposed to the external environment.

For a construction company, hot-dip galvanising is not just a technical solution, but also a strategic cost-saving measure:

1. Minimisation of operating costs: Galvanised components do not require periodic repainting. This eliminates maintenance costs for 20–30 years.
2. Speed of installation: Galvanised components arrive at the construction site ready for installation. There is no need to spend time applying anti-corrosion paint on site.
3. Structural integrity: Unlike cold galvanising or painting, the hot-dip galvanising process ensures complete coverage of the structure, including hard-to-reach internal cavities within profiled tubes.

Our technician’s view: “In construction projects, we often see how structures galvanised using the hot-dip method retain their original strength even 40 years after installation. The key requirement is correct structural design, so that the zinc can freely penetrate all the structural openings.”

Hot-dip galvanising in the agricultural sector: how to protect grain silos and hangars from corrosion

For an agribusiness, steel structures form the backbone of its production facilities. However, in today’s farming environment, simply painting metal becomes a never-ending and costly cycle of maintaining facilities in working order. Hot-dip galvanising offers a solution that means you can forget about anti-corrosion treatment for 50 years.

Key structures in the agricultural sector requiring galvanisation

1. . Galvanisation of grain elevator equipment

Silo frames, conveyor supports and load-bearing steel structures are subject to heavy loads. Hot-dip galvanising not only provides protection against rust but also ensures a smooth surface, which is important for removing dust and grain residue.

2. Galvanising of hangar and grain storage facility frames

Large-scale hangar structures require no maintenance whatsoever once hot-dip galvanised. This eliminates the need for work at height to repaint the structures, resulting in significant savings for the company.

3. Galvanising of irrigation (watering) systems

Pipes and fittings for irrigation systems are in constant contact with water. Hot-dip galvanising coats the metal both inside and out, ensuring that no rust forms inside the pipes.

Benefits for agribusiness: Why is it cost-effective?

1. Full payback: The cost of hot-dip galvanising is higher than that of painting only at the installation stage. However, over the following 10 years, the cost of painting exceeds that of galvanising by a factor of 3–5.
2. Product safety: The galvanised coating is environmentally safe and does not release harmful substances when in contact with foodstuffs (grain, seeds), which is important for certification to international standards.
3. High resistance to mechanical damage: Paint is easily scratched during loading, unloading or the installation of equipment. The zinc layer is metallurgically bonded to the steel, so it does not peel off even when subjected to heavy impacts.

Our technician’s view: ‘In the agricultural sector, we often work with non-standard structural components. Hot-dip galvanising has a unique advantage — it ‘coats’ all hard-to-reach areas, welded joints and the internal cavities of profiled pipes. No brush or spray gun can provide such protection at structural joints.” — Alona Tomashchuk

Hot-dip galvanising in the energy and telecommunications sectors:

Energy infrastructure is often located in remote areas, where carrying out regular maintenance work is technically challenging and financially burdensome.

Benefits for the sector:

• Protection in hard-to-reach areas: It is virtually impossible to paint pylons regularly when they are situated in marshy terrain, fields or along power lines. The zinc coating ‘works’ autonomously, requiring no monitoring.
• Resistance to vibrations and loads: Mobile phone masts are subjected to constant wind loads. Hot-dip galvanising does not crack under deformation, unlike paint and varnish materials, which become brittle over time.
• Absence of ‘localised’ corrosion: Rust most often appears at bolted joints in structures. The hot-dip galvanising process ensures that every component, including threaded holes and the edges of the metal, is fully protected.

What types of structures require galvanising in the energy sector

1. Power line pylons: Both the main load-bearing structures and auxiliary components (cross-arms, brackets).
2. Telecommunications towers and masts: From tall structures for base stations to compact antenna masts in urban areas.
3. Gantry structures and substations: Steel structures for outdoor switchgear operating under constant voltage and exposed to the elements.
4. Cable support systems: Galvanised trays and brackets providing protection and cable routing within power distribution centres.

An expert approach: what MetalInvest’s specialists focus on

The design of structures for the energy sector has its own specific characteristics, which we take into account when accepting orders:

«When galvanising telecommunications masts and power line pylons, we always advise clients to avoid creating enclosed air cavities. If there are cavities in the steel structure, we help to correctly position the process openings for zinc ingress and air escape. This guarantees a perfect coating quality both on the outside and inside of the profiled tubes,» notes our technologist – Lyudmila Fait, Head of the Quality Control Department.

How do I order hot-dip galvanising for a metal product?

Are you planning a large-scale project? We’ll provide reliable protection for your metal structures that will stand the test of time and withstand harsh weather conditions.

Find out more about the service and submit a request for hot-dip galvanising.