Polyurethane flaking or peeling of a polyurethane topcoat is one of the most typical failures in industrial and decorative coatings. Although various reasons can lead to this failure, the most important cause is poor surface preparation prior to application.
Besides there are other main reasons like, due to weather conditions such as high humidity, extreme heat, windy, and dusty conditions. And also, followed by a lack of preparations like not carrying out light abrading, air blowing, and paint agitation issues, such as insufficient and improper mixing at the time of application.
Most importantly, one must strictly follow the paint manufacturer’s product datasheets.
Another important reason to note for this kind of failure is the high DFT application. Moreover, after the very first application, the wet film thickness checks should be carried out, which is highly recommended.
Polyurethane Material: An Overview
Polyurethane (PU) is a general term for a flexible polymer material produced by the reaction of an isocyanate with a polyol (an alcohol with greater than two reactive hydroxyl groups per molecule). It can be processed into various forms, ranging from soft flexible foams to hard solids, so it is used in a broad variety of applications.
Key Properties of Polyurethane
- High durability and abrasion resistance
- Good chemical resistance
- Flexibility and elasticity
- Excellent insulation (thermal and sound)
- Strong adhesion to various substrates
- Moisture resistance
- UV resistance (in aliphatic polyurethanes)
Types of Polyurethane Resins:
- Aromatic Polyurethane Resins
- Aliphatic Polyurethane Resins
Properties:
– Excellent adhesion to a wide range of substrates
– High abrasion and chemical resistance
– Flexible or rigid depending on the formulation
– Fast curing with good mechanical properties
– Applications in paints, coatings, adhesives, sealants, and elastomers
Polyurethane resins are offered in one-component and two-component systems with cure mechanisms that may be moisture-activated or chemically activated.
What is Polyurethane
Polyurethane is a flexible polymer created by reacting an isocyanate with a polyol (an entity containing several alcohol groups). It can be produced in many different forms—rigid, flexible, or even liquid—depending on its formulation.
Polyurethane Uses
The uses are primarily for corrosion protection, abrasion resistance, and chemical resistance in the oil and gas sector. Polyurethane is applied to pipelines, storage tanks, offshore platforms, and drilling equipment to safeguard metal surfaces from aggressive environments.
Polyurethane creates a hard, flexible film that resists water, oil, chemicals, and harsh weather conditions and is thus suitable for both onshore and offshore environments. It also serves to prolong the life of equipment and infrastructure by mitigating rust, impact damage, and wear due to exposure to saltwater, oil, and industrial chemicals.
Such coatings are also commonly applied to pipe linings, valve coatings, and protective coatings on concrete surfaces in processing facilities and refineries.
Polyurethane Coating
Polyurethane coating is a protective coating composed of polyurethane resin. It creates a hard, flexible, and chemical-resistant film when it’s applied over surfaces, which makes it suitable for shielding material subjected to harsh conditions. The coating can be applied over metal, wood, concrete, plastic, and other surfaces.
Polyurethane coating finds extensive applications across various industries like oil and gas, construction, automobiles, and marine. In the oil and gas sector, they shield pipelines, tanks, and machinery from corrosion, abrasion, chemical exposure, and extreme weather.
The coating serves as a shield that resists water, oil, and chemicals, thereby increasing the longevity of infrastructure and lowering maintenance expenses.
There are two broad categories: aliphatic and aromatic polyurethane coatings. Aliphatic forms are more resistant to UV and preferably used in exterior applications, whereas aromatic forms are commonly used in industrial or buried applications because they are very strong and chemical-resistant.
Polyurethane coatings can be spray applied, brushed on, or rolled out and cure to create a tough, protective film that retains its performance even under harsh conditions.
What is Flaking?
Flaking generally occurs due to adhesion failures; in other words, flaking means the lifting of the coating material from the substrate, that is, in the form of scales or flakes.
What is Polyurethane Coating – Industrial?
Polyurethane paint is non-reversible, meaning thermosetting paint. Once fully cured, it will not melt even after being exposed to heat it hence, it will burn but not melt.
The recommended humidity is 40% because Polyurethane is a moisture-curing paint. Polyurethane coatings are durable compared to Epoxy coatings hence are more resistant to abrasion and are less prone to scratches and dents.
The recommended thickness must not be higher than 75 microns, as they are exposed to direct sunlight, hence peeling or flaking is a possibility.
Polyurethane is more of a decorative coating rather than a rust preventive, as it protects from deterioration. Moreover, polyurethanes are versatile enough to be formulated to handle a wide variety of service environments.
Common Causes of Flaking and Peeling
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Improper Surface Preparation
One of the main causes of coating failure is skipping or improperly doing basic prep work. These include:
– Failure to perform light abrading
– Omitting air blowing
– Poor or poor-quality mixing (paint agitation)
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Adverse Weather Conditions
Weather conditions can have a considerable influence on the quality of polyurethane coatings, particularly during application. Challenging conditions are:
– High humidity
– Severe heat
– Dusty or windy conditions
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Not Following Manufacturer Guidelines
It is vital to follow the product datasheet supplied by the paint manufacturer. These include critical details regarding surface preparation, mixing ratios, drying times, and environmental conditions.
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Excessive Film Thickness (High DFT)
Over-applying the Coating may cause early failure. Therefore, wet film thickness should be monitored during application to prevent this.
Conclusion
Although there are many possible reasons for coating failures, most protective coatings work well for their full life when applied properly. Even so, early problems like flaking or peeling can still happen. This is often due to poor surface preparation, unsuitable weather conditions during application, or not following the product’s instructions. In addition, skipping important steps or rushing the job can also lead to trouble. As a result, the coating may not last as long or protect the surface as it should.
This often results from inadequate surface preparation, unsuitable environmental conditions, or failure to follow product specifications. In many cases, these issues could have been avoided with proper attention to detail and adherence to guidelines.
Identifying and mitigating these problems is fundamental to a successful, long-lasting polyurethane coating.
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