UV Exposure: Protecting the Self-Regulating Cables from UV radiations
Ever wondered if your heating cables enjoy a nice suntan—or if UV rays are actually plotting to turn them into brittle plastic pieces?
Abstract
This article addresses the impact of UV radiation on self-regulating (SR) heating cables, which are prone to insulation degradation and mechanical failure under prolonged sunlight exposure. It examines how UV affects each cable layer, from the outer jacket to internal conductors, highlighting risks like cracking, moisture ingress, and reduced efficiency. The article presents effective strategies for protection, including UV-resistant materials, protective conduits, coatings, and regular maintenance, ensuring SR cables' long-term durability, reliability, and performance in outdoor applications.
Problem Statement
Self-regulating heating cables (SR cables) are widely used in industrial and residential applications to maintain temperatures in pipes, tanks, and other equipment. While these cables are designed for long-term durability, they are often installed outdoors where they are exposed to ultraviolet (UV) radiation from the sun. UV exposure poses a significant threat to the longevity of these cables by causing degradation of the cable's insulation and outer jacket. Prolonged exposure to UV rays weakens the mechanical strength of the cable, leading to cracking, reduced flexibility, and potential failure. Industries relying on SR cables are facing increased maintenance costs and unexpected system downtime due to the damaging effects of UV radiation.
Purpose
The purpose of this article is to raise awareness about the detrimental effects of UV exposure on self-regulating heating cables and provide effective strategies to mitigate this risk. By understanding the science behind UV damage and implementing practical protective measures, industries can enhance the durability and performance of their Self-Regulating cables, minimizing failures, extending service life.
How UV Exposure Affects Self-Regulating Cable layers
To understand how SR cables are affected by UV exposure, we need to first have an overview of SR cable’s layers and then we will discuss effect of UV on each layer, their consequences.
Introduction to SR cable layers
A typical self-regulating heating cable consists of multiple layers, each serving a specific purpose in ensuring the cable's functionality, durability, and safety:
Outer Jacket: This is the outermost protective layer, typically made from durable polymers like polyvinyl chloride (PVC), thermoplastic elastomers (TPE), or fluoropolymers (FEP or PTFE). It protects the inner components from external environmental factors such as moisture, chemicals, and mechanical damage. However, while these polymers are generally durable, not all of them are inherently resistant to ultraviolet (UV) radiation. Prolonged exposure to UV rays can cause even these tough polymers to degrade over time through processes like photo-oxidation, leading to brittleness, cracking, and reduced performance.
Insulation Layer: Beneath the outer jacket lies the insulation layer, which electrically isolates the conductive elements from the external environment. This layer prevents short circuits and ensures safe and efficient electrical performance.
Self-Regulating Core: The core is the functional heart of the SR cable. It is a semiconductive polymer matrix embedded with conductive carbon particles. The core regulates the heat output by adjusting its electrical resistance based on the temperature. As the temperature rises, the core reduces its heat output, and as the temperature drops, it increases the heat output.
Internal Conductors: These are the electrical wires, usually made from copper or tinned copper, that carry the electrical current through the cable. The conductors are vital for powering the cable and allowing the self-regulating core to function.
Effect of UV on Outer Jacket of SR cable
Photo-Oxidation: UV rays break the chemical bonds in the polymer chains of the outer jacket, causing a phenomenon known as photo-oxidation. This process involves the absorption of UV energy by the material, leading to the formation of free radicals and the subsequent oxidation of the polymer which leads to the deterioration of the polymer chains.
UV radiation + polymer bonds → free radicals
Free radicals + oxygen → oxidation of polymer
The photo-oxidation process is accelerated by the presence of oxygen in the environment, which reacts with the polymer, causing oxidation and further degradation. The rate of degradation can be described using the following formula, which relates the intensity of UV radiation to the degradation of the material:
Where:
D is the degree of degradation,
I is the intensity of UV radiation (in W/m²),
t is the exposure time (in hours), and
k is a material constant that depends on the type of polymer and the conditions of exposure.
Loss of Mechanical Integrity: As the jacket becomes brittle, it loses its tensile strength and flexibility. This makes the cable more vulnerable to mechanical stress, such as vibrations, bending, or abrasion, particularly in outdoor or industrial environments where the cable may be exposed to movement or impact.
Brittleness and Cracking: Over time, photo-oxidation causes the outer jacket to become brittle. This brittleness results in cracks and fissures in the jacket, exposing the underlying layers to environmental stress.
Discoloration: Prolonged UV exposure can also lead to visible changes, such as discoloration or a chalky surface, which are early signs of degradation.
Consequences
Moisture Ingress: Cracks in the outer jacket allow water and other contaminants to enter the cable, leading to corrosion of the internal layers and electrical faults.
Mechanical Weakness: The outer jacket loses its ability to protect the inner components from mechanical stress, increasing the risk of damage from impact, vibration, or abrasion.
Shortened Cable Lifespan: A compromised outer jacket accelerates the overall degradation of the cable, leading to premature failure and the need for early replacement.
Effect of UV on Insulation layer
Secondary UV Damage: Although the insulation layer is not directly exposed to UV radiation, damage to the outer jacket from prolonged UV exposure can indirectly impact the insulation.
Exposure to Moisture and Debris: Once the outer jacket is damaged, moisture and contaminants can penetrate into the insulation layer, reducing its electrical resistance.
Degradation of Insulation Properties: Continuous exposure to moisture and dirt can degrade the insulation, leading to a loss of its dielectric properties, which are essential for preventing electrical failures.
Consequences:
Electrical Short Circuits: If the insulation layer becomes compromised, it may allow electrical current to leak or short-circuit, leading to equipment failure or safety hazards.
Reduced Safety: Degraded insulation increases the risk of electrical shock or fires, making it essential to regularly inspect and maintain this layer.
Effect of UV on Self Regulating Core
The self-regulating core is the most critical component of the SR cable, responsible for adjusting the cable’s heat output in response to temperature changes. Although the core is protected by the outer jacket and insulation, UV-induced damage to these outer layers can indirectly affect the core.
Increased Thermal Stress: Although the self-regulating core is shielded by the outer layers, damage to the insulation and jacket due to UV exposure can lead to thermal instability. Cracks in the jacket may allow heat to escape unevenly, leading to temperature fluctuations in the core. This results in inefficient self-regulation and uneven heat distribution, which can cause hot spots and accelerate the degradation of the core material.
Moisture Ingress and Contamination: Once UV-induced cracks allow moisture and other environmental contaminants to penetrate the cable, the self-regulating core can become electrically compromised. Moisture ingress may alter the electrical properties of the semiconductive polymer, leading to a reduction in its ability to properly regulate heat. Over time, this can cause irreversible damage to the core, leading to failure of the self-regulating functionality.
Consequences:
Degradation of the self-regulating core results in loss of efficiency and uneven heating, defeating the purpose of using SR cables for precise temperature control.
Damaged cores often lead to overheating or underheating of the system, which can cause safety issues or equipment malfunction in critical applications.
Effect of UV on Internal Conductors
The innermost layer of an SR cable consists of the electrical conductors (usually copper or tinned copper), which carry the electrical current that generates heat within the self-regulating core.
Corrosion: When cracks in the outer jacket allow moisture to reach the internal conductors, the copper wires may begin to corrode. Corrosion reduces the efficiency of electrical current transmission, which impairs the cable’s overall performance.
Electrical Resistance: As corrosion builds up, the resistance in the conductors increases, which can lead to power loss and reduced heating efficiency.
Consequences:
Short Circuits and Electrical Failures: Corroded conductors can short-circuit, leading to system-wide electrical failures or even dangerous conditions such as fires.
Decreased Performance: Corrosion reduces the conductivity of the wires, leading to inefficient heat generation and unreliable temperature control.
Summary
Strategies to Mitigate UV Damage
Several preventive strategies can be implemented to protect self-regulating heating cables from the harmful effects of UV exposure:
Use UV-Resistant Materials with UV stabilizers
Despite the outer jacket of self-regulating (SR) cables being made from UV-resistant polymers like PVC, thermoplastic elastomers (TPE), or fluoropolymers, prolonged exposure to intense sunlight can still cause degradation over time. Even UV-resistant materials can experience photo-oxidation, leading to gradual weakening, brittleness, and cracking. However, by using these materials in combination with UV stabilizers—which absorb and dissipate harmful UV radiation—or applying protective coatings like silicone or polyurethane, the damaging effects of UV exposure can be significantly reduced. These enhancements provide an additional layer of protection, extending the lifespan of the SR cable in outdoor environments while maintaining its performance.
UV Coatings
For SR cables installed in highly UV-exposed environments, additional layers of protection can be provided through coatings that act as shields against UV radiation.
Silicone-Based Coatings: Applying silicone-based coatings to the outer jacket creates a flexible, weather-resistant layer that blocks UV rays. Silicone coatings are particularly effective in outdoor environments with extreme temperatures and sunlight.
The primary feature of high-temperature coatings(Silicone based coatings) is their ability to withstand extreme heat without breaking down. These coatings can endure temperatures ranging from 200°C (392°F) to over 1000°C (1832°F), depending on the specific formulation. For example, silicon-based coatings are often used for applications up to 650°C (1202°F). This resistance ensures the structural integrity of the coated surface is maintained, even under intense heat.
Various Silicon coatings, their UV resistance and UV protection mechanism are shown in table below:
Which are preferred?
For self-regulating (SR) heating cables used in outdoor environments, the preferred silicone coating type for UV protection is typically a silicone elastomeric coating or a silicone resin-based coating. Here’s how these specific silicone coatings work effectively for SR cables: Silicone elastomeric coatings are flexible and can withstand continuous exposure to sunlight without breaking down. Their structure absorbs and deflects UV rays, preventing the cable’s outer material from degrading. Resin-based coatings form a durable, cross-linked matrix that provides excellent UV resistance while also withstanding moderate temperature variations. This type is more rigid than elastomers and can be combined with additives for enhanced UV stability, making it suitable for SR cables in consistently sunny and stable temperature environment. Two primary types of Silicone resin coatings are: Methyl Silicone Resin, Organic Resin Modified Silicone Resins. For detailed information refer
Silicone Resins: High-Performance Heat Resistant Coatings
Polyurethane Coatings:
These coatings offer a durable, UV-resistant layer that can be sprayed or painted onto the cable. Polyurethane is highly resistant to both UV radiation and moisture, making it a suitable choice for outdoor cables. Various Polyurethane Coatings and their comparison is mentioned below
Which are preferred and why?
For self-regulating (SR) cables, Aliphatic polyurethane coatings are typically preferred due to their exceptional UV resistance and broad temperature stability. This type of coating resists yellowing and deterioration from prolonged sunlight exposure, ensuring long-term durability, which is critical for outdoor applications.
Additionally, aliphatic polyurethane remains stable up to around 100°C, handling moderate temperature fluctuations without cracking, making it ideal for maintaining the cable's integrity in varying environmental conditions. This combination of UV resilience, temperature range compatibility, and mechanical durability makes aliphatic polyurethane the optimal choice for protecting SR cable outer jackets in demanding outdoor settings.
UV-Resistant Electrical Tapes:
Wrapping UV-resistant electrical tapes around exposed sections of the cable adds an extra layer of protection, especially in areas where sunlight exposure is intense. These tapes can be periodically replaced to maintain UV resistance over time.
Various types of UV-resistant Electrical tapes are:
3M Scotch Super 33+ Vinyl Electrical Tape
UV Resistance: High, with robust resistance to abrasion, moisture, and various chemicals.
Temperature Range: Effective from 0°F to 221°F (-18°C to 105°C).
Application: Primarily used for insulating and protecting electrical wires and cables; suitable for both indoor and outdoor settings due to its durability and flexibility. It is highly conformable: resists UV rays, abrasion, corrosion, Alkalies and acids in all weather applications.
3M Scotch Rubber Mastic Tape 2228
UV Resistance: High, with a thick mastic construction that enhances its durability under UV exposure. Offers resistance to moisture and ultraviolet exposure and is intended for both indoor and weather-exposed outdoor applications.
Temperature Range: Effective up to 194°F (90°C).
Application: Best for sealing and insulating electrical splices and protecting against moisture in outdoor installations. Its thick build makes it ideal for irregular or high-stress cable areas.
Conclusion
In conclusion, mitigating UV damage to self-regulating heating cables is essential to ensure long-term durability and performance in outdoor environments. By utilizing UV-resistant materials, protective coatings, and physical shielding such as conduits, industries can significantly reduce the harmful effects of UV exposure. Regular maintenance and strategic cable placement further extend the lifespan of these cables, minimizing costly repairs and ensuring reliable heating system operation. Implementing these strategies offers enhanced protection and efficiency, safeguarding your investment over time.