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Redefining pipeline coating performance

The field of oil pipeline coating has been revolutionised by visco-elastic coatings, which are an easily applied, environmentally sound and highly flexible solution to pipeline corrosion and sealing

Gurinder Singh Sethi, business director of India and sales for South East Asia at SFL, and Stopaq BV's Dr JF Doddema and Dr D.Cudic provide their expert insight into this versatile technology.

Pipelines in the oil and gas industries represent a huge investment and have to operate safely and continuously for their design life. The basic property of strong adhesion is vital when considering external pipeline coatings. For underground applications like oil, gas and water pipelines resistance to cathodic disbondment (where the formation of hydrogen ions leads to the disbondment of protective coatings) is also vitally important.

The majority of conventional coatings are not energy efficient and are cumbersome difficult to apply. The success or performance of a coating is highly dependent on the conditions when applied and the applicator’s skill level.

Coating systems should protect the pipeline from external corrosion and coating degradation can lead to the creation of serious corrosion risks. Increased safety and integrity considerations mean that the demand for reliable, failure proof coating systems is high and increasing.

Comprehensive research and application studies have led to the development of a coating system that can be applied with minimum surface preparation and also has a long life, even under harsh conditions; Visco-elastic (VE) coating is a non-polar, non-crosslinkable, non-curing and fluid-like polymer. It has a glass transition temperature that is lower than -65°C and a very low surface tension, exhibiting visco-elastic behaviour.

VE coating is primarily made from polyisobutylene (PIB) with processing and blending. It is impervious to moisture and gases, meaning corrosion cannot occur beneath the surface. Fully amorphous, it forms no crystalline regions, in contrast to PE or PP or liquid/powder multi-component coatings. Therefore, no physical ageing or stress generation occurs due to post-crystallisation in conventional coatings.
The composition itself does not show coldflow but the coating's composition means that coldflow is under control at temperatures of up to 150°C. On a molecular level the material wets steel and other pipe coatings and, to a certain extent, heals defects and damage.

Furthermore, as the inherent coating remains visco-elastic even below zero Celsius, any breach in the mechanical top layer causes the inner layer to flow out and 'self-heal' the top layer therefore eliminating maintenance concerns. The coating forms a monolithic coating within seconds as it flows into itself, thereby not allowing 'tenting' or spiral corrosion to occur which has been an industry issue for when using traditional wrap, liquid, powder and sleeve coatings.

The benefits VE coating provides end-users include:

• Green technology - no emissions, no pollution, safe to human and environment
• Cold temperature adhesion – self-healing at -45°C
• Energy free and time saving application
• No special application tools required
• Application does not depend on high labour skills
• Unlimited shelf-life of products and no special storage conditions
• No cathodic disbondment phenomenon; self-sealing
• No pre-heating of steel or material is needed, cold application possible
• Minimum surface preparation required - no primer needed
• Underwater application – off-shore sub-sea and splash-zone applications
• Does not require curing time
• No under creep, no risk of osmosis – dependable long life of structure
• Stays flexible forever, does not crack or tear
• Can be applied while pipeline in service
• Meets ISO/Shell and TUV requirements in accordance with ISO 21809 or ISO 12068
• Product performance warranty

The new visco-elastic polymer technology exhibits physical properties that meet the properties of conventional coating systems. On top of that the new coating material has some new additional 'life saving' properties inherent to the coating material like self-healing (or rehabilitation) of small damages due to its viscous nature and no cathodic disbondment.

Pipe coatings are also vulnerable to ageing caused by factors such as fluctuations in operational temperature, mechanical stress and vibration, and exposure to varying ambient conditions. It is known that the adhesion properties of several types of coating deteriorate significantly after hot water immersion testing. After exposure for 100 days, the peel test result was the same as the un-aged sample. Visco-elastic material is therefore an anti-aging corrosion prevention system.

Anti-corrosion coating failures are a significant factor in the reduced operational life of pipelines and can result in leaks requiring repair, clean up and in some cases the replacement of the pipeline. The costs of repair and replacement are significant, as are costs associated with spill containment and clean ups. The cost, environmental impact and negative publicity associated with failures are something every major oil and gas company seeks to avoid.

Traditional coating systems exhibit high failure rates, resulting in either major repair works or the replacement of expensive distribution systems, while the chemical and physical properties of visco-elastic coating material do not cause such degradation problems. The visco-elastic coating technology has been designed and tested to fit the field application and performance requirements of oil, gas and water pipelines.

The total VE coating system (coating material + mechanical protection) can be tailored to meet the specific impact, shear and temperature requirements of the end-user. VE coating technology is now being widely used as a factory applied coating, for pipeline coating rehabilitation and as for field joint projects worldwide and is widely specified by many major oil and gas companies. Visco-elastic coatings are emerging as a versatile and cost-efficient solution to corrosion prevention and sealing.