Boosting Pipeline Performance and Savings with Dual-Layer Barrier Systems

Sponsored by Sherwin-Williams

By Dr. Jeffrey D. Rogozinski, Global Product Director – Fusion-Bonded Epoxy/Pipe, Sherwin-Williams Protective & Marine Coatings

Two Layers Are Better Than Three

Oil and gas pipelines take a beating – both before and after they’re installed underground. From transportation and storage to installation and service, pipes face potential scrapes, impacts, flexions and more. These stresses threaten the integrity of the pipes themselves and, especially, the external barrier systems that protect pipes from corrosion.

Such barrier systems feature a base layer of an anti-corrosive fusion-bonded epoxy (FBE) – with some systems using just a single-layer FBE and others adding layers on top to protect that base from damage. The base layer needs to remain as intact as possible throughout a pipe’s life to prevent the pipe from corroding and developing a potentially dangerous leak or exploding. Therefore, pipeline owners and operators frequently specify multi-layer systems, which can protect the base layer from damage and moisture.

Stakeholders have two primary options for that protection. The most widely used systems feature a single FBE coating topped with an intermediate adhesive layer and a polyolefin wrap, but these three-layer barrier systems aren’t compatible with the cathodic protection (CP) systems commonly used as backup pipeline corrosion protection. In addition, they’re particularly labile during field joint coating applications in which complex application processes are prone to errors and moisture trapping, which can accelerate pipe corrosion.

The alternative option is a dual-layer system that offers outstanding damage resistance characteristics with added benefits. These novel dual-layer systems feature enhanced moisture, gouge and impact resistance, while simultaneously having higher dielectric strength. This increases overall pipeline integrity, reduces installation and commission times, and can reduce the long-term costs of CP systems.

Necessary Protection to Boost Pipeline Safety

The base FBE layer – applied in single-, dual- and triple-layer barrier systems – is the steel substrate’s first line of defense against corrosion. However, that defense can be compromised by a single scrape that exposes the substrate. Such areas become an initiation point for corrosion to take hold and proliferate, eventually requiring the pipe to be unearthed for coatings, repairs or even replacement. The base FBE layer may be damaged due to scratches from handling, impacts from backfilling, and scrapes from underground soil movement and pipe expansion and contraction. With damage potential high, adding a damage-resistant barrier to protect the base layer is advisable.

Enhance Durability with Dual-Layer Systems

Newer dual-layer coating systems feature a base anti-corrosive FBE layer topped with an abrasion- and moisture-resistant FBE overcoat.

They’re designed to protect the base layer from scratches caused by horizontal directional drilling and backfilling, as well as mitigate moisture penetration into the coating. Blocking moisture absorption helps to greatly reduce the potential for the coatings to delaminate due to fundamental adhesion loss or cathodic disbondment, a phenomenon that poses a greater concern with three-layer systems, which trap moisture, and a lesser concern with older dual-layer systems that only feature abrasion resistance. Recent enhancements to dual-layer systems include adding robust moisture resistance to the coating, such as with Pipeclad® 2060 MRO Abrasion-Resistant Overcoat (ARO) from Sherwin-Williams Protective & Marine. This reformulation of the company’s time-tested Pipeclad 2040 Flex ARO system marries abrasion and gouge resistance with a moisture barrier that inhibits water from penetrating the base-level anti-corrosion coating. Together, the two layers protect the pipe substrate from being exposed to prevent pipeline corrosion. This combination offers superior performance attributes that should translate into cost savings for a variety of stakeholders. The new dual-layer system has an inherently higher dielectric strength, which results in fewer false-positive holidays (discontinuities in the coating) during testing. This feature is associated with the system’s low-moisture absorption and reduced water vapor transmission rates compared to classical FBE chemistries.

Improved Options for Pipeline Owners

Dual-layer protective coating systems are already approved external barrier system options in specific countries, and they are gaining in popularity due to their ideal combination of benefits derived from single-layer and three-layer systems. Specifically, dual-layer systems prevent corrosion, like single- and three-layer systems; they protect the anti-corrosion layer, as seen in three-layer systems; and they enable pipeline corrosion monitoring in the same way as single-layer systems. With the availability of enhanced dual-layer coating systems that improve upon tried-and-true ARO technology, pipeline owners and operators have a new viable option to protect their critical assets. Adopting the MRO and ARO dual-layer coating system will enhance their potential to lower installation and long-term ownership costs while meeting the needs of a growing and diverse global energy market.

Rigorous Testing Demonstrates Field Performance Capabilities

To confirm the performance of Pipeclad 2060 MRO ARO, Sherwin-Williams Protective & Marine sponsored extensive lab testing that attempted to damage the coating using field-scenario simulations. Findings showed that the coating’s improved impact resistance eliminates the need to wrap pipes with polymeric padding, which can potentially shield cathodic protection (CP) systems before burying them to protect their barrier systems from being chipped or gouged by falling rocks and dirt. They also showed how the coating’s enhanced moisture-resistance properties reduce cathodic disbondment potential to enable longer corrosion protection.

For one test (NACE TM0215-2015), technicians applied an ASTM-specified R33 drill bit to the overcoat to attempt to gouge the coating. Applying 32 kg of pressure barely affected the coating, and 62 kg of pressure illustrated a compression of the coating at the drill bit interface and not a classical “gouge.”

During a subsequent test to evaluate the coating system’s flexibility, testers bent a coated pipe, attempting to wrinkle and compromise the coating. Whereas the pipe itself wrinkled, the coating did not, and no holidays were formed.

The above tests—as well as impact-resistance tests involving dropping rocks and dirt onto coated pipes from several feet above — demonstrate that installers can cover pipes featuring the new barrier system with the same dirt that came out of the hole, provided it conforms to prescribed specifications. No additional crews are required for specialized backfilling or application of polymeric padding, speeding up installation times and, thereby, reducing installation costs.

The tests performed also confirm that the moisture-resistant overcoat (MRO) system not only protects pipes when being handled above ground by cranes or chains, but also shields pipes from any damage caused by the inevitable underground shifting and movement of dirt. In addition, it can keep pipes safe from jarring and gouges that can occur during horizontal directional drilling.

Lab technicians also tested the coating system for its resistance to cathodic disbondment, which can occur when moisture penetrates the interface between the pipe and the coating, making the coating more likely to delaminate and lose adhesion. Minimizing that risk, the new moisture- and abrasion-resistant overcoat system has enhanced substrate-coating interaction, while simultaneously reducing the amount of water that can reach the pipe.

The new MRO system also demonstrated improved cathodic protection performance, as technicians observed no cathodic disbondment after attempting to peel the coating from a prepared sample that was subjected to salt water testing in an oven.

Ultimately, the comprehensive testing showed that applying the moisture- and abrasion-resistant overcoat on top of the base anti-corrosion FBE layer can demonstrably improve the ability of pipes to deliver long-term service with minimum corrosion potential.

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About The Author

Dr. Jeffrey D. Rogozinski, Global Product Director – Fusion-Bonded Epoxy/Pipe. With more than 30 years experience in coatings and academia, Rogozinski is responsible for developing protective coatings, powder coatings, resins and additives for the oil and gas, pipeline, and bridge and highway markets. His coatings science emphasis is on researching and testing polymer synthesis and structure-property characterization. He is a member of several coatings associations and a consultant for global specification writing for CSA Group, the International Organization for Standardization (ISO), ASTM International, NACE International and others. Rogozinski holds a doctorate in applied science for polymer and composite chemistry. Contact: jeffrey.rogozinski@sherwin.com

 

Learn more about Sherwin-Williams Pipeclad® 2060 by clicking here.

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