Riser Technology Protecting People, Structures and Equipment
Collin Gaskill
Product Development Engineer
Trelleborg Offshore

Patrick Waal
Head of Sales
Trelleborg Offshore

The oil and gas industry is renowned for continuously pushing the limits. The exploration of offshore oil and gas continues to move into deeper waters and the demands for drilling operations to perform faster and more effectively to provide higher cost savings and safe well completions, have grown. Added to this challenge is the requirement to extract more oil and gas than ever before, and exploit ever harsher reservoir environments in new locations around the world. With these factors in mind, this article looks at why next-generation corrosion-free, polymer-based solutions can be the vital element to ensure the protection of people, structures and equipment from surface to seafloor.

Although technology has advanced to better address the everchanging needs of the offshore environment, customers still require superior, cost-effective solutions with an increased focus on onboard safety and extended ser vice life; increasing to up to 40 years from 20 years.

For both of these focus areas, choosing the most appropriate material is imperative and not surprisingly, polymer materials are becoming a more popular choice within the offshore industry. Polymer-based materials such as rubber and polyurethane are naturally flexible and very durable. Compared to alternative materials, such as steel, ceramic wool or fiberglass, polymer -based materials can withstand greater temperature extremes, weather conditions, and vessel movements, while offering an exceptionally high durability. It is a diverse group of materials that can perform at every level to damp, seal and protect, and most of all has an extremely long lifespan.

Extending service life though corrosion protection
One of the most effective methods of extending the service life of a riser is to protect it from corrosion, particularly in the highly corrosive splash zone region. The splash zone is the area immediately above and below the water's surface and is a major corrosion concern for offshore installations. As the water level rises and falls the metal surfaces of the riser are alternately wet and dry, which causes the metal to corrode when the saline water is exposed to oxygen.

External surfaces exposed in the splash zone region should be protected with special corrosion protection systems. Rubber-based coating on risers as a form of corrosion protection is an extremely popular solution and is widely recognized in the offshore industry as the most effective method of riser corrosion protection, particularly in the highly corrosive splash zone region.

When selecting a corrosion coating for a riser, manufacturers should ensure that the supplier they select can fully customize the coating material to meet specific project needs. Most rubber-based solutions can incorporate a range of protective qualities such as anti-fouling to inhibit marine growth. Additionally, rubber-based corrosion protection solutions are resistant to abrasion, chemicals, wear, blast, impact, jet fire, ozone, UV and salt water .

An important feature of any riser corrosion coating is the fact that the coating is chemically bonded to the metal surface or substrate permanently and won't crack or disbond. As a material specifically engineered to protect against sea and weather conditions, rubber corrosion coatings will guard against corrosion for the lifetime of the riser.

In addition to the splash zone, rubber-based riser corrosion protection can be applied as a robust rubber lining for any exposed steel components located on a riser.

Safety for Challenging Environments
It is no surprise that onboard safety is a key priority for the offshore riser platforms but this is becoming progressively difficult in increasingly challenging environments as installations move further offshore.

Advanced fire protection systems are critical to ensuring onboard safety, whether it is the platform's surface protection, an onboard deluge system or coating for the pipes and flanges for example. The performance of these systems is essential for the safety of personnel, asset protection and preventing fire escalation.

So, in the offshore oil and gas sector where the risk of uncontrolled, rapid fire spread is greater than most, firestop solutions need to provide full assurance to the onboard team that they will not fail to protect against fire. If damage is caused, costly shutdowns and repairs would be required and in the worst case scenario, the platform may fail altogether.

The harsh offshore weather environment causes metal products and components to be susceptible to rust and corrosion, which is detrimental to the performance and function of the platform. Additionally, ceramic wool and similar materials used for fire protection will become less

effective when wet. These less than optimal solutions simply are not an option when protecting people, structures, and equipment.

Protection from surface to seafloor
The drill riser provides a conduit for the drill string and drilling fluids from the ocean floor to the rig. A drilling riser typically has a large diameter, lowpressure main tube with external auxiliary lines that include high-pressure choke and kill lines for circulating fluid. All of these lines need to be protected during handling, storage, deployment/retrieval and drilling operations.

Some of the most trusted protec tion systems for bare riser joints include polymer-based protection covers. These protection covers are manufactured from polyurethane or polypropylene and are specifically designed to protect the drilling riser from impact damage when running or retrieving through the drill floor and moon pool area or during handling operations in the riser storage bay.

Drilling risers, which can reach lengths of 10,000 feet or more and weigh millions of pounds, must be kept in tension to ensure safe operation of the equipment. In order to reduce the requirement on vessel tensioning systems to a more manageable level, discrete buoyancy units can be fitted along the length of the riser to reduce the weight of riser joints in water. These buoyancy units are made out of a polymer-based foam that not only reduces the weight of the riser string to a manageable amount but also protects the riser and auxiliary lines from impact and abrasion subsea.

Taking the protection to the next level, a newly designed and tested helically grooved buoyancy option is available on the market that not only optimizes uplift, it also effectively eliminates riser motions and higher levels of drag in onerous offshore current environments compared to traditional riser buoyancy. The new multi-functional solution integrates the technology to suppress vortex - induced vibrations (VIV) and reduce drag into riser buoyancy equipment during manufacturing, essentially eliminating the requirement of ancillary suppression equipment, alleviating complicated and time intensive riser running and retrieval procedures.

Similarly, buoyancy technology is used to offset tension loads on deep water umbilicals and risers for floating production systems. Distributed Buoyancy Modules are used reduce the top tension loads by providing uplift to sections of the riser to generate pre-defined configurations that allow the vessel a full range of surface movement without putting undue stress on subsea lines. These configurations include "Lazy Wave", "Steep Wave", "Lazy -S", "Steep-S", and "Pliant Wave".

Evolving riser technology for the future
As more complicated exploration and production activities target more challenging reser voirs an evolution of current riser technology will be required to ensure continued safe and cost-effective operations. Advanced engineering analysis and simulation design tools provide the ability to effectively develop new riser equipment technologies considering the real world environmental and operational challenges they will be required to perform under.

Computational Fluid Dynamics (CFD) analysis studies provide the means for exploring optimized equipment designs with consideration of minimizing hydrodynamic loading. Riser technology can be successfully designed to be multifunc tional, suppressing VIV and reducing drag simultaneously while performing its primary protection and buoyancy roles. Local and global Finite Element Analysis (FEA) allows for equipment to be designed smarter, minimizing required size and material while optimizing loading paths, performance, and design lives. Employing these advanced engineering tools will help advance riser technology moving into the future to expand and extend the capabilities of the industry.

While deep water drilling and production has been revolutionized by increasingly advanced technology in recent years, making high performance and dependable solutions has never been more important. This is because the requirement for equipment to operate safely and effectively while providing peace of mind is be coming more challenging in these demanding and dangerous environments.

By installing effective and reliable polymer corrosion and protection systems, the safety of hydrocarbons transportation installations will be increased. In the harsh offshore oil and gas industry, operators need the assurance of a material that delivers proven performance, without fail. It is the responsibility of the manufacturer to ensure that they can provide high performance and reliable solutions, now more than ever. Similarly, operators should look to work with manufacturers who can provide the most advanced solutions which will guarantee performance and importantly, safety.