A flexible solution for corrosion mitigation

It is not uncommon for the outer sheath of flexible risers and umbilicals to be damaged during installation or to become ruptured by annulus vent blockages. According to Oil & Gas UK, the annulus integrity of flexibles represents 35% of all flexible pipe-related issues worldwide. If the problem is left unaddressed, it can lead to rapid corrosion of tensile armor layers and premature pipe failure.

The enclosed area inside an I-tube is particularly problematic because there is restricted access for inspection, and damage often occurs around the splash zone level where oxygenated seawater can cause aggressive corrosion.

Flexlife carried out extensive R&D to identify FlexGel’s corrosion-inhibiting properties and other essential data. The gel’s specific gravity and viscosity can be tuned to allow a sufficient plug to completely encapsulate any area of concern. (Images courtesy of Flexlife)

Flexlife recently carried out a successful first application of its FlexGel product in a UK North Sea operation for an independent oil company. FlexGel is an oil-based product that is nonsoluble in water with a density that can be tuned depending on the application. It was devised to mitigate corrosion of damaged areas of flexible risers or umbilicals within I-tubes and help safely extend the operating life of assets within the oil and gas production process.

How it works

One of its advantages is that it can be deployed from topside or subsea without the need for costly intervention by rope access or diving teams and the associated health and safety risks of those types of operations.

The substance can be pumped into an I-tube to completely surround a riser with an annulus breach, displacing seawater and preventing further corrosion in the structural tensile armor wires of the flexible pipe and increasing the possible lifespan of the riser. Once the product is in place, Flexlife carries out predictive engineering and testing, setting a benchmark for continued operations and allowing the pipe to remain in safe service rather than having to be changed out at considerable expense. FlexGel has the following properties:

• Density: Customizable 0.79-0.88 g/cc;
• Maximum working temperature: Up to 150°C; and
• Viscosity: Customizable from 50 cP to more than 50,000 cP.

Prevention and repair

The gel provides a highly efficient solution for operators and major subcontractors faced with costly change-outs of risers. The company's products are devised not only to resolve issues but also to prevent them from happening in the first place. There is a huge potential international market for the gel since it is ideally suited for the large number of flexible pipe-driven field developments offshore Brazil, Asia Pacific, and West Africa as well as the North Sea. In fact, it is suitable for any platform where I-tubes are used and so is not restricted to deep water.

Deployment

This is one of a variety of different gels and is essentially an adaptation of a gel pig, which is commonly used in pipelines of varying diameters. Flexlife realized this gel floated and was immiscible, leading company scientists to identify a specific project requirement where a client had a riser with a small breach in the corrosion-critical splash zone region. This breach was within an I-tube, meaning that a more conventional repair was very difficult to conduct.

Approximately 70% of damage to flexible risers is caused during installation. FlexGel has the potential to act as both a lubricant and corrosion inhibitor, helping to alleviate this problem.

The company carried out extensive R&D to identify the corrosion-inhibiting properties of the gel, failure modes of various gels, and essential operational data including the flash point and environmental suitability. FlexGel has been approved by the Center for Environment, Fisheries, and Aquaculture Science as suitable for use offshore and does not pose a risk to marine life. The gel also was found to be robust and long-lasting unless exposed to ultra-violet light, which is not an issue within the confines of an I-tube.

The company then deployed the gel using the natural protective containment of the I-tube as a receptacle to contain the gel in place. The gel's specific gravity and viscosity can be tuned to allow a sufficient plug of gel to completely encapsulate any area of concern. The viscosity means the gel will rise and fall within the I-tube in sympathy with tidal ebb and flow or changes to vessel craft. However, its viscosity is such that it is not affected by short-period movements such as wave action.

The first commercial deployment of FlexGel was carried out following consultation with the UK's Health and Safety Executive for an independent oil company in the UK North Sea.

An annulus breach was discovered during testing in a 4.5-in. gas main flexible riser at a point

4.5 m (15 ft) subsea. A total of 9,500 liters of FlexGel was deployed to fill the I-tube from 11.5 m (38 ft) above seawater levels to 33.5 m (110 ft) subsea. The product was pumped in approximate 1-m increments above the mean sea level within the I-tube. This deployment method allowed time for the FlexGel to settle and displace all water and to fully surround the breach.

Future developments

Further potential uses include installing FlexGel prior to riser pull in as a preventative solution. It also can be used where the I-tube itself has been damaged to prevent further corrosion.

According to industry statistics, approximately 70% of damage to flexible risers is caused during installation, and FlexGel has the potential to act as a lubricant and corrosion inhibitor, helping to alleviate this problem.

There also is an issue of corrosion internally within I-tubes, which is equally difficult to address, so if clients have a concern that I-tubes may be corroded, the company can address that.

Further potential uses for the product and other gels developed include fire suppression; Flexlife is currently carrying out tests for this application. Assuming these tests prove successful, it may open up another significant potential market.

This schematic shows the layout of the FlexGel operation in the UK North Sea to repair a flexible riser breach.