Marine Structures: Offshore Corrosion Protection 101

Marine Structures: Offshore Corrosion Protection 101
5/24/2017 12:13:35 PM

It takes huge investments of capital and effort to keep offshore oil and gas fields running.

Much of this investment goes to protecting the infrastructure that makes production possible.

Indeed, offshore oil and gas producers in the Gulf and around the world need corrosion protection for their marine structures. Corrosion is a serious issue for offshore operations, because it can result in unsafe working conditions, it can make machines and platforms unreliable, and it can drain operations of time and money while repairs are made or new structures are installed.


 

Corrosion, one of the most common forms of equipment degradation, is split into two major categories: crevice corrosion and corrosion under insulation. Any equipment that comes into contact with electrolytes and has gaps or contact areas is susceptible to both types.

Corrosion happens when an electrochemical reaction that takes place in the presence of an electrolyte as a result of its interaction with the working environment. Corrosion on offshore marine structures is caused by:

 

  • Salt water
  • Salt present in the air
  • Alternating wet/dry conditions (caused by tides)
  • Exposure to ultraviolet sunlight
  • Dissolved oxygen and carbon dioxide in seawater
  • The corrosion of carbonate scales on metal risers
  • Sulfate-reducing bacteria

If corrosion is the number one enemy of offshore structures, pipeline coatings are the first line of defense. That’s why it’s crucial to choose the right coating. Protecting your structures the right way will help prevent corrosion and maintain pipeline integrity over the long-term.

 

Steps to Take

 

Here are some considerations when choosing anticorrosive coatings for offshore structures and other marine applications.

What type do you need?Coatings come in many varieties. Paint application such as zinc-rich primers, higher build epoxies and polysiloxane coatings are popular. However, elastomer applied during the fabrication process provides better protection against harmful seawater, ozone and ultraviolet rays. For fully immersed surfaces, you might opt for a combination of a barrier coating like Splashtron along with cathodic protection (electrochemical corrosion control). Splashtron is Mark Tool’s bonded-on elastomer that provides permanent metal protection for splash zone problems such as corrosion, wave action, moisture, oxygen and sea life. It also offers excellent resistance to weathering, fungus, marine life, and most oils.

Be sure to prepare surfaces correctly.This means scale, grime, grease and rust must be removed from the substrate before the application of a coating begins. This is often done via shot blasting for offshore structures and ships. For structural metals like steels and alloy steels, an abrasive cleaning method is also used.

Whatever corrosion protection you use, it needs to be applied according to the manufacturer’s prescribed conditions, and the necessary surface preparations must be made. Because Splashtron is applied in Mark Tool Co’s plant (where the environment and production processes can be closely controlled and the steam autoclave curing vehicle can be employed), on-site surface preparation is not needed. The coating is chemically bonded (not mechanically bonded), to the metal surface; in fact, this bond is stronger than the tough yellow elastomer itself.

Are your structures easily accessed? Because these coatings are used on structures that aren’t easily accessed, there needs to be very little need for routine maintenance. An important feature of Splashtron in pipeline coating applications is the fact that it is completely and permanently bonded to the metal surface. And because it is flexible, it won't crack or disbond as the risers or other structures bend, expand, and contract. This means you won’t have to check up on your structures to ensure they’re holding up.



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What are the environmental considerations? Coatings manufactures must adhere to strict environmental regulations. Most marine and offshore platform coatings use antifouling biocide coatings that inhibit algae and other organisms. However, biocide accumulation in harbors is harmful to ecosystems, and there are restrictions in place for the use of biocides. The emission of volatile organic compounds (VOCs) is another consideration.

 

Don’t forget monitoring. Pipeline coatings must be carefully monitored for continued effectiveness following application. Once in the field, you’ll need to monitor your corrosion protection systems for ongoing efficacy. Barring physical damage, a coating like Splashtron can be expected to last for the life of the platform or pipeline. In fact, there are Splashtron-coated platforms and risers have been in service for four decades. As long as damage does not expose bare metal, there is no need to repair it. If bare metal is exposed, trim away the lose material, wire brush the metal, and apply a resilient epoxy patch material (available from Mark Tool).

While barnacles and other marine growth will build up on Splashtron, they will not adversely affect it because there is nothing in Splashtron that sea life can feed on. Where marine growth is a problem, such as off the California coast, we suggest the use of BIO-SHIELD, a patented product composed of a layer of Splashtron with a cladding of 90-10 copper-nickel bonded permanently to the outside.

Conclusion

You can do something to combat the high cost of corrosion in the oil and gas industry. Splashtron protects against corrosion for the life of the platform and has proven its effectiveness in offshore areas around the world for decades. It is used by the leading producers of oil and gas, and most transmission companies.

Whether you need splash zone coatings for risers, J-Tubes, bends, spools, Vortex Induced Vibration (VIV) Suppression Strakes, pipe field jointcoating or have issues with bio-fouling, Splashtron is the product of choice in splash zone areas. Common Splashtron applications include pipeline coatings, platform structural members (legs and diagonals), conventional risers, pipelines pulled through J-tubes, conductors and the lining of riser clamps.

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