In many areas of the world, marine life such as barnacles, mussels, and algae don't accumulate much more than a few inches. The waters off the coast of California, however, are a different story.
There (and anyplace where waters are relatively cold and hold more nutrients), biofouling can build up to as much as three feet thick and can weigh up to 150 pounds per cubic foot, depending on the type of growth.
At these levels, oil platforms can become danger zones: The added weight increases the rig's strength requirements and causes greater fatigue on the structure, shortening its life. The risk of the platform overturning also becomes more of a concern.
When biofouling becomes extreme, engineers must make platforms much stronger than typically necessary, or the excessive growth must regularly be removed.
Corrosion is also a factor. The splash zone is the most susceptible area due to its continuous contact with highly-aerated sea water and the corrosive effects of spray, wave, and tidal actions. The results are two-fold: waves erode the metal members and exposure to oxygen leads to corrosion.
Bio-Shield Corrosion, Biofouling Preventative
To remedy the problem, Mark Tool worked with Shell Development Company, a research facility of Shell Oil, to produce an anti-corrosive, anti-foulant product called Bio-Shield®.
Bio-Shield prevents biofouling on conductors, platform legs and diagonals, J-tubes, risers, or any piping or structure in the area of high buildups, such as the splash zone. It allows designers to take full advantage of the cleaner profiles and eliminates the need for biofoulant removal operations, which can run into the multiplied thousands of dollars per job.
In a typical application, Mark Tool applies a 1/2" thick layer of SplashTRON®, our trademark elastomer coating, bonded completely to the pipe, and a 1/16" thick plate of 90-10 Cu-Ni (copper-nickel) bonded to the outside of the SplashTRON®. That entirely insulates the alloy from contact with the steel and serves to retain its anti-fouling ability for the projected life of the installation.
(Cu-Ni alloy is particularly useful for marine structure sheathing because it provides corrosion protection and resists biofoulant build up at the same time.)
Shell's Eureka Platform Case Study
The first large scale application of Bio-Shield was on Shell's Eureka platform, installed on sixty 24" OD conductors in more than 700 feet of water off the California coast.
The installation saved Shell 152 tons of structural steel in the design of the platform because it did not have to make room for the effects of the added wave, tidal, and current loading on conductors fouled with 24" or more of marine growth.
Money was also saved in reduced steel for corrosion allowance and lower fatigue loads in the major platform joints (structural nodes).
Estimated savings realized from installing Bio-Shield came to $377,000. You can see the breakdown here:
Also, savings per biofoulant cleaning and removal were valued at $50,000 to $100,000 per instance, which means hundreds of thousands of dollars (or more) will be saved in maintenance expense over the platform’s 40-year lifespan.
Clearly, this installation of the Cu-Ni/SplashTRON® sheath system Bio-Shield proved to be highly cost-effective.