Metal Fatigue Failure Sinks Salmon Farm

Metal fatigue can have serious, or even deadly consequences. But sometimes it’s the more absurd stories of failure that best illustrate this mechanical menace.

Take the recent incident involving a failed salmon farm enclosure in Washington state. Authorities estimate that as many as 162,000 Atlantic Salmon escaped into the waters around Puget Sound after their fatigued enclosure failed during high tides.
The suspect pen had previously been identified as structurally deficient, with the owners applying for a permit from the Washington Department of Natural Resources to replace the aging structure.
From the permit: “The current condition of the existing pen structure can be described as used and nearing the end of serviceable life… Steel net pen systems located in the marine environment are subject to the corrosive effects of salt water and to metal fatigue from the constant wave energy, storm events, and the extreme forces that are exerted on them from tidal current. The corrosion on the metal walkway grating and substructures is accelerating and some metal hinge joints show signs of excess wear.”
Despite these concerns, the weakened pen was holding more than three million pounds of Atlantic salmon at the time of the breach. Now, state agencies are asking local anglers to catch as many of the escaped fish as possible, and members of the community are looking for answers amidst this potential environmental nightmare.

“The Atlantic salmon bring with them pollution, virus and parasite amplification,” said Kurt Beardslee, director of the Wild Fish Conservancy Northwest in an interview with NPR. “All that harms Pacific salmon and our waters of Washington.”
It’s unclear how long cleanup efforts will take, and what impact the potentially invasive species will have on the local ecosystem. What is clear is that dangerous metal fatigue symptoms were not addressed by operators or regulators despite fishing industry best practices.
Fish pens and enclosures are subject to a variety of factors that contribute to metal failure. Submerged structural components experience high levels of corrosion, and tidal swells put repetitive strain on load-bearing fasteners and joints. At many sites, these structures are under constant strain from perpetual currents, and weakened metal supports may give way during strong storms or heavy waves.
In fact, the definitive textbook Fish Farming Technology directly addresses the industry hazards of metal fatigue: “Perhaps the best test of any fish enclosure is its ability to withstand the seemingly endless train of smaller waves that can cause accumulated minor degradation of the components until fatigue or wear builds to the threshold of final failure.”¹

The company operating the failed enclosure is now facing potential lawsuits and government penalties, while their application to expand a separate salmon farm has been put on hold.
The lesson in all of this is that metal fatigue failures can have a wide variety of negative consequences. From life-threatening accidents to environmental catastrophes, once the failure has occurred any attempts at remediation are too late. All load-bearing metal components will fatigue, and all fatigued components will eventually fail. You can delay treatment or replacement in an effort to save costs, but the consequences of failure always end up costing more.
Laser peening is a cost-effective method for protecting metal parts from fatigue failure. The process is proven to inhibit crack propagation, and to slow the degenerative effects of corrosion, fretting, and creep. Laser peened parts last as much as ten times longer than shot peened components, reducing maintenance, replacement, and repair costs throughout the extended life of the part.
Ignore metal fatigue at your own peril. Putting it off today could mean cleaning up a big mess tomorrow.
Don’t leave fatigue failures to chance. Contact LSPT about superior metal enhancement.
References:

1. Fish farming technology: Proceedings of the First International Conference on Fish Farming Technology, Trondheim, Norway, 9-12 August 1993 Helge Reinertsen – Balkema – 1993 (p. 245)

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