COMBATING THE DETRIMENTAL MARINE ENVIRONMENT EFFECTS ON MOORING HARDWARE THROUGH DESIGN AND PROPER SELECTION OF MATERIAL BEST SUITED FOR AQUACULTURE INDUSTRY

Throughout its lifetime, all mooring equipment is affected by various factors based on the surroundings. These environmental effects degrade the equipment over time, and could cause a significant failure to the given system without warning. This failure could be prevented through proper selection of the hardware material, as well as choosing the appropriate inspection guide designed for the rough seas.

There are three main challenges when it comes to mooring in coastal areas: fatigue, corrosion and brittleness. All of these factors affect the steel properties, and their interaction affect the service life of the product. Fatigue, the most common problem present in any engineering application, is often overlooked. Fatigue failure could occur at a lower load than the intended working load limit (WLL). The following figure illustrates steps of fatigue.

• Step 1: Initiation of a crack in the material
• Step 2: Plastic zone forms during tension loading
• Step 3: Growth of crack at the end of cycle loads

Second, corrosion is the most obvious challenge in a marine environment. Seawater is a complex chemical system affected by concentration and access of dissolved oxygen, salinity, concentration of minor ions (e.g. Ca2+, Mg2+), biological activity and pollutants. These in turn are affected by temperature, depth, and ocean currents. Depending on the access of available oxygen, the steel will either corrode or be immune towards corrosion.

Lastly, brittleness is important to consider as the properties of material change when the temperature drops. These equipment are designed to elongate before they break, acting as a safety feature. The user can see that the product is being used incorrectly and can stop before catastrophic failure. However, as the temperature drops, steel passes through the stages where it becomes brittle and subject to early failure.

This paper will outline how we design against these three main environmental factors, especially in the extreme conditions that we commonly find in the aquaculture. To ensure the safety and longevity of the mooring equipment utilized in the net pens design, proper consideration of material selection, procurement and best- use practices are the utmost importance.