Selecting the right materials for use in aqueous environments can be challenging, but high-performance nickel alloys are well-equipped to handle the task. Aqueous systems, especially those utilizing seawater, present numerous factors that influence material suitability.These systems are integral to various industries, including offshore oil and gas production, shipping, desalination, and certain industrial processes. Many of these applications rely on seawater for cooling, which plays a crucial role in their operation.Choosing appropriate materials for each component of an aqueous system involves balancing corrosion resistance with cost considerations. Several nickel alloys are designed for aqueous environments, providing effective solutions. However, it’s essential first to understand the factors impacting material selection.
Key Considerations in Material Selection
Corrosion is a primary concern when selecting materials. Corrosion of critical components can lead to system failures over time. Aqueous environments, particularly those involving seawater, are highly corrosive to most metals and alloys.Aqueous corrosion initiates oxidation, forming a protective oxide film. Materials that develop a dense, stable oxide layer are better shielded from further corrosion. In contrast, flaky oxide layers, like rust, are more susceptible to penetration. However, aggressive substances such as hydrochloric acid can compromise even robust protective layers, leading to deeper corrosion and structural integrity issues.While various protective measures, such as coatings or paints, can mitigate corrosion, it’s best to start with a metal alloy inherently resistant to seawater and other aqueous conditions.In addition to corrosion resistance, materials must also withstand stress corrosion cracking, particularly in harsher aqueous environments. Other factors affecting material selection include fluid velocity, which influences pipe and valve sizing, adding to project costs. Higher fluid velocities can increase pressure, accelerating corrosion. Conversely, larger diameters can reduce pressure but may also raise costs and allow more oxygen into the system, potentially heightening corrosion risks. Some materials may also be vulnerable to crevice corrosion and pitting, impacting their longevity and integrity.
Operating temperature is another consideration in aqueous environments. For instance, in oil and gas production, materials may face high temperatures that can exacerbate corrosion problems.Seawater introduces additional complexities, containing not only water but also inorganic salts, organic matter, and dissolved gases. These elements are crucial in material selection for offshore oil and gas applications and shipping.As a designer tasked with selecting materials for these challenging conditions, you must consider fluid velocity, aeration, operating temperature, water pressure, and the local marine environment, including potential marine fouling and the types of organisms present.
Suitable Nickel Alloys
Fortunately, several high-performance nickel alloys are designed to excel in challenging aqueous conditions, many of which are available from Corrotherm.
INCONEL Alloy 625is a versatile option for various industrial applications, including seawater use. It is particularly resistant to pitting, crevice corrosion, and chloride-ion stress corrosion cracking—common issues in seawater systems. Its high corrosion fatigue strength and tensile strength enable it to withstand extreme pressure. As a result, INCONEL 625 is widely used in the marine industry, including for propeller blades, propulsion motors, sour gas pipelines, and seawater heat exchangers.
INCONEL Alloy C-276is another excellent choice for aqueous environments. This nickel-chromium-molybdenum alloy is used in various chemical processes involving seawater or brine, as well as in gas wellhead fluids and waste fluid treatment plants. It offers exceptional resistance to seawater, particularly under crevice conditions.
INCONEL Alloy 22 though sometimes overlooked, is a strong contender for certain aqueous applications. Its nickel-iron-chromium composition provides high strength and good corrosion resistance, making it suitable for marine uses. Notably, it performs well at elevated temperatures compared to many other nickel alloys.
MONEL Alloy 400is also utilized in marine applications due to its resistance to rapidly flowing seawater. As a more cost-effective material, it helps keep overall project expenses down and is used for wave protection sheathing on platform risers and steel pylon legs on offshore rigs, as well as for storage tanks containing gasoline or potable water.
