Water and wastewater treatment are vital processes that ensure the availability of clean and safe water for various applications.
In these treatment facilities, the choice of materials for components and equipment is crucial to ensure durability, corrosion resistance, and overall performance.
One such material that finds extensive use in water and wastewater treatment applications is Type 316 and 316L stainless steel. But which one should we use for water and sewage treatment applications?
In this article we will dive into the 316 and 316L stainless steel world in the context of water and wastewater treatment.
Table of Contents
Introduction to Type 316 and 316L Stainless Steels
Type 316 and 316L are austenitic stainless steel grades that contain molybdenum, which enhances their corrosion resistance, particularly against pitting and crevice corrosion.
These grades are widely used in various industries, including water and wastewater treatment, due to their excellent combination of mechanical properties and corrosion resistance.
There is a variety of different types of 316 stainless steel. Some common types are the L, F, N, and H variants. Each is slightly different, and each is used for different purposes. The "L" designation means 316L steel has less carbon than 316.
For these reasons it’s important to choose the correct stainless steel grade when dealing with water, wastewater, and sewage. When should we prefer 316, 316L or 304 stainless steel?
Qualities of Type 316 and 316L Stainless Steel
Type 316 steel is an austenitic chromium-nickel stainless steel that contains between two and 3% molybdenum. The molybdenum content increases corrosion resistance, improves resistance to pitting in chloride ion solutions, and increases strength at high temperatures.
Type 316 grade stainless steel is particularly effective in acidic environments. This grade of steel is effective in protecting against corrosion caused by sulfuric, hydrochloric, acetic, formic, and tartaric acids, as well as acid sulphates and alkaline chlorides.
The lower carbon content in 316L minimizes deleterious carbide precipitation (carbon is drawn out of the metal and reacts with chromium due to heat, weakening the corrosion resistance) as a result of welding. Consequently, 316L is used when welding is required to ensure maximum corrosion resistance.
Differences Between 316 and 316L
316 stainless steel has more carbon in it than 316L. This is easy to remember, as the L stands for "low." But even though it has less carbon, 316L is very similar to 316 in almost every way.
Their cost is very similar, and both are durable, corrosion-resistant, and a good choice for high-stress situations.
316L, however, is a better choice for a project that requires a lot of welding because 316 is more susceptible to weld decay than 316L (corrosion within the weld). However, 316 can be annealed to resist weld decay. 316L also is a great stainless steel for high-temperature, high-corrosion uses, which is why it's so popular for use in construction and marine projects.
Neither 316 nor 316L is the cheapest option. 304 and 304L are similar but lower-priced. And neither are as durable as 317 and 317L, which have higher molybdenum content and are better for overall corrosion resistance.
Qualities Shared By 316 and 316L
While similar to Type 304, which is common in the food industry, both type 316 and 316L exhibit better corrosion resistance and are stronger at elevated temperatures. They also are both non-hardenable by heat treatment and can be readily formed and drawn (pulled or pushed through a die or smaller hole).
Annealing (a treatment to reduce hardness and increase ductility, or the ability to accept plastic deformation) 316 and 316L stainless steels require heat treatment of between 1,900 and 2,100 degrees Fahrenheit (1,038 to 1,149 degrees Celsius) before rapidly quenching.
Properties and Composition of 316 and 316L Stainless Steels
Physical Properties of type 316 and 316L steels are as follows:
Density: 0.799g/cubic centimetre
Electrical resistivity: 74 microhm-centimeters (20 degrees Celsius)
Specific Heat: 0.50 kilojoules/kilogram-Kelvin (0–100 degrees Celsius)
Thermal conductivity: 16.2 Watts/meter-Kelvin (100 degrees Celsius)
Modulus of Elasticity (MPa): 193 x 103 in tension
Melting Range: 2,500–2,550 degrees Fahrenheit (1,371–1,399 degrees Celsius)
Here is a breakdown of the percentages of various elements used to create type 316 and 316L steels:
Corrosion Resistance Properties
Alloys often are added to steel to increase desired properties. Marine-grade stainless steel, called type 316, is resistant to certain types of corrosive environments.
Type 316 and 316L stainless steels exhibit exceptional resistance to corrosion in both acidic and alkaline environments. The addition of molybdenum in their composition enhances their resistance to chlorides, which are commonly present in water and wastewater treatment processes. This makes them highly suitable for components and equipment exposed to corrosive media.
Strength and Durability
Type 316 and 316L stainless steels offer excellent strength and durability, even in harsh operating conditions.
They maintain their mechanical properties at elevated temperatures, making them suitable for applications where high temperatures are involved, such as hot water treatment processes.
Their robustness ensures long-term performance and reduces the need for frequent maintenance and replacement.
Heat Resistance and Thermal Stability
In water and wastewater treatment facilities, components and equipment are often subjected to thermal cycling and variations in temperature.
Type 316 and 316L stainless steels possess good heat resistance and thermal stability, allowing them to withstand temperature fluctuations without significant degradation.
This characteristic is crucial for ensuring the reliability and longevity of the equipment used in the treatment processes.
Weldability and Fabrication
Type 316 and 316L stainless steels are known for their excellent weldability, which simplifies the fabrication process of components and equipment. They can be easily welded using common techniques, such as TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) welding.
This flexibility in fabrication enables the production of complex and customized designs required in water and wastewater treatment applications.
Applications of 316 and 316L Stainless Steel in Water and Wastewater Treatment
Type 316 and 316L stainless steels find extensive use in various water and wastewater treatment components and equipment. Some common applications include:
Pumps and Valves
Stainless steel pumps and valves play a critical role in water and wastewater treatment processes. Type 316 and 316L stainless steels are preferred materials for manufacturing these components due to their corrosion resistance and compatibility with the treated media.
Efficient and reliable pipelines and fittings are essential for the transportation of water and wastewater within treatment facilities. Type 316 and 316L stainless steels are utilized for their corrosion resistance and structural integrity, ensuring the smooth flow of fluids without the risk of contamination.
316 and 316L Stainless Steel Tanks and Reactors
Tanks and reactors are key elements in water and wastewater treatment plants. Type 316 and 316L stainless steels are commonly used for their resistance to corrosion, durability, and ability to withstand high-pressure conditions, making them suitable for storing and treating various liquids and chemicals.
Screens and Filters
Screens and filters are employed to remove impurities and solid particles from water and wastewater during treatment. Type 316 and 316L stainless steels are selected for their corrosion resistance and longevity, enabling efficient filtration and preventing clogging or blockages.
Type 316 and 316L stainless steels are invaluable materials for water and wastewater treatment components and equipment. Their remarkable corrosion resistance, strength, durability, heat resistance, and weldability make them ideal for various applications within treatment facilities.
By utilizing 316 and 316L stainless steel grades, YASA can ensure the longevity, reliability, and efficiency of their water and wastewater treatment processes.
For more information you can get in touch with our team.
Q1. Are Type 316 and 316L stainless steels suitable for seawater desalination plants?
Yes, Type 316 and 316L stainless steels are widely used in seawater desalination plants due to their excellent resistance to corrosion caused by chloride exposure.
Q2. Can Type 316 and 316L stainless steels be used for underground wastewater pipelines?
Absolutely. Type 316 and 316L stainless steels offer excellent corrosion resistance, making them suitable for underground wastewater pipelines exposed to aggressive soil conditions.
Q3. What maintenance is required for Type 316 and 316L stainless steel equipment in water treatment facilities?
Regular inspection, cleaning, and preventive maintenance are recommended to ensure the optimal performance and longevity of stainless steel equipment in water treatment facilities.
Q4. Are Type 316 and 316L stainless steels compatible with different types of water treatment chemicals?
Yes, Type 316 and 316L stainless steels exhibit good compatibility with various water treatment chemicals, ensuring their effectiveness and preventing any adverse reactions.
Q5. Can Type 316 and 316L stainless steels withstand high-temperature sterilization processes?
Yes, Type 316 and 316L stainless steels possess excellent heat resistance and can withstand high-temperature sterilization processes commonly employed in water and wastewater treatment.