Advantages of 304 and 316 stainless steel pipes in urban wastewater treatment

In the United States, stainless steel pipes have become the standard material in the field of municipal wastewater treatment. The initial use of stainless steel pipes instead of galvanized and painted carbon steel was to reduce maintenance and repair costs because stainless steel pipes have better corrosion resistance.

Low carbon stainless steel types 304L and 316L are used for welded structures. This type of low carbon steel is used mainly to resist intergranular corrosion without heat treatment after welding. Stainless steel models with higher carbon content are mainly used to make valve stems and pump shafts because of their better strength. These parts do not need to be welded, and higher strength can improve the design. The resistance to local corrosion of molybdenum-containing stainless steel is relatively good. It is best used in highly corrosive environments or to avoid accidents that may occur at any time to achieve a safer effect. The casting products of these steel types have and Corrosion resistance and similar mechanical properties.

304 and 316 series stainless steel pipes are the main standard materials in municipal wastewater treatment equipment. The weight loss corrosion rate of 304 and 316 stainless steel is <0.1 mil/year. This means that the effective life of the material is at least greater than 20 years. It also shows that there is no need to maintain a corrosion allowance in the wall thickness when designing stainless steel equipment, but other materials such as carbon steel need to leave a corrosion allowance. From this point of view, a lot of stainless steel materials can be saved.

304 and 316 stainless steel materials have many advantages. The first is that they are resistant to atmospheric corrosion. The addition of chromium to their chemical composition enhances the corrosion resistance. The chromium content required for stainless steel materials to exert their stainless properties can be determined based on content changes. Stainless steel with a chromium content of 12.5% or more has very low weight loss after being exposed to marine atmosphere for 25 years. Their surface layer has a layer of rust, and they are not suitable for use in many atmospheric environments where appearance is particularly important.

Secondly, they are resistant to corrosion by chlorine at the typical concentrations found in wastewater treatment equipment. Data show that 304 and 316L stainless steel have good corrosion resistance in well water with residual chlorine content up to 2ppm, which is much higher than the corrosion rate of carbon steel and cast iron. In addition, because ozone is a relatively popular oxidant substitute, it can be used alone or together with chlorine. 316L stainless steel is already the best material for manufacturing ozone generators.

304 and 316 stainless steel are also resistant to corrosion by general chemical additives. In an environment with a ferric chloride content of 250-300ppm, there is not only pitting corrosion but also crevice corrosion. The corrosion resistance of 316 stainless steel to ferric chloride is slightly better than that of 304 stainless steel, so it can be used as a more conservative choice.

In addition, 304 and 316 stainless steel are also resistant to microbial corrosion. Standard stainless steel is sometimes prone to microbial corrosion in and around welds in stagnant and slow-flowing water.

The last point is that the cost advantage of stainless steel materials is relatively obvious. Although the initial investment cost of stainless steel materials may be higher than other materials, it can actually effectively reduce costs due to its long service life and low total maintenance costs. 304L and 316L stainless steel pipes have been effectively used in pipes in wastewater treatment plants and many other purposes.