Proper use of materials in chemical plants CS(SS400)/SS(SUS304)

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We will explain how to properly use CS(SS400) and SS(SUS304) materials in chemical plants.

It’s easy because it’s used depending on whether it has corrosion resistance or not, isn’t it?

You may think so, but in fact there are many different usage patterns in chemical plants.

Here is an example.

If you know this content, I think you will reach a fairly detailed level as knowledge of materials used on site.

Differences in material properties between SS400 and SUS304

First, let’s briefly introduce the difference in materials between SS400 and SUS304.

corrosiveAmount of money
SS400susceptible to corrosioncheap
SUS304Corrosion resistantexpensive

That much understanding is enough.

A comparison based on metallic properties is meaningful from an academic and research perspective in relation to composition, but it is “irrelevant information” for engineers who struggle on a daily basis at the factory floor.

SUS304 for highly corrosive areas

SS400 and SUS304 will not be a problem in highly corrosive areas.

Normally SUS304 is used.

When handling more corrosive liquids, we will upgrade to SUS316L, Hastelloy, glass lining, and fluorine resin lining.

The place where SUS304 is used is originally a highly corrosive place.

If there are metal devices or pipes that are not painted on the outside in the factory, it would be better to assume that they contain dangerous chemicals .

From the outside, it doesn’t look corroded, so we tend to feel relieved.

Utility is SS400

For utility systems, SS400 or SGP should be used.

It’s cheap.

SS400 is for large equipment such as tanks and SGP is for piping, but both are cheap carbon steel groups.

Usually used for water, steam, air, etc.

In some cases, low-temperature brine, sulfuric acid, or caustic soda may also be used.

Even flammable liquids (organic solvents) classified as Dangerous Goods 4 may use iron-based materials.

SS400 can withstand alcohol and heavy oil in many cases.

Since it is used frequently, the idea of ​​SS400 comes from making it a dedicated device.

Even with organic solvents, SUS304 is safer for equipment and piping where the liquid is changed depending on the product, because you don’t know what kind of liquid will come.

In that sense, I personally think that SS400 for organic solvents is a bit adventurous.

SUS304 is used for places where there is a possibility of contamination with the process.

I wrote that SS400 is fine for utilities, but there are exceptions.

That ‘s the line that mixes with the process .

In this case, it is better to use SUS304.

To be more specific, the line after removing dust with a strainer is SUS304.

SUS304 (material)

If the part to be made of SUS304 is made as short as possible, the equipment cost will be reduced.

Since a strainer is required, regular cleaning is required, which is a minor disadvantage in terms of operation.

It would be nice if all the rust generated from SS400 could be removed by the strainer, but if the strainer opening is too large or fine rust occurs, iron rust will enter the SUS304 side.

This will cause the SUS304 pipes to gradually corrode, and above all, the possibility that iron rust will enter the process and deteriorate the process safety is more scary.

If there are many such lines, the ideal method is to assemble a header on the secondary side of the strainer and assemble it to each device.

The primary side of the strainer is SS400/SGP, and the secondary side is SUS304.

Lining if you want to make it even a little cheaper

If it is pumped with SUS304, it is certainly safe.

If you want to keep costs down, consider lining.

It is in the form of SS400 + SUS304 lining .

If the plate thickness is relatively large, the price difference between SS400 and SUS304 is large, so the base material is SS400, and only a few millimeters thick is lined with SUS304 at the part that comes into contact with the liquid.

For example, manholes are a good example.

The same concept can be applied to tank reactors. SUS304 is used inside the tank because corrosive chemicals are used, and SS400 is used for the jacket because only utilities are used.

SUS304 lining looks effective at first glance, but it has its disadvantages. Since SS400 and SUS304 are not completely adhered to each other, the lining can easily break in harsh environments such as high temperature/high pressure conditions, temperature fluctuations, pressure fluctuations, and vibrations. The more discontinuities in the target device, the higher the risk.

Dare SS400

It’s an applied idea, but there are times when I dare to choose the SS400 .

For example, the drainage system may be SS400.

SS400 corrodes, but trend monitoring is easy, while SUS304 does not corrode easily, but may crack suddenly.

There is a feature.

SUS304 has a deterioration pattern called stress corrosion cracking.

Wastewater often contains salts that have been neutralized with acids and alkalis.

Depending on the salt concentration and temperature, it can be a factor that causes stress corrosion cracking.

It is important to perform wastewater treatment stably, and if it breaks down, the operation of the plant must be stopped.

It looks sober and is very important.

I spent a lot of money on SUS304, but when I was relieved that I could not predict the deterioration, suddenly trouble occurred.

If it’s just a matter of making a fuss about it, my aim is to use SS400 to stably corrode it and manage it.

This method uses the fact that the corrosion of SS400 is general corrosion .


Knowledge of materials is important for chemical plant engineers.

Knowledge about stainless steel is especially important, so the following books will be helpful.


I introduced the way of thinking when using SS400 and SUS304 properly in a chemical plant.

The basic idea is to use SUS304 for highly corrosive materials and SS400 for utilities.

When using SUS304 for utilities, SUS304 may be overlapped with SS400, and some applications are possible.

Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (Comments are at the bottom of this article.)

*We will read all the comments and reply seriously.