Pressure of Flange | Fundamentals of Plant Machine Parts

flange pressure
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I will explain how to properly use the flange nominal pressure 

There is a problem that it is difficult to know which one to use for all types.

The problem is that there are many types of technical knowledge, not just chemical plants.

We will introduce an example of a batch-type chemical plant so that you can use them appropriately.

The flange standard is based on the JIS flange.

Flange Nominal Pressure

You may think that the nominal pressure of the flange indicates the pressure resistance of the piping.

How much pressure can the piping and equipment withstand? This is a story that is effective in equipment design and piping design construction.

The nominal pressure is an index that is directly linked to the pressure resistance of the flange.

The flange is the weakest part of the pipe-flange system.

Therefore, if you know the nominal pressure, you can know the pressure resistance of the piping system.

I don’t think you need to understand the definition of nominal pressure.

For example, it is expressed as JIS10K .

It is enough to know that the letter K at the end indicates the unit of kgf/cm 2 (≒0.1MPa) .

The JIS10 flange is recognized as a flange that can withstand up to 1 MPa .

This time we will focus on butt weld flanges.


I don’t pay much attention to it. . .


JIS10K flanges are probably the most commonly used flanges in Japan.

Of course, JIS10K is most often used in batch chemical plants.

It is so standard that JIS10K should be used for the time being if you are worried about the flange nominal pressure .

By using JIS 10K flanges for both piping and equipment, the piping flanges can be unified, making design easier.

Actually, there is a flange called JIS5K, which is one of the weaker grades of JIS10K, but I am a little worried about its strength.

If the pump lift is about 40m and the liquid has a density of about 1.2, the shut-off pressure (maximum working pressure) may be about 500kPa.

JIS5K can withstand that much, but if the nominal pressure and the maximum working pressure are quite close, it is not preferable from the point of view of piping design and strength design.

JIS10K for the time being


JIS5K, which has a weaker nominal pressure than JIS10K, is used in certain situations.

It is understood that the flange can withstand up to 0.5MPa, which is half the pressure of 10K.

  • Atmospheric pressure tank manhole
  • Almost normal pressure gas line

What they have in common is “weak working pressure” and “large caliber”.

If the nominal pressure is high, the flange thickness will be thick and the flange weight will be heavy, so we would like to avoid this if possible.

In particular, the larger the diameter, the greater the effect on weight.

If there is an opportunity to use it, I would like to actively use JIS5K.

JIS5K for large diameter with low pressure


There is a grade called JIS2K for pressure lower than JIS5K.

Since this is limited to 450A or more, it is possible to use it in manholes.

JIS2K cannot be used for 400A manholes, and JIS5K is used, so we are forced to decide whether to take weight or diameter.

JIS2K if there is a chance with a large diameter


JIS20K is a flange that withstands up to 2MPa, which is twice as high as JIS10K.

20K flanges, which are 2 MPa, are very rarely used in batch-type chemical plants, where use at 1 MPa or less is overwhelming.

  • Certain high pressure process lines
  • High pressure lines such as hydraulic lines

will be limited to about

Special gaskets such as spiral wound gaskets are used for high-pressure process lines, so it is easy to make a lasting impression.

Hydraulic lines can run at much higher pressures, so 20K may not be the way to go.

I think it would be good if there was recognition that it was that special.

Is it one of the few advantages of batch-type chemical plants that they are rarely used at high pressure like continuous plants?

Special high pressure line is JIS20K

country rules

Flanges have certain rules such as shape and dimensions.

This rule differs from country to country, for example.


Roughly, you should know this much.

For batch-type chemical plants, JIS standards alone are basically OK.

Think of ASME and ANSI as American standards.

American standards are global standards.

A standard called JPI has been established so that the US standard can be used in Japan.

This is the same way of thinking in China, for example.

Differentiate between American standard and national original standard .

Flanges of different standards have slightly different dimensions, so there are many cases where they cannot be installed.

It’s just a matter of size, but be careful.

Let’s recognize that JIS10k can be used up to 1000kPa, that is, 1MPa.

Class 150 such as ASME flanges are in pounds. It may also be written as lb.

1 lb = 7 kPa, so 150 lb = 1050 kPa is almost the same as JIS 10k.


Flanges are the basis of piping design, so there are plenty of books available.

Acquire a wide range of knowledge about flanges, not limited to nominal pressure.

created by Rinker
¥3,850(2023/09/28 22:36:19時点 Amazon調べ-詳細)

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I explained how to properly use the pipe flange nominal pressure in a batch chemical plant.

More than 99% are JIS10K, so there are many JIS10K.

JIS5K or 2K is used for large diameters, and JIS20K is used for high pressure lines.

It’s okay to understand “JIS10K for the time being”, but I think it’s good to know the types of nominal pressure as peripheral knowledge.

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.