Pressure Vessel Classification in Japan

A pressure vessel is a container intended to apply pressure to the inside of a vessel.
In Japan, pressure vessels are classified into several types according to their specifications and contents. Therefore, this column explains the standards for pressure vessels in Japan, focusing on First Class Pressure Vessels and Second Class Pressure Vessels.

Contents of this article

  • Pressure vessels are divided into First Class Pressure Vessels, Second Class Pressure Vessels.
  • The key point is whether or not gas is generated inside the vessel when pressure is applied.
  • Pay attention to laws and regulations, and do not neglect inspections.

Pressure vessels can be dangerous under pressure, so standards are established according to the magnitude and conditions of the pressure.
If they are not strong enough, serious accidents can occur. In Japan, the Industrial Safety and Health Act and Ordinance on Safety of Boilers and Pressure Vessels specify the structure of pressure vessels in detail.

Vessels are classified according to their size and the amount of pressure they handle, and some vessels require certification.
Classifications include First Class Pressure Vessel, Small-sized Pressure Vessel, Second Class Pressure Vessel, and (simplified) vessels.

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Many results in the pharmaceutical industry. What is the highest grade of electropolishing?

What is electropolishing?

Electropolishing is a polishing method in which metal ions are eluted from the metal surface to smooth the surface.
This process adds functions to the metal surface such as “removing oil, buffing powder, and other contaminants” and “inhibiting the adhesion of microorganisms.
For stainless steel, it also increases the chromium concentration on the metal surface and improves corrosion resistance.

Electropolishing is essential for pharmaceutical manufacturers who seek to avoid contamination and corrosion resistance from the surface, from the perspective of GMP and validation.

Electropolished stainless steel has a slightly shiny black surface (tank in the center of the photo).

When electrolytic polishing is applied, the surface of the metal will melt in a wisp.
It does not melt so much that you can tell by touching it with your hand that it has become flimsy. The thickness of the surface is about 1/3 of a sheet of copy paper. (20 to 30 μm)

The surface is thinly melted to add functionality, so it may be easy to imagine it as “reverse plating”.

Advantages of Electropolishing

Electropolishing has the following advantages

  • Removes stains that cannot be removed by normal cleaning
  • Resistance to residual stains and easy removal of stains
  • Improves corrosion resistance and rust resistance

Removes dirt that cannot be removed by normal cleaning

This product can remove (degrease) oil stains from stainless steel rolled, pressed, or buffed after welding.

These contaminants are embedded in the intricately deformed surface of stainless steel and are difficult to remove by normal cleaning.
Electropolishing melts the stains from the convex surfaces to a smooth surface, allowing the stains to surface and be easily removed.

Image of the surface

Material Surface
(Rough surface)

Buffing surface
(buffing powder, oil stains)

Electropolished surface
(smooth surface without contamination)

Less likely to leave stains and easier to remove

It is not only when the product is new that it remains clean.

As you can see from the image above, the electropolished surface is very smooth and has a smaller surface area.
Compared to the buffed surface, where the surface is uneven and has many small gaps, the new surface remains clean and easy to remove dirt even after repeated use and washing.

In addition, research conducted by the U.S. Department of Agriculture has shown that electropolished surfaces are less likely to retain biofilm (a collection of microorganisms).

Thus, electropolishing can easily maintain hygienic metal surfaces.

Improved corrosion resistance and rust resistance

As with the opening sentence, electropolishing increases the concentration of chromium on the metal surface. This is called chromium richness, and the metal surface is then covered with a strong passive film, which improves corrosion resistance.

The passive film prevents the iron contained in stainless steel from combining with oxygen (i.e., rusting). This is inherent in stainless steel itself, but the chromium richness makes it stronger.

Disadvantages of Electropolishing

Electropolishing itself does not have any negative effects on metal surfaces, but it does have a secondary disadvantage (risk).

  • Expensive.
    In our case, the price is about 2 to 3 times that of a buffed container.
    There is a risk of electrolytic solution getting into the gaps.
  • It is necessary to consider the application of electrolytic polishing from the design stage, and to make a structure with a small number of gaps.

Are there different grades of electrolytic polishing?

Electropolishing has no direct disadvantages and is a good thing, but if the proper technique is not used, the desired effect may not be achieved.

Have you ever had any of the following problems with electropolished stainless steel containers?

  • The container cannot be used without repeated washing.
  • White tablets became dirty and blackish.
  • Red rust (rouge) occurred.

These phenomena are caused by insufficient electropolishing.
The difference is caused by the way electropolishing is applied.

As a stainless steel container manufacturer, we would like to introduce our commitment to electropolishing.

General Electropolishing Methods

Electrode plates are placed on both sides of an electrolytic tank containing electrolytic solution (a mixed acid solution of phosphoric acid and sulfuric acid), and the product is placed between them.
When the product is connected to the + electrode and the electrode plates to the – electrode, an electric current flows through the electrolytic solution and the product is electropolished.

This method is suitable for electropolishing small parts, but not for stainless steel containers such as those we handle.
Although it is desirable to apply electropolishing firmly to the inner surface, which is in direct contact with the contents, with this method, the electric current flowing to the inner surface is weak, which means that electropolishing can only be applied weakly.

How Nitto Kinzoku Kogyo Electropolishes for High Grade Finishes

Nitto Kinzoku Kogyo uses a method that allows for firm electrolytic polishing to be applied to the inner surface of the container.

The difference from the general method is in the electrode plate.
Electropolishing is performed using special electrode plates that are dimensionally matched to the inner surface of the container.
This allows for stronger and more uniform processing, and the container is finished by taking full advantage of the benefits of electropolishing.

We are able to provide dedicated electrode plates tailored to each container because we are able to perform the entire process of container design, production, and electropolishing.
This is the secret to Nitto Kinzoku Kogyo’s high-grade electropolishing.

We have delivered many electrolytic polishing products to pharmaceutical companies

Electropolishing certificates can be issued, please contact us.

Examples of electrolytically polished stainless steel products

Essential for factory automation! All about Customizing Stainless Steel Containers

In recent years, the trend toward automation (robotization/factory automation) has accelerated in pharmaceutical and cosmetics factories. In NITTO KINZOKU KOGYO, customers who want to use stainless steel containers in automated production lines are increasing rapidly, especially the requests of custom-made containers.

By customizing the stainless steel container according to the equipment and work to be used, you can take full advantage of the equipment’s performance and solve process problems.

In this column, we introduce customizations and products recommended for stainless steel containers to be introduced into the automation process.

How to Make Stainless Steel Containers "Easy to Handle" in the Automation Process?

To match the size of your needs

NITTO KINZOKU’s containers can be manufactured with a size that matches your work allowable size, storage space, input amount, etc. Our company works primarily with customizing height dimensions.

We can also customize the inner diameter of the container, but basically, we have to choose from the following sizes. We can also make the container of the original diameter if you would like to bear the corresponding cost such as making the mold from scratch.

Inner Diameter of our company Standard Lineup (mm)

180/210/240/270/300/330/360/387/430/470/565/635/770/1000

*Other sizes may be available. 

* The available sizes may also be limited depending on the container specifications.

To avoid interference

For example, you can customize the mounting position when the handle on the container interferes. If you don’t need the handle itself, you can choose “No Handle”.

To make it easy holding

When there is a lifting action

 

If you have an action like “ to lift the container and put it on a different pallet ”, you might want to customize it by attaching a bracket to the side of the container. The bracket can be designed to meet the specifications of the robot, so it can be held securely.

If there is no interference or other problems, you can install both a handle for people and a robot bracket.

* The handles on ordinary containers are designed to be handled by human hands and are not intended for use in robots or lifters.

When there is a grasping motion

If you have needs like “grab and flip ” handling action, you might want to customize it by machining ribs on the sides of the container. By processing the width and position of the rib according to the width of the arm and claw on the grip side, it is hard to shift and can be firmly grasped. Ribs also have the effect of increasing the strength of the container side.

The jacket can be attached to the outer surface of the container to customize the size to match the robot hand chuck.

Enhance the Stability

If the contents are heavy, the bottom of the container may swell outward, causing the container to shake and become unstable when placed or transported on a conveyor. In this case, customizing the bottom is recommended. For example, if you attach a “Skirt” to the lower part of the container, the bottom will not touch the conveyor and stability will be improved.

It can also be customized to reinforce the bottom by attaching a plate that matches the diameter of the bottom to the outside of the bottom. The bottom is hard to deform and stability is improved. It is also possible to raise the thickness of the container itself without using a reinforcing plate.

You can also customize the bottom by embossing it to increase its strength of the bottom. In addition to increasing the strength of the bottom to prevent it from bulging, the center of the bottom, which tends to bulge, does not come in contact with the conveyor, which improves the stability.

For Easy-Opening

Open by Just Lifting the Lid


If the lid is easy to open and close, it will be easy to be automated. It is recommended to customize the container based on a cover type container, rather than an airtight container with parts to fix the lid. The cover can also be customized with a handle or bracket that matches the robot hand.

Just turn the cap to open it!


If rotating (twisting) motion is possible, a container with a screw cap is recommended. Screws are mainly used in small-capacity bottles. It is also airtight compared to a cap lid.

How to Make Stainless Steel Containers "Easy to Wash" in an Automated Process?

Improve the cleanability of the inner surface of the container

It is recommended to apply electrolytic polishing to the inner surface of the container which directly touches the contents so that it does not get dirty easily. By electrolytic polishing, the inner surface of the container, the residue on the surface is removed and the surface becomes smooth, preventing dirt from sticking.

If you are handling highly viscous liquids, we recommend you to apply fluorine resin coating. It has features such as non-stickiness, which prevents most substances from sticking, and water repellency, which repels water and oil, and can remove dirt quickly.

Improve the washability of the outer surface of the container

There are many parts on the outer surface of the container, and it is a place where unevenness occurs after washing. The parts where dirt and cleaning solution are likely to remain can be customized in consideration of cleanability. Our company can propose sanitary specifications that are superior in cleanability.

For example, we recommend customizing the edge of the container with a curl seal (fully circumferential welding) that completely closes the gap. 

For the handle, we recommend a round bar handle (sanitary type) that can be sealed by welding all the mounting parts.

How to Make Stainless Steel Containers "Manageable" in the Automation Process?

Adding Laser Mark to the Container

Laser-marking is recommended because it is a printing method that does not peel off and does not disappear even after washing, and also prevents tampering. The original control number or QR code can be printed on the side of the container or on the lid.

Add a label pad

It is recommended to add a seal seat which is easy to peel off the label when the label is reattached after managing with bar code labels.

Add a card holder

If you use a paper card, we recommend adding a card holder to prevent it from getting wet and dirty.

Management with RFID
When managed by RFID, the container can be managed by attaching an RF tag. You can customize the container according to how the RF tag is installed.

Designed and manufactured stainless steel containers for automation and robotization

Please let us know the details such as the shape of the container you want, the usage, and the working condition. We will propose the most suitable stainless steel container for you. Please feel free to contact us for information such as product availability and quotation.