Introducing fluororesin gasket.
It is a very popular material as a gasket for piping that requires corrosion resistance.
Fluororesin gaskets and fluororesin-wrapped gaskets are probably famous.
There are many ways to express it, but it is especially famous in batch chemical plants.
For Nichias, Tombo.No.9007 and 9010, and for Valqua, 7010 and 7030 are the model numbers for fluororesin and fluororesin-wrapped products, respectively.
Just knowing these expressions will make you feel like a veteran mechanical and electrical engineer, so let’s understand them!
Fluororesin gaskets are highly corrosion resistant materials
Characteristics of fluororesin gasket and fluororesin-wrapped gasket
Let’s take a look at how the two types of fluororesin gaskets are used properly in a batch-type chemical plant.
Fluororesin gaskets can be broadly classified into two types.
The left is a fluororesin gasket , and the right is a fluororesin-wrapped gasket.
The one on the left is a pure fluororesin gasket , also known as a solid PTFE gasket.
The one on the right is made of PTFE- based fluororesin only on the outside, and has a joint sheet inside.
The joint sheet varies depending on the manufacturer.
Joint sheets originally used asbestos, but after the health hazards caused by asbestos arose, non-asbestos products were introduced.
It is also called non-asbestos joint sheet.
However, non-asbestos has completely penetrated, so is it non-asbestos now? We are living in an era where.
Fluororesin gasket (solid gasket)
Fluororesin gaskets can be used almost anywhere.
Many users will find it useful.
This gasket is the first candidate for places where corrosion resistance is required .
In batch chemical plants, fluororesin gaskets are almost the only choice for stainless steel piping and high-grade metal piping.
A disadvantage of fluororesin is that some gases can pass through it.
This also happens with fluororesin-wrapped gaskets.
There are no other gaskets that can be used, so it is a rare case to use a special gasket to avoid penetration.
The key is to use fluororesin gaskets as standard.
Fluororesin wrapped gasket (jacket gasket)
Fluororesin-wrapped gaskets are considered to be a rare case.
The advantages of fluororesin-wrapped gaskets are as follows:
Advantages of fluororesin gasket
- Slightly cheaper
- cushioned
On the other hand, there are disadvantages as follows.
Disadvantages of fluororesin gasket
- Special handling required for vacuum
- Cannot be processed into complex shapes
Slightly cheaper
Fluororesin-wrapped gaskets are cheaper.
This is simple.
This is because the amount of fluororesin is small.
cushioned
This is the biggest advantage of fluororesin-wrapped gaskets.
PTFE is basically hard.
It has the property of stretching when force is applied, but it is hard.
If a fluororesin gasket is used for glass-lined or fluororesin-lined piping, the glass or fluororesin on the flange surface may be deformed or cracked.
This is because the fluororesin gasket is hard.
For glass-lined or fluororesin-lined piping, it is necessary to make the gasket as soft as possible to make it easier to deform.
The flange surface of glass lining or fluororesin lining is not flat.
In order to create a proper seal here, the gasket must deform significantly.
Special support for vacuum
Fluororesin-wrapped gaskets tend to be sensitive to vacuum.
When operating under vacuum, the outer fluoropolymer part may be drawn inside.
As a countermeasure, there is a method of connecting the outer periphery.
However, this leads to increased costs.
If you are concerned about this, it is easier to use a solid fluororesin gasket.
I want to keep it simple and have as few types of gaskets as possible.
Cannot be constructed into complicated shapes
Fluororesin-wrapped gaskets cannot be constructed into complex shapes.
A good example is the tube sheet gasket of a shell-and-tube heat exchanger.
For one pass, the gasket can be donut-shaped like normal piping and tanks.
More than 2 passes require a gasket inside the donut.
This cannot be achieved with a fluororesin-wrapped gasket.
Gaskets for 1-pass tubesheet on the left and 2-pass on the right.
If more than 2 passes are required, it is physically difficult to install the enveloping gasket.
That’s how much the cost goes up.
In that case, wouldn’t a solid fluororesin gasket be fine? I think.
In the first place, heat exchangers that require fluororesin-wrapped gaskets are limited to glass-lined or fluororesin-lined heat exchangers, and such heat exchangers are basically manufactured in only one pass.
Put a fluororesin-wrapped gasket there.
Contact area of gasket
Since the gasket is wrapped with PTFE, the size changes greatly depending on how the PTFE is wrapped.
How to wrap
There are several ways to wrap PTFE.
- Wrapping only the inner diameter side of the gasket
- A gasket that wraps both the inner diameter side and the outer diameter side of the gasket
- Items wrapped in a way that prevents liquid from accumulating
There are various types like this.
All of these were probably created as a result of user requests.
All of these types have different gasket sizes.
A particularly easy-to-understand comparison is the one that wraps only the inner diameter side of the gasket and the one that wraps both the inner and outer diameter sides.
Since a gasket larger than the bolt hole in the flange cannot be made, the gasket is made smaller by the amount that covers the outer diameter side.
The contact surface of the gasket will change depending on the circumstances of the gasket side.
Flange lining thickness and accuracy
Examples of piping that use PTFE-wrapped gaskets include glass-lined and PTFE-lined piping.
The thickness and precision of these linings vary depending on the manufacturer.
There is a big difference in PTFE lining in particular.
Even though it’s called lining, there are some patterns where it’s not in close contact with the pipes and is just inserted.
Even if you try to match the contact surface of the gasket to the piping side, the contact surface may change due to the circumstances of the piping manufacturer, and the amount of liquid pooling may change.
Accuracy of valves, etc.
The contact surface changes not only depending on the piping side, but also on the accuracy of the valve, etc.
You can easily understand this by comparing the dimensions of the piping, valves, and gaskets used at your factory.
I think there are cases where the contact surface of the gasket can be specified on the valve side rather than on the piping side.
For example, if a PTFE lined valve is used for PTFE lined piping, we expect that the contact surface will not change much.
However, glass lining is thinner than PTFE lining, so if a PTFE lined valve is used for glass lining piping, the contact surface on the glass lining piping side will determine the thickness.
If the valve uses high-grade materials instead of PTFE lining, it may work on the side where the contact surface is smaller than glass-lined piping.
soft type
A slightly unusual type of fluororesin gasket is the “soft” type.
The soft type is sold under the name of Code Seal <Soft> by Valqua, and Soft Seal by Nichias.
Some call it a marshmallow.
This soft type fluororesin gasket is said to be used as an emergency measure.
Soft type fluororesin is for first aid purposes
It seems like it would only be used for first aid purposes, but it can actually be used for a variety of purposes.
I’ll show you how to use it.
First aid purpose
It cannot be denied that soft type fluororesin gaskets are basically used for emergency measures.
For example, use it as follows.
- Use in the flange gap to prevent leakage from the flange
- Used for sealing when tightening with a backing plate and band against pinholes in piping
- Used to seal threaded joints
The soft type is characterized by being able to configure seals of almost any shape.
Taking advantage of this feature, it is very active as an emergency measure.
A molded, fixed shape like a donut-shaped gasket can only be used in a fixed place.
The soft type is not molded, so the range of application is not high.
If the pressure and temperature are as low as in a batch chemical plant, it can be used for a certain amount of time, but if the conditions are harsh, it will only last for a short period of time.
It should be considered as a “connection” until proper repair by SDM.
Soft types, especially tape types, are used on a daily basis for screw connections, but I would classify them in the emergency treatment category.
Because at my workplace, the threaded joint itself is used as a first aid.
Threaded joints are unreliable, and the idea is to think of flange joints as absolute justice.
This area is absolutely not understood by some equipment manufacturers.
Atmospheric equipment seal
The soft type fluororesin gasket can also be used as a seal for atmospheric pressure equipment.
Atmospheric pressure equipment is often equipment that cannot have a pressure-resistant structure in the first place.
A typical example is an outdoor tank.
When the size exceeds a certain scale, it becomes unrealistic to have a general-purpose flange with the facility strength to withstand the flange nominal pressure.
In such an atmospheric pressure facility with a split structure, it is necessary to attach a seal to prevent leakage against subtle pressures.
The soft type can be used as a seal to withstand the slight pressure of large equipment.
General-purpose molded gaskets are expensive due to their large size, but they are not expected to have a high pressure resistance.
In that case, wouldn’t a soft type be better? Don’t you think so?
It can be finished in almost any shape and can withstand a slight pressure.
The characteristics of the soft type itself match the seals of atmospheric pressure equipment.
Transform the joint sheet into a wrapping type
Although it is a feat, the joint sheet can be made into a fluororesin-wrapped gasket.
Among the soft types, the seal type comes into play.
When you wrap the seal around the joint sheet, it’s a wonder.
Doesn’t the joint sheet become a fluororesin-wrapped gasket? (laughs)
Compared to gaskets completely wrapped in fluororesin, the service life is shorter, but it is still sufficient as an emergency measure.
Depending on the usage environment and material procurement environment,
Isn’t there a company that uses a general-purpose joint sheet gasket with a seal wrapped around it instead of a large-diameter fluororesin-wrapped gasket?
Considering that the soft type is made of fluororesin, this is an example of how it can be used in principle.
Fluororesin Gasket Options
Fluoropolymer gaskets are basically made of PTFE.
It is also called a punched gasket.
In a sense, it is a simple product made of PTFE itself and molded as a gasket.
- Temperature : Above 100℃ is not recommended in the manufacturer’s catalog
- Pressure : Up to about 1.0MPa, more than sufficient performance for batch-type chemical plants.
- Thickness: There are several types, but you will only use one of them.
It’s simpler than a general-purpose sheet gasket!
Additive
Gaskets made of PTFE alone have more than sufficient performance, but adding additives can further improve performance.
Fluorine resin is amazing after all.
Excellent reliability.
Except for static electricity and creep…
silica
Adding silica increases overall power.
It can be used at temperatures up to 150-200℃ and at pressures up to 2-3MPa.
For systems that have problems with PTFE alone, it would be a good idea to use a silica-added type as an exception.
carbon
Carbon may be added instead of silica.
Carbon may improve heat resistance and strength, but carbon is weak against nitric acid and sulfuric acid.
It is better not to use it too much as it will lose its versatility.
alumina
Like silica and carbon, inorganic alumina may also be added.
It has higher heat resistance and is stronger than silica.
But of course it’s expensive.
If silica doesn’t work, I think it’s OK to use alumina.
Fluoropolymer-wrapped gasket option
There are various options for fluororesin-wrapped gaskets.
Inner diameter shape
One of the gasket options is in the shape of the inner diameter.
If the inner diameter shape is available as an option, then the outer diameter shape is also available as an option.
First, let’s understand the characteristics of the shape of the inner diameter.
The basic form is as follows.
This type is an inexpensive type that emphasizes ease of production.
Prepare two sheets of fluororesin, sandwich a joint sheet, etc. between them, and weld the inner diameter sides.
The horizontal “Y” shape on the inner diameter side is the result of welding.
This area can cause liquid to pool.
For pharmaceutical products, etc. where liquid should not accumulate, the shape shown in the figure below is used.
It is a so-called “U” shape.
There is no excess liquid pooling, but extra man-hours are required for welding and shaping.
This will lead to an increase in unit prices.
The choice of which basic form to use will depend on whether you dislike liquid puddles or the increase in cost.
I feel like the “U” shape is often treated as an exception…
Outer diameter shape
Next to the shape of the inner diameter is the shape of the outer diameter.
The image below is an option.
A horizontal “Y” shape is also set on the outside.
This is used when there is a vacuum inside the pipe.
Under vacuum, only the fluororesin envelope is sucked into the pipe, leading to troubles such as increased leakage and damage to the gasket.
In order to prevent it from being drawn in even under vacuum, it is OK as long as the outer side is closed.
The following patterns can be considered for closing the outer diameter side, but the idea is the same.
- welding
- sewing together
The following patterns are added to these two types.
- all around
- part
“Sewing” and “part” are the patterns with the lowest degree of adhesion.
A sense of being somehow stuck together.
Since you can see the core, it may be a good option if you want to use different cores with the same closed outer diameter.
“Welded” and “All around” are the patterns with the highest degree of adhesion.
It seems to be used when the degree of vacuum is high.
It may also be used to prevent foreign matter from entering or as a countermeasure against static electricity.
Realistically, you will be limited to either “sewing”, “partial”, “welding”, or “full circumference”.
stainless steel sheet
A thin stainless steel plate is available as an option for the core.
This is to forcibly secure the sealing surface between the gasket and flange.
It is often used for lining flanges where the strain on the flange surface cannot be properly removed.
This applies to both glass lining and fluororesin lining.
Although it is rarely used for pipe flanges, thin stainless steel plates are actively used for nozzles around tanks.
There are two options for stainless steel thin plates.
- flat plate
- corrugated plate
Corrugated sheets can reduce the contact area, resulting in better sealing performance.
Thickness
As with joint sheets, there are several thickness options.
Like the joint sheet, it is difficult to change the existing piping gasket thickness.
Once the thickness is set, it is difficult to change.
In the case of fluororesin-wrapped gaskets, the thickness of the fluororesin-wrapped gasket can be an option in addition to the joint sheet, which is the core.
The thicker the fluororesin wrap, the more difficult it is to be drawn in under vacuum and the more difficult it is for gas to pass through.
However, it is the same in the sense that once the thickness is set, it is difficult to change.
size
It is not enough to set the gasket dimensions according to JIS or ASME flanges.
It is conceivable to change the inner diameter and outer diameter of the lining pipe.
Glass lining and fluorine resin lining are also different.
This is because the thickness of the lining and the R part of the nozzle are different.
In this area, if you contact the manufacturer and say “for ○○”, they will select it.
reference
Related article
Related information
lastly
We have introduced the characteristics of fluororesin gaskets.
Fluororesin gaskets are more versatile, but wrapped gaskets also have advantages such as cushioning and cost.
I think different companies and factories use different methods, but try to determine what is important to you.
Please feel free to post any concerns, questions, or concerns you may have regarding the design, maintenance, and operation of chemical plants in the comments section. (The comment section is at the bottom of this article.)
*We will read all comments received and respond seriously.