PTFE (Polytetrafluoroethylene) lined and other fluoropolymers Columns / vessels are widely used in the chemical industry due to their exceptional chemical resistance, non-stick properties, and high thermal stability. Here’s why they are preferred:

How Fluoropolymer column / Vessels are manufactured

1. Using paste extruded liner.

In the process using paste-extruded PTFE liners, column segments are fabricated according to the customer’s drawing specifications, using materials such as MS or other required materials. Where branches or nozzles are present on the segment, specially machined flanges (This weakens original flange structure) are welded onto the column body. If flanges are not machined, pipes are welded between the column segment and flange. After completing the fabrication process, a PTFE paste-extruded liner is lined on the segment. Part of the liner is stretched from the nozzle, and this stretched portion is flared onto the nozzle flange. However, a challenge with this method is that the flared portion is thinner than the column segment liner. As this process relies heavily on the worker’s craftsmanship, there is a possibility of leakage at the joining point. In some cases, this method may fail during hydro testing.

2. Using Sheet lining

PTFE (Polytetrafluoroethylene) sheet welding is commonly used for lining large tanks to provide a chemically resistant and non-stick surface. Since PTFE has a high melting point and is chemically inert, special techniques are required for welding.

PTFE Sheet Welding Methods for Large Tanks

Butt Welding (Fusion Welding)

Used to join PTFE sheets by applying heat and pressure.

The sheets are heated to the melting point and pressed together.

Suitable for thick PTFE sheets (above 3 mm).

Requires precise temperature control to avoid degradation.

Overlap Welding (Hot Gas Welding)

Involves overlapping two PTFE sheets and applying hot air or a heated wedge.

A special welding rod may be used as filler material.

Suitable for thinner sheets (1–3 mm) and curved tank linings.

Ensures a continuous, leak-proof seam.

Thermal Bonding

Uses a special heat-activated adhesive to bond PTFE sheets.

Used in applications where direct welding is challenging.

Often reinforced with mechanical fasteners for tank linings.

Pressure Welding

Utilizes a combination of heat and mechanical pressure.

PTFE sheets are heated and pressed together under controlled conditions.

Provides high-strength joints for industrial tanks.

Key Considerations for PTFE Welding in Large Tanks

Temperature Control: Precise heating is crucial as PTFE decomposes above 400°C.

Surface Preparation: The sheets must be clean and free from contaminants.

Seam Strength: The welds must withstand chemical exposure and mechanical stress.

Equipment Used: Hot air welders, heated plates, or wedge welders are typically used.

3. Roto Lining

This is most proven but very expensive (In case of PFA) process for fluoropolymer column and lined vessel manufacturing.  General fluoropolymer resin used are ETFE, PFA, FEP, PVDF. Roto lining is a seamless, high-performance lining technique used to coat the interior of metal tanks, pipes, and process equipment with PFA. This method provides a strong, uniform, and chemical-resistant surface, making it ideal for industries such as chemicals, pharmaceuticals, and food processing. PFA is a fluoropolymer similar to PTFE but has better melt-processability, allowing it to be rotationally molded. It offers excellent thermal and chemical resistance, making it suitable for highly corrosive environments.

Advantages of Roto Lining with PFA

Seamless Lining: Unlike sheet welding, rotational lining eliminates weak points or joints, significantly reducing the risk of leakage.

Excellent Chemical Resistance: PFA withstands exposure to highly aggressive chemicals, including strong acids, bases, and solvents.

High Temperature Resistance: PFA can operate continuously at 260°C and withstand intermittent exposure up to 300°C.

Superior Adhesion and Durability: The liner is fully bonded to the metal surface, providing long-term durability even under mechanical stress.

Non-Stick and Low Friction Properties: PFA’s non-stick surface prevents material buildup, making it ideal for food, pharmaceuticals, and chemical applications.

Uniform Thickness: The process ensures an even distribution of PFA throughout the interior surface.

Limitations of PFA Roto Lining

High Initial Cost: The specialized equipment and material cost are higher compared to traditional lining methods.

Size Constraints: Large tanks and complex geometries may require customized rotational equipment.

Controlled Process: Requires precise temperature and rotation control to ensure even thickness and proper adhesion.

Conclusion

When lining a column, it is crucial to design and fabricate its segments properly, as this process depends entirely on the column designer. Paste-extruded lining is the most widely used method in India and worldwide, but it requires a skilled workforce for successful implementation. Paste-extruded columns are generally limited to 600 NB; beyond this size, sheet lining is preferred. However, only a few companies can manufacture liners beyond 600 NB.

PFA roto lining is the most reliable and durable method for column and vessel lining, even for irregular shapes, but it is also the most expensive process and still in development stage.

Why PTFE, ETFE, PFA, FEP, PVDF Resins are used for column and vessel lining?

Chemical Resistance of PTFE (Polytetrafluoroethylene)

Fluoropolymers are the one of the most chemically resistant materials available, making it a preferred choice for handling aggressive and corrosive substances in various industries. Below is a detailed breakdown of its chemical resistance properties:

General Chemical Resistance

Highly Resistant To:

• Strong acids (e.g., Hydrochloric acid, Sulfuric acid, Nitric acid, Hydrofluoric acid)
• Strong bases (e.g., Sodium hydroxide, Potassium hydroxide, Ammonia)
• Organic solvents (e.g., Acetone, Benzene, Toluene, Chloroform)
• Oxidizers (e.g., Chlorine, Bromine, Peroxides)
• Alcohols and ketones
• Gases (e.g., Hydrogen, Oxygen, Nitrogen, Halogens)
• Salts and aqueous solutions

Limited Resistance To:

• Alkali metals (e.g., molten Sodium, Potassium, Lithium) can react with PTFE at high temperatures.
• Fluorine gas at elevated temperatures can degrade PTFE.
• Some highly reactive halogenated compounds may affect PTFE over extended periods.

Corrosion Protection of PTFE (Polytetrafluoroethylene)

PTFE is widely used for corrosion protection in industrial applications due to its exceptional chemical resistance, non-reactivity, and non-stick properties. It serves as a protective barrier against aggressive chemicals, moisture, and extreme environmental conditions.

1. Why PTFE is Corrosion-Resistant?

PTFE’s corrosion resistance is primarily due to:

· Strong Carbon-Fluorine (C-F) Bonds – One of the strongest bonds in chemistry, making it highly stable and non-reactive.

· Non-Polar and Hydrophobic Nature – Prevents water and chemical penetration.

· Low Surface Energy – Reduces adhesion of corrosive substances.

· High Thermal Stability – Withstands temperatures up to 260°C (500°F) without degradation.

2. How PTFE Provides Corrosion Protection?

PTFE protects materials from corrosion in three key ways:

A. PTFE Coatings (Spray or Dip Coating)

• Applied as a thin layer on metal surfaces to protect against chemical exposure.

B. PTFE Linings (Thicker Protective Layer)

• Used in chemical storage tanks, reactors, and pipes to prevent metal corrosion.
• Provides superior resistance to acids, alkalis, and solvents.
• Common in industries handling hydrochloric acid, sulfuric acid, nitric acid, and chlorine.

C. Fluro Polymers Roto Lining

• PFA, ETFE, FEP, PVDF Like fluoropolymers roto lining grades are used for lining of vessels.

3. Advantages of PTFE Corrosion Protection

·         Extends Equipment Life – Reduces replacement and maintenance costs.

·         Works in Extreme Conditions – Handles high temperatures and harsh environments.

·         Low Maintenance – Non-stick surface reduces chemical buildup.

·         Ensures Safety – Prevents leaks and chemical reactions in industrial settings.

High Temperature Resistance

PTFE can withstand temperatures up to 1500C to 260°C (500°F) while maintaining its properties.

This makes it suitable for chemical reactions and processing at elevated temperatures.

Non-Stick & Low Friction

PTFE has a very low coefficient of friction, preventing material buildup inside the vessel.

This helps in easy cleaning, reduces contamination, and improves process efficiency.

Electrical Insulation

PTFE is an excellent electrical insulator, making it useful in processes where electrochemical reactions occur.

Safety & Purity

Since PTFE does not react with most chemicals, it ensures product purity.

It is commonly used in industries like pharmaceuticals, food processing, and semiconductors.