How to Choose the Right Mounting Flange Material and Gasket for a PTFE Heater

The PTFE heater is mounted to the tank on the mounting flange. The flange material must be suitable with the tank wall to prevent galvanic corrosion and the gasket must seal against the process fluid without degradation. "Choosing the right flange and gasket materials is critical to system integrity and long-term performance.

Typical Flange Materials for PTFE Heaters Applications
The material of the mounting flange is critical to provide a dependable leak-free connection of the PTFE heater to the tank. The flange materials should be suitable with the tank material to avoid galvanic corrosion and to create a tight seal. Common materials for flanges are:

316L Stainless Steel
The most frequent and universal material for mounting flanges is 316L stainless steel. It has good corrosion resistance, especially in chloride-rich conditions, and is hence suited for many industrial applications. This material is very robust and works well in high and low temperature ranges. This makes it a great choice for most tank systems.

Plastic Tank Flanges
For tanks of polypropylene (PP), polyvinyl chloride (PVC) or polyvinylidene fluoride (PVDF) it is necessary to select a matching flange made of plastic to avoid galvanic corrosion. In these circumstances, a PTFE-lined steel flange can be utilised, which combines the advantages of a solid metal structure with chemical resistance of PTFE, giving a stable bond without the possibility of galvanic couples. These kind of flanges are especially useful for chemical processing areas where tanks of plastic materials are ubiquitous.

Titanium Flange
Titanium flanges are a great alternative for the most harsh chloride conditions like seawater or very corrosive chemical operations. Titanium is a great material for demanding industrial applications owing to its high strength-to-weight ratio and superior corrosion resistance, especially in the presence of chlorides.

In practice, the material of the mounting flange for PTFE heater applications needs to be selected in accordance with the construction of the tank. Corrosion : Using different materials might cause corrosion which weakens the flange and can break the seal.

Selection of Gasket Materials
The gasket forms the essential seal between the PTFE heater and the tank, avoiding leaks and preserving system integrity. The material selected must be compatible with the bath chemistry and able to endure the operating temperature. Some of the most prevalent gasket materials are:

PTFE Gaskets (Solid or Envelope) 
PTFE gaskets are resistant to a lot of chemicals, thus they are appropriate for most applications requiring PTFE heaters. Depending on the sealing requirements, both solid PTFE gaskets and envelope gaskets (with a PTFE envelope surrounding another material) are utilised. PTFE gaskets offer universal chemical resistance and are suited for corrosive or high-temperature applications.

A typical standard is solid PTFE for extremely corrosive fluids and envelope gaskets when extra mechanical support is required, especially in dynamic or high pressure applications.

Viton Gasket
Viton is resistant to acids and high temperatures; appropriate for use in applications where acidic fluids are present. Viton is elastic and seals well but is not good for strong caustic solutions as it can deteriorate in that environment. Viton is widely used for chemical processing applications in acids but should be avoided in strong bases.

EPDM Rubber Gasket
EPDM (Ethylene Propylene Diene Monomer) gaskets are widely utilised on hot water, steam and alcohols applications. EPDM is very resistant to high temperatures and water vapour. However, EPDM gaskets swell in the presence of oils and solvents and are therefore not advised for use with them.

The gasket is an inexpensive part yet a key seal that is important for leak-free operation. Avoiding premature degradation and failure is critical and depends on the selection of the proper material considering the bath chemistry and the operating temperature.

Technical Aspects of Flange and Gasket Selection
Technical standards have to be addressed while defining the mounting flange and gasket materials:

Flange Standards: Flange design and bolt patterns are standardised by ANSI, DIN and JIS. It is important that the flange bolt pattern match the tank nozzle to guarantee good installation and sealing.

Gasket Compression Set: The gasket should be able to maintain a stable seal over time without compression set. Compression set and chemical resistance information is usually available from the gasket makers and should be considered in material selection.

Material Compatibility Chart
The following table gives some common tank materials and process fluids with recommended flange and gasket options to help you select the proper materials for your flange and gasket.

Tank Material Flange Material Gasket MaterialTypical Process Fluid 
Polypropylene Steel with PTFE or Plastic liner Solid PTFE or EPDMAlkalis, Acids
PVC Plastic or ptfe walled steel Solid ptfe or EPDM Water, acids
PVDF Plastic or PTFE-lined Steel Solid PTFE or Viton Strong acids, solvents 
Stainless Steel Stainless Steel 316L PTFE, Viton or EPDM Chlorides, solvents, water
Titanium Titanium PTFE / Vitonchloride extreme situations
Summary
The gasket and mounting flange are important parts of a leak-free, corrosion resistant installation of a PTFE heater. Proper attention to flange material compatibility with the tank design and cautious gasket material selection based on bath chemistry and temperature will result in reliable performance during the life of the heater. The gasket and flange materials must be designed to withstand the chemical environment as well as mechanical loads to produce a long term, maintenance free seal. Moreover, the heater is part of a bigger system and all interfaces have to be designed for compatibility in order to keep the system integrity and performance.