Category Archives: Perfluoroelastomers

How to Choose the Best Sealing Materials Based on Chemistry & Strong Oxidizers

Strong oxidizers can damage metal, causing pitting or rust and treating possible safety concerns.

In chemistry, strong oxidizers are substances (like chromic acid) that can cause other substances (like seals and gaskets) to lose electrons. So, an oxidizer is a chemical species that undergoes a reaction that removes one or more electrons from another atom.

This causes a change in mass. Metals will turn into their respective heavier oxides, and the carbon in graphite will oxidize into carbon dioxide—which, although molecularly heavier, is a gas at room temperature.

This happens in pumps, valves, pipelines or any other equipment that have seals and gaskets carrying a strong oxidizer. It will cause pitting or rust and, depending on your choice of seal material, may require shorter service intervals. Ultimately, you may have to look for a more suitable material that can handle strong oxidizers.

More importantly, an oxidizing agent can cause or contribute to the combustion of another material.

The U.S. Department of Transportation defines oxidizing agents specifically. DOT’s Division 5.1(a)1 means that a material may enhance combustion or quickly raise pressure causing a rapid chemical reaction. A fire may start or, even worse, create or facilitate an explosion.

There have been instances of fires or explosions in mining, chemical process and even fertilizer factories where strong oxidizers were used.

Deadly Force

A West Texas fertilizer company storage and distribution facility caught fire on April 17, 2013. As firefighters attempted to extinguish the blaze, the plant exploded with the force of 10 tons of TNT, killing 15 people and injuring 200. It destroyed 60 nearby homes and left a 93-foot-wide crater where the plant once stood.

All said, it is important to choose the right sealing material for strong oxidizers. There are multiple products on the market for the chemical processing, oil and gas, mining and aerospace industries.

Gasket Selection - PTFE
PTFE (Polytetrafluoroethylene) Molecule

A fluoropolymer, such as polytetrafluoroethylene (PTFE), can handle most strong oxidizers, as long as the temperature is below 260 C (500 F). This is also true with a modified PTFE because they are chemically inert and stable.

Strong oxidizers will weaken most other material to various degrees. Much of a material’s capability to withstand a strong oxidizer depends on the used concentration, the service temperature and the service pressure. Therefore, consult with the sealing material manufacturer to ensure compatibility.

How Graphite Handles Strong Oxidizing Environments

Graphite starts as natural mineral flake and is mined in various parts of the world. The flakes form a layered structure of completely crystalline graphite, which is essentially elemental carbon. In this form, it is used for products like powdered lubricant and lead in pencils. It has excellent lubricity in this form.

Expanded graphite is produced with the use of strong oxidizing agents such as sulfuric and nitric acids. The acids weaken the bonds between the graphite layers, the flakes are then rinsed, dried and exposed to high heat.

The heat causes the layers to separate and expand dramatically to form expanded worm-like macro structures. The structures can then be recompressed into flexible graphite forms.

Graph Lock Flexible Graphite Garlock
Garlock’s Flexible Graphite, GRAPH LOCK

Flexible graphite is a soft material that is resistant to many strong chemicals and high heat. It has a low coefficient of friction and is proven to be advantageous over braided carbon or graphite fiber packings mainly as it is a better conductor of heat—a plus on moving shafts.

Flexible graphite is also naturally lubricious, conformable and resilient. It has good corrosion resistance and is compressible, allowing it to conform to most mating surfaces or valve cavities.

The chemical compatibility of flexible graphite can be enhanced with a blocking agent like PTFE. However, flexible graphite’s temperature limit will be restricted by PTFE’s limit of 260 C (500 F). If high temperature is an issue, this configuration will not work.

Flexible graphite, in combination with PTFE, is an extremely effective material in sealing fugitive emissions or volatile organic compounds (VOCs). VOCs have been targeted by several government agencies as a source of air pollution. Although, flexible graphite alone has a long way to go in stopping all fugitive emissions, it is a trusted sealing material for valves, flanges and stems in the chemical process, power generation, and oil and gas industries.

Flexible Graphite Pitfalls

Flexible graphite may be susceptible to chemical attack in the presence of strong oxidizing fluids, including air at extremely high temperatures. These include liquids such as 20 percent concentration of nitric acid or a 98 percent concentration sulfuric acid, the same chemicals that are used to break down mined graphite into expanded graphite flake.

Some flexible graphite compositions include oxidation inhibitors or are physically structured to extend temperature capability when exposed to these extra strong oxidizers.

The class of organic chemicals that should not be used are those that are highly oxidizing like nitrates, persulfates, perbenzoates and peroxides. Unacceptable compatibility for inorganic chemicals includes molten sodium, potassium hydroxide and chlorine dioxide.

However, many of the chemicals depend on the concentration, and some engineering groups can create an inhibitor that is right for a specific oxidizer. For instance, a 704 stainless steel cladding provides the user with protection against strong oxidizers while still providing the benefits of flexible graphite.

When in doubt, do a test loop using a pump to pressurize the strong oxidizer exposing it to flexible graphite. The pressure, temperature and concentration of the oxidizer must be exact as used in service, as to provide some idea of how the material will react to a given chemical.

It is easier to list the chemicals that are not compatible with flexible graphite (about 50) than those that are (more than 600 tested). A list of incompatible materials are listed below:

Strong Oxidizers for Flexible Graphite

  • Aqua Regia
  • Bromine (dry)
  • Calcium Chlorate
  • Calcium Hypochlorite
  • Calcium Nitrate
  • Chlorazotic Acid
  • Chlorine Dioxide
  • Chlorine Trifluoride
  • Chloric Acid
  • Chloroazotic Acid
  • Chloronitrous Acid
  • Chromates
  • Chromic Acid
  • Chromic Anhydride
  • Chromium
  • Chromium Trioxide
  • Dichloropropionic Acid
  • Dichromates
  • Hydrogen Dioxide
  • Hydrogen Peroxide
  • Lime Nitrate
  • Lime Saltpeter
  • Molten Alkaline
  • Nitrates
  • Nitric Acid
  • Nitric Oxide
  • Nitrocalcite
  • Nitrohydrochloric Acid
  • Nitromuriatic Acid
  • Norge Niter
  • Norwegian Saltpeter
  • Oleum (Fuming
  • Sulfuric Acid)
  • Oxygen (above +600 F)
  • Ozone
  • Perchloric Acid
  • Permanganate Solutions
  • Persulfates
  • Perbenzoates
  • Perborates
  • Peroxide Potassium
  • Bichromate
  • Potassium Chlorate
  • Potassium Chromate
  • Potassium Dichromate
  • Potassium Nitrate
  • Sodium Chlorite*(over 4%)
  • Sodium Hypochlorite
  • Sodium Peroxide
  • Sulfuric Acid
  • Sulfur Trioxide

For more information about which materials would be the best fit for your specific chemical application, contact Gallagher Fluid Seals today.

This original article was featured on the Pumps & Systems website and was written by Mark Freeman.

Elastomer Seals for Instrumentation: Seal/Groove Design

Seal Design: Instrumentation IndustryGallagher recently released our High Performance Elastomer Seals for the Instrumentation Industry White Paper.  This was written by Russ Schnell, an Elastomer Consultant contracted by Gallagher Fluid Seals, and a former Senior Application Engineer with the Kalrez® perfluoroelastomer parts business at DuPont.  This white paper is now available for download on our Resources page.

Below is the third and final section of the white paper, which will discuss the importance of proper seal and groove design.


Proper Seal & Groove Design

Elastomer Seal: Perfluoroelastomer PartsProper seal design is a necessity for elastomer seals to perform reliably over the long term. Many of the instrument applications mentioned above use o-ring seals. The suggested compression for an elastomer o-ring seal to perform properly is typically a minimum of 16%, and a maximum of 30%. However, this range must also take into account the thermal expansion of an elastomer at elevated temperatures as well as any swell due to chemical exposure. Many of the elastomer seals used in instruments are small o-rings, which can create design issues. This is especially true for perfluoroelastomer parts which have a relatively high coefficient of thermal expansion (CTE). Fluoroelastomers have a lower CTE, making seal design easier at elevated temperatures.

Continue reading Elastomer Seals for Instrumentation: Seal/Groove Design

Elastomer Seals for Instrumentation: Laboratory Equipment

Elastomer Seals for Instrumentation: Laboratory EquipmentGallagher recently released our High Performance Elastomer Seals for the Instrumentation Industry White Paper.  This was written by Russ Schnell, an Elastomer Consultant contracted by Gallagher Fluid Seals, and a former Senior Application Engineer with the Kalrez® perfluoroelastomer parts business at DuPont.  This white paper is now available for download on our Resources page.

Below is the second section of the white paper, diving into applications where the measurement is made in analytical laboratories which employ numerous solvents in a wide range of analyses and test equipment.


Laboratory Equipment

The final set of instrumentation is laboratory test equipment. As opposed to the laboratories in chemical plants, which often perform the same routine analyses on plant process streams, general analytical labs employ numerous solvents in a wide range of analyses and test equipment. As such, the ability of seals to resist a breadth of chemicals without degradation or leaching contaminants into a sample is of great importance. Although instrument seals are easily replaced in a laboratory environment, this operation still takes a technician time. It is always easier if the system can be flushed with a cleaning solvent and then be ready to run the next sample versus having to change out an elastomer seal due to incompatibility with a solvent.

Continue reading Elastomer Seals for Instrumentation: Laboratory Equipment

FFKMs Protect Components in Enhanced Oil Recovery

FFKMs, also known as perfluoroelastomers, were first developed in the 1960s for applications involving high temperatures and/or aggressive chemicals.  Perfluoroelastomers exhibit many properties similar to PTFE (polytetrafluoroethlyene, or Teflon®), and are considered inert in almost all solvents.  However, PTFE is a plastic, and when compressed, it will not recover to its original shape.  On the other hand, elastomers contain crosslinks, which act as springs to give the material resiliency and the ability to recover after a part has been compressed – this resistance to permanent compression gives the material the ability to maintain a seal over time. (To learn more about perfluoroelastomers, download our Introduction to Perfluoroelastomers White Paper).

The article below was recently published on FlowControlNetwork.com, and discusses how FFKMs are being used in oil & gas exploration, as production companies are increasingly operating in high-pressure, high-temperature (HPHT) downhole conditions.


HOW FFKMS PROTECT COMPONENTS IN ENHANCED OIL RECOVERY OPERATIONS

Companies are increasingly operating in high-pressure, high-temperature downhole conditions.
Enhanced oil recovery uses gas, steam or chemical injection to improve flow rate. All graphics courtesy of AGC

Improving technologies and methods to increase the recovery of oil from existing reservoirs is a global challenge. In the U.S., oil production at reservoirs can include three phases: primary, secondary and tertiary (or enhanced) recovery. The U.S. Department of Energy (DOE) estimates that primary recovery methods — which rely on the natural pressure of the reservoir or gravity to drive oil into the wellbore, combined with pumps to bring the oil to the surface — typically tap only 10 percent of a reservoir’s oil. Furthermore, secondary efforts to extend a field’s productive life — generally by injecting water or gas to displace oil and drive it to a production wellbore — still only push recovery totals to between 20 and 40 percent of the original oil in place. Clearly, much untapped oil and gas remains in existing wells.

Continue reading FFKMs Protect Components in Enhanced Oil Recovery

Elastomer Seals for Instrumentation: In-Line Process

High Performance Elastomer Seal for InstrumentationGallagher recently released our High Performance Elastomer Seals for the Instrumentation Industry White Paper.  This was written by Russ Schnell, an Elastomer Consultant contracted by Gallagher Fluid Seals, and a former Senior Application Engineer with the Kalrez® perfluoroelastomer parts business at DuPont.  This white paper is now available for download on our Resources page.

Below is the first section of the white paper, diving into applications where the measurement is made at the process and the results then transmitted to a control system.  This section will review the four types of in-line measurement devices, all involving slightly different elastomer sealing applications.

In-Line Process Applications

Flowmeters

Flowmeter - Elastomer Seal for InstrumentationFlowmeters are used to measure the flow of liquid. In this section we will only consider the measurement of liquid flow in a closed piping system. Several examples of flow measurement devices include: flowmeters, Venturi tubes and orifice plates.

Note that these devices are “in-line” and require isolating the process line to remove and repair, or replace the measurement device. Shutting down a process to remove a device is time consuming, involves loss of production, and may require specific procedures to protect the operators and environment when a line is opened. All of these devices require seals to prevent leakage of the process to the environment and the elastomer seals should last the life of the flowmeter. For aggressive chemicals or high temperature applications, FKM or FFKM seals are an excellent choice. These products offer a long service life and resist deterioration in harsh environments.

Continue reading Elastomer Seals for Instrumentation: In-Line Process

NEW! Elastomer Failure Modes – Part 4

Failure ModesGallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site.  This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the fourth and final section of our new white paper, discussing Volatiles (offgassing) and Particle Generation.  To download the white paper in its entirety, visit our Resources Page, or click on the image to the right.


Failure Modes of Elastomers in the Semiconductor Industry

Failure ModesHigh performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.

Continue reading NEW! Elastomer Failure Modes – Part 4

NEW! Elastomer Failure Modes – Part 3

Failure ModesGallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site.  This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the third section of our new white paper, discussing O-Ring Stretch, Chemical Attack, Plasma Cracking, and Permeation.  To download the entire white paper, visit our Resources Page, or click on the image to the right.


Failure Modes of Elastomers in the Semiconductor Industry

Failure ModesHigh performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.

Continue reading NEW! Elastomer Failure Modes – Part 3

NEW! Elastomer Failure Modes – Part 2

Failure ModesGallagher recently published its Failure Modes for Elastomers in the Semiconductor Industry White Paper, now available for download on our site.  This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the second section of our new white paper, discussing Loss of Sealing Force, and Extrusion.  To download the white paper in its entirety, visit our Resources Page, or click on the image to the right.


Failure Modes of Elastomers in the Semiconductor Industry

Failure ModesHigh performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.

Continue reading NEW! Elastomer Failure Modes – Part 2

NEW! Elastomer Failure Modes White Paper

Failure ModesGallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site.  This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the first section of our new white paper, discussing groove design and seal leakage.  To download the entire white paper, visit our Resources Page, or click on the image to the right.


Failure Modes for Elastomers in the Semiconductor Industry

Failure ModesHigh performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.

Continue reading NEW! Elastomer Failure Modes White Paper

Semiconductor Manufacturing – Summary

Semiconductor Manufacturing - Wet Processes

NEW White Paper Available!

Gallagher Fluid Seals recently added a new white paper to its Resources Page, Perfluoroelastomers for the Semiconductor Industry, written by Russ Schnell.  Below is an excerpt from the new white paper discussing the key reasons to choose perfluoroelastomers over fluoroelastomers for semiconductor manufacturing.  You can download the white paper in its entirety by clicking on the thumbnail to the right.

 


Perfluoroelastomers (e.g. Kalrez® parts), often replace fluoroelastomer (e.g. Viton®) in semiconductor applications. However, even though perfluoroelastomers are the highest performance elastomers, there are still subtle differences between products. It is suggested that the elastomer supplier be contacted regarding the optimum product and seal design for specific applications. As mentioned above the key characteristics of perfluoroelastomers include:

  • Lower offgassing than other elastomers, especially at temperatures above 200°C, which lowers the risk of product contamination.
  • Better sealing force retention (lower compression set) at temperatures over 200°C, which is critical for longer service.
    Best overall chemical resistance of any elastomer family.
  • Formulations with extremely low particle generation in aggressive process environments.
  • Generally higher gas permeation than fluoroelastomers.
  • Higher coefficient of thermal expansion when compared to fluoroelastomers. Proper seal design will account for this and optimize performance.

Continue reading Semiconductor Manufacturing – Summary