Aggressive chemicals, such as acids, and alkalis, represent hazards to personnel and the environment. When selecting a gasket for aggressive chemical service, it is important that the gasket material is compatible with the chemical or media being sealed. If the material is not compatible, chemical attack will begin to degrade it and break it down. In this blog, we give some guidance that buyers should consider when selecting gaskets for aggressive chemicals.
What are aggressive chemicals?
Aggressive chemicals include the following:
- Strong acids (i.e., nitric acid, sulphuric acid, hydrofluoric acid, etc.)
- Strong alkalis (i.e., sodium hydroxide, potassium hydroxide, etc.)
- Halogens (i.e., bromine, chlorine, etc.)
- Aromatic hydrocarbons (i.e., benzene, toluene, etc.)
- Bleaching agents (i.e., sodium hypochlorite)
What types of applications require gaskets for aggressive chemicals?
Applications and equipment that often involves aggressive chemicals include pumps, mixers, instrumentation, filling systems, etc. Because the gaskets used in this equipment face operating conditions that normal seals do not encounter, key factors that should be considered in material selection include the following:
- The gasket material must be resistant to both chemical attack and premature aging due to the presence of the chemical being sealed.
- The gasket material must not leach anything that could cause an adverse reaction with the chemical being sealed.
- If the gasket is being used in equipment or a device which must cleaned or sterilized, the material should be capable of withstanding these activities.
What types of gasket materials are appropriate for sealing aggressive chemicals?
The following material types are often used to fabricate gaskets for aggressive chemicals. The choice of a particular material depends upon the media being sealed and the compatibility of the material.
Nitrile (or NBR) rubber is used with fuels and oils. It has very good resistance to these substances, and is able to seal when fluctuations of temperature are present. Nitrile is generally used in automotive and machine environments, or anywhere that fuel and oil are commonly used.
This elastomer offers good resistance to ozone, steam, strong acids and alkalis, but is not suitable for solvents and aromatic hydrocarbons.
This elastomer is a fluorinated hydrocarbon which offers excellent resistance to acids, alkalis, aliphatic hydrocarbons, oils and many aggressive chemicals. It is not suitable for amines, esters, ketones or steam. Viton® is a brand of fluoroelastomer developed by DuPont. Viton® GF-S material demonstrates excellent resistance to strong caustics. Following immersion in a 30 percent potassium hydroxide solution for 1 week at 100°C, this polymer exhibited high retention of properties and low volume swell, even versus a dedicated base resistant TFE / Propylene copolymer.
PTFE rubber has extremely wide chemical resistance – PTFE gaskets are attacked only by molten alkali metals and fluorine gas. PTFE gaskets also have high compressibility, which allows them to conform well to flange surface irregularities. While these gaskets are easy to handle, have low permeability and an extremely low coefficient of friction, the material can be prone to relaxation and creep. To avoid issues with relaxation and creep, CRG manufactures PTFE gaskets using the following materials:
- Restructured manufactured PTFE sheet. Restructured manufactured sheet is now the preferred gasket material for strong caustic service where the operating temperature is less than 204.4°C (400°F). Restructured PTFE sheet will do an excellent job in these applications. CRG uses Tealon™ TF 1570, TF 1580, and TF 1590 restructured PTFE gasket material for moderate and strong caustic service. Tealon™ sheet, manufactured by Teadit North America, is a premium quality restructured sheet that is the exact material equivalent of Gylon®. The unique manufacturing process for Tealon™ results in a sheet that has less creep and cold flow than that normally associated with PTFE gasket material.
- Multi-directionally expanded PTFE sheet. CRG supplies gaskets manufactured from Teadit 24SH sheet. 24SH gasket sheet is manufactured by expanding 100% virgin PTFE using a proprietary process that produces a uniform and highly fibrillated microstructure with equal tensile strength in all directions. The resulting product exhibits characteristics significantly different than conventional PTFE sheet. This style is much softer and more flexible than regular PTFE sheet and thus conforms easily to irregular and rough surfaces. In addition, the material is easier to compress and minimizes creep and cold flow. Gaskets made from 24SH sheet will seal all aggressive chemicals over the entire 0-14 pH range, except for molten alkali metals and elemental fluorine.
CRG can supply gaskets for aggressive chemicals made from a wide range of materials. All gaskets we make are precision cut using the latest CNC technology in our ISO 9001:2015 certified facility. We offer responsive service and high quality, and no order is too large or small for us to produce. To find out more about the gaskets for aggressive chemicals that we can supply, please contact our sales team at email@example.com.