Aggressive chemicals, such as strong acids and caustics, can eat through some gasket materials, causing leaks which can be hazardous to health and safety. Besides depositions of the leaked materials, leaked chemicals can also vapourize, releasing hazardous fumes and toxins into the surrounding atmosphere.
Selecting gasket materials for sealing aggressive chemicals
Chemical compounds usually classified as aggressive 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)
When choosing gaskets for sealing aggressive chemicals, it is critical to match the gasket material to the chemical compound being sealed. A material which seals one aggressive chemical effectively may not necessarily work as well when used with a different compound. Experienced and reputable gasket manufacturers will be able to give guidance on what material works best against a given type of compound.
Applications that involve the aggressive chemicals noted above include those often found in industrial and resource-based processes. Equipment that requires gaskets and seals resistant to aggressive chemicals includes pumps, mixers, instrumentation, filling systems, valves and pipework, etc. For these uses, it is important to consider the following points when selecting gaskets for sealing aggressive chemicals:
- The gasket material must be resistant to attack and premature aging resulting from contact with 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 be cleaned or sterilized, the material should be capable of withstanding these activities.
Gaskets for sealing aggressive chemicals
At CRG, when we are fabricating gaskets and seals for aggressive chemical applications, we often use the following elastomeric materials:
- Nitrile (NBR). Nitrile rubber has very good resistance to fuels and oils. This material can be used to fabricate gaskets which are used in automotive and machine environments, or those where fuel and oil are commonly used.
- EPDM. This elastomer offers good resistance to ozone, steam, and strong acids and alkalis, but is not suitable for sealing solvents and aromatic hydrocarbons.
- Fluoroelastomer (FKM). Commonly known as Viton, a DuPont brand, this elastomer is a fluorinated hydrocarbon which offers high resistance to acids, alkalis, aliphatic hydrocarbons, oils, and many other aggressive chemicals. FKM possesses very good resistance to most acids, including sulphuric acid (except fuming), hydrochloric acid, nitric acid (except >50% concentration and red fuming), and other acidic media. Gaskets made from FKM elastomer are not suitable for sealing amines, esters, ketones or steam.
- PTFE. 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). For these applications, CRG uses Tealon™ TF 1570, TF 1580, and TF 1590 restructured PTFE gasket material for moderate and strong caustic service. This material is the exact 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. Gaskets made from this material have characteristics significantly different than those made from conventional PTFE sheet – the material is much softer and more flexible than regular PTFE sheet, conforming more readily to irregular and rough surfaces. In addition, the material is easier to compress and minimizes creep and cold flow. Gaskets made from this material will seal most aggressive chemicals over the entire 0-14 pH range, except for molten alkali metals and elemental fluorine.
CRG can help guide customers on which materials are appropriate for a given application, depending upon the chemicals being used and their fluid rating against various elastomers. When multiple chemicals are being used in an application, the chemical with the most aggressive fluid rating should be used to evaluate the appropriate material to select. Irrespective of whichever material is selected, a good rule to follow when sealing aggressive chemicals is to limit each gasket to a single use. Reusing gaskets to save costs is inadvisable due to the risks of failure and serious injury to personnel. In aggressive chemical applications, all used gaskets should be safely destroyed immediately after use to prevent any inadvertent reuse.
CRG can supply a wide range of custom-cut gaskets for sealing aggressive chemicals. All gaskets we make are produced 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 sealing aggressive chemicals that CRG can supply, please contact our sales team at firstname.lastname@example.org.