Chemical Resistance - Caps and Plugs

One purpose of caps and plugs is to protect your application from the damaging effects of chemicals. Beware when you make your choice. Not all caps and plugs are equal in providing the protection you need, which is why your choice of material is critical. In this article we cover: 

• The chemical resistance of caps and plugs
• Plastics at a glance
• Rubber at a glance
• The masking process
• General Purpose
• Masking
• Hose and Cable Protection
• Automotive
• Oil and Gas

View our range of caps and plugs

The chemical resistance of caps and plugs

Chemicals can come into contact with any application. It doesn’t have to be part of the manufacturing process. Here’s a look at the plastics chemical resistance of the materials that caps and plugs are made of. We’ll start with plastics, according to the British Plastics Federation:

Chemical Resistance	LDPE	HDPE	Nylon	EVA	PP	PVC	TPE
Dilute Acids	Excellent	Excellent	Poor	Excellent	Very good	Very good	Excellent
Dilute Alkalis	Excellent	Excellent	Moderate	Excellent	Very good	Very good	Excellent
Oils and Grease	Moderate (Variable)	Moderate (Variable)	Excellent	Good	Moderate (Variable)	Good (Variable)	Excellent
Aliphatic Hydrocarbons	Poor	Poor	Excellent	Excellent	Poor	Very good	Excellent
Aromatic Hydrocarbons	Poor	Poor	Excellent	Poor	Poor	Poor	Poor
Halogenated Hydrocarbons	Poor	Poor	Good (Variable)	Poor	Poor	Moderate (Variable)	Poor
Alcohols	Excellent	Excellent	Good (Variable)	Excellent	Very good	Good (Variable)	Excellent

 

Plastics at a glance:

• Low Density Polyethylene (LDPE): Can withstand the cold, specifically temperatures down to -50ºC before it becomes brittle.
• High-density polyethylene (HDPE): Low permeability to gases and moisture makes it a good choice for protecting NPT thread ports from dirt and other contaminants.
• Nylon: Most nylons are semi-crystalline. Usually very tough materials, nylons offer good thermal and chemical resistance.
• Ethylene Vinyl Acetate (EVA): Has low-temperature toughness, stress-crack resistance, and hot-melt adhesive waterproof properties. It’s also resistance to UV radiation.
• Polypropylene (PP): An extremely versatile material, tough with good chemical and fatigue resistance.
• Polyvinyl Chloride (PVC): Most popular polymer in the world, PVC is durable and long lasting.
• Thermoplastic elastomers (TPE): Soft and resistant to UV rays. Some manufacturers class TPE as a rubber.

Rubbers

The following table gives an overview on the chemical resistance of rubbers.

Chemical Resistance	EDPM	Nitrile	Silicone	TPR
Resistance to weather and UV rays	Excellent	Poor	Poor	Excellent
Water resistance	Excellent	Good	Excellent	Excellent
Chemical resistance	Excellent	Excellent	Very good (Variable)	Excellent
Resistance to gas permeability	Excellent	Excellent	Poor	Excellent
Resistance to ageing due to stream	Excellent	Fair to good	Poor at temperatures over 150°C / 302°F
Compatibility with ketones	Excellent	Poor	Poor to fair
Compatibility with alcohols	Excellent (Variable)	Fair to good	Poor

 

Rubber at a glance:

• Ethylene Propylene Diene Monomer (EPDM): Very flexible and similar to silicone, but with a lower temperature range.
• Nitrile: While noted for its excellent resistance to oil, it’s resistance to DOT 3 brake fluids is less than satisfactory.
• Silicone: In addition to providing the ideal material for masking caps and plugs, silicone’s chemical inertness makes it well suited for surgical and food-processing equipment.
• TPR: High resistance to chemicals; combines the properties of rubber with the moulding capabilities of thermoplastics.

The masking process

Different materials are used to suit different purposes. For instance, caps and plugs made of low-density polyethylene (LDPE) are ideal for protecting applications during shipping because of its high-impact strength. It does offer excellent resistance to some chemicals, but it would not be suitable for the intensity of masking processes. When placed in high temperatures, it becomes soft, making it more susceptible to the effects of many chemicals. So what materials should your caps and plugs be in that instance?

Your aim is to protect holes, studs and electrical contact points, of course. Here’s a look at how materials common to masking caps and plugs stand up to the process you have in mind:

Application	TRP	Paper	EPDM	PVC	Silicone	Nylon 6.6	High-Temp Vinyl
Powder Coating	✔	✔	✔	✔	✔		✔
E coating	✔		✔	✔	✔		✔
Anodising	✔		✔	✔	✔		✔
Plating	✔		✔	✔	✔		✔
Wet Paint	✔	✔	✔	✔	✔	✔	✔

 

General Purpose

• Moss caps and plugs: Stands up to oil and greases and resists acids
• Finned hole plugs: Ideal for use in thin-walled copper tube recommended
• Moss plugs: Recommended for hydraulic and general engineering applications
• Grease nipple caps: Protect grease nipples from ingress of dirt when not engaged with its mating part
• UNF standard threaded plugs: Opt for plugs with an optional O-ring, which gives an ultra-tight seal to protect against leakage
• UNF standard threaded molded O-ring plugs: Prevents oil leaking and ingress of contaminants
• Threaded protection plugs:: Protects against dirt, moisture and corrosion
• NPT threaded plugs: Protects threads from contaminants and moisture
• Pipe plugs: Resistant to most chemicals, moisture and salt water
• Fluid absorption plugs: Absorbs different substances with inherent chemical resistance
• Threaded protection caps: Protects against moisture and dust

 

Masking

• High-temperature plugs: Excellent sealing capacities for plain and threaded holes
• High-temperature caps: Can also be used as plug to mask threaded and non-threaded holes. Useful to protect threaded components.
• Easy Pull Masking Cap: Internal seal prevents paint ingress
• Moss caps and plugs: Good resistance to acids

Hose and Cable Protection

 

• Heatshrink end caps: Provides a water-tight seal against moisture, dirt and corrosionsuitability
• Fire Protection Sleeves:: Protects against liquid metal splashes
• Hose protection sleeves: Resistant to ozone
• Expandable cable sleeves: hose protection that provides chemical resistance
• Hexagonal caps: protects hydraulics by sealing liquids
• Quick Release Plugs: Fits at the end of hoses to protect against moisture and corrosion
• Pull tab hose plug: seals hydraulic hoses to protect against liquids

Automotive

• Stud protection caps: Protect BSP and UNF threads against contaminates
• Driveshaft protection caps: Doesn’t just resist tears and splitting, but also resists oils and most chemicals.

 

Oil and Gas

• LPG caps: These products helps prevent dangerous gas leaks
• Gas cylinder valve caps: These products protects against ingress of dust and dirt and available with a vent flat to allow the safe release of gas
• Clear adhesive discs: This range is resistant to petrol, oil and non-oxidisation acids
• Protects petroleum, gas and water type valve flanges

Download free CADs and try before you buy

Download free CADs and request free samples, which are available for most of our solutions. It’s a great way to ensure you’ve chosen exactly what you need. If you’re not quite sure which product will work best, our experts are always happy to advise you.

Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.

Questions?

Email us at sales@essentracomponents.co.uk or speak to one of our experts for further information on the ideal solution for your application 0345 528 0474.