Phenolic Insulating Washers
Product Description
Product Detail
Phenolic Insulating Washers for Flange Bolt Isolation — OEM Bulk Supply
Phenolic insulating washers fit on the studs between the flange and the flat steel washers, breaking the electrical path between the fastener and the flange face. Together with an insulating gasket at the joint face and insulating sleeves through the bolt holes, they complete the three-component isolation system used on every mixed-metal or cathodically protected flanged joint.
Manufactured from fabric-reinforced laminated phenolic (also available in non-asbestos sheet), these washers deliver good mechanical strength and dimensional stability, excellent dielectric strength, and low moisture absorption. They work with any standard sleeve material — polyethylene, Mylar, Minlon or phenolic — and are stocked in standard metric and imperial bolt sizes for immediate supply.
What Phenolic Insulating Washers Are and Where They Are Used
Phenolic insulating washers are dielectric washers fitted onto the flange studs between the nut (or bolt head) and the flat steel washer. Their job is to isolate the fastener from the flange metal so no current can flow between the two sides of the joint — the third of the three dielectric components that together isolate a flanged joint.
The base material is fabric-reinforced laminated phenolic — a composite made from woven fabric impregnated with phenolic resin and cured under heat and pressure into a dense, dimensionally stable sheet. Unlike a moulded plastic washer, the laminate holds its shape and strength under sustained bolt load, so the isolating layer does not creep or extrude when the joint is torqued to specification.
Washers are stocked in standard metric and imperial bolt sizes for immediate supply, and are also supplied as complete kits with matching gasket and sleeves, or cut to non-standard dimensions on request.
Technical Specifications
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- Material
- Fabric-reinforced phenolic laminate
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- Thickness
- 1/8" (3.175 mm) standard
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- Alternative Material
- Non-asbestos laminate on request
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- Surface
- Plain-faced phenolic standard
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- Standard Sizes
- Metric and imperial bolt sizes
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- Custom Sizes
- Cut to ID / OD / thickness
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- Compatible Sleeves
- Mylar, Minlon, Polyethylene, Phenolic
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- Supply Format
- Individual or complete kit
Key Properties of Phenolic Laminate
Phenolic vs G-10 vs Mylar — Material Selection
Three insulating washer materials are commonly specified in the pipeline industry. Phenolic is the default, cost-efficient choice for most standard joints. G-10 / G-11 glass epoxy is specified where the joint runs hotter or where higher mechanical strength is required. Mylar is generally used for sleeves rather than washers. Compare the three below.
Standard choice for most pipeline joints. Balanced cost and performance.
- Good mechanical strength
- Excellent dielectric strength
- Low moisture absorption
- Stocked in metric and imperial sizes
- Works with all standard sleeves
Higher temperature and higher strength option. See G-10 and G-11 pages.
- Higher mechanical strength
- Higher max service temperature
- Very low water absorption
- Higher cost per piece
Generally used for bolt-hole sleeves rather than washers. See Mylar sleeve.
- Excellent dielectric strength
- Very low water absorption
- Flexes rather than cracks
- Thin-section only
Where the Washer Sits in the Isolation System
Insulating a flanged joint requires breaking every current path through the connection. In a fully insulated joint that means three dielectric components working together — remove any one and the isolation fails.
At the flange face. Type D, E or F geometry depending on the flange standard.
Through each bolt hole. Typically Mylar, Minlon, polyethylene or phenolic.
On the stud between the flange and the flat steel washer. Breaks the fastener-to-flange path.
Between the phenolic washer and the nut — protects the washer from scuffing under the torque.
Typical B2B Applications
Ordering Phenolic Insulating Washers
Washers are supplied in standard metric and imperial bolt sizes or cut to your specific inside diameter, outside diameter and thickness. Send the following details and Kaxite will return a quotation — typically within one working day for standard sizes.
Phenolic Insulating Washer — FAQ
What is a phenolic insulating washer made from?
It is made from fabric-reinforced laminated phenolic — a composite of woven fabric impregnated with phenolic resin, cured under heat and pressure into a dense sheet, then machined to the required ID, OD and thickness. A non-asbestos laminate variant is also available on request.
How does the phenolic washer fit into a flange insulation kit?
A fully insulated joint has three dielectric components: the gasket at the flange face, the sleeve through the bolt hole, and the washer on the stud between the flange and the flat steel washer. The phenolic washer is the third of these — it breaks the current path between the fastener and the flange face. Removing or omitting any one of the three will cause the isolation to fail.
What is the difference between phenolic and G-10 / G-11 washers?
Both are dielectric laminates. Phenolic is the standard, cost-efficient choice for most pipeline joints. G-10 and G-11 are woven glass fabric laminates with higher mechanical strength and higher maximum service temperature — see the G-10 and G-11 pages. If the joint runs hot or needs higher strength, specify G-10 or G-11; for standard joints phenolic is usually sufficient.
Can phenolic washers be supplied with matching sleeves and gaskets?
Yes. Washers are supplied as individual components or as part of a complete flange insulation kit with matched sleeves and gaskets. Available sleeves include Mylar, Minlon, polyethylene and phenolic — see the phenolic sleeve and insulation sleeve pages.
Do you supply standard metric and imperial sizes from stock?
Yes. Standard metric and imperial bolt sizes are stocked for immediate supply — typically 5–10 days depending on quantity. Custom non-standard ID / OD / thickness combinations are produced to order, generally 10–20 days.
What thickness is standard, and is custom thickness available?
The standard thickness is 1/8" (3.175 mm). Custom thicknesses are available on request — send the required finished thickness and we will confirm feasibility and lead time.
What quantity is required for OEM / wholesale pricing?
OEM and wholesale pricing applies from the first order for standard metric and imperial sizes, and from 500 pieces per size for custom-cut washers. Send the annual or project quantity and we will quote the volume tier.
Can phenolic washers be used together with Mylar sleeves?
Yes. Phenolic washers are compatible with any standard sleeve material — Mylar, Minlon, polyethylene or phenolic. The sleeve material is chosen separately based on the joint's temperature and mechanical requirements; the washer material is chosen for its dielectric and mechanical properties under the bolt head.
Request a Phenolic Insulating Washer Quotation
Send the bolt diameter, washer OD, thickness and quantity — or the flange standard and size for a complete kit quotation. Kaxite supplies phenolic washers for OEM flange insulation kits, maintenance replacement, and standalone electrical insulation applications.