G-10 Glass Epoxy Washer
Product Description
Product Detail
G-10 Glass Epoxy Washer Manufacturer — Flange Insulation Washer for Galvanic Corrosion & Cathodic Protection, Standard & Custom Sizes
The Third Dielectric Barrier — and the One Most Often Left Out
A Flange Insulation Kit Has Three Barriers, Not One
The central gasket isolates the flange faces. The sleeve isolates the bolt shank from the bolt hole. The G-10 glass epoxy washer isolates the nut and bolt head from the flange face — the third dielectric barrier. In a fully insulated flange joint, all three must be present. A kit installed without the washers, or with washers that have cracked or been replaced with steel washers during maintenance, leaves the bolting in direct contact with the flange. That single contact point shorts out the cathodic protection system and opens a galvanic corrosion path between dissimilar metals. The washer is not an accessory. It is a functional component of the isolation system.
G-10 Washer vs Phenolic Washer — Material Choice in a Flange Kit
| Dimension | G-10 Glass Epoxy (this page) | Phenolic washer |
|---|---|---|
| Compressive strength | 65,000 psi | 25,000 psi (typical) |
| Water absorption | 0.05% | 1.6% (typical) |
| Continuous temperature | 150°C (302°F) | 104°C–120°C (typical) |
| Dielectric strength class | 550–800 V/mil (batch dependent) | 500 V/mil (typical) |
| Best for | High bolt load, humid/wet service, higher temperature, long service life | Standard pressure, dry service, cost-sensitive kits |
In a flange isolation kit, the washer sits under the nut and carries the full bolt load through a small contact area. A phenolic washer can crush or absorb moisture under high load; a G-10 washer maintains thickness and dielectric strength under the same load. If the kit is specified for cathodic protection on a pipeline, G-10 is the default washer material. For the complete kit where the central gasket is phenolic or G-10, see Type E full-face isolation kits or Type F raised-face kits.
Technical Data — NEMA LI-1 G-10 Washer
| Material | Continuous woven glass fabric, epoxy resin laminate |
|---|---|
| Standard | NEMA LI-1 G-10; ASTM D709 G-10; IEC 60893 EP GC 201 |
| Compressive strength | 65,000 psi |
| Flexural strength | 65,000 psi |
| Tensile strength | 50,000 psi |
| Water absorption | 0.05% |
| Continuous operating temperature | 150°C (302°F) |
| Dielectric strength | 550–800 V/mil class (confirm batch data sheet for the specific thickness) |
| Standard flange-kit thickness | 1/8″ (3.175 mm) |
| Standard bolt sizes | Metric M3–M24; imperial #4–1″ |
The G-10 washer is one component in a complete isolation kit. For the full kit configuration — central gasket, sleeves and washers — see the flange insulation gasket kit range. For G-10 sleeves as the matching component, see G10 insulation sleeves.
Standard Bolt Sizes and Custom Dimensions
| Bolt size | Typical ID | Typical OD | Common thickness |
|---|---|---|---|
| M3 / #4 | 3.2–3.5 mm | 7–9 mm | 0.5–1.5 mm |
| M4 / #8 | 4.3–4.5 mm | 9–12 mm | 0.5–2.0 mm |
| M5 / #10 | 5.3–5.5 mm | 10–14 mm | 0.8–2.0 mm |
| M6 / 1/4″ | 6.4–6.7 mm | 12–18 mm | 1.0–3.0 mm |
| M8 / 5/16″ | 8.4–8.7 mm | 16–24 mm | 1.0–3.0 mm |
| M10 / 3/8″ | 10.5–10.8 mm | 20–30 mm | 1.5–4.0 mm |
| M12 / 1/2″ | 13.0–13.5 mm | 24–37 mm | 2.0–5.0 mm |
| M16–M24 / 5/8–1″ | 17–25 mm | 30–56 mm | 2.0–6.0 mm |
Dimensions above are industry reference ranges for standard bolt-clearance washers. For flange-kit service, the washer OD and thickness are matched to the nut and the flange facing; 1/8″ thickness is the flange-kit standard. Custom ID/OD/thickness combinations are machined to drawing. State the bolt size and kit requirement at inquiry.
Applications — Where the G-10 Washer Is Specified
The G-10 washer is the standard insulating washer in flange isolation kits for cathodic protection systems, where the bolting must be electrically isolated from the flange to prevent the protection current from grounding through the fastener. It is also specified for galvanic corrosion isolation between dissimilar metal flanges — aluminum to stainless, carbon steel to stainless, copper alloy to steel — where a metal-to-metal contact at the nut would create a corrosion cell. Other uses include replacement washers for existing kits, electrical isolation on busbar and switchgear hardware, and any bolted assembly where a non-conductive washer must carry bolt load without crushing. For a complete VCS kit where the washer is supplied with a metal-core gasket, see the VCS very critical service kit.
MOQ, Lead Time and Ordering Specification
Standard bolt sizes: ship in 5–10 days. Custom ID/OD/thickness: 10–20 days. Custom cut MOQ: 500 pieces per size. OEM and wholesale pricing applies for volume orders. To quote correctly, specify: bolt size (or ID × OD × thickness), quantity per size, whether the washer is a standalone replacement or part of a complete kit, and any standard or drawing requirement (NEMA LI-1 G-10 / ASTM D709 G-10). This is a machined laminate part, not a catalog washer — the more precisely the dimensions and standard are stated, the faster the quotation.
Buyer FAQ
- What does the G-10 washer actually do in a flange insulation kit?
- It isolates the nut and bolt head from the flange face — the third dielectric barrier after the central gasket and the bolt sleeve. Without it, the bolting provides a conductive path that shorts out cathodic protection and allows galvanic corrosion between dissimilar metals.
- G-10 vs phenolic washer — which should I use?
- G-10 for high bolt load, humid or wet service, higher temperature (150°C), and cathodic protection systems where dielectric stability matters. Phenolic is acceptable for standard pressure, dry service, and cost-sensitive kits where bolt load is moderate.
- What is the standard thickness for a flange-kit G-10 washer?
- 1/8″ (3.175 mm) is the flange-kit standard. Other thicknesses are available for custom kits; state the nut size and kit requirement.
- Can I order G-10 washers as a replacement for an existing kit?
- Yes. Standard metric and imperial bolt sizes ship in 5–10 days. Match the ID to the bolt/stud size and the OD/thickness to the original washer; if the original dimensions are not known, send the bolt size and flange rating.
- What standard does the G-10 washer meet?
- NEMA LI-1 G-10, equivalent to ASTM D709 G-10 and IEC 60893 EP GC 201. Batch material certificates are available on request.
- What is the MOQ for custom-cut G-10 washers?
- 500 pieces per size for custom ID/OD/thickness. Standard bolt sizes have no custom-cut MOQ and ship in 5–10 days. OEM/wholesale pricing applies from the first order for standard sizes.
Send bolt size or ID × OD × thickness, quantity, and whether this is a standalone replacement or a complete kit requirement. Engineering team confirms material grade, standard and lead time.
Request G-10 Washer Quotation