A flange insulation kit has three dielectric barriers: the central gasket at the faces, the sleeve through each bolt hole, and the washer under each nut and bolt head. The last two are a pair. The sleeve isolates the stud shank from the flange bore; the washer isolates the nut from the flange face. If the sleeve is present but the washer is missing (or replaced with steel during maintenance), the nut contacts the flange and the cathodic protection circuit grounds through the bolting. If the washer is present but the sleeve is missing, the stud shank touches the flange bore and the same thing happens. Both are required — they are not interchangeable, and neither one alone completes the barrier.
Slides over each stud bolt and fills the annular gap between the bolt shank and the flange bolt hole.
Sits under each nut and typically under each bolt head, isolating the fastener from the flange face.
| Dimension | G10 Insulation Sleeve | G-10 Glass Epoxy Washer |
|---|---|---|
| Function | Isolates stud shank from flange bolt hole | Isolates nut/bolt head from flange face |
| Standard thickness | 1/32″ wall (≈0.7–0.8 mm) | 1/8″ thickness (3–3.2 mm) |
| Length / OD/ID | Length set by joint stack-up; diameter range 8–800 mm | Matched to bolt size; standard metric and imperial |
| Material standard | NEMA LI-1 G-10; ASTM D709 G-10 | NEMA LI-1 G-10; ASTM D709 G-10 |
| Compressive strength | 50,000–66,000 psi (form/method dependent) | 50,000–66,000 psi (form/method dependent) |
| Dielectric strength | 550–800 V/mil class (batch dependent) | 550–800 V/mil class (batch dependent) |
| Continuous temperature | 130°C–150°C (form/standard dependent) | 130°C–150°C (form/standard dependent) |
The sleeve and the washer share the same G10 material system but have different dimensional logic. The sleeve length is calculated from the flange thickness, gasket thickness and washer thickness — a stock tube cut to any length is not a functional sleeve. The washer is matched to the nut and bolt size, with 1/8″ being the flange-kit standard. For a deep dive on each component, see the G10 insulation sleeve page and the G-10 glass epoxy washer page.
| Material | Compressive Strength | Continuous Temperature | Best For | Avoid When |
|---|---|---|---|---|
| G10 Glass Epoxy | 50,000–66,000 psi | 130°C–150°C | Cathodic protection, high bolt load, humid/wet service, long life | Cost-sensitive dry service where phenolic is sufficient |
| Phenolic | 25,000 psi (typical) | 104°C–120°C (typical) | Standard pressure, dry service, cost-sensitive kits | Wet/humid service, high bolt load, cathodic protection |
| Mylar (PET) | Not load-bearing; lower compressive resistance | ≈105°C–120°C | Low-pressure, low-temperature kits; cost-down | Cathodic protection, high bolt load, vibration/thermal cycling |
G10 is the default for washers and sleeves in cathodic protection kits because it holds wall thickness, dielectric strength and compressive strength under bolt load and moisture. Phenolic is the cost-down option for dry, moderate-duty service. Mylar is a valid sleeve material for low-pressure isolation where bolt load and thermal cycling are modest, but it is not the material to specify when the joint is under cathodic protection. For the complete kit where the sleeve and washer are supplied with a gasket, see the flange insulation gasket kit range.
These components are often ordered as a set. To quote correctly, state:
1. Sleeve: bolt/stud size, flange bolt hole diameter, flange thickness, gasket thickness, washer thickness — the sleeve length is calculated from this stack-up. 2. Washer: bolt size or ID × OD × thickness; 1/8″ is the flange-kit standard. 3. Quantity: pieces per size. 4. Material grade: NEMA LI-1 G-10 (standard) or alternative. 5. Order type: sleeve only, washer only, or both as a pair. Standard sizes ship in 5–10 days; custom dimensions in 10–20 days; custom cut MOQ 500 pieces per size.
For high-pressure or RTJ service where a standard G10 washer/sleeve pair is not sufficient, see the VCS very critical service kit.
Send bolt size or ID × OD × thickness/length, quantity, and whether ordering sleeve, washer, or both. Engineering team confirms G10 grade, dimensions and lead time.
Request Washer & Sleeve QuotationA flange isolation kit has three dielectric barriers, and the sleeve is the one that goes through the hole. The central gasket isolates the flange faces. The G10 insulation sleeve slides over each stud bolt and fills the annular gap between the bolt and the flange bore — without it, the bolt shank touches the flange hole and the cathodic protection circuit grounds through the fastener. Kaxite manufactures NEMA LI-1 G-10 sleeves from epoxy-impregnated woven glass tube: 1/32″ standard wall, 8–800 mm diameter range, ≥400 V/mil sleeve-grade dielectric strength, 130–150°C continuous. Standard sizes ship in 5–10 days; custom diameters cut from 500 pieces per size.
A flange insulation kit has three dielectric components, 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 barrier, and the one most often left out during maintenance. Kaxite manufactures NEMA LI-1 G-10 washers from continuous woven glass fabric laminated with epoxy resin: 65,000 psi compressive strength, 0.05% water absorption, 150°C continuous, dielectric strength in the 550–800 V/mil class depending on batch thickness. Standard bolt sizes in metric and imperial, 1/8″ flange-kit thickness, custom ID/OD cut from 500 pieces per size. Standard sizes ship in 5–10 days; custom in 10–20 days.
