What pitfalls should you watch out for when purchasing insulating gaskets
An insulating gasket kit is bought for one reason: to keep a flanged joint electrically isolated while it holds pressure. Most purchasing mistakes are made before the purchase order is signed: a low quote, a vague data sheet, or a supplier who answers technical questions with marketing words. The three pitfalls below cover material substitution, missing parameters and weak supplier qualification, and each one comes with a check that exposes it. The same discipline applies to ordinary flange gaskets, where the material certificate decides service life as much as the price.
Low Quotes and Material Substitution
Insulating performance is decided by the gasket compound and its reinforcement, not by the drawing or the label on the box. The lowest offer in a tender usually cuts cost at exactly that point, and the difference only shows up after installation.
- Reclaimed rubber or low-grade resin in place of the specified compound: the sheet shows irregular bubbles and inclusions, the edge breaks easily and a sharp smell may be present.
- Thinner or softer reinforcement than the approved sample, so the gasket extrudes under bolt load and the insulating layer is lost.
- Test reports that are missing, copied, or silent on the two values that matter: dielectric strength and volume resistivity.
Ask for samples before the order and inspect them properly: check the surface, cut an edge, note any strong odour. Then request third-party test reports and read dielectric strength (for example >=14 kV/mm) and volume resistivity first. A price comparison that ignores these two numbers is not a comparison at all.
Insulating gasket set: gasket, insulating sleeves and insulating washers.
Parameters Buyers Leave Undefined
Thickness and outside diameter are easy to check, so most buyers stop there. Whether the kit survives service depends on other values, and every one of them belongs in the purchase specification.
Where pipe flanges work at high pressure, the fire-resistance rating of the gasket (API 6FB, for example) and its behaviour at temperature matter more than any single dimension: a kit that fails during a fire or a hot excursion takes the whole joint with it.
| Parameter | What to request | Why it matters |
|---|---|---|
| Dielectric strength | Third-party report, e.g. >=14 kV/mm | Decides whether the joint isolates at the working voltage |
| Volume resistivity | Reported value at service temperature | Surface moisture and heat drive resistivity down |
| Temperature range | Continuous and short-term limits | Compounds age and lose strength above their limit |
| Fire behaviour | Fire-resistance certificate such as API 6FB | Required where the joint must hold during a fire |
| Thickness vs voltage | Matching rule, e.g. 5 mm for 10 kV insulation mats | Undersized thickness arcs over at rated voltage |
Table 1. Parameters to write into an insulating gasket purchase specification.
For critical equipment request type test certificates rather than routine factory inspection reports, and write the acceptance values into the order, not only the material name.
Flange insulation kit assembled on a pipeline joint.
Screening Suppliers Before the Order
Insulating gaskets cover a wide range of duty, from silicone pads for electronic assemblies to fire-resistant insulation kits on petrochemical pipelines, and the requirements are nothing alike. A supplier who cannot tell a high-temperature vermiculite gasket from an ordinary rubber one will not give useful advice.
- Credentials: ISO 9001/14001/45001 plus the qualification that matters for your industry - API 6FB fire resistance for petrochemical duty, nuclear-grade seal manufacturing permits for nuclear plant, UL flammability ratings for electronics.
- Independent testing: send randomly selected samples to a recognised laboratory and let dielectric strength, volume resistivity and ageing results decide.
- Case history: ask for references in similar duty - high temperature, high pressure or strongly corrosive media - and for the problems that were solved, not for the number of certificates collected.
- Service: design review against your drawings, handling of non-standard sizes, installation guidance and periodic inspection advice.
Procuring insulating gaskets is buying safety and reliability. Reject the lowest quote that cannot prove its material, define the parameters in the specification, and screen suppliers on credentials, verified data and relevant case history: that is what protects the equipment and the people who work around it.
FAQ
What is the difference between an insulating gasket and a standard flange gasket?
An insulating gasket adds electrical isolation to the seal: the gasket, sleeves and washers break the metallic path across the joint, while a standard flange gasket only seals.
Which parameters belong in the purchase specification?
Material compound, thickness, dielectric strength, volume resistivity, temperature range, pressure class and fire-resistance requirements, each with its acceptance value stated.
How can I verify that the delivered material matches the approved sample?
Compare the delivered sheet with the retained sample, then confirm dielectric strength and volume resistivity on a third-party report against the values written into the order.
Can an insulating gasket kit be reused after the joint is opened?
Plan on a new kit. Gaskets, sleeves and washers take a permanent set under bolt load, and reusing them risks both leakage and loss of isolation.
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