Seal Face Materials: Carbon, SiC, and Tungsten Carbide
How to match seal face material pairs to the actual service — carbon/SiC, SiC/SiC, and WC/WC, when each runs, and where each fails.
The seal plan picks the seal — but inside the seal, the face material decision is yours.
Three pairs you'll see on every pump in the field. Picking the wrong pair is the difference between a five-year run and a five-month one.
Carbon vs SiC — the workhorse pair
Carbon-graphite primary face running against a silicon carbide seat is the workhorse pair. Self-lubricating, forgiving on dry-running for short events, cheap to replace. John Crane Type 1, EagleBurgmann MFL85N, Flowserve ISC2, Chesterton 280 — all sell variants of this pair.
Where it works: clean water, light hydrocarbons, ambient temperatures, PV under 500,000 (psi × ft/min).
Where it fails: abrasives, sustained dry running, anywhere the carbon will pull blisters.
SiC vs SiC — the abrasion-resistant pair
Both faces silicon carbide. Hard, hard, and hard. PV up to 1,500,000+, abrasion-resistant, runs in slurries. The catch: SiC vs SiC has zero tolerance for dry running. Lose flush flow for 30 seconds and you'll glaze the faces.
This pair lives or dies on Plan 32 reliability and on operators who actually watch the flush flow indicator.
Tungsten Carbide vs Tungsten Carbide — the thermal-shock pair
The thermal-shock-resistant pair. Used on hot hydrocarbons, temperature-cycling services, and anywhere SiC will fracture. Less abrasion-resistant than SiC, but it survives a thermal swing that would crack a SiC face.
Trade-off: more expensive, harder to lap to a flatness spec, runs hotter under the same load.
The match most field techs miss
Matching the face pair to the actual service, not to what was in the BOM the last time the seal was rebuilt. A lot of pumps are running on inherited specs that were right ten years ago and aren't right now because the process changed.
If you're running carbon vs SiC on a slurry service, the seal won't tell you it's wrong. The wear-metal trend in the bearing oil report will. We covered how to read those reports in Reading a Journal Bearing Oil Report — copper spikes and rising iron can both point at upstream seal issues.
The face material decision is downstream of the plan selection. Get the API 682 plan right first. Then match the faces to the service the plan is controlling.
Are you a pump or seal specialist? Build your verified profile on MechTie — list your API 682 OEM authorizations, your Plan 53A/B field hours, your factory training. Plants searching for specific seal experience will find you.
