The Short Answer
Colour change usually means staining, which is harmless. Brown or grey discolouration with embrittlement means thermal damage, which is not. Distinguishing them takes one squeeze test.
The Four Causes
1. Thermal damage — the one that matters
PTFE begins to degrade above roughly 300°C, and sustained operation above its 260°C service limit causes progressive breakdown. The visual signature is brown, tan or grey discolouration, usually accompanied by the ball becoming brittle, chalky or crumbly at the surface.
Test: press the discoloured area with a fingernail. Healthy PTFE is soft and waxy and marks smoothly. Thermally damaged PTFE feels chalky and may powder.
If you find this, the ball is not your problem — your process temperature is. Look for local hot spots: bulk fluid temperature can be well within range while the ball sees something much hotter at a pump head or near a heating element. No PTFE grade fixes an over-temperature condition.
2. Media staining — the common and harmless one
PTFE is non-absorbent, but pigments, dyes, rust particles and organic residues can adhere to the surface or lodge in machining marks. Dye house balls come out coloured. Balls in iron-bearing water come out orange-brown. Balls in oil service come out amber.
Test: the ball is still soft, flexible and waxy, and the colour often matches something identifiable in the process. Dimensions are unchanged. This is cosmetic — the material is unaffected and the ball can go back in unless the staining itself is a product-contamination concern.
3. Filler exposure on filled grades
If you are running a filled grade, colour change with wear is expected. Glass-filled starts off-white and greys as glass is exposed. Carbon-filled is black from the start. Bronze-filled darkens and can develop green or blue-green corrosion products in wet service — and if you see that in a water or food application, the wrong grade was specified.
4. Reprocessed resin — it was never white
Virgin PTFE is opaque white. Balls molded from reprocessed or reground material are frequently off-white, grey, cream or slightly mottled straight out of the bag. If new balls arrive discoloured before they have seen any service, you have a supply question rather than a process question.
Check a new ball from the same consignment against a known virgin sample. If both are off-colour, ask the supplier directly which resin was used — and treat evasion as an answer.
Quick Diagnostic
| Observation | Likely cause | Action |
|---|---|---|
| Brown/grey, chalky, brittle | Thermal damage | Find and fix the hot spot |
| Coloured but still soft and waxy | Media staining | None — cosmetic |
| Progressive greying on a filled grade | Filler exposure | Normal wear; check interval |
| Green/blue on bronze-filled in water | Bronze corrosion | Wrong grade — switch to virgin |
| Off-white when new, unused | Reprocessed resin | Query the supplier |