Scope of this guide
Management version: pitting as cost and claim risk — the metrics, the audit points, and the record discipline that wins disputes.
Pitting is the most-asked bright nickel defect on finishing forums — and most answers online jump straight to anti-pitting additive. This series (four levels) starts from classification instead.
The triage table: six pits, six causes
Magnifier pass first. Every pit type has a signature; match before you mix anything.
| Pit type (magnifier) | Signature look | Root cause | First fix |
|---|---|---|---|
| Gas pit | Teardrop tail, shiny bottom | Hydrogen sticking to the part | Raise surface tension to 35–45 dyn/cm |
| Solids pit | Gritty rough bottom | Particles in bath or on part | Filter finer; improve pre-dip |
| Burn pit | Dendritic, on high-CD zones | Local current density too high | Lower CD / reposition anodes |
| Base-metal pit | Pit in substrate visible under deposit | Porosity or scale on casting | Bake-test; fix upstream casting |
| Oil pit | Doughnut ring, wet look | Oil droplet pinned to surface | Skim, degrease, check cleaner |
| Organic pit | Irregular, random spread | Decomposed brightener | Hull cell test; carbon treat |
Cost, FPY and claims
Beyond the triage table, this is your working layer:
| Cost line | Driver | Metric | Lever |
|---|---|---|---|
| Rework hours | Chronic pit share | FPY by defect family | Anode/agitation fix, not additives |
| Chemical spend | Blind anti-pitter dosing | Surface tension log compliance | Dose by measurement only |
| Claims | No tank records | Tank card completion rate | Audit 5 cards per week |
| Scrap | Base-metal pits re-plated | Bake-test rejection rate | Push porosity upstream |
The 10-minute routine
- Photograph the part before touching it — pit pattern is evidence
- Magnifier pass: classify each pit by the table (tail = gas, grit = solids, ring = oil)
- Position test: mark rack row of each pit cluster (bottom row = agitation dead zone)
- Swap test: move suspect rack position to the middle for the next load
- Run one corrective action only; Hull cell before and after
- Log dose, readings and outcome on the tank card
Engineer notes
- Most pitting calls are gas pits misdiagnosed — measure surface tension before adding anything
- Bottom-row pitting with a clean bath means agitation dead zone, not chemistry
- Boric acid below 40 g/L burns before it pits; keep 40–50 g/L in Watts
- Air agitation louder is not better: coarse bubbles pin to surfaces
- Pits that show substrate metal are not a plating problem — fix casting first
Hydrogen from bright nickel baths is explosive in enclosed air at 4–75% volume. Keep tank lids open, ventilate, no flames. Nickel salts are skin sensitisers — nitrile gloves, apron, eyewash at the tank.
FAQ
What does chronic pitting cost us?
Rework at 8% means one in twelve pieces double-handled; the case study cut 8% to 0.5% with anode and agitation changes only — no chemistry purchase.
Which metric exposes pitting early?
FPY by defect family per week; pitting share rising two weeks in a row is the trigger to audit surface tension and filtration.
How do we defend a customer claim on pitting?
With the tank card log: surface tension, filter hours, Hull cell photos. Claims settle on records, not arguments.