Step 1
Electroless deposition
Nickel is deposited chemically, without external current – so the layer grows evenly, with no build-up on edges.
Nickel diffusion coating
Corrosion protection at the surface – without changing the alloy.
Hard, chloride- or detergent-bearing water attacks an uncoated stainless sheath and builds scale on it. In nickel diffusion coating, an electroless nickel layer is deposited on the stainless-steel sheath and diffused into the surface by heat treatment, giving an adherent, nickel-rich surface that resists corrosion.
Layer thickness: typically 10 – 15 µm, checked with our coating-thickness gauge on every batch; a specific thickness is agreed on the drawing.
For washing-machine and water-heater elements in hard water it is a lower-cost option to an Incoloy 825 sheath. The coating is applied by our division Balçık Brazing.
Water heating
How it is made
Two steps: deposit evenly, then diffuse.
The layer is built up chemically and then bonded into the sheath by heat – it does not sit on the surface like a plated skin.
Step 2
Diffusion heat treatment
Heat diffuses the nickel into the stainless surface: the layer is bonded to the base metal and stays adherent in service.
What it protects against
Pitting and scale – where plain AISI 304 reaches its limit.
In hot wash water and hard tap water, chlorides attack an uncoated 304 sheath, and lime builds up on the hottest surface in the appliance – the element.
Corrosion
A dense, nickel-rich surface protects the sheath against chloride pitting and detergent attack.
Scale
Lower scale adhesion on the sheath. A moderate surface load remains the first defence against lime.
Same element design
Only the surface changes: geometry, coil, terminals and fittings of the element stay as they are.
Limits: it is a surface treatment, not a bulk alloy – for the most aggressive media specify Incoloy 825. Scale still forms in hard water. Mechanical damage that cuts through the layer exposes the base metal.
Where it is used
Washing machines and water heating: coat the surface or upgrade the alloy.
Both groups list the coated sheath next to higher alloys on our Specifications page. The values below are taken from there.
Washing machines
Detergent and chlorides, 2 to 40 °dH
- Sheath diameter 8.0 – 8.5 mm
- AISI 304 nickel-diffusion coated, AISI 316L, Incoloy 825 for hard-water and premium ranges
- 5 – 10 W/cm² on the heated sheath for double hairpins (hard water at the low end)
Water heating
Hard or aggressive water
- Sheath diameter 6.5 – 16 mm; 8.0 – 10 mm for storage heaters
- Copper (tinned or nickel-plated), AISI 304, AISI 316L, Incoloy 800, Incoloy 825, nickel-diffusion coated stainless; titanium on request
- 6 – 12 W/cm² on the heated sheath for storage heaters (lower in hard water)
| Sheath option | What changes | Typical choice for |
|---|---|---|
| AISI 304, uncoated | Base austenitic stainless grade | Clean or softened water |
| AISI 316L | Bulk alloy with molybdenum for better pitting resistance | Tap water with chlorides, detergent solutions |
| Stainless, nickel-diffusion coated | Diffused surface layer; the alloy stays the same | Hard or aggressive water in washing machines and water heaters, at lower cost than Incoloy 825 |
| Incoloy 825 | Bulk nickel–iron–chromium alloy with molybdenum and copper | Aggressive, brackish or acidic water, where the whole tube – bends and brazed joints included – must resist the medium |
Temperature limits and corrosion notes for each grade are in the sheath material table of our design guide.
Test evidence
Tested in your medium – not reduced to one number.
Corrosion depends on water chemistry, temperature and surface load, so we do not quote a single corrosion rate. The coating is verified on samples and tested under the conditions you specify.
- Coating thickness – measured in our laboratory on samples.
- Coverage – visual inspection for a complete, uniform surface.
- Corrosion and salt spray – neutral salt spray to ISO 9227 on samples, where specified.
- Every element – insulation resistance and high-voltage dielectric test before packing.
- Hot leakage current – on samples and at type approval.
Results are reported per project, for the medium and conditions agreed with you.
Related
Coating, sheath and seal – decided together.
Balçık BrazingNickel diffusion coating, bright annealing and furnace brazing services
Design guideSheath materials and watt density by medium
Washing machine elementsThermofuse, NTC and coated sheaths
Water heating elementsFlange, screw-in and immersion heaters
STF terminal sealingMoisture-tight terminal ends
CalculatorsCheck the surface load for hard water
Hard water in your target market?
Tell us the water hardness, the detergent and the duty cycle. We propose the sheath – coated, AISI 316L or Incoloy 825 – and the surface load to match.