Stainless Steel Electrical Enclosures: 304, 316 and When Each One Fails
Stainless steel is not one material, and the wrong grade will fail in a way that looks like a manufacturing defect. 304 pits at the welds in chloride-laden air; 316 costs more but survives it. 430 is cheaper again and stains where 304 would not. This page is about choosing the grade for the environment, not about the polish.
Fulei Metal builds stainless electrical enclosures from customer drawings in 304, 316 and 430, in a 2,500 m² plant in Ningbo, China, since 2016 — cutting, bending, welding, brushing, mirror polishing and assembly in our own workshop, with passivation and coating routed to audited partner lines.
Grade selection by environment
| Environment | Grade | Why | What goes wrong if you get it wrong |
|---|---|---|---|
| Indoor, dry, urban | 304 | Cost-effective corrosion resistance, widely available | Little — 304 is the default for a reason |
| Food, dairy, pharmaceutical washdown | 304 or 316 | Resists cleaning chemicals; continuous welds avoid trap points | Bacteria in unsealed seams; pitting under chlorinated cleaners |
| Coastal, marine air, de-icing salt | 316 | Molybdenum resists chloride pitting | 304 pits at welds and cut edges within a few years |
| Chemical exposure, swimming pools | 316 | Better resistance to chlorides and acids | 304 pits; 430 stains |
| Cost-driven indoor, magnetic parts acceptable | 430 | Cheapest ferritic stainless | Rusts in humid or polluted air; poor weldability |
| Appearance parts, brushed fascia | 304 | Takes a consistent brush grain | 430 shows an uneven grain |
Aluminium is the other option when weight or heat matters: 5052, 5754 and 6061, from 0.5 to 10 mm. It is lighter and conducts heat better, but it is not stainless and it is not chosen for corrosion alone.
Thickness and what it buys you
| Thickness | Typical enclosure use | Note |
|---|---|---|
| 0.8–1.2 mm | Wall-mount boxes, small junction enclosures | Needs stiffeners on large flat panels |
| 1.5–2 mm | Standard cabinets, doors, mounting panels | The workhorse range for stainless cabinets |
| 2.5–3 mm | Floor-standing cabinets, frames, load-bearing doors | Bending needs the right tooling; springback is higher than mild steel |
We run stainless from 0.5 to 15 mm. Gauge buys stiffness, not corrosion resistance — a 2 mm door that bows and opens the seal is worse than a 1.5 mm door with a stiffener.
Welding stainless: the part that decides whether it corrodes
Most stainless enclosure corrosion starts at the weld, not the parent metal. Three things decide it:
| Factor | What we do |
|---|---|
| Filler matching | Weld wire matched to the parent grade — 316 needs 316 filler, not 308 |
| Heat input | Controlled to avoid sensitisation, which is what makes the heat-affected zone corrode |
| Post-weld treatment | Passivation after welding, on an audited partner line, to the specification you name |
Passivation is not optional on a welded stainless enclosure that will see moisture. It removes the free iron that welding leaves behind. Tell us the specification you need it performed to, and whether a record has to travel with the batch — if your incoming inspection needs the record, ask for it at quotation stage rather than after delivery.
Finishes: what runs in our own workshop
| Finish | Where | Notes |
|---|---|---|
| Brushed (grain direction) | In-house | Agree grit and grain direction on a sample panel before production |
| Mirror polishing | In-house | For fascia panels and visible trim |
| Passivation | Audited partner line | Specification confirmed at quotation; record available if requested |
| Electropolishing | Audited partner line | For food and pharmaceutical surfaces; removes the passivating layer’s roughness |
| Powder coating | Audited partner line | When colour is required; mask threads, mating faces and earth points |
| Plating | Audited partner line | Rarely appropriate on stainless; usually for a contact face, not a body |
Anodising is for aluminium, not stainless. If your drawing calls for anodised stainless, that is a signal the material was chosen wrongly — flag it and we will discuss.
The four things that go wrong on stainless enclosures
1. Tea-staining on a roof. 304 in an outdoor or coastal position develops brown streaks where water sits and dries. It is surface contamination, not structural failure, but it looks like a defect on a delivered cabinet. A sloped roof, a drain, or 316 solves it.
2. Weld corrosion on a food-grade cabinet. An un-passivated weld in a washdown area pits within months. If the cabinet is for food, dairy or pharmaceutical service, passivation and continuous welds with no trap corners are the requirement, not the upgrade.
3. Cross-contamination from mild steel tooling. Stainless that has been cut, ground or brushed with tooling previously used on carbon steel picks up free iron and rusts at those spots. We segregate tooling for stainless work; if you have had rust spots on stainless parts before, this is usually why.
4. Galvanic corrosion at a mixed-material joint. A stainless body with aluminium panels and steel fasteners, in a wet environment, forms a cell. Dissimilar metals need isolation at the joint, and the drawing has to say so.
What to put on the drawing
- Grade and specification — “304” is not the same as “304 to EN 10088”; name the standard if acceptance depends on it
- Passivation requirement — the specification, and whether a record travels with the batch
- Weld standard — continuous, ground flush, or cosmetic only
- Grain direction on brushed surfaces, and the grit
- Masking list — threads, mating faces, earth points, gasket channel
- Dissimilar metal joints — where isolation is required
- Material certificate requirement — mill cert for the sheet, if your inspection needs it
Related reading
Medical device enclosure guides
- Medical device enclosure materials: 304, 316 and 5052
- Medical enclosure cleanability: the seven features that fail
- Medical electronics enclosures and EMC shielding
- Medical device enclosures in low volume
- Diagnostic equipment enclosures
- Medical carts and stands: what the ward demands
- Electrical enclosures and cabinets: the full selection guide
- Weatherproof electrical enclosures
- IP66 enclosures: what the rating really means
- Custom electrical cabinet manufacturing in China
Frequently asked questions
Do you supply material certificates?
Yes, for the material we buy. Material certificates and dimensional inspection records for the parts we make are available with the first article. If your incoming inspection needs them, say so at quotation stage so they are included in the plan rather than chased afterwards.
Can you match an existing brushed finish on a replacement cabinet?
Usually, yes. Send a sample panel or a photograph in raking light and we will match grit and grain direction on a sample before production. Matching a finish that has been in service for years is harder — the original surface has aged.
Is 316 worth the cost for an indoor cabinet?
Usually not. For dry indoor service 304 is the sensible choice, and 430 can work where appearance and magnetic behaviour do not matter. 316 earns its cost in chloride exposure — coastal, de-icing, pool, chemical.
Do you passivate in-house?
No. Passivation, electropolishing, plating and powder coating run on audited partner lines that we specify and inspect. We do not own those lines, and we say so up front.
What lead times apply to a stainless cabinet?
Simple samples 3–7 days; complex first articles 15–20 days; production batches 25–35 days, quoted after drawing review. Freight is quoted separately to your port.
Do you hold ISO 9001 certification?
Our quality system is documented to ISO 9001. We do not hold a third-party ISO 9001 certificate and do not claim one. Third-party audit evidence is available under NDA: TÜV Rheinland MIC-ASI243729 and Bureau Veritas MIC-ASR263630.
Send the drawing and the environment
Send the drawing with the service environment — dry indoor, washdown, coastal, chemical — and the finish you need. Those two decide 304 versus 316, and whether passivation has to be in the plan from the start. We will tell you what your design needs rather than quoting the thinnest gauge that fits.