304 vs 316 stainless steel outdoor furniture
A practical guide to 304 vs 316 stainless steel outdoor furniture: what to check on site, what a photograph cannot establish, and what to write in your purchase specification.
Outdoor furniture lives outside, in salt air, and hardware is what fails first. The grade of the stainless steel matters more than the appearance.
Grades
| Grade | Composition | Where it belongs |
|---|---|---|
| 430 | Ferritic, low cost | Indoors only. Rusts in coastal air. |
| 304 | Austenitic, 18-8 | Inland outdoor use. Coastal exposure shortens life. |
| 316 | Austenitic with molybdenum | Coastal and marine. The default for coastal projects. |
| Plain zinc-plated | Zinc coating | Dry indoor use only. |
What can be checked on site
- Marking. Most quality hardware is stamped or etched with the grade. Absence of a marking is itself a finding.
- Magnet response. 304 and 316 are non-magnetic. A magnet that attracts strongly suggests a plated mild steel part masquerading as stainless.
- Surface at weld points. Welds are where corrosion starts. Check for continuous weld, undercut, and spatter removal.
- Coating on the fixings. Zinc-plated washers on a 316 bracket are a common mixed-spec error.
outdoor furniture verification includes the hardware grade check.
What requires a laboratory
Quantitative alloy verification. XRF analysis settles it. Salt spray testing (ASTM B117) and UV ageing (ASTM G154) are accelerated tests taking hundreds of hours.
Where a contract specifies a salt spray duration, the right action is to verify that a report exists, covers the standard and the hours, and names the product — not to assume the coating will perform.
What to write in your specification
"All exposed hardware to be 304 minimum; 316 required for coastal installation. Grade marking visible on all fixings. Mixed-grade hardware within one assembly is a finding."
Common questions
Can I verify goods without sending anyone to the factory?
Partially. A remote photo review can identify gross problems but cannot establish count, dimensions, materials or physical performance. Those require someone on site.
Do laboratory reports replace on-site inspection?
No. They answer different questions. A laboratory report tells you whether a product meets a standard. An inspection tells you whether these goods match what you ordered.
What should my purchase specification contain?
Model and quantity, dimensions with tolerance, materials named rather than described generically, colour standard with a grey scale value, and any standard the goods must meet.
Verifying a furniture order?
We check your goods at the factory against your PI, your agreed specification and your approved sample. Three levels, published prices, report within 24 hours.