The choice between 304 stainless and galvanised steel comes down to the limit of each material. 304 is limited by chlorides and temperature; galvanising is limited by coating thickness and by how fast the environment uses up the zinc. The two limits below settle most decisions.
304 limit: chlorides and temperature. Outokumpu's datasheet for Core 304/4301 describes the grade as 18% chromium and 8% nickel steel. Outokumpu adds that where chlorides or pollutants are present in high amounts, as in certain industrial areas or marine splashing zones, higher-alloyed grades from the Forta duplex or Ultra ranges may need to be considered, especially if the environment is also hot or humid.
Under tensile stress, chloride solutions above about 50 °C raise the risk of stress corrosion cracking, and Outokumpu says these conditions should be avoided. A hot chloride wash is therefore a criterion of its own: keep the stressed areas of a 304 part, such as a bent sheet or a tightened joint, away from hot chloride washing.
Galvanising: coating thickness and zinc rate
For hot-dip galvanising, EN ISO 1461:2022 sets the minimum coating. For steel over 6 mm the local minimum is 70 µm and the mean minimum 85 µm; for steel from 3 mm to 6 mm it is 55 µm and 70 µm, and for steel from 1.5 mm to 3 mm it is 45 µm and 55 µm. The American Galvanizers Association's summary of ISO 9223 gives a zinc corrosion rate of 0.7 to 2.1 µm per year for category C3.
| Steel | ISO 1461 local min | ISO 1461 mean min | Rough life at C3 (local min, 2.1 to 0.7 µm per year) |
|---|---|---|---|
| over 6 mm | 70 µm | 85 µm | 33-100 years |
| 3-6 mm | 55 µm | 70 µm | 26-79 years |
| 1.5-3 mm | 45 µm | 55 µm | 21-64 years |
The estimate is simple: the local minimum thickness is divided by a constant corrosion rate. For 1.5-3 mm steel, 45 µm / 2.1 µm per year = 21 years; 45 µm / 0.7 µm per year = 64 years. Cut edges and scratches are not part of this sum, so read the table as a way to rank options, not as a fixed service life.
Product examples: MRF and Co.Par
On MRF Peares handles, the last three digits of the code set the material: 253 is AISI 304 and 153 is zinc plated DD13. The same pattern appears on the 16, 20, 22 and 27 mm handles.
| Handle | Stainless code | Zinc code |
|---|---|---|
| 16 mm, embracing base | 202290253 | 202290153 |
| 16 mm, simple base | 202100253 | 202100153 |
| 20 mm | 202070253 | 202070153 |
| 22 mm | 202050253 | 202050153 |
| 27 mm | 202040253 | 202040153 |
MRF lists the zinc option as 'zinc plated', not hot-dip galvanised, so the ISO 1461 minimums above do not apply to it directly. For a wet or salted location, get the coating type and thickness in writing from Aris Makina before choosing zinc.
Co.Par's metal division offers the same size in two materials: stainless 304 GPBHG425A00 and galvanised GPBZP425A00, both 1500 × 1000 × 425 mm. The Co.Par general catalogue lists the 'U' underbody support for IDROBOX 60 as 'hot dip galvanized steel', which is the hot-dip category the ISO 1461 table covers.
Decision: exposure and coating together
Dry freight in a covered space can take galvanising, provided the coating type and thickness are confirmed in writing. Where the site has sea spray, a high chloride load or hot chloride washing, 304 alone may not be enough; Outokumpu says higher-alloyed grades from the Forta and Ultra ranges may need to be considered.
Send Aris Makina three facts: the environment (dry, wet or chloride exposed), the wash temperature and chemical, and the sheet thickness. We match them to an MRF or Co.Par code.
