Quick answer
Choose 304 for general-purpose service where the environment is not chloride-rich. Choose 316 when the tube will see salt, coastal air, chlorides, acids or process chemicals, because its molybdenum content resists pitting and crevice corrosion far better.
Composition and properties
| Property | Grade 304 | Grade 316 |
|---|---|---|
| Chromium | ~18–20% | ~16–18% |
| Nickel | ~8–11% | ~10–14% |
| Molybdenum | none | ~2–3% |
| Chloride / pitting resistance | Moderate | Much higher |
| Typical use | Food, general piping, interior railings, enclosures | Marine, coastal, chemical, pharmaceutical, process lines |
| Relative cost | Lower | Higher (molybdenum and nickel) |
| Low-carbon version | 304L | 316L |
Values are typical ranges from common ASTM specifications; always check the grade limits in the standard you are ordering to.
When to specify the L grades
304L and 316L limit carbon to about 0.03–0.035%. That reduces chromium carbide precipitation in the heat-affected zone of welds, protecting against intergranular corrosion. If the tube will be welded in the field and not solution-annealed afterwards, the L grade is the safer option.
Tubes for boilers and heat exchangers
For boiler, superheater and heat-exchanger tubes, seamless tube to ASTM A213 is common, and welded tube to ASTM A249. For general stainless tubing, ASTM A269 applies. Read the standards explained.
Which grade for railings and architecture?
304 is the usual choice indoors and in mild outdoor sites. Near the sea, around swimming pools, or where de-icing salts are used, 316 avoids the tea-staining and pitting that 304 can show. See architectural metal products.
What to send when requesting a quote
Grade, standard, outside diameter, wall thickness, length, quantity, finish and the test certificate you need. Ruby Infra Projects supplies 304, 304L, 316, 316L and 321 stainless steel tubes — send your specification.