304 vs 316 Stainless Steel: Which Grade Should You Specify?

A stainless steel quote often comes down to one line: 304 or 316. The price gap is easy to see. The cost of choosing wrong is harder to see, because it usually appears later as rust spots on a coastal facade or pits in a process line.

The short answer is that 304 suits many everyday environments, while 316 is the usual step up when chlorides are involved. But 316 is not "marine grade" in every marine situation, and the L versions solve a different problem altogether. This guide explains the differences and how to write them into an inquiry.

304 vs 316 at a Glance

Both are austenitic stainless steels. The defining difference is that 316 contains molybdenum, which improves its resistance to pitting and crevice corrosion.

Property	304	304L	316	316L
Chromium (Cr)	About 18–20%	About 18–20%	16–18%	16–18%
Nickel (Ni)	About 8–11%	8–12%	10–14%	10–14%
Molybdenum (Mo)	None specified	None specified	2–3%	2–3%
Carbon (C), max	0.07–0.08%	0.03%	0.08%	0.03%
Yield strength, min	205 MPa	170 MPa	205 MPa	170 MPa
Tensile strength, min	515 MPa	485 MPa	515 MPa	485 MPa

Approximate ASTM A240 values for plate, sheet and strip. Limits have changed between editions and differ in other standards and product forms, so check the edition named in your order.

Why Molybdenum Matters

Stainless steel usually fails in chloride service through localized attack and not by thinning evenly. Small pits form on the surface, or corrosion starts inside a tight gap such as a lap joint or under a gasket. Most of the surface can still look perfect while a pit grows through the wall.

A common way to compare grades is the Pitting Resistance Equivalent Number:

PREN = %Cr + 3.3 × %Mo + 16 × %N

On that basis, 304 sits at around 19 and 316 at around 24–26, depending on actual composition and the nitrogen multiplier used. PREN is useful for ranking grades, but it is only an estimate. It does not tell you how a specific part will behave in service.

How Much Chloride Can Each Grade Handle?

Atlas Steels' technical note on pitting and crevice corrosion gives these rough guide levels for water:

Grade	Warm ambient	At 60°C
304	About 200 mg/L chloride	About 150 mg/L chloride
316	About 1,000 mg/L chloride	About 300 mg/L chloride

Seawater contains about 20,000 mg/L chloride, far above either guide level. The same note describes 304 as susceptible to pitting in seawater above about 10°C. It says 316 is commonly used near ambient seawater, but that its resistance is marginal, so it can be attacked in crevices or if the temperature rises even slightly.

Treat these numbers as a starting point, not a guarantee. Conditions can make a real system much harsher than its water analysis suggests:

• Stagnant liquid: still water is more likely to cause attack than flowing water, especially where particles settle.
• Evaporation: chlorides concentrate as liquid dries. Low-chloride hydrotest water left pooled in pipes and tanks has caused serious pitting.
• Crevices: overlapping surfaces, gaskets and incomplete weld penetration create sites for attack.
• Surface condition: a clean, smooth finish helps, while contamination from mild steel greatly accelerates the start of attack.

Moving up to 316 does not solve every chloride problem. In chloride-containing water above about 60°C, austenitic grades including both 304 and 316 can also be at risk of stress corrosion cracking.

Which Grade Fits Your Application?

Situation	Usual starting point	What to check
Dry indoor architecture and equipment	304	Cleaning chemicals, especially those containing chlorine
Food equipment with low salt exposure	304	Food-contact rules and the cleaning process
Brines, salty foods and chloride cleaning	316 or 316L	Chloride level, temperature and contact time
Coastal facades and railings	316	Surface finish, rain washing and a maintenance plan
Heavy welding with no post-weld anneal	304L or 316L	Required strength and the design code
Seawater immersion or hot chloride service	Get a specialist review	Whether a duplex or higher-alloy grade is needed

Coastal sites deserve particular attention. "Tea staining", a brown surface discoloration, is common there. It is usually superficial, but it can be a real problem on visible architectural work. Grade alone does not prevent it, so finish and cleaning matter as well.

When to Specify 304L or 316L

The L means low carbon, and it addresses a different risk from chlorides. During welding, the heat-affected zone can form chromium carbides at the grain boundaries. This is known as sensitization, and it can leave the area open to intergranular corrosion. Limiting carbon to 0.03% reduces that risk.

The trade-off is a slightly lower minimum strength, as the table above shows. You will often see material dual-certified as 304/304L or 316/316L, meaning it meets the requirements of both grades. If your design relies on the higher strength and your fabrication needs low carbon, ask for this explicitly.

How to Verify the Grade You Receive

304 and 316 look identical, so appearance tells you nothing. Use these checks instead:

• Mill Test Certificate: match the heat number on the certificate to the marking on the material, then check the chemistry against the standard you ordered.
• Portable alloy test (PMI): a handheld XRF analyzer can check for molybdenum and separate 304 from 316. Standard XRF does not reliably measure carbon, so it cannot confirm an L grade. That needs spark optical emission testing, handheld LIBS or a laboratory.
• Do not rely on a magnet: annealed austenitic steel is generally non-magnetic, but cold working can make it slightly magnetic. A magnet cannot tell 304 from 316.
• Third-party inspection: for critical orders, agree the scope and sampling before the material ships.

Grade Names Across Standards

Common name	UNS	EN	JIS	GB
304	S30400	1.4301	SUS304	S30408
304L	S30403	1.4307 / 1.4306	SUS304L	S30403
316	S31600	1.4401	SUS316	S31608
316L	S31603	1.4404	SUS316L	S31603

These are close equivalents, not exact matches. Limits differ between standards, so if your specification names one standard, keep that standard in the order and do not simply substitute another.

What to Include in Your Inquiry

"Stainless 316" is not enough for an accurate quote. A clear line looks like this:

Stainless steel plate, ASTM A240 316L, 6 × 1500 × 6000 mm, No.1 finish, EN 10204 3.1 certificate, 20 tons, CIF [destination port].

Include these details, and if you are not sure of the grade, describe the service too:

• Product form, size, standard and grade
• Surface finish, such as 2B, BA, No.4 or pickled
• Certificate and inspection requirements
• Quantity, delivery terms and destination
• The service environment: chloride level, temperature, whether liquid can stagnate, and whether the parts will be welded

Choosing Between Them

Start with the environment, not the price. 304 is often the sensible choice where chlorides are low, and paying for 316 may add little. Where chlorides, crevices or coastal exposure are real concerns, 316 is the usual starting point, but it still has limits. For seawater or hot chloride service, ask a corrosion specialist before you order.

Shanghai Banzhijia Steel supplies stainless sheet and plate, coil and strip, seamless pipe, welded pipe, square and rectangular tube, round bar, square, flat and hex bar, and angle and channel. Send us your specification or describe the service conditions, and our sales team will reply with a quote. You can also browse the full stainless steel range.