What is the difference between 304 and 304L?

The key difference is carbon content. 304L has a maximum carbon of ≤0.030% (EN 1.4307) or ≤0.035% (ASTM A403 WP304L), compared to ≤0.070% (EN 1.4301) or ≤0.08% (ASTM WP304) for standard 304. The low carbon in 304L prevents chromium carbide precipitation at grain boundaries during welding — a phenomenon called sensitization — which would otherwise deplete the HAZ of chromium and cause intergranular corrosion. 304L is the default choice for welded constructions. Standard 304 (1.4301) is only preferred where no welding is involved and slightly higher mechanical strength is needed.

What is the difference between 304L and 316L pipe fittings?

316L (EN 1.4404) adds 2.0–2.5% molybdenum to the 18Cr-8Ni base composition, which raises the Pitting Resistance Equivalent (PRE) to approximately 24 versus approximately 18 for 304L (1.4307). The molybdenum in 316L significantly improves resistance to chlorides, pitting corrosion, and crevice corrosion in aggressive environments such as seawater, chloride-containing process streams, and many chemical duties. 304L is the standard choice for general duty, water treatment, food and beverage processing, and cryogenic applications where chloride levels are low. 316L should be specified for chemical processing, pharmaceutical, marine, and offshore applications where chloride exposure is significant. The cost premium for 316L over 304L is typically 15–20%.

ASTM A403 WP304L EN 1.4307 EN 10253 Type B No PWHT Required ✓

304L Buttweld Pipe Fittings

ASTM A403 WP304L / EN 1.4307 (X2CrNi18-9) — 18Cr-8Ni low-carbon austenitic stainless for general chemical service, water treatment, food & beverage, and cryogenic applications. No PWHT. EN 10253-2 Type B and ASME B16.9. EN 10204 3.1/3.2. Ships to Europe, UK, Middle East, Americas.

½″–48″

Size Range

PRE ~18

Pitting Index

485 MPa

Min UTS (ASTM)

EN 10204

3.1 Std / 3.2 On Req.

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304L Grade Equivalents

ASTM	EN W.Nr.	EN Name	UNS	ASME P-No.
A403 WP304L (fittings)	1.4307	X2CrNi18-9	S30403	8, Gr 1
A182 F304L (flanges)	1.4307	X2CrNi18-9	S30403	8
A312 TP304L (pipe)	1.4307	X2CrNi18-9	S30403	8
A240 304L (plate)	1.4307	X2CrNi18-9	S30403	8

Chemical Composition — 304L / 1.4307

Standard	C	Cr	Ni	Mn	Si	N
ASTM A403 WP304L	≤0.035	18.0–20.0	8.0–12.0	≤2.0	≤1.0	—
EN 1.4307 (X2CrNi18-9)	≤0.030	17.5–19.5	8.0–10.0	≤2.0	≤1.0	≤0.11

No molybdenum — PRE ~18 vs ~24 for 316L (1.4404). Suitable for non-chloride environments. For seawater or chemical service with chloride exposure, specify 316L (1.4404).

Mechanical Properties — 304L / 1.4307

Standard	Min. UTS (MPa)	Min. YS (MPa)	Elongation (%)	Max. Hardness	HT Condition
ASTM A403 WP304L	485	170	≥35%	202 HBW	Solution annealed
EN 1.4307 (EN 10253-2)	440–680	≥175	≥45%	215 HBW	Solution annealed

Heat Treatment & Welding — No PWHT

✓ No PWHT Required — 304L is used in the solution annealed condition (1010–1120°C, water quench). No post-weld heat treatment needed.

The low carbon content (≤0.030%) of EN 1.4307 prevents chromium carbide precipitation at grain boundaries during welding. After welding, 304L joints can be placed directly into service without any heat treatment cycle.

Filler Metal (GTAW/TIG)

ER308L (AWS A5.9). Low-carbon filler matches base metal carbon control, preventing sensitization in the weld deposit.

Filler Metal (SMAW)

E308L-16. Confirm filler certifications — do not use standard E308 (higher carbon) on welded pressure service.

Inter-pass Temperature

Maximum 150°C. Control heat input to minimise grain growth and maintain corrosion resistance of the HAZ.

Preheat

Generally not required for austenitic stainless steel. Preheat above ambient is not recommended as it increases the risk of sensitization.

Sensitization Note

Low carbon ≤0.030% prevents chromium carbide precipitation at grain boundaries. For prolonged service in the sensitization range (425–850°C), specify 321 (EN 1.4541, Ti-stabilised) instead.

ASME P-Number

P-No. 8, Group 1. Standard WPS qualification for austenitic stainless steel. No special PQR required beyond Group 1 qualification.

304 vs 304L — Key Differences

Property	304 (WP304 / EN 1.4301)	304L (WP304L / EN 1.4307)
C max	≤0.070%	≤0.030%
Sensitization risk in HAZ	Yes	No
Preferred for welded construction	No	Yes
Min YS	≥205 MPa	≥170 MPa
EN W.Nr.	1.4301	1.4307

Available 304L Fitting Types

90° LR Elbows

Long radius (1.5D). ASME B16.9 and EN 10253-2 Type B. ½″–48″. All schedules.

45° LR Elbows

Long radius. ASME B16.9 / EN 10253-2 Type B. ½″–48″.

Equal Tees

ASME B16.9 and EN 10253-2 Type B. All schedules.

Reducing Tees

All standard reducing combinations. ASME B16.9 / EN 10253-2.

Concentric Reducers

ASME B16.9 / EN 10253-2 Type B. Full range.

Eccentric Reducers

ASME B16.9 / EN 10253-2 Type B. Full range.

End Caps

ASME B16.9 / EN 10253-2 Type B. ½″–48″.

180° Returns

Long and short radius. ASME B16.9. Food, beverage and process loops.

Stub Ends

Lap joint stub ends. MSS SP-43 / EN 10253-2. For removable flanged joints.

304L vs 316L — Quick Selection Guide

Property	304L (1.4307)	316L (1.4404)
Mo content	None	2.0–2.5%
PRE	~18	~24
Chloride resistance	Moderate	Good
Cost	Lower	Higher (~15–20%)
Typical use	Water, food, general chemical	Chemical, pharma, marine

EN 1.4307 Fittings (European) 304 Pipe Fittings 316L Pipe Fittings 321 Pipe Fittings EN 10253 Type B Guide

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