RFQ Today
Certifications: EN 10204 3.1 / 3.2 material test certificates, PMI verification, and complete export documentation packages.
Stainless 304
(UNS S30400)
A world-class technical reference for EPC contractors, mechanical and architectural engineers, procurement heads, and TPI inspection agencies specifying Stainless Steel 304 — the “18-8” baseline austenitic stainless grade — covering alloy metallurgy, why 304 lacks molybdenum and what that means in practice, the well-documented chloride-vapour stress corrosion cracking failure mode in indoor pool and similar environments, and the QC and documentation discipline required for general industrial, food service, and architectural component supply.
Why No Molybdenum
& Selection Logic
Stainless 304 (UNS S30400) is the original, most widely produced austenitic stainless steel grade worldwide — the “18-8” chromium-nickel baseline from which every higher-performance grade discussed throughout RR Hydraulic’s materials reference library (316L, 904L, duplex, and beyond) represents a deliberate, cost-adding step up in alloy content for a specific corrosion resistance improvement.
1.1 — What “Stainless 304 (UNS S30400)” “18-8” Means
Stainless 304 (UNS S30400) colloquial name, “18-8,” directly describes its nominal composition — approximately 18% chromium and 8% nickel — the foundational chromium-nickel austenitic stainless steel composition from which the entire austenitic stainless steel family descends. Unlike 316/316L (RR Hydraulic’s dedicated references), 304 contains no deliberate molybdenum addition — this is the single defining compositional distinction discussed throughout this reference, and the reason 304’s corrosion resistance, while good for a broad range of mild environments, falls meaningfully short of 316L’s performance in chloride-bearing and moderately reducing acid conditions.
1.2 — PREN and 304’s Position at the Base of the Selection Ladder
PREN = 18.5 + (3.3 × 0) + (16 × 0.03) = 18.5 + 0 + 0.48 = ≈ 19.0
This is the lowest PREN value across RR Hydraulic’s full stainless and corrosion-resistant alloy reference library — meaningfully below 316L’s ~24–26 (per RR Hydraulic’s dedicated reference), and far below duplex, super duplex, 904L, or nickel alloy grades. 304 sits at the very base of the corrosion-resistant alloy selection ladder discussed in detail in RR Hydraulic’s SS 316L reference — the correct starting point for evaluating whether a more highly alloyed grade is actually needed for a given application, not a grade to select by default without considering the specific service environment.
1.3 — Key Engineering Properties
Good General Atmospheric and Mild Aqueous Corrosion Resistance
304 provides reliable, well-documented corrosion resistance for mild, non-chloride-dominant environments — dry or moderately humid indoor atmospheres, general food-contact service, mild aqueous exposure, and typical architectural/decorative applications not involving marine, coastal, or de-icing-salt exposure.
Excellent Weldability and Formability
Straightforward welding using standard austenitic stainless practice, excellent cold-forming characteristics, and good general fabricability — 304 is among the easiest and most widely available materials to fabricate across RR Hydraulic’s full materials range, supporting its extensive use in general equipment, kitchen/food service, and architectural fabrication.
Good Hygienic and Food-Contact Suitability
Smooth, cleanable surface characteristics and widely recognised food-contact material compliance make 304 the standard, most cost-effective specification for general food service, kitchen equipment, and consumer-facing hygienic applications not requiring 316L’s additional corrosion margin.
Lowest Cost Among Common Austenitic Stainless Grades
304’s absence of molybdenum and generally lower nickel content compared to higher-alloy grades makes it the most cost-effective stainless steel option across RR Hydraulic’s austenitic range — the appropriate default wherever the service environment genuinely does not require 316L or higher-alloy performance.
304 vs. 304L
& Comparison to 316/316L
304 is manufactured across every common product form, with the same standard-vs.-low-carbon “L” grade distinction discussed throughout RR Hydraulic’s stainless references, and a clear upgrade path to 316/316L where 304’s limitations (Part 3) become a genuine concern.
Submit form, size, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Governing Standards
ASTM A240 / ASME SA-240 — Plate, Sheet, and Strip
Governs flat-rolled 304 product — plate, sheet, and strip for general fabrication, kitchen equipment, and architectural applications.
ASTM A312 / ASME SA-312 — Seamless and Welded Pipe
Governs seamless and welded 304 pipe for general process piping applications not requiring 316L’s molybdenum-enhanced corrosion resistance.
ASTM A182 (Grade F304) — Forged Flanges and Fittings
Governs forged 304 flanges, fittings, and valve bodies, referenced alongside RR Hydraulic’s ANSI B16 flange dimensional reference.
ASTM A276 / A479 — Bar
Governs stainless bar stock for machined components and fastener manufacture in 304 — including the corresponding ASTM A193 Grade B8 bolting family (the 304-based counterpart to the B8M grade discussed in RR Hydraulic’s SS 316 reference).
ASTM A213 — Boiler and Heat Exchanger Tube
Governs seamless 304 tube for general boiler and heat exchanger applications within the alloy’s appropriate service envelope.
2.2 — 304 vs. 304L: The Same Low-Carbon Principle
304 follows the identical standard-vs.-“L” carbon distinction discussed throughout RR Hydraulic’s stainless references — standard 304 permits up to 0.08% carbon, while 304L restricts carbon to 0.03% maximum for improved weldability without sensitisation risk. As with 316L, 304L has become the default, most commonly stocked variant for general welded fabrication, while standard 304 remains relevant for non-welded bar stock and the ASTM A193 Grade B8 Class 1/Class 2 stainless bolting family (the 304-based counterpart to B8M, discussed in detail for the molybdenum-bearing grade in RR Hydraulic’s SS 316 reference) where higher achievable cold-worked strength is a design consideration.
2.3 — Comparison to 316/316L: The Molybdenum Upgrade Decision
| Property | SS 304 | SS 316L |
|---|---|---|
| Molybdenum | None | 2.0–3.0% |
| PREN | ~18–19 | ~24–26 |
| Chloride pitting/crevice resistance | Limited — see Part 3 critical caution | Meaningfully better, though still limited at the highest chloride severity |
| Relative cost | Lower | Higher (typically 15–30% premium, market-dependent) |
| Typical selection driver | Mild, dry, or non-chloride-dominant environments; cost-sensitive applications | Any meaningful chloride exposure, marine atmosphere, or general chemical process service |
in Indoor Pool/Chloride-Vapour
Environments
304’s most important, well-documented, and frequently underestimated limitation is its vulnerability to chloride- induced stress corrosion cracking in environments where chloride exposure is not obviously “marine” or “coastal” — indoor swimming pool enclosures being the best-known industry example.
3.1 — The Indoor Pool Chloride-Vapour SCC Failure Mode
3.2 — Design and Specification Implications
Do Not Specify 304 for Indoor Pool Structural/Fixture Applications
Current industry best practice and, in many jurisdictions, building code guidance explicitly excludes 304 (and even 316L in some documented cases at the highest exposure severity) from structural fixtures, roof hangers, and fasteners in indoor pool building environments — duplex stainless steel (per RR Hydraulic’s Duplex 2205 reference) or higher-alloy materials are increasingly specified instead for these specific applications, given the documented severity and structural safety consequence of this failure mode.
Recognise Chloride-Vapour Exposure Beyond Obvious Marine Settings
The broader lesson for materials selection: chloride exposure risk is not limited to visibly “marine” or “coastal” settings — any environment with volatile chloride compounds (chlorinated water treatment facilities, certain chemical processing atmospheres, de-icing salt storage areas with airborne exposure) can create a chloride-vapour-condensation risk profile for 304 components analogous to the indoor pool mechanism, even without direct liquid chloride contact.
Adequate Ventilation Reduces But Does Not Eliminate Risk
While improved building ventilation reduces chloride vapour accumulation and condensation risk, ventilation alone is not considered a reliable substitute for correct material selection in indoor pool and similar chloride-vapour environments — the documented failure history reflects cases across a range of ventilation conditions, and material selection (avoiding 304 for structural/fixture applications in this exposure category) remains the primary, code-recognised risk mitigation.
3.3 — General Fabrication Guidance
Beyond the specific chloride-vapour caution above, 304 fabrication follows standard austenitic stainless practice — GTAW/GMAW/SMAW welding with matched ER308/ER308L filler metal, good cold-forming characteristics, and work-hardening machining behaviour consistent with the broader austenitic stainless family discussed throughout RR Hydraulic’s materials references. No specific heat treatment or sigma-phase precipitation concern applies to 304 in normal service temperature ranges, unlike the duplex and high-chromium grades discussed elsewhere in RR Hydraulic’s library.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified stainless steel heat to finished, tested, and packed 304 component shipment. Chemical composition and mechanical verification are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Acceptable for non-critical general applications | Low-consequence architectural/general fabrication (per project QA/QC procedure) |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report | Mandatory — all EPC supply | All process, food/beverage, and general EPC component supply |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Conditional — owner-specified critical items | Critical general process equipment per project requirement |
4.3 — Applications by Industry
Food Service and Kitchen Equipment
304 as the standard, cost-effective material for commercial kitchen equipment, food preparation surfaces, and general food-contact fixtures in typical indoor, non-aggressive-chloride environments — one of the highest-volume application categories for this grade worldwide.
Architectural and General Fabrication
304 sheet, tube, and bar for architectural cladding, handrails, decorative fixtures, and general fabrication in typical building environments — cost-effective and straightforward to fabricate wherever coastal/marine exposure and the chloride-vapour concerns discussed in Part 3 do not apply.
General Industrial Equipment (Mild Environments)
304 components for general industrial equipment housings, instrumentation, and fixtures in dry or moderately humid indoor environments — the appropriate, cost-effective default wherever the specific service environment has been confirmed as genuinely mild and non-chloride-dominant.
4.4 — Export Packaging Specification
- Tube, pipe, and bar ends protected to prevent contamination and mechanical damage during transit
- Heat/lot number stamped or tagged on each item, cross-referenced to the accompanying material test certificate, with clear grade marking (304 vs. 316L vs. 304L) to prevent confusion at site receiving inspection given the significant corrosion performance difference between grades
- Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting the alloy’s corrosion performance
- Documentation in a waterproof pocket: EN 10204 3.1/3.2 (or 2.1/2.2 where acceptable) MTC, chemical composition report, mechanical properties report, PMI report, and packing list with form/size breakdown per item
- ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the stainless steel product category
Submit your form, size, and quantity to RR Hydraulic for a complete, certified commercial offer.