Type 316L stainless steel
Specifying low-carbon UNS S31603 by product form and condition, with bounded plate values, corrosion distinctions and product-specific welding guidance.
Tags: materials, stainless-steel, austenitic
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Identity and purchasing basis
ATI's 316L plate listing under ASTM A240 and ASME SA-240 gives 485 MPa minimum tensile, 170 MPa minimum yield, and 0.030% maximum carbon. Its bulletin links lower carbon to reduced intergranular attack after short thermal exposure such as welding. It reports no advantage for chloride stress-corrosion cracking. ATI plate data, ATI 316/316L bulletin
Type 316L is low-carbon austenitic chromium-nickel-molybdenum stainless steel, UNS S31603. ATI's plate listing gives 16–18% Cr, 10–14% Ni, 2–3% Mo and carbon ≤0.030%, with other controlled elements. Those selected limits are not the complete acceptance specification or a delivered heat analysis. ATI 316L product listing
Outokumpu distinguishes Supra 316L/4404, /4432 and /4435, all associated with S31603 but with different EN identities and typical compositions. Retain the exact producer product and specification rather than accepting every name containing 316L as an identical offering. Outokumpu Supra designations and composition
Why the low-carbon suffix matters
ATI's combined bulletin contrasts 316 carbon ≤0.08% with 316L ≤0.030%. Lower carbon improves resistance to intergranular attack associated with carbide precipitation during short thermal exposures such as welding. The same bulletin warns that prolonged exposure can still be harmful and explicitly states that L grades offer no advantage in chloride stress-corrosion-cracking resistance. ATI 316/316L technical bulletin, intergranular corrosion and SCC
The suffix therefore answers a particular material-selection question; it does not mean stronger, immune to corrosion or acceptable for every welded service. Check carbon, mechanical requirements, code allowances and final condition independently before substituting 316L for 316 or accepting a dual-certified product.
Keep the relevant mechanisms separate when reviewing a failure or a compatibility claim. Intergranular attack, pitting, crevice corrosion and SCC need different evidence. A favorable test for one mechanism cannot establish resistance to all the others.
A bounded plate-property example
ATI publishes the following 316L plate entries alongside ASTM A240 and ASME SA-240. The live summary does not supply a complete temperature, specimen and direction protocol beside these entries; confirm those requirements in the governing order and certificate. ATI plate properties
| Quantity | Published entry |
|---|---|
| Tensile strength | ≥485 MPa |
| Yield strength | ≥170 MPa |
| Elongation | ≥40% |
| Hardness | ≤95 HRB |
Do not transfer these entries to every S31603 form, cold-worked stock or additive part. Keep a specification minimum distinct from a typical value and a shipment test result. No single tensile number establishes allowable pressure, fatigue life or an attachment's resistance.
Calculated nominal-stress illustration: a uniform 100 mm² section under 4,000 N has stress 40 MPa. Relative to the listed 170 MPa yield entry, 40/170 ≈0.235. This arithmetic is not a safety-factor determination: it omits the actual condition, local stress concentrations, joints, fatigue, corrosion loss and governing design method.
For a design review, reconcile dimensions and condition with the selected material row before assigning inputs. Reassess stiffness, stability and load path when a substitution changes thickness or section geometry, even if the nominal alloy name remains similar.
Corrosion needs an exposure definition
Outokumpu lists PRE 24 for Supra 316L/4404, 25 for /4432, and 26 for /4435. Its PRE comparison is composition-based; surface condition and other factors determine actual corrosion behavior. These numbers are neither corrosion rates nor guaranteed service-temperature limits. Outokumpu PRE table and guidance
The guide warns that strong mineral acids can attack these materials and that aggressive chloride conditions may require higher-alloyed grades. It distinguishes uniform corrosion, localized attack and SCC rather than assigning a universal seawater rating. Outokumpu corrosion guidance
Describe fluid composition, concentration, contaminants, pH, temperature, oxidants, aeration, flow, deposits, crevices and stress. Include cleaning, startup, shutdown and upset exposures. Obtain evidence for the final surface and fabricated condition, not only an open coupon in a different solution.
For a gasket, fastener, weld or dissimilar-metal interface, assess the assembled geometry. Define acceptable general-corrosion rate and localized-attack criteria before selecting tests. If published data do not match the duty, seek producer advice or representative qualification rather than inventing a chloride concentration limit.
Product-specific welding guidance
Alleima's 3R60 seamless tube/pipe is a low-carbon product with minimum 2.5% Mo, separately offered in a Urea Grade variant. This named product is more specific than the generic 316L label. Alleima 3R60 product description
For 3R60, Alleima recommends welding without preheat, normally without subsequent heat treatment, with heat input <2.0 kJ/mm, interpass temperature <150°C, and ER316L among its recommended GTAW/GMAW fillers. These are recommendations for its material, not a qualified procedure for arbitrary S31603 supply or every dissimilar joint. Alleima welding section
Resolve preparation, joint geometry, filler, shielding, thermal controls, sequence and inspection through the approved procedure. Establish required properties and cleanliness in weld and heat-affected regions separately from incoming stock. A parent-metal certificate cannot qualify the completed weld.
ATI warns that carbon-steel brushes can embed particles that subsequently rust. Surface preparation and post-fabrication cleaning therefore belong in the process plan, with acceptance appropriate to the service. ATI welding and cleaning guidance
Manufacturing and release
Plan machining, forming, allowances and inspection around the supplied condition and actual geometry. Qualify tooling and parameters on representative stock. Review added heating or repair operations before assuming that the original material evidence remains sufficient.
Retain specification, producer, heat/lot, condition, certificate, drawing and fabrication history with final inspection results. Define leak, pressure, fatigue, dimensional or corrosion acceptance where the application requires it. Application lists identify candidate uses; they do not qualify an individual pressure boundary, food-contact assembly or implant.
Source versions
ATI's combined bulletin prints Version 1, 18 April 2012. Outokumpu's PDF prints 1561EN:4, November 2022. Alleima's 3R60 tube/pipe sheet identifies 30 September 2025. The live ATI listing has no technical revision date used here. These are source identities, not assurances of current contractual standard editions. Review date: 2026-11-01, America/Los_Angeles.