Customized 316 and 316L Stainless Steel Plates: Selection Guide

316 vs 316L Plate: What Is the Difference

316 and 316L are the same molybdenum-bearing austenitic alloy family, UNS S31600 and UNS S31603, differing only in carbon content. 316 allows carbon up to 0.08 percent; 316L restricts it to 0.030 percent. This single difference controls weldability: when 316 is heated in the range of about 425 to 815 degrees C, carbon can combine with chromium at grain boundaries, depleting the surrounding matrix and leaving the weld heat-affected zone vulnerable to intergranular corrosion. 316L with its very low carbon content avoids this sensitisation, so it can be welded in heavy sections without post-weld solution annealing. For the same reason, 316L is preferred for equipment that will later see service above roughly 425 degrees C, such as chemical vessels and food-processing tanks.

Chemical Composition per ASTM A240

Composition limits for plate, sheet and strip follow ASTM A240. Chromium and nickel stabilise austenite, molybdenum provides chloride corrosion resistance, and carbon is the only element that differs between the two grades.

Element	316 S31600	316L S31603
Carbon, max	0.08	0.030
Manganese, max	2.00	2.00
Phosphorus, max	0.045	0.045
Sulfur, max	0.030	0.030
Silicon, max	0.75	0.75
Chromium	16.0-18.0	16.0-18.0
Nickel	10.0-14.0	10.0-14.0
Molybdenum	2.0-3.0	2.0-3.0
Nitrogen, max	0.10	0.10

Mechanical Properties per ASTM A240

Minimum annealed properties for plate are listed below. The lower carbon of 316L reduces its minimum tensile and yield strengths slightly; where a component is not welded and strength matters, 316 can be used, and cold working raises both grades above these minimums.

Property	316 S31600	316L S31603
Tensile strength, min	515 MPa	485 MPa
Yield strength, min 0.2 percent offset	205 MPa	170 MPa
Yield strength, min 1 percent offset	260 MPa	260 MPa
Elongation, min	40 percent	40 percent
Hardness, max	95 HRB	95 HRB

Welding and Intergranular Corrosion

Both grades are welded by TIG, MIG, plasma, submerged arc and resistance processes. In multi-pass welds on thick 316 plate, repeated heating of earlier passes into the sensitisation range can cause chromium-carbide precipitation; specifying 316L removes this risk, which is why tanks, pipelines and chemical containers are almost always built from 316L. Where design rules require a stabilised or low-carbon grade for elevated-temperature service above about 425 degrees C, 316L is again the standard choice. Weld procedures should still be qualified, and pickling and passivation after welding restore the corrosion resistance of the heat-affected zone.

Plate Forms, Dimensions and Custom Procurement

Plate and sheet dimensions are typically defined to ASTM A480 tolerances, with common thicknesses from 4 to 100 mm, widths from 1000 to 3500 mm and lengths to suit fabrication, for example 2440 and 6000 mm. Standard finishes include NO.1 hot-rolled annealed and pickled, 2B cold-rolled, BA bright annealed and No.4 brushed. Custom procurement should specify grade and UNS number, standard, dimensions, edge condition, surface finish, and inspection level. Material documentation commonly includes a mill test certificate to EN 10204 3.1, chemical and mechanical reports, and, where specified, PMI verification of molybdenum content, ultrasonic testing and third-party inspection. Density for weight calculation is about 7.99 g/cm3.

Frequently Asked Questions

Q: Should I order 316 or 316L plate? For any welded tank, vessel or pipeline, choose 316L to avoid intergranular corrosion in the weld zone. For non-welded machined or cold-formed parts, 316 offers slightly higher minimum strength.

Q: What is the price difference between 316 and 316L? The two grades are normally priced very close to each other; the low-carbon version costs slightly more per tonne but saves the cost and risk of post-weld heat treatment.

Q: Can 316L plate be formed and machined? Yes. Austenitic grades are ductile and form well; they work-harden faster than carbon steel, so machining uses lower speeds and positive feed, with rigid tooling.

Q: What finish is supplied for food or pharmaceutical use? 2B, BA or No.4 finishes are common; electropolishing is used where the lowest surface roughness and best cleanability are required.

Q: How is plate thickness verified at receiving? Measure with a calibrated ultrasonic gauge at multiple points and check against ASTM A480 thickness tolerances; verify the certificate to EN 10204 3.1 for traceability.

Q: Can 316 plate be used at high temperature? Both grades lose strength rapidly above about 500 degrees C and are not creep-resistant; for sustained elevated-temperature service, 316H or heat-resisting grades are specified.

Frequently Asked Questions

Q1. What are the UNS designations of 316 and 316L?
UNS S31600 and UNS S31603; the two belong to the same molybdenum-bearing austenitic family and differ only in carbon content (0.08 max versus 0.030 max).

Q2. What are the minimum mechanical properties per ASTM A240?
316: tensile 515 MPa and yield 205 MPa; 316L: 485 MPa and 170 MPa; both show 260 MPa yield at 1 percent offset, 40 percent elongation and 95 HRB max hardness.

Q3. What plate dimensions are commonly available?
Thicknesses from 4 to 100 mm, widths from 1000 to 3500 mm and lengths such as 2440 and 6000 mm, with tolerances per ASTM A480.

Q4. Which welding processes are used for these grades?
TIG, MIG, plasma, submerged arc and resistance processes; pickling and passivation after welding restore the corrosion resistance of the heat-affected zone.

Q5. What documentation accompanies custom plate supply?
A mill test certificate to EN 10204 3.1, chemical and mechanical reports, and optionally PMI verification of molybdenum content, ultrasonic testing and third-party inspection; density is about 7.99 g/cm3.