316H Stainless Steel: High-Temperature Corrosion Resistance Explained

What Is 316H Stainless Steel?

316H is the high-carbon variant of the 316 family, designated UNS S31609 and covered by ASTM A240 for plate, sheet and strip, ASTM A312 for pipe, and ASTM A213 for boiler and superheater tubes, where it is ordered as TP316H. The H suffix identifies a controlled carbon range of 0.04 to 0.10 percent, deliberately higher than standard 316, because carbon is the element that provides high-temperature creep strength to austenitic stainless steels.

Like the whole 316 family, 316H contains 2.00 to 3.00 percent molybdenum. The combination of controlled high carbon and molybdenum makes it a core material for components that must carry stress at elevated temperature while resisting corrosion from sulfur-bearing, chloride-bearing or acidic media. It is specified where the low-carbon grades lose strength too quickly and where 304H does not provide enough corrosion resistance.

Chemical Composition of 316H

The heat-analysis ranges below are required by ASTM A240 for UNS S31609. The same chemistry applies to TP316H under ASTM A312 and A213.

Element	Content, wt %
Carbon, C	0.04 - 0.10
Manganese, Mn	2.00 max
Phosphorus, P	0.045 max
Sulfur, S	0.030 max
Silicon, Si	0.75 max
Chromium, Cr	16.0 - 18.0
Nickel, Ni	10.0 - 14.0
Molybdenum, Mo	2.00 - 3.00
Iron, Fe	Balance

The Japanese equivalent is SUS316H under JIS G4303 and G4304. EN 10088-2 does not list a 316H grade; European projects typically cross-reference TP316H per ASTM A312/A213 or specify an equivalent high-carbon molybdenum-bearing chemistry.

Mechanical Properties and High-Temperature Strength

Per ASTM A240, solution-annealed 316H plate and sheet shall meet the following room-temperature requirements:

Property	Requirement
Tensile strength	515 MPa min
Yield strength, 0.2 % offset	205 MPa min
Elongation in 2 in (50 mm)	40 % min
Hardness	217 HBW max, 95 HRB max

At temperature, the controlled carbon content pins grain boundaries and slows dislocation movement, which raises creep strength compared with 316L. The practical service window for 316H is approximately 425 to 870 °C for continuous operation. Design codes such as ASME Section VIII and B31.3 cap pressure-retaining service near 816 °C for this grade; above that range, higher-alloy heat-resistant grades are required. In flue-gas and sulfur-bearing atmospheres, the molybdenum addition gives markedly better resistance to hot corrosion than 304H in the same service, which is why 316H is selected for the hot sections of boilers, reactors and incinerators.

Corrosion Resistance at Elevated Temperature

Two mechanisms matter in high-temperature corrosive service:

Oxidation and sulfidation: chromium forms the protective Cr2O3 scale, while molybdenum helps resist sulfur attack in reducing and sulfidizing atmospheres. In sulfur-bearing flue gas near 800 °C, molybdenum-bearing grades are consistently more resistant than the plain 18-8 grades.

Chloride attack: the pitting resistance equivalent number of 316H, calculated from its nominal composition, is approximately 25 to 27, compared with about 19 to 20 for 304H, indicating substantially better resistance to pitting and crevice corrosion in chloride-containing deposits and condensates.

Care is still required: in strongly oxidizing chloride environments, or where molten salts or polythionic acids are present, dedicated higher-alloy grades or stabilized grades should be evaluated.

Welding and Fabrication of 316H

Filler metal: use ER316H filler per AWS A5.9, whose carbon and molybdenum levels match the base metal. Low-carbon ER316L filler reduces the creep strength of the weld and should not be used for high-temperature design.

Heat input: keep heat input moderate and control interpass temperature to avoid excessive carbide precipitation in the heat-affected zone.

Heat treatment: 316H is normally used in the solution-annealed condition, 1040 to 1120 °C followed by rapid cooling. Post-weld heat treatment is not required for corrosion recovery in most cases and can be harmful if it holds the material in the sensitization range.

Forming: hot forming must finish above the sensitization range, followed by solution annealing; cold forming follows the usual austenitic rules with attention to springback and work hardening.

Selecting Between 316H, 316L and 316Ti

Condition	Recommended grade	Reason
Continuous stress at 425 - 870 °C, corrosive media	316H	High creep strength plus molybdenum corrosion resistance
Welded service below about 450 °C	316L	Low carbon, no sensitization, lower cost
Long-term static service 400 - 900 °C with welding	316Ti, UNS S31635	Titanium stabilization prevents sensitization without high carbon
Mild high-temperature service, dry air, cost sensitive	304H	No molybdenum required, lower alloy cost

Typical Applications

Boiler components and superheater and reheater tubing in power generation

High-temperature chemical reactors and transfer lines handling chlorine- or sulfur-bearing media

Heating surfaces and flue-gas components of waste incinerators

High-temperature piping and manifolds on offshore platforms

Furnace fittings, valve cores and fan components in process plants

Frequently Asked Questions

Q: What does the H in 316H mean?

A: It denotes a controlled carbon range of 0.04 to 0.10 percent, which provides the creep strength needed for sustained high-temperature service. The grade is covered by ASTM A240 as UNS S31609 and by ASTM A312/A213 as TP316H.

Q: What is the difference between 316H and 316L?

A: 316H has 0.04 - 0.10 percent carbon versus 0.035 percent maximum for 316L. The higher carbon gives 316H much better creep strength above roughly 500 °C, while 316L offers better weldability and as-welded corrosion resistance at lower temperatures.

Q: Why is molybdenum important in 316H?

A: Molybdenum improves resistance to pitting and crevice corrosion in chloride-bearing media and to sulfur attack in hot flue gases. It is the reason 316H outperforms 304H in corrosive high-temperature service.

Q: What filler metal should be used to weld 316H?

A: ER316H per AWS A5.9, with carbon and molybdenum matching the base metal. ER316L filler should be avoided because the low-carbon weld will have significantly lower creep strength at design temperature.

Q: What is the maximum operating temperature of 316H?

A: Continuous service is practical up to about 870 °C, while pressure design codes limit design stress calculations to near 816 °C. Above this range, heat-resistant grades with higher chromium and nickel are needed.

Q: How is the high-temperature performance of 316H verified?

A: Creep rupture testing at elevated temperature, typically reported as rupture life under defined stress and temperature, is the core verification, supplemented by intergranular-corrosion testing such as the Strauss test per ASTM A262 for welded components.

Frequently Asked Questions

Q1. Which standards cover 316H and what are its designations?
316H is designated UNS S31609 and covered by ASTM A240 for plate, sheet and strip, ASTM A312 for pipe and ASTM A213 for boiler and superheater tubes, where it is ordered as TP316H; the Japanese equivalent is SUS316H under JIS G4303 and G4304, while EN 10088-2 does not list a 316H grade.

Q2. What is the chemical composition of 316H?
Per ASTM A240 for UNS S31609: carbon 0.04-0.10, manganese 2.00 max, phosphorus 0.045 max, sulfur 0.030 max, silicon 0.75 max, chromium 16.0-18.0, nickel 10.0-14.0 and molybdenum 2.00-3.00 percent, with iron as balance.

Q3. What are the room-temperature mechanical requirements?
Solution-annealed 316H plate and sheet shall meet minimum tensile strength 515 MPa, 0.2 percent offset yield strength 205 MPa, elongation 40 percent in 2 in (50 mm) and hardness 217 HBW or 95 HRB maximum.

Q4. What is the practical service window of 316H?
Continuous operation is practical from approximately 425 to 870 C, and design codes such as ASME Section VIII and B31.3 cap pressure-retaining service near 816 C for this grade; its pitting resistance equivalent number is approximately 25 to 27, compared with about 19 to 20 for 304H.

Q5. How is 316H selected against 316L and 316Ti?
Choose 316H for continuous stress at 425-870 C in corrosive media where creep strength plus molybdenum corrosion resistance are needed; 316L for welded service below about 450 C; and 316Ti, UNS S31635, for long-term static service at 400-900 C with welding because titanium stabilization prevents sensitization without high carbon.