316H Stainless Steel: High-Carbon Grade for High-Temperature Corrosive Service

What Is 316H Stainless Steel?

316H is a high-carbon version of type 316 stainless steel intended primarily for elevated-temperature service. The H suffix designates a controlled carbon range of 0.04-0.10%, significantly higher than the 0.03% maximum of 316L. Higher carbon content increases creep rupture strength and stress-to-rupture life at temperatures above about 500 deg C, so 316H is the standard choice for pressure vessels, boiler components and piping systems that operate in the creep range and are governed by high-temperature design codes. The grade is specified in ASTM A240 for plate, sheet and strip, ASTM A312 for pipe, and ASTM A213 for boiler, superheater and heat exchanger tubes, with the designation TP316H in tube and pipe standards. It retains the molybdenum-enhanced corrosion resistance of the 316 family, which is why it is selected where heat and corrosive process media act together.

Chemical Composition (ASTM A240 / A312 / A213)

Element	Specified Range (wt%)
Carbon (C)	0.04 - 0.10
Silicon (Si)	0.75 max
Manganese (Mn)	2.00 max
Phosphorus (P)	0.045 max
Sulfur (S)	0.030 max
Chromium (Cr)	16.00 - 18.00
Nickel (Ni)	10.00 - 14.00
Molybdenum (Mo)	2.00 - 3.00
Nitrogen (N)	0.10 max

The H designation also carries a grain size requirement: for plate, sheet and strip supplied to ASTM A240, the material must have a grain size of No. 7 or coarser, which is part of the reason H-grades behave more predictably in the creep range. In the EN system there is no separate H-grade designation; 316H-type material is ordered to ASTM practice using the base composition of EN 1.4401. In Japan, the high-temperature boiler and heat exchanger tube form is standardized as SUS316HTB in JIS G3463.

Mechanical Properties and High-Temperature Performance

Property (annealed)	Requirement
Tensile strength, min	515 MPa
Yield strength, min	205 MPa
Elongation, min	40%

At room temperature the mechanical properties of 316H are essentially the same as those of standard 316. The advantage of the higher carbon content appears only in the creep range, roughly 500-800 deg C: 316H maintains a higher stress-to-rupture and lower creep rate than 316 or 316L at the same temperature and stress, which is why design codes allow higher allowable stresses for the H-grade at elevated temperature. The grade also forms a stable chromium oxide scale that resists oxidation and scaling in air at service temperature. In strongly oxidizing, sulfidizing or molten-salt atmospheres, more highly alloyed heat-resistant grades should be considered instead.

Welding and Fabrication

316H is weldable by TIG, MIG and shielded metal arc processes. To preserve the creep strength of the joint, the filler metal should match the high-carbon analysis of the base metal; low-carbon fillers such as 316L-type deposits would create weld metal with lower creep strength than the base material. Heat input should be controlled to limit grain growth and carbide precipitation in the heat-affected zone, and for thick sections a post-weld solution annealing or stress-relief treatment may be specified according to the design code. Because the high carbon content makes the alloy more sensitive to sensitization, 316H is not normally used in the as-welded condition where intergranular corrosion is a concern at lower temperatures; that duty belongs to 316L.

316H vs 316 vs 316L and Applications

316L (carbon 0.03% max) offers the best weldability and intergranular corrosion resistance and is the right grade for welded equipment below the creep range. Standard 316 (0.08% max) is a general-purpose grade. 316H (0.04-0.10% carbon, controlled grain size) is specified when the design temperature enters the creep range, typically above about 500 deg C. Typical 316H applications include chemical plant furnace and heater tubes, high-temperature corrosive piping, offshore oil and gas heat exchangers and wellhead components, power plant steam piping and superheater components, and pressure vessels operating at elevated temperature in corrosive service. The combination of molybdenum-based corrosion resistance and high-temperature strength makes 316H a cost-effective choice compared with higher-alloy heat-resistant grades in chloride-bearing high-temperature duties.

Frequently Asked Questions

What makes 316H suitable for high-temperature corrosive environments?

Two features work together: the 0.04-0.10% carbon range strengthens grain boundaries and raises creep strength for long-term high-temperature service, while the 2-3% molybdenum resists chloride pitting and corrosion from process chemicals. The chromium oxide scale prevents excessive oxidation at service temperature.

How does the creep strength of 316H compare with 316 and 316L?

At temperatures above about 500 deg C, 316H shows higher creep rupture strength and lower creep rate than 316, and both outperform 316L, whose low carbon content gives the lowest high-temperature strength of the three. Design codes reflect this by assigning higher allowable stresses to the H-grade in the creep range.

Can 316H be welded for high-temperature structures?

Yes. Use a filler metal matching the high-carbon analysis, control heat input to limit grain growth, and consider post-weld solution annealing for thick sections. Low-carbon filler must be avoided where the weld is expected to carry creep loads.

Why is 316H used in offshore oil and gas applications?

Offshore equipment faces both heat, from steam injection and process streams, and seawater chloride corrosion. The molybdenum content of 316H resists pitting, while the controlled carbon content maintains creep strength in components such as heat exchanger tubes and high-temperature piping.

When should 316H be avoided?

Avoid 316H where service temperature is low and the welded structure is exposed to corrosive media, because the high carbon content promotes sensitization and intergranular corrosion; 316L is the better choice there. 316H is also not intended for cryogenic service or for applications requiring extensive cold forming.

What are the equivalent designations of 316H?

316H is UNS S31609 in the ASTM system, with plate covered by A240 and tube and pipe by A213 and A312. In Japan the high-temperature tube form is SUS316HTB per JIS G3463. The EN system has no separate H-grade; the base composition corresponds to EN 1.4401.