AISI 316H Stainless Steel: Guide to Properties, Applications & Fabrication

AISI 316H stainless steel stands out as a high-carbon variant of the popular 316 alloy, designed for extreme high-temperature service. Its unique composition and mechanical properties make it a top choice for industries like power generation, petrochemicals, and refining. This guide breaks down everything you need to know—from chemical specs to real-world applications—to help you make informed decisions for your high-heat projects.

1. Material Overview & Key Specifications

Understanding the core characteristics of AISI 316H is critical for selecting it for the right job. Below is a detailed breakdown of its composition, standards, and mechanical properties.

Chemical Composition & Standards

The AISI 316H composition is tailored for high-temperature strength, with a carbon range of 0.04–0.10 % (higher than 316L’s <0.03% carbon). This carbon content enhances creep resistance, a must for long-term use at elevated temperatures. Other key elements include 16–18% chromium, 10–14% nickel, 2–3% molybdenum, and trace amounts of manganese and silicon. There is no single 316H chemical formula; instead, it follows strict elemental ranges set by global standards:

• 316H UNS S31609 (Unified Numbering System)
• 316H ASTM A240 / 316H ASME SA-240 (for plates, sheets, and strips)
• 316H EN 1.4918 equivalent (European standard for similar high-carbon 316 variants)

Mechanical & Physical Properties

AISI 316H delivers consistent performance across demanding conditions. Key metrics include:

For example, a power plant in Texas specified 316H ASTM A240 plates for a boiler’s high-pressure section, citing the alloy’s ability to meet the 515 MPa tensile strength requirement even at 600 °C.

2. High-Temperature Properties & Creep Resistance

AISI 316H’s biggest advantage is its performance under heat. Unlike standard 316, its higher carbon content improves 316H high-temperature strength and resistance to creep—the gradual deformation that occurs under long-term stress at high temperatures.

Critical High-Temperature Metrics

• Creep Rupture Data: The 316H 100,000-hour creep strength (a key industry benchmark) is ~100 MPa at 650 °C, making it suitable for 20+ year service in power plants.
• Oxidation Resistance: It resists oxidation up to 925 °C, with a slow 316H steam oxidation rate (≤0.1 mm/year at 800 °C in pure steam).
• Service Temperature Limit: The maximum 316H service temperature limit is 870 °C for short-term use and 760 °C for continuous operation.
• Sigma Phase Embrittlement: A potential risk—316H sigma phase embrittlement after long-term exposure (800–900 °C) can make the material brittle. To avoid this, avoid prolonged heating in this range.

A case study from a European refinery: Their 316H refinery hydrogen reformer tubes (operating at 750 °C) showed no significant creep deformation after 15 years, thanks to the alloy’s robust creep resistance.

3. Heat Treatment, Microstructure & Grain-Size Control

Proper heat treatment ensures AISI 316H maintains its strength and corrosion resistance. The goal is to control grain size and prevent harmful phase formation.

Key Heat Treatment Processes

• Solution Annealing: Heat to 1040–1100 °C, hold for 30–60 minutes, then water-quench. This dissolves carbides and restores a uniform austenitic microstructure.
• Grain Size Control: The 316H grain size ASTM 7 minimum (finer grains = higher strength) is required by standards like ASME SA-240. Finer grains also improve creep resistance.
• Stabilizing Anneal: Optional for reducing residual stresses, but not required for corrosion resistance.
• Residual Stress Relief: For welded parts, heat to 450–600 °C to relieve stresses without causing sensitization.

Sensitization Behavior

316H sensitization behavior at elevated carbon is a concern: if cooled too slowly from 800–1000 °C, carbon can combine with chromium to form carbides, reducing corrosion resistance. Solution annealing prevents this by keeping carbides in solution.

4. Welding, Fabrication & Machining Guidelines

Welding and machining AISI 316H require careful technique to preserve its properties.

Welding Best Practices

• Consumables: Use 316H welding consumables ER316H (for TIG/MIG welding) to match the base metal’s carbon content. 316H filler metal carbon matching is critical—using 316L filler will lower creep strength.
• Preheat & PWHT: No preheat is needed for thin sections, but 316H post-weld heat treatment (PWHT) (600–650 °C) is recommended for thick parts to restore creep resistance in the heat-affected zone (HAZ).
• HAZ Considerations: The 316H HAZ creep strength can drop by 10–15% if welding parameters are poor. Use low heat input (≤1.5 kJ/mm) to minimize HAZ size.

Machining Tips

• Speeds & Feeds: 316H machining speeds and feeds should be 15–20% lower than for carbon steel. For example, use 100–120 m/min speed with coated carbide tools.
• Tool Life: 316H tool life with coated carbide (e.g., TiAlN coatings) is 2–3x longer than with uncoated tools, reducing costs.
• Distortion Control: 316H distortion control during welding is key—use backspacing, intermittent welding, and fixturing to minimize warping.

5. Product Forms, Sizes & Supply Chain

AISI 316H is available in a wide range of forms to suit different applications.

Common Product Forms

• Plates: 316H stainless steel plate thicknesses range from 3 mm to 200 mm, with 316H pressure vessel plate (ASTM A240) for high-pressure applications.
• Pipes & Tubes: 316H pipe schedule chart includes Schedule 40 to Schedule 160; 316H seamless tube ASTM A213 is used for boiler and superheater tubes.
• Bars: 316H round bar stock (10 mm to 300 mm diameter) and 316H flat bar sizes (5 mm x 20 mm to 20 mm x 100 mm).
• Fittings: 316H forged fittings (elbows, tees) for piping systems.

Supply Chain Tips

Work with 316H global stockists to ensure quick delivery. Many suppliers offer 316H custom cut plate to reduce waste, and 316H coil suppliers provide coils for large-scale fabrication.

6. Industry Applications & Case Studies

AISI 316H’s high-temperature and corrosion resistance make it ideal for harsh environments.

Key Applications

• Power Generation: 316H boiler tubes, 316H superheater headers, and 316H power plant headers (operate at 600–750 °C).
• Petrochemicals: 316H refinery hydrogen reformer tubes and 316H ethylene cracking coils (resist hydrogen attack and high heat).
• Other Uses: 316H heat exchanger shells, 316H steam distribution manifolds, and 316H flare stack tips (resist oxidation and weathering).

Real-World Example: A Japanese petrochemical plant replaced their 316L ethylene cracking coils with 316H ethylene cracking coils—maintenance costs dropped by 40% because 316H resisted creep and cracking better at 800 °C.

Yigu Technology’s Perspective

At Yigu Technology, we recognize AISI 316H’s value in high-temperature industrial projects. We often recommend it for clients in power and petrochemical sectors, as its creep resistance and oxidation performance outperform standard 316 variants. Our team works with trusted suppliers to source 316H seamless tube ASTM A213 and 316H pressure vessel plate, ensuring compliance with ASTM/ASME standards. We also provide technical support for welding and heat treatment, helping clients avoid common pitfalls like sigma phase embrittlement. For projects requiring long-term reliability at 600+ °C, AISI 316H remains a cost-effective choice.

FAQ

1. What is the difference between 316H and 316L stainless steel?
   The main difference is carbon content: 316H has 0.04–0.10% carbon (for high-temperature strength), while 316L has <0.03% carbon (for better corrosion resistance in low-heat environments). 316H is better for creep resistance, while 316L is ideal for food processing or marine applications.
2. Can AISI 316H be used in hydrogen service?
   Yes—316H refinery hydrogen reformer tubes are a common application. Its molybdenum content resists hydrogen embrittlement, and its high carbon content maintains strength at 700–800 °C, typical for hydrogen reformers.
3. What is the maximum service temperature for AISI 316H?
   The 316H service temperature limit is 870 °C for short-term (hours) use and 760 °C for continuous (years) use. Exceeding these temperatures can lead to oxidation, creep, or sigma phase embrittlement.