• 310S (UNS S31008) is the industry-standard austenitic stainless steel for petrochemical furnace tubes rated to 1100 °C continuous service.
• Its 25 % Cr / 20 % Ni composition forms a dense, self-repairing Cr₂O₃ oxide scale that blocks oxygen and sulfur ingress.
• Wall thickness must be calculated under API 530 creep-rupture rules once metal temperature exceeds 900 °C.
• For service above 1050 °C or in heavy carburizing/sulfidizing atmospheres, upgrade to 310H, HK40, or Alloy 601.
• All furnace tubes in refinery service require periodic UT inspection per API RP 573 every 2–4 years.
310S Key Parameters
| Key Parameter | Value / Specification |
| Alloy Designation | UNS S31008 / AISI 310S / EN 1.4845 |
| Chromium Content | 24.0 – 26.0 wt% |
| Nickel Content | 19.0 – 22.0 wt% |
| Max Continuous Service Temp. | 1100 °C (2012 °F) in air |
| Max Intermittent Service Temp. | 1050 °C (1922 °F) in cycling service |
| Oxidation Resistance Limit | Up to 1150 °C (mild oxidizing atmosphere) |
| Primary Governing Standard | ASTM A213 / ASME SA-213 (seamless tubes) |
| Minimum Tensile Strength (RT) | ≥ 515 MPa (74.8 ksi) |
| Minimum Yield Strength (RT) | ≥ 205 MPa (29.7 ksi) |
| Min. Elongation (RT) | ≥ 35% |
| Room-Temperature Hardness | ≤ 187 HBW |
| Density | 7.90 g/cm³ |
| Thermal Conductivity (20 °C) | 15.9 W/(m·K) |
| Coefficient of Thermal Expansion | 16.0 × 10⁻⁶ /°C (20–1000 °C) |
Sources: ASTM A213/ASME SA-213, ASTM A240; ASM Handbook Vol. 2 - Properties and Selection: Nonferrous Alloys and Special-Purpose Materials; EN 10216-5; manufacturer certified mill test reports.
Introduction
Petrochemical furnace tubes are among the most thermally demanding components in any process plant. Fired heaters in crude distillation, naphtha reforming, and ethylene cracking routinely expose tube metal to temperatures between 800 °C and 1100 °C while carrying hydrocarbon fluids under pressure.Selecting the wrong alloy leads to accelerated oxidation, creep failure, or catastrophic tube rupture - events that cause unit shutdowns, environmental incidents, and, in the worst cases, fires and explosions.
Selecting an over-specified alloy wastes capital unnecessarily. 310S sits in the sweet spot for this temperature range: it offers sufficient oxidation resistance up to 1100 °C, acceptable creep strength, excellent weldability, and a material cost far below nickel-base superalloys.
This guide explains what 310S is, why it works at 1100 °C, how to design with it, and when to choose an alternative. Data tables are sourced from internationally recognized standards and peer-reviewed literature to support engineering decisions.
What Is Stainless Steel 310S?
Chemical Composition
310S is a high-alloy austenitic (face-centered cubic) stainless steel. Its defining feature is an unusually high chromium and nickel content compared to common grades such as 304 or 316. Table 2.1 presents the composition limits per ASTM A240 and ASME SA-240.
| Element | C | Mn | Si | P | S | Cr | Ni |
| Max / Range (wt%) | ≤ 0.08 | ≤ 2.00 | ≤ 1.50 | ≤ 0.045 | ≤ 0.030 | 24.0–26.0 | 19.0–22.0 |
Table 2.1 - Chemical composition of 310S (UNS S31008). Source: ASTM A240 / ASME SA-240, Table 1; ASTM A213 / ASME SA-213, Table 1.
Why 25 % Chromium and 20 % Nickel?
Chromium (Cr): At concentrations above ~20 wt%, chromium reacts preferentially with oxygen to form a thin, adherent, and self-repairing chromium oxide (Cr₂O₃) scale on the steel surface. This scale acts as a diffusion barrier, dramatically slowing further oxidation. With 24–26 % Cr, 310S forms a robust scale that remains protective up to approximately 1150 °C in clean oxidizing atmospheres.
Nickel (Ni): Nickel stabilizes the face-centered cubic (austenite) crystal structure at all temperatures down to cryogenic. This prevents the brittle body-centered cubic (martensite) transformation that would otherwise occur in high-Cr ferritic steels. Nickel also improves resistance to carburization - a critical concern in reformer and cracking furnaces where hydrocarbon vapors are present.
Low Carbon (≤ 0.08 %): The 'S' designation in 310S stands for 'low carbon'. Limiting carbon to a maximum of 0.08 wt% suppresses carbide precipitation (sensitization) in the heat-affected zone during welding, preserving corrosion resistance and ductility. This is especially important for field-welded tube joints in furnace construction.
High-Temperature Mechanical Properties
Engineering a furnace tube requires understanding how 310S steel behaves at elevated temperatures - not just at room temperature. Two failure modes dominate at temperatures above 800 °C: (a) oxidation/corrosion of the tube wall and (b) creep rupture under sustained pressure load.
Tensile and Creep Data at Elevated Temperatures
Table 3.1 summarizes the elevated-temperature mechanical properties and creep-rupture data for 310S. The tensile values are representative data from ASM Handbook and manufacturer test reports. Creep-rupture stresses represent the stress required to cause rupture at the stated temperature in the given time period.
| Temperature | Tensile Strength (MPa) | 0.2% Yield Strength (MPa) | Elongation (%) | Creep Rupture Stress 100h (MPa) | Creep Rupture Stress 10,000h (MPa) |
| Room Temp. (20 °C) | ≥ 515 | ≥ 205 | ≥ 35 | - | - |
| 600 °C (1112 °F) | ~330 | ~175 | ~40 | - | - |
| 700 °C (1292 °F) | ~270 | ~155 | ~42 | ~70 | ~40 |
| 800 °C (1472 °F) | ~190 | ~120 | ~45 | ~38 | ~18 |
| 900 °C (1652 °F) | ~110 | ~85 | ~50 | ~16 | ~6 |
| 1000 °C (1832 °F) | ~60 | ~50 | ~55 | ~7 | ~2 |
| 1100 °C (2012 °F) | ~32 | ~28 | ~60 | ~2.5 | < 1 |
Table 3.1 - Elevated-temperature mechanical and creep-rupture properties of 310S (UNS S31008). Sources: ASM Handbook Vol. 2 (2nd ed.); ASME BPVC Section II Part D (Subpart 3, Table 1-100); manufacturer issued high-temperature data sheets. Values are representative; use ASME allowable stresses for code calculations.
What Does 'Creep' Mean for a Furnace Tube Engineer?
Creep is the slow, permanent deformation of a metal under sustained stress at high temperature - even when the stress is well below the conventional yield strength. For a furnace tube, creep manifests as gradual wall thinning ("bulging") and, ultimately, rupture if the design life is exceeded.At 1100 °C, 310S retains only about 2–3 MPa creep-rupture stress for a 10,000-hour design life.
This means furnace tubes operating at 1100 °C must be designed with very low internal pressure, thin walls, or short service intervals. API 530 provides the engineering framework for calculating allowable tube thickness in this regime.
Oxidation and Corrosion Resistance at 1100 °C
Oxidation Resistance Mechanism
When 310S is first exposed to a high-temperature oxidizing environment, chromium diffuses to the surface and oxidizes selectively, forming a thin (1–5 μm) and adherent Cr₂O₃ layer. Once established, this layer grows parabollically - meaning the growth rate decreases with time as the oxide layer itself becomes a diffusion barrier. The result is a material that oxidizes slowly for years under steady operating conditions.
Key oxidation data (source: Industeel ArcelorMittal SIRIUS 310S datasheet; ASM Handbook Vol. 13C):
• Continuous service in dry air: up to 1100 °C (some sources cite 1150 °C for clean atmospheres).
• Intermittent (cyclic) service: limit to 1050 °C because repeated thermal cycling causes the protective oxide scale to spall.
• Maximum cyclic temperature for mild cycling conditions: 1050 °C, with controlled ramp rates below 200 °C/h.
• In atmospheres with > 2 g/m³ sulfur content: upper limit drops to ~1000 °C (Industeel SIRIUS 310S datasheet).
Carburization and Sulfidation Resistance
Beyond simple oxidation, petrochemical furnace environments often contain carbonaceous gases (CO, CH₄, C₂H₄) and sulfur compounds (H₂S, SO₂). These attack stainless steels through different mechanisms:
Carburization: Carbon diffuses into the steel, forming chromium carbides that deplete the matrix of the chromium needed for oxidation protection. 310S offers moderate carburization resistance due to its high Cr and Ni content, but it is not immune - particularly in strongly reducing, high-carbon-activity environments such as steam reformer furnaces. In such service, HK40 or Alloy 601 (with >20 % Cr + aluminum addition) are preferred.
Sulfidation: Sulfur compounds react with chromium and nickel to form low-melting sulfide phases that can penetrate the oxide scale. 310S handles low-sulfur environments (< 50 ppm H₂S) adequately up to about 1000 °C; in heavily sulfidizing service, higher-chromium cast alloys (HK40, HP-Modified) or alumina-forming alloys are specified.
Material Comparison: 310S vs. Competing Alloys
Not every furnace tube application requires 310S. Table 5.1 compares 310S against five commonly specified alternatives across dimensions that matter to petrochemical engineers.
| Property | 310S (UNS S31008) | 310H (UNS S31009) | 321H (UNS S32109) | HK40 (UNS J94204) | Alloy 800H (UNS N08810) | Alloy 601 (UNS N06601) |
| Cr (wt%) | 24–26 | 24–26 | 17–19 | 26–30 | 19–23 | 21–25 |
| Ni (wt%) | 19–22 | 19–22 | 9–12 | 19–22 | 30–35 | 58–63 |
| C (max, wt%) | 0.08 | 0.04–0.10 | 0.08 | 0.35–0.45 | 0.10 | 0.10 |
| Max. Cont. Temp. (°C) | 1100 | 1150 | 925 | 1150 | 1100 | 1200 |
| Oxidation Resistance | ★★★★☆ | ★★★★☆ | ★★★☆☆ | ★★★★☆ | ★★★★☆ | ★★★★★ |
| Carburization Resist. | ★★★☆☆ | ★★★☆☆ | ★★★☆☆ | ★★★★☆ | ★★★★☆ | ★★★★★ |
| Creep Strength @ 1000 °C | Moderate | Good | Low | High | Good | Excellent |
| Weldability | Excellent | Good | Good | Difficult | Good | Good |
| Relative Material Cost | Low | Low | Medium | Medium | High | Very High |
| Typical Application | Furnace tubes, radiant tubes | Creep-critical furnace parts | Boiler tubes (≤925 °C) | Steam reforming tubes | Pyrolysis/cracking coils | Extreme oxidizing service |
Table 5.1 - Alloy comparison for petrochemical furnace tube service. ★ ratings are qualitative assessments based on published oxidation and corrosion data. Sources: ASM Handbook Vol. 13C - Corrosion: Environments and Industries; Special Metals Corporation (Alloy 800H, Alloy 601 technical bulletins); ASTM International standards; manufacturer technical datasheets. Cost ratings are relative and market-dependent.
310S vs. 310H: When to Choose Which?
This is the most common question in furnace tube specification. The answer is straightforward: use 310S when weldability and resistance to sensitization are the primary concerns (e.g., field-welded tube replacements); use 310H when maximum creep strength is required and welding is done under controlled shop conditions.
310H (UNS S31009) has a carbon content of 0.04–0.10 % - higher than 310S. This additional carbon provides solid-solution and carbide strengthening that improves creep resistance by roughly 20–30 % at 900–1000 °C. The trade-off is a higher risk of carbide precipitation in the heat-affected zone during welding (sensitization). For this reason, 310H welding typically requires more stringent preheat and PWHT controls.
Frequently Asked Questions (FAQ)
The following questions are extracted from engineering consultations and represent the most common queries about 310S in petrochemical furnace tube service.
Q1: What is the maximum service temperature for 310S stainless steel?
The maximum continuous service temperature for 310S (UNS S31008) in air is 1100 °C (2012 °F). For intermittent (cyclic) service, the recommended limit is 1050 °C (1922 °F) due to the risk of oxide scale spallation during thermal cycling. In sulfur-containing atmospheres (> 2 g/m³), the limit drops to ~1000 °C. These limits are based on oxidation testing data published by Industeel ArcelorMittal and industry alloy manufacturers.
Q2: Can 310S be used above 1100 °C?
Short answer: no, not for sustained service. Above 1100 °C, the Cr₂O₃ protective scale begins to transition to volatile CrO₃ in oxidizing environments, rapidly losing its protective function. Creep rates also become impractically high (rupture life in the thousands of hours rather than tens of thousands). For service above 1100 °C, specify Alloy 601 (alumina-forming), Alloy 602CA, or a ceramic-lined system.
Q3: What standard governs 310S furnace tube thickness design in a refinery?
API Standard 530 ("Calculation of Heater-Tube Thickness in Petroleum Refineries," 7th edition) is the primary standard. It defines allowable stresses for 310S in both the elastic and creep-rupture regimes. For creep-limited conditions (tube metal temperature > 900 °C), API 530 Appendix C provides the necessary time-temperature rupture curves. ASME BPVC Section II Part D provides the underlying allowable stress values used in API 530 calculations.
Q4: What is the difference between 310S and 310H for furnace tube applications?
310S (UNS S31008): Carbon ≤ 0.08 %. Preferred when weldability, resistance to sensitization, and ease of field welding are priorities. Slightly lower creep strength than 310H.
310H (UNS S31009): Carbon 0.04–0.10 %. Chosen when maximum creep strength is required (e.g., high-pressure radiant tubes, long spans). Welding requires stricter controls. Both grades share the same Cr and Ni content.
Definitive conclusion: Specify 310S as the default; upgrade to 310H only when creep life calculation shows insufficient remaining margin with 310S.
Q5: Does 310S require post-weld heat treatment (PWHT)?
No - PWHT is generally not required for 310S, and is potentially harmful. Heating 310S in the range 600–900 °C during PWHT can precipitate brittle sigma phase and chromium carbides. The as-welded condition is typically acceptable for most petrochemical service. If residual stress relief is critically needed (e.g., severe cyclic thermal loading), consult a welding metallurgist before applying any heat treatment.
Q6: What are the applicable ASTM standards for procuring 310S furnace tubes?
The primary ASTM standards are: ASTM A213 / ASME SA-213 (seamless tubes for boilers and heat exchangers) for Grade TP310S, and ASTM A249 / ASME SA-249 (welded tubes) for Grade TP310S. For associated piping, ASTM A312 / ASME SA-312 applies (Grade TP310S). All materials procured for ASME Code construction must include a Mill Test Report (MTR) per ASTM A450 (general requirements for tubes) with full chemical analysis and mechanical test results.
Q7: How often should 310S furnace tubes be inspected in refinery service?
API RP 573 ("Inspection of Fired Boilers and Heaters") recommends external visual and UT thickness inspection at a minimum frequency of every 2–4 years, or at each planned maintenance turnaround - whichever comes first. Tubes operating continuously above 950 °C, or in corrosive atmospheres, should be inspected more frequently. Remaining-life assessments using the API 530 Larson-Miller approach should be updated at each inspection based on the actual temperature history from operating logs and data historians.
