Boiler Tube: Standards, Grades & Selection Guide
Selecting the right boiler tube is a materials engineering decision with direct safety and operational consequences. The wrong standard — or the right standard with the wrong grade — means creep failure, stress corrosion cracking, or premature tube replacement in equipment that is expected to run continuously for 25+ years. The four major ASTM standards covering boiler tubes (A192, A210, A213, A335) each serve distinct pressure and temperature regimes, and the grade within each standard determines maximum service temperature, creep resistance, and long-term reliability.
ZC Steel Pipe manufactures and exports seamless boiler tubes to ASTM, ASME, DIN, EN, JIS, and GB standards, supplying power generation projects, petrochemical plants, and industrial boiler manufacturers across Africa, the Middle East, and South America. This guide covers the complete boiler tube selection framework — from low-pressure carbon steel through to advanced alloy grades for ultra-supercritical service.
1. The Four Core Boiler Tube Standards
Boiler tubes are not a single product — they span a wide range of materials from simple carbon steel to complex 9–12% chromium alloys, each governed by different ASTM specifications. The choice of standard is determined first by service temperature, then by pressure, and finally by the specific boiler component (waterwall, superheater, reheater, economiser, header).
ASTM A192
ASME SA-192
Material: Carbon steel (single grade)
Max temp: ~400°C (750°F)
Tensile min: 325 MPa (47 ksi)
Use: High-pressure boiler tubes, waterwalls
Carbon Steel ASTM A210
ASME SA-210
Material: Medium-carbon steel
Grades: A-1, C
Max temp: ~450°C (840°F)
Tensile min: 415–485 MPa
Use: Boiler tubes & superheater tubes
Carbon Steel ASTM A213
ASME SA-213
Material: Ferritic & austenitic alloy steel
Grades: T5, T9, T11, T22, T91, T92, TP304H, TP316H…
Max temp: Up to 650°C+ (alloy-dependent)
Use: Superheaters, reheaters, heat exchangers
Alloy / Stainless ASTM A335
ASME SA-335
Material: Ferritic alloy steel pipe
Grades: P1, P2, P5, P9, P11, P22, P91, P92…
Max temp: Up to 650°C (P91/P92)
Use: Headers, steam lines, boiler connections
Alloy Pipe ASTM VS ASME DESIGNATION — WHAT'S THE DIFFERENCE?Every boiler tube standard has both an ASTM designation (e.g., A192) and an ASME counterpart (SA-192). The technical requirements are identical — ASME adopts the ASTM standard by reference. The difference is certification: materials for ASME Code-stamped pressure vessels and boilers must be certified to the SA designation by an ASME-approved manufacturer. When specifying for power plant or pressure vessel applications, always confirm whether ASME certification is required and order accordingly.
2. ASTM A192 — High-Pressure Carbon Steel Boiler Tubes
ASTM A192 is the simplest boiler tube specification — a single-grade seamless carbon steel tube designed specifically for high-pressure boiler service. It is one of the most widely used boiler tube standards globally, particularly for waterwall tubes in industrial and utility boilers operating at subcritical pressures.
ASTM A192 Chemical & Mechanical Requirements
| Property | Requirement | Notes |
| Carbon (C) | 0.06–0.18% | Low carbon limits hardness and improves weldability |
| Manganese (Mn) | 0.27–0.63% | Narrow range for consistency |
| Phosphorus (P) | 0.035% max | Residual control |
| Sulfur (S) | 0.035% max | Residual control |
| Silicon (Si) | 0.25% max | — |
| Tensile Strength | 325 MPa (47 ksi) min | No maximum specified |
| Yield Strength | 180 MPa (26 ksi) min | — |
| Elongation | 35% min (in 50mm) | Excellent ductility for forming and welding |
| Hardness | No requirement | — |
| Heat Treatment | Hot finished or cold drawn + annealed | — |
ASTM A192 Typical Size Range
| OD Range | Wall Thickness Range | Common Application |
| 15.9 mm (5/8") to 76.2 mm (3") | 2.1 mm to 7.1 mm | Boiler waterwall and generating tubes |
| Larger OD available to order | Up to 12.7 mm+ | Headers and drum connections |
Procurement Note — A192 vs A106 Grade BA192 and ASTM A106 Grade B are both carbon steel seamless tubes and are sometimes incorrectly treated as interchangeable. They are not. A106 is a process piping standard optimised for high-temperature, high-pressure fluid service — it has no flattening test requirement and its chemistry permits higher carbon content. A192 is specifically optimised for boiler tube service, with tighter chemistry controls, a mandatory flattening test (critical for detecting seams and laps), and a bend test. For boiler tube replacement or new boiler construction, always specify A192 (or SA-192 for ASME applications) — substituting A106 may not be code-compliant.
3. ASTM A210 — Medium-Carbon Steel Boiler Tubes
ASTM A210 provides higher strength than A192 through a slightly higher carbon content, available in two grades. It is used where A192's minimum tensile of 325 MPa is insufficient for the wall thickness calculations at the required working pressure.
ASTM A210 Grade Comparison
| Property | Grade A-1 | Grade C |
| Carbon (C) | 0.27% max | 0.35% max |
| Manganese (Mn) | 0.93% max | 0.29–1.06% |
| Tensile Strength | 415 MPa (60 ksi) min | 485 MPa (70 ksi) min |
| Yield Strength | 255 MPa (37 ksi) min | 275 MPa (40 ksi) min |
| Elongation | 30% min | 30% min |
| Max Service Temp | ~425°C | ~450°C |
| Typical Use | Boiler tubes, economiser tubes | Higher-pressure boiler service |
Engineering Insight — When to Step Up from A192 to A210The decision between A192 and A210 A-1 is typically a wall thickness calculation. If the minimum required wall thickness under the ASME boiler code's pressure formula results in a wall that is inconveniently thick or heavy for the tube OD you're working with, A210 A-1's higher allowable stress at temperature lets you specify a thinner wall for the same working pressure. In practice, for boilers operating above roughly 5 MPa (725 psi) working pressure, A210 becomes the more economical specification once the wall thickness trade-off is calculated.
4. ASTM A213 — Alloy Steel & Stainless Boiler Tubes
ASTM A213 covers the widest range of boiler tube materials — from low-alloy ferritic grades for moderate elevated temperature service, through chrome-moly grades for superheater and reheater service, to austenitic stainless steel grades for ultra-high temperature applications. The choice of A213 grade is driven primarily by service temperature and, secondarily, by creep-rupture strength requirements at that temperature.
Ferritic Alloy Grades — Cr-Mo Family
T11 (1¼Cr–½Mo)
Cr: 1.00–1.50%
Mo: 0.44–0.65%
Tensile: 415 MPa min
Max temp: ~570°C (1060°F)
Heat treat: Full anneal or normalize + temper
Use: Superheaters, reheaters — moderate temp
T22 (2¼Cr–1Mo)
Cr: 1.90–2.60%
Mo: 0.87–1.13%
Tensile: 415 MPa min
Max temp: ~580°C (1075°F)
Heat treat: Full anneal or normalize + temper
Use: Superheaters, reheaters, steam lines
T91 (9Cr–1Mo–V)
Cr: 8.00–9.50%
Mo: 0.85–1.05%
V+Nb+N: Modified (creep-optimised)
Tensile: 585 MPa min
Max temp: ~620°C (1150°F)
Use: Supercritical superheaters, reheaters
T92 (9Cr–2W–Mo–V)
Cr: 8.50–9.50%
W: 1.50–2.00%
Mo: 0.30–0.60%
Tensile: 620 MPa min
Max temp: ~630°C (1165°F)
Use: Ultra-supercritical power plants
T5 (5Cr–½Mo)
Cr: 4.00–6.00%
Mo: 0.45–0.65%
Tensile: 415 MPa min
Max temp: ~620°C (oxidation limit)
Use: Petroleum refining, hydrogen service
T9 (9Cr–1Mo)
Cr: 8.00–10.00%
Mo: 0.90–1.10%
Tensile: 415 MPa min
Max temp: ~600°C
Use: Predecessor to T91 — legacy installs
Austenitic Stainless Grades (A213)
| Grade | Composition | Tensile Min | Max Service Temp | Typical Use |
| TP304H | 18Cr–8Ni (high carbon) | 515 MPa | ~700°C | High-temp superheaters, headers |
| TP316H | 16Cr–12Ni–2Mo (high carbon) | 515 MPa | ~700°C | Chloride-containing high-temp service |
| TP321H | 18Cr–10Ni–Ti (high carbon) | 515 MPa | ~700°C | High-temp service, sensitisation resistance |
| TP347H | 18Cr–10Ni–Nb (high carbon) | 515 MPa | ~750°C | Ultra-supercritical superheaters |
Critical Engineering Point — T91 PWHT RequirementsT91 (9Cr-1Mo-V) is one of the most demanding materials to weld in boiler construction. It requires strict preheat (minimum 200°C), controlled interpass temperature, and post-weld heat treatment (PWHT) at 730–780°C — without exception. Failure to PWHT T91 welds results in a martensitic heat-affected zone with extremely low toughness that will crack under thermal cycling. This is a known and documented failure mode in T91 boiler tube installations where PWHT was skipped or performed incorrectly. When sourcing T91 tubes, confirm that the mill's heat treatment procedure is documented and traceable in the MTC.
Field Note — T91 vs T22: The Grade Upgrade DecisionT22 (2¼Cr-1Mo) was the workhorse superheater grade for decades and remains widely specified for subcritical and some supercritical boilers. T91 has roughly 40% higher allowable stress at elevated temperature, which translates directly into thinner tube walls, lighter weight, and better heat transfer. The trade-off is cost (T91 is significantly more expensive) and fabrication complexity. For new supercritical and ultra-supercritical units, T91 is the standard choice. For subcritical boiler retrofits where the existing tube bank is T22, the upgrade to T91 requires a complete re-engineering of the support structure and weld procedures — it is not a simple like-for-like swap.
5. ASTM A335 — Chrome-Moly Alloy Pipe for Boiler Headers & Steam Lines
ASTM A335 covers the same Cr-Mo alloy family as A213, but in larger-diameter pipe form rather than small-diameter tube. The 'P' prefix in A335 grades corresponds directly to the 'T' prefix in A213 — P11 and T11 are the same alloy, P22 and T22 are the same alloy, P91 and T91 are the same alloy. The distinction is in product form and application.
| A335 Grade | A213 Equivalent | Alloy | Tensile Min | Typical Boiler Application |
| P1 | T1 | C–½Mo | 380 MPa | Low-alloy steam lines, moderate temp service |
| P11 | T11 | 1¼Cr–½Mo | 415 MPa | Superheater headers, connecting piping |
| P22 | T22 | 2¼Cr–1Mo | 415 MPa | Main steam headers, high-temp connections |
| P5 | T5 | 5Cr–½Mo | 415 MPa | Refinery heaters, high-temp hydrogen service |
| P9 | T9 | 9Cr–1Mo | 415 MPa | Legacy high-temp steam systems |
| P91 | T91 | 9Cr–1Mo–V | 585 MPa | Supercritical steam headers, main steam pipes |
| P92 | T92 | 9Cr–2W–Mo–V | 620 MPa | Ultra-supercritical main steam systems |
Engineering Insight — Why T and P Grades Coexist in the Same BoilerA typical supercritical power boiler will contain both A213 T91 tubes (in the superheater and reheater tube bundles) and A335 P91 pipe (in the headers, downcomers, and steam leads connecting those tube bundles to the turbine). Both are 9Cr-1Mo-V material, but the dimensional standard, NDE requirements, and end-use differ. When specifying a complete boiler tube package, confirm with the EPC contractor which components fall under A213 tube supply and which fall under A335 pipe supply — mixing the two creates procurement and documentation complexity.
6. Grade Selection by Service Temperature
The primary selection driver for boiler tube grade is maximum continuous service temperature. The chart below provides a starting-point selection guide — final grade selection must be confirmed by a qualified pressure vessel engineer using ASME Section II allowable stresses for the specific operating pressure and tube geometry.
| Service Temperature | Pressure Class | Recommended Standard | Recommended Grade | Typical Boiler Component |
| < 400°C (< 750°F) | Low–medium pressure | ASTM A192 | Single grade | Industrial boilers, economisers, waterwalls |
| 400–450°C (750–840°F) | Medium–high pressure | ASTM A210 | A-1 or C | Boiler generating tubes, lower superheater |
| 450–570°C (840–1060°F) | High pressure | ASTM A213 | T11 | Superheaters, subcritical utility boilers |
| 570–590°C (1060–1095°F) | High pressure / supercritical | ASTM A213 | T22 | Superheaters, reheaters, supercritical boilers |
| 590–620°C (1095–1150°F) | Supercritical | ASTM A213 | T91 | Superheaters, reheaters — supercritical plant |
| 620–650°C (1150–1200°F) | Ultra-supercritical | ASTM A213 | T92 or TP347H | Final superheater stage, USC plant |
| > 650°C (> 1200°F) | Advanced USC | ASTM A213 | TP304H / TP316H / TP347H | High-temperature superheaters, austenitics |
International Standard Equivalents
Projects in Europe, Asia, and the Middle East frequently specify boiler tubes to non-ASTM standards. The table below cross-references the most commonly encountered equivalents:
| ASTM Grade | ASME Equivalent | DIN / EN Equivalent | JIS Equivalent | GB (China) Equivalent |
| A192 | SA-192 | EN 10216-1 P235GH | JIS G3461 STB 340 | GB 3087 10 |
| A210 A-1 | SA-210 A-1 | EN 10216-1 P265GH | JIS G3461 STB 410 | GB 3087 20 |
| A213 T11 | SA-213 T11 | EN 10216-2 13CrMo4-5 | JIS G3462 STBA 22 | GB/T 5310 12CrMo |
| A213 T22 | SA-213 T22 | EN 10216-2 10CrMo9-10 | JIS G3462 STBA 24 | GB/T 5310 12Cr2Mo |
| A213 T91 | SA-213 T91 | EN 10216-2 X10CrMoVNb9-1 | JIS G3462 STBA 28 | GB/T 5310 10Cr9Mo1VNbN |
| A335 P11 | SA-335 P11 | EN 10216-2 13CrMo4-5 | JIS G3458 STPA 22 | GB/T 5310 12CrMo |
| A335 P91 | SA-335 P91 | EN 10216-2 X10CrMoVNb9-1 | JIS G3458 STPA 28 | GB/T 5310 10Cr9Mo1VNbN |
Procurement Note — Cross-Standard SubstitutionEquivalent standards are technically close but not always identical. Chemical composition limits, heat treatment requirements, and permitted NDE methods can differ between ASTM, EN, JIS, and GB standards for nominally equivalent grades. When a project specification calls for EN or JIS grades and you are sourcing from a Chinese manufacturer to GB/T 5310, request a formal equivalency comparison from the mill showing side-by-side chemical and mechanical requirements. For ASME code-stamped applications, substitution is not permitted without a Code Case — only SA-designated material is acceptable.
7. Dimensions, Wall Thickness & Common Schedules
Boiler tube dimensions are specified by outer diameter (OD) and minimum wall thickness — not by pipe schedule, which is a pressure pipe convention. This is an important distinction: boiler tubes ordered to "Schedule 40" or "Schedule 80" without specifying minimum wall thickness may not meet the pressure requirements at temperature.
Typical Boiler Tube Dimension Ranges by Standard
| Standard | OD Range | Wall Thickness Range | Wall Tolerance | Length (standard) |
| ASTM A192 | 15.9–76.2 mm (5/8"–3") | 2.1–7.1 mm | −12.5% / +no limit | 4.9–7.3 m (16–24 ft) |
| ASTM A210 | 15.9–101.6 mm (5/8"–4") | 2.1–9.5 mm | −12.5% / +no limit | 4.9–7.3 m (16–24 ft) |
| ASTM A213 (alloy) | 3.2–127 mm (1/8"–5") | 0.4–12.7 mm (min wall) | Per ASTM A1016 | Custom lengths to order |
| ASTM A213 (stainless) | 6.4–127 mm (1/4"–5") | 0.8–12.7 mm (min wall) | Per ASTM A1016 | Custom lengths to order |
| ASTM A335 | 21.3 mm (NPS ¾) and up | SCH 10 to XXS | −12.5% on wall | 6–12 m or random |
Required Testing by Standard
| Test | A192 | A210 | A213 (alloy) | A335 |
| Tensile test | Yes | Yes | Yes | Yes |
| Flattening test | Yes | Yes | Yes | No |
| Bend test | Yes | Yes | On request | No |
| Hydrostatic or NDE | Yes (both options) | Yes | Yes | Yes |
| Hardness test | Not required | Not required | Yes (alloy grades) | Yes |
| Impact test | No | No | On request (SS grades) | Supplementary |
8. Frequently Asked Questions
What is the difference between ASTM A192 and ASTM A210 boiler tube?
ASTM A192 is a single-grade carbon steel specification with minimum tensile of 325 MPa, designed for high-pressure boiler tube service where moderate strength is sufficient. ASTM A210 provides higher strength in two grades — A-1 (415 MPa minimum tensile) and C (485 MPa minimum tensile) — through slightly higher carbon content. Use A210 when wall thickness calculations under the ASME boiler code require higher allowable stress than A192 can provide at the service pressure and temperature.
What is ASTM A213 T91 boiler tube used for?
T91 is a modified 9Cr-1Mo-V ferritic alloy tube (ASTM A213) developed specifically for superheater and reheater service in supercritical power generation boilers. Its addition of vanadium, niobium, and nitrogen to the 9Cr-1Mo base produces a tempered martensitic microstructure with superior creep-rupture strength at temperatures up to 620°C — roughly 40% higher allowable stress than T22 at the same temperature. It is the standard grade for supercritical and ultra-supercritical superheater tube bundles in modern power plants.
What is the difference between ASTM A213 and ASTM A335?
Both standards cover the same Cr-Mo alloy families but in different product forms. A213 covers seamless alloy steel tubes — smaller diameter, thinner wall products used in the heating surface of the boiler (waterwalls, superheaters, reheaters, economisers). A335 covers seamless alloy steel pipe — larger diameter products used for headers, steam lines, and connecting piping. The grade designations are directly parallel: T11/P11, T22/P22, T91/P91 are the same alloy in tube (T) and pipe (P) form respectively.
What boiler tube standard is required for supercritical power plants?
Supercritical boilers (above 22.1 MPa / 374°C) and ultra-supercritical plants typically specify ASTM A213 T91 for superheater and reheater tubes, A213 T22 for lower-temperature waterwalls, and ASTM A335 P91 for headers and main steam pipes. Ultra-supercritical plants operating above 620°C may require austenitic stainless grades such as A213 TP347H for the final superheater stage. All materials for ASME pressure part applications must be certified to the SA counterpart standard (SA-213, SA-335).
What sizes does boiler tube come in?
ASTM A192 and A210 typically range from 15.9 mm (5/8") to 76.2–101.6 mm OD, with wall thickness from approximately 2.1 mm to 9.5 mm. ASTM A213 alloy tubes range from 3.2 mm (1/8") to 127 mm OD, with wall thickness from 0.4 mm to 12.7 mm. Larger sizes and custom lengths can be produced to order. All boiler tubes should be specified by OD and minimum wall thickness — not by pipe schedule. ZC Steel Pipe can produce boiler tubes in any standard size range and to custom dimensions.
What certifications should a boiler tube supplier provide?
For every shipment: Mill Test Certificates (MTCs) showing heat number, chemical composition, and mechanical test results traceable to each tube. For ASME applications: SA-designation certification from an ASME-authorised manufacturer. For international procurement: third-party inspection by SGS, Bureau Veritas, TÜV, or equivalent is standard practice. Certificates should also include heat treatment records, hydrostatic or NDE test results, and dimensional inspection reports. ZC Steel Pipe provides full documentation packages including third-party inspection support for all boiler tube supply.
