What are the common grades of carbon & carbon alloy steel used in boiler and pressure vessels

In power, petrochemical, and refinery service, the materials you specify for boiler tubes, headers, superheaters, and pressure vessels determine how long the plant runs between shutdowns. Carbon & carbon alloy steel covers a wide family of grades, from plain low-carbon tubes for condensers to 9% chromium alloys designed for 600 °C steam lines. This guide walks through the grades most often called out for boiler and pressure-vessel service, what each grade actually delivers in the field, and how to shortlist the right one for your project.

EZ Steel Industrial supplies a full range of these grades from its Yangzhou, Cangzhou, and Lishui facilities, with mill test certificates issued to ASTM, ASME, EN, JIS, GOST, and GB/T standards. The selection guidance below is based on what EPCs, boiler makers, and refinery clients most commonly request.

Why Grade Selection Matters in Boiler and Pressure-Vessel Service

Boiler and pressure-vessel tubes operate under a combination of internal pressure, cyclic temperature, and creep loading that is unusual in normal piping. Three drivers shape the grade decision:

• Strength at temperature. Plain carbon steel loses yield strength rapidly above 400 °C. Alloys with chromium and molybdenum hold strength well past 500 °C, which is why superheater and reheater lines almost always specify Cr-Mo grades.
• Resistance to oxidation and corrosion. Steam-side oxidation and hot-corrosion attack dictate the chromium content. 0.5% Mo is acceptable for water walls; 2.25% Cr-1% Mo is the workhorse for superheaters; 9% Cr and 12% Cr alloys are used where metal temperatures exceed 600 °C.
• Weldability and fabrication. Higher alloy content generally means more attention to preheat, post-weld heat treatment, and hardness limits. Selecting a stronger grade than needed complicates fabrication and inspection without real operating benefit.

In practice, the grade is fixed by the design code (ASME Section I for power boilers, Section VIII for unfired pressure vessels, EN 13445 or PED for European projects) combined with the design metal temperature. Once those are set, the choice between carbon and alloy steel is mostly a matter of cost-versus-temperature.

Common Carbon Steel Grades for Boiler and Pressure-Vessel Tubes

Carbon steel is the default choice for economizers, water walls, and low-temperature sections of a boiler. The most frequently ordered grades are:

• ASTM A179 / A179M. Seamless low-carbon steel tubes for heat exchanger tube and condenser service. Typical use: air-cooled and shell-and-tube exchangers where wall temperatures stay below 400 °C. Tensile strength around 325 MPa, with good formability for U-bends.
• ASTM A192 / A192M. Higher-carbon minimum-wall tubes for high-pressure boilers. Tighter dimensional tolerances make A192 the standard for older utility boilers where tube integrity is the priority.
• ASTM A210 / A210M. Medium-carbon seamless tubes in Grade A-1 and Grade C. Grade A-1 is widely used for superheater and economizer elements; Grade C is for higher-pressure sections. EZ Steel Industrial supplies both A-1 and C grades per A210 with full mill test reports.
• GB/T 3087 and GB 5310. Chinese national standards that frequently appear in domestic boiler fabrication. 20G (GB 5310) is the Chinese equivalent of a medium-carbon boiler tube and is interchangeable with SA210 Grade A-1 in most designs.

For pressure vessels themselves, the matching plate specification is usually ASTM A516 (Grade 55, 60, 65, 70) for moderate and low-temperature service, or ASTM A537 for improved toughness. The seamless tube side keeps the same A179/A192/A210 family.

Common Carbon-Molybdenum and Cr-Mo Alloy Grades

Once the metal temperature crosses roughly 450 °C, carbon steel stops being economical and the conversation shifts to alloy steel tube grades. The carbon-molybdenum and Cr-Mo families dominate this range:

• ASTM A209 T1. A 0.5% Mo carbon-molybdenum tube for higher temperatures than A192 can handle. Often used for superheater elements in industrial boilers.
• ASTM A335 P2 / P12. 0.5% Cr-0.5% Mo. The P12 grade is the most common alloy in refinery process heaters and is also specified for power plant headers at moderate temperatures.
• ASTM A335 P11 / P22. 1.25% Cr-0.5% Mo (P11) and 2.25% Cr-1% Mo (P22) are the workhorses of high-temperature service up to about 600 °C. P22 in particular sees heavy use in hydrocrackers, ethylene plants, and utility boiler headers. EZ Steel Industrial stocks P5 through P122 seamless ferritic alloy pipe in this family.
• ASTM A335 P5. 5% Cr-0.5% Mo. Used where higher resistance to sulfidation is required, typically in refinery and petrochemical furnace tubes.
• ASTM A213 T5, T9, T11, T22, T91. The boiler-tube counterpart to A335. T91 (9% Cr-1% Mo-V-Nb) is the standard choice for modern ultrasupercritical units operating above 600 °C and is a key grade for new high-efficiency coal-fired and combined-cycle plants.
• GB 5310 12Cr1MoVG and 12Cr2MoG. Chinese equivalents widely used in domestic ultrasupercritical and CFB boilers. 10Cr9Mo1VNb is the GB counterpart of T/P91.
• EN 10216-2. European pressure-piping standard covering the 16Mo3, 13CrMo4-5, 10CrMo9-10, and X10CrMoVNb9-1 grades, with the latest 2024 edition updating tensile, impact, hydrostatic, and NDT requirements for high-temperature reliability.

Heat treatment matters as much as chemistry in these grades. P11 and P22 are typically supplied in normalized-and-tempered condition; P91 and P92 require normalizing, tempering, and careful control of hardness below 250 HB to avoid Type IV cracking in welds.

Practical Selection: How to Shortlist the Right Grade

A workable approach is to filter on four parameters: design code, design metal temperature, fluid or process medium, and required service life. A short workflow that EPCs and end users often follow:

1. Confirm the governing code first. ASME Section I and Section VIII carry different rules even when the same nominal grade appears on the data sheet.
2. Set the design metal temperature. Below 400 °C, a carbon steel such as A210 A-1 or A192 will normally satisfy both strength and oxidation requirements.
3. Match the medium. Hydrogen service, sour service (NACE MR0175), and chloride exposure each push the choice toward specific compositions or overlays.
4. Decide on fabrication strategy. If field bending and shop welding are heavy, lean toward grades with known weldability (P11, P22) and avoid over-specifying P91 unless creep strength actually requires it.

In refineries and petrochemical plants, the most common pairings are A106/A210 for lower-temperature piping and A335 P11/P22 for the hot end. In utility boilers, the move toward ultrasupercritical conditions has pushed A335 P91 and P92 (and the equivalent T91/T92 boiler tubes under A213) to the top of the bill of materials. For processes where corrosion is the main concern rather than heat, the conversation shifts to stainless steel and copper-nickel grades covered in separate guides.

Quality, Testing, and Documentation You Should Expect

Regardless of grade, the boiler and pressure-vessel codes expect full traceability and destructive testing. A reliable supplier will provide:

• Mill test certificate (MTC) to EN 10204 3.1 or 3.2, with heat number, chemical analysis, and mechanical test results.
• Hydrostatic testing of every tube length, or as agreed per standard.
• Non-destructive testing: ultrasonic and/or eddy current per the relevant ASTM A1016 / A450 requirements.
• Positive material identification (PMI) for alloy grades, to avoid mix-ups between P11, P22, and P91 on site.
• Dimensional inspection against ASME B36.10 / B36.19 tolerances.

EZ Steel Industrial's three-facility network is set up to deliver carbon, Cr-Mo, and stainless grades with the documentation that EPCs and inspectors expect, and the company provides bundled project supply, technical documentation, and just-in-time delivery for large boiler and pressure-vessel packages.

Quick-Reference Grade Summary

The table below summarizes the most common grades and where they fit in a boiler or pressure-vessel specification. Use it as a starting point for discussion with your engineering team and your supplier.

Closing Notes

For most boiler and pressure-vessel projects, the practical grade family is small: a carbon steel such as A210 or A192 for the cool end, a Cr-Mo alloy such as P11 or P22 for the hot end, and a T/P91 or P92 grade only when ultrasupercritical steam conditions truly demand it. The right partner can hold the right mix in stock, supply complete documentation, and support field welding and inspection — which is usually the difference between a smooth erection and a costly rework.

To request a quotation on carbon, carbon-molybdenum, or Cr-Mo alloy steel tubes for boiler and pressure-vessel service, contact EZ Steel Industrial at export@ezsteelpipe.com or visit the EZ Steel Industrial product catalog.