ASTM A335 P91 Alloy steel Pipe specification

ASTM A335 P91 Alloy Steel Pipe Specification

ASTM A335 P91 alloy steel pipe specification covers seamless ferritic alloy steel pipes intended for high-temperature and high-pressure service.
Grade P91 is a 9Cr-1Mo-V-Nb alloy steel developed for advanced power generation systems requiring excellent creep strength, oxidation resistance, and long-term thermal stability.

This Page is to introduce the ASTM A335 P91 alloy steel pipe specification, including chemical composition, mechanical properties, heat treatment requirements, and typical industrial applications.

Overview of ASTM A335 P91 Alloy Steel Pipes

ASTM A335 P91 is a high-chromium alloy steel grade designed for elevated temperature service, particularly in supercritical and ultra-supercritical power plants.

P91 pipes are typically supplied in the normalized and tempered condition to achieve the required microstructure and mechanical performance for long-term high-temperature operation.

Chemical Composition & Mechanical Properties

The ASTM A335 P91 pipe specification PDF includes detailed requirements for:

  • Chemical composition limits for chromium, molybdenum, vanadium, and niobium

  • Mechanical properties such as tensile strength, yield strength, and elongation

  • Heat treatment requirements including normalizing and tempering

  • Hydrostatic testing, nondestructive testing, and certification requirements

These requirements ensure the safety and reliability of P91 alloy steel pipes under extreme operating conditions.

ASTM A335 P91 Chemical Composition

Comparison: P91 Type 1 vs P91 Type 2

 Chemical Composition

Element P91 Type 1 P91 Type 2 Main Difference
Carbon (C) 0.08–0.12 Heat: 0.08–0.12
Product: 0.07–0.13		 Type 2 allows slightly wider range for product
Manganese (Mn) 0.30–0.60 0.30–0.50 (Heat) Tighter control in Type 2
Phosphorus (P) ≤ 0.020 ≤ 0.020 Same
Sulfur (S) ≤ 0.010 ≤ 0.005 Stricter in Type 2
Silicon (Si) 0.20–0.50 0.20–0.40 Lower max in Type 2
Chromium (Cr) 8.00–9.50 8.00–9.50 Same
Molybdenum (Mo) 0.85–1.05 0.80–1.05 Slightly wider in Type 2
Vanadium (V) 0.18–0.25 Heat: 0.18–0.25
Product: 0.16–0.27		 Wider control in Type 2
Nitrogen (N) 0.030–0.070 0.035–0.070 Higher minimum in Type 2
Aluminum (Al) ≤ 0.020 ≤ 0.020 Same
Nb, Ti, B, Ni, etc. Controlled More tightly specified Type 2 is more restrictive

P91 Type 2 is an enhanced version of P91 alloy steel with tighter chemical composition control compared to Type 1. The reduced sulfur and silicon levels, along with optimized microalloying elements, provide improved creep strength, structural stability, and long-term reliability for high-temperature and high-pressure applications.

ASTM A335 P91 Mechanical Properties

Property Requirement
Tensile Strength ≥ 585 MPa
Yield Strength (0.2% Offset) ≥ 415 MPa
Elongation (in 50 mm) ≥ 20%
Reduction of Area Not specified

Typical Applications of ASTM A335 P91 Pipes

ASTM A335 P91 alloy steel pipes are widely used in:

  • Supercritical and ultra-supercritical power plants

  • High-temperature steam piping systems

  • Boiler and pressure piping

  • Heat recovery steam generators (HRSG)

  • Refinery and petrochemical high-temperature units

P91 material is selected for applications requiring superior creep resistance and long-term thermal performance.

Related Standards & Equivalent Grades

ASTM A335 P91 is commonly referenced alongside:

  • ASME SA335 P91

  • ASTM A213 T91 (boiler tubes)

  • ASTM A387 Grade 91 (plate)

  • ASTM A182 F91 (forgings)

  • EN 1.4903 (X10CrMoVNb9-1)

These standards define equivalent 9Cr alloy steels supplied in different product forms.

Download

Download ASTM A335 P91 Alloy Steel Pipe Specification (PDF)
👉 [Download ASTM A335 P91 Alloy Steel Pipe Specification PDF]

👉 [Download ASTM A335 Standard Specification PDF]

Related Products

The ASTM A335 P91 specification applies to the following products: