What are the properties and applications of A387 Grade 11 Class 1 Steel?
Overview
ASTM A387 Grade 11 Class 1 is a chromium-molybdenum (Cr-Mo) alloy steel plate specifically designed for welded pressure vessels operating at elevated temperatures. Its composition and controlled heat treatment make it a superior choice over carbon steel for high-temperature and high-pressure service.
Key Properties
1.Chemical Composition (Typical):
Chromium (Cr): 1.00 - 1.50% - Provides increased resistance to oxidation (scaling) and corrosion, particularly against sulfur compounds.
Molybdenum (Mo): 0.45 - 0.65% - Enhances high-temperature strength and creep resistance (resistance to gradual deformation under stress).
2.Mechanical Properties (As-Specified Minimums):
Tensile Strength: 415 - 585 MPa (60 - 85 ksi)
Yield Strength: 205 MPa (30 ksi) min.
Key Advantage: It retains a significant portion of its strength at temperatures above 400°C (750°F), where carbon steel weakens rapidly.
3.Heat Treatment (The "Class 1" Distinction):
Condition: Supplied in the Normalized or Stress-Relieved condition.
Normalizing refines the grain structure for improved uniformity and toughness.
Implication: Class 1 material is intended for fabricators who will perform Post-Weld Heat Treatment (PWHT) after forming and welding. This allows for stress relief and restoration of properties in the final fabricated component.
4.Weldability & Fabrication:
It is weldable with proper procedures, but requires strict control.
Preheating (150-200°C / 300-400°F) is mandatory to prevent cracking.
Mandatory Post-Weld Heat Treatment (PWHT) is critical, typically between 595-720°C (1100-1325°F). This step relieves stresses, tempers the weld zone, and ensures optimal corrosion resistance and toughness.
Primary Applications
Due to its properties, A387 Gr.11 Cl.1 is a standard material in industries where equipment operates under high temperature and high pressure (HT/HP):
Petroleum Refineries:
Catalytic cracking units (reactors, regenerators)
Hydrocracking and hydroprocessing reactors
High-temperature/high-pressure separators and vessels
Chemical & Petrochemical Plants:
Vessels for processes involving hydrogen (it offers good resistance to hydrogen attack at elevated temperatures)
Ammonia converters
High-pressure heat exchangers
Power Generation:
Sections of fossil-fuel power plant boilers (e.g., steam drums, headers)
Heat recovery steam generators (HRSGs)
General Pressure Vessel Fabrication: For any service where temperatures exceed the safe limit for carbon steel (e.g., ASME Boiler and Pressure Vessel Code Section I or Section VIII, Div. 1 service).
Comparison with Class 2
For context, A387 Grade 11 Class 2 is supplied in the Normalized and Tempered (or Quenched & Tempered) condition. Class 2 has higher as-delivered strength and is often used when the final PWHT by the fabricator is not possible or when higher initial strength is required. Class 1 is more common for fabrications involving significant welding and forming, followed by a full vessel PWHT.
Summary
In essence, ASTM A387 Grade 11 Class 1 is a normalized 1.25%Cr-0.5%Mo alloy steel that provides an excellent balance of high-temperature strength, oxidation resistance, and fabricability. Its primary role is in the construction of critical pressure vessels and reactors in the energy and chemical processing industries, where reliability under thermal and mechanical stress is paramount.
What is A387 grade 11 material?
The ASTM A387 specification is the Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum intended primarily for use in welded boilers and pressure vessels designed for elevated temperature service. SSAB can supply A387 Grade 11 to the tension test requirements for Class 1 and/or Class 2.
What is the composition of A387 steel?
Composition: ASTM A387 steel plates typically contain chromium (up to 9% or more) and molybdenum (up to 2.25% or more), which enhance their strength and corrosion resistance at high temperatures.
What is the difference between A182 and A387?
Both ASTM A182 grade F11 class 2 and ASTM A387 grade 22 steel are iron alloys. They have a very high 99% of their average alloy composition in common. There are 32 material properties with values for both materials. Properties with values for just one material (1, in this case) are not shown.
What is ASTM A387 Grade 11 equivalent to?
ASTM A387 grade 11 equivalent steel is ASME SA387 grade 11. ASTM A387 grade 11 covers A387 grade 11 class 1 and A387 grade 11 class 2, which are equivalent to ASME SA387 grade 11 class 1 and SA387 grade 11 class 2 respectively.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
