What is the maximum allowable stress value for ASME SA387 Grade 11 Class 1 ？

ASME SA 387 GRADE 11 Class 1 Pressure Vessel Steel Plate

The maximum allowable stress for ASME SA387 Grade 11 Class 1 isn't a single number but varies with temperature, determined by the ASME Boiler & Pressure Vessel Code (BPVC) Section II, Part D, using its yield (35 ksi) and tensile (60-85 ksi) strength minimums, factoring in design temperatures, corrosion allowances, and safety factors, with typical values around 12.5 ksi (86 MPa) to 25.5 ksi (176 MPa) for common service temperatures, but always refer to the official Code for specific design applications.

ASME SA387 Grade 11 Class 1 is a chromium-molybdenum (Cr-Mo) alloy steel plate designed for high-temperature, high-pressure welded boilers and pressure vessels, offering excellent creep resistance, thermal strength, and corrosion resistance, especially in sour gas (H₂S) environments, featuring lower tensile/yield strengths than Class 2 (60-85 ksi tensile, 30-35 ksi yield). The manufacturing process involves rigorous control over the melting and rolling stages to ensure a clean steel structure with minimal impurities, typically supplied in annealing or normalizing and tempered conditions to refine the grain structure and relieve internal stresses.

In the global industrial landscape of 2026, this material remains a preferred choice for the oil, gas, and petrochemical sectors for the fabrication of weldable pressure vessels and industrial boilers that operate in "sour" environments where hydrogen sulfide and other corrosive gases are present at high temperatures. Refineries utilize this grade for hydroprocessing units, catalytic crackers, and heat exchangers because it must resist hydrogen attack and sulfur corrosion while maintaining structural stability. The Class 1 variant is particularly valued in scenarios where the vessel design requires significant forming or where operating conditions favor higher elongation properties, allowing for the construction of large-diameter vessels and thick-walled reactors.

Categorized under ASME P-Number 4, Group 1, this classification is vital for determining welding procedures. Due to its alloying elements, the steel is susceptible to hydrogen-induced cracking and air-hardening, necessitating preheating during welding and a carefully controlled cooling cycle. By balancing strength with workability, Class 1 provides fabricators with a reliable substrate for complex geometries, ensuring final vessels meet stringent safety standards for modern industrial infrastructure.

Key Characteristics

Composition: Chromium and Molybdenum alloy for enhanced properties.

Service: Elevated temperature service, resistant to sour gas (H₂S).

Applications: Pressure vessels, boilers, heat exchangers, power plants, petrochemical equipment.

Class 1 vs. Class 2

Class 1: Lower strength, higher ductility (e.g., 60-85 ksi tensile).

Class 2: Higher strength (e.g., 75-100 ksi tensile, 40-45 ksi yield), but slightly lower elongation.

Industry Use

Industries: Petrochemical, Power Generation, Refinery, Gas Processing.

Components: Vessels, Heat Exchangers, Reactors.

SA387 GR 11 CLASS 1 Plate Specification :

Width: 1000mm-4500mm
Thickness: 5mm to 150mm
Length: 3000mm-18000mm
Supply Condition : As Rolled, Normalized Rolling, Furnace Normalizing, Vacuum Degassing, Simulated Post-Weld Heat Treatment or as per customer requirement.
Impact tested: -52° C
Process of Manufacturing: Hot-Rolled (HR)

What precautions should be taken when welding ASME SA387 Grade 11 Class 1 steel?

When welding SA387 Grade 11 Class 1 steel (a low-alloy chromium-molybdenum steel), key precautions involve proper preheating (around 250°F/121°C minimum) to prevent cracking, selecting appropriate filler materials (like EB2 group), controlling interpass temperatures, applying Post Weld Heat Treatment (PWHT) (around 1200°F/650°C) to relieve stress, ensuring good ventilation, and using full Personal Protective Equipment (PPE), while cleaning the surface thoroughly.

What is the maximum allowable stress value for ASME SA387 Grade11 Class1?

For ASME SA387 Grade 11 Class 1, the maximum allowable stress values are determined by ASME Section II, Part D (Table 1A), and vary significantly based on the operating temperature; for instance, at a typical temperature of $650^\circ\text{F}$ ($345^\circ\text{C}$), the allowable stress is approximately 13.8 ksi (95 MPa), but this value decreases as temperatures rise toward its upper limit of $1000^\circ\text{F}$ ($538^\circ\text{C}$) to account for reduced material strength and creep resistance.

What is the P number of ASME SA387 Grade 11 Class 1 steel?

The P-number for ASME SA387 Grade 11 Class 1 steel is 4. this assignment applies to both Class 1 and Class 2 of Grade 11, as they share the same nominal chemical composition of 1.25Cr-0.5Mo-Si.1 This grouping identifies the material as a low-alloy steel containing chromium and molybdenum, typically used for elevated temperature service in pressure vessels.

Specifications for ASME SA387 Grade 11 Alloy Steel Plates

Alloy Steel ASTM A387 GR 11 CL. 1 / 2 Plates Chemical Composition :

Tensile Requirements for ASME SA387 Grade 11 Alloy Steel Plates Class 1 Plates

1What is ASME SA387 Grade 11 Class 1 equivalent to?

ASME SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel primarily used for welded boilers and pressure vessels designed for elevated temperature service.5 It is virtually identical to ASTM A387 Grade 11 Class 1, with the primary difference being the governing regulatory code.

2What is the hardness of ASME SA387 Grade 11 Class 1 steel?

ASME SA387 Grade 11 Class 1 steel's hardness isn't directly listed in Brinell or Rockwell scales in typical spec sheets, but its yield strength is a key indicator, around 240 MPa (35 ksi), with tensile strength between 415-585 MPa (60-85 ksi), and it's usually supplied normalized and tempered, providing good strength for elevated temperature service in pressure vessels.

3What is ASME SA387 Grade 11 Class 1 material?

ASME SA387 Grade 11 Class 1 is a chromium-molybdenum (Cr-Mo) alloy steel plate, specified for welded boilers and pressure vessels needing high-temperature strength and corrosion resistance, common in oil, gas, and power industries, offering good oxidation/corrosion resistance, especially in sour gas.

4What is the ASME SA387 Grade11 Class1 standard?

ASME SA387 Grade 11 Class 1 is a chromium-molybdenum alloy steel plate for high-temperature pressure vessels and boilers, offering good creep, corrosion, and oxidation resistance, with lower strength but better elongation than Class 2, making it suitable for refineries and petrochemical plants in sour gas or hydrogen service.6 Key elements are ~1.25% Chromium (Cr) and ~0.5% Molybdenum (Mo), providing strength and stability for demanding environments, typically supplied normalized and tempered.

5What are the typical application fields of ASME SA387 Grade 11 Class 1 steel?

ASME SA387 Grade 11 Class 1 steel is primarily used in high-temperature, high-pressure applications, especially in the oil & gas, petrochemical, and power generation industries, for equipment like pressure vessels, boilers, heat exchangers, piping, and storage tanks, benefiting from its chromium-molybdenum content for enhanced strength, creep resistance, and resistance to oxidation and corrosion, particularly in sour gas environments.10

6Is ASME SA387 Grade 11 Class 1 carbon steel?

No,ASME SA387 Grade 11 Class 1 is not a carbon steel; it is a low-alloy chromium-molybdenum (Cr-Mo) steel. While it contains carbon (typically between 0.05% and 0.17%), it is specifically categorized as an alloy steel due to the intentional addition of chromium and molybdenum to enhance its performance in high-temperature and high-pressure environments.

7What temperature is ASME SA387 Grade 11 Class 1 steel?

In the lower end of the temperature range SA 387 Gr 11 (1150 °F min tempering temperature) , and SA 387 Gr 22 (1250 °F min tempering temperature) are used.3 These grades can be specified in either class 1 or 2 and can also be provided in the Normalized & Tempered or Quenched and Tempered.

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