ASME SA 387 GRADE 11 Class 1 Pressure Vessel Steel Plate
ASME SA387 Grade 11 Class 1 refers to a specific type of chromium-molybdenum (Cr-Mo) alloy steel plate for high-temperature service, used in boilers and pressure vessels, offering good weldability, corrosion resistance (especially from hydrogen sulfide), and strength, with "Grade 11" indicating its alloy content (approx. 1.25% Cr, 0.5% Mo) and "Class 1" specifying its mechanical properties, which are lower strength but better ductility than Class 2.
These standards serve as a defining compass, delineating the permissible range of quality and properties that a material or final product should embody. Among the array of plates, ALLOY STEEL SA 387 GR. 11 CL. 1 / 2 plates assume a prominent role, mirroring their widespread usage.
Speaking of the Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum, the Grade 11 alloy, encompassing class 1 or 2 plates, conforms to standard 387. Delving further into the article, a plethora of additional standards and specifications shall be expounded upon. However, prior to that, it's essential to grasp the foundational elements constituting the alloy.
The mechanical performance of ASME SA387 Grade 11 Class 1 is defined by its balance of tensile strength and ductility. According to ASME specifications, Class 1 plates must exhibit a tensile strength ranging from 60 to 85 ksi (415 to 585 MPa) and a minimum yield strength of 35 ksi (240 MPa). These values are intentionally lower than those of Class 2 to ensure a minimum elongation of 19% to 22%, depending on the specimen size. This high level of ductility is a safety feature; it allows the material to undergo plastic deformation before reaching its breaking point, providing a buffer against unexpected pressure surges or thermal shocks. Engineers utilize these specific values in their design calculations to determine the required wall thickness of a vessel, ensuring it can safely contain its contents under specified temperature and pressure ratings. The material's impact toughness is also a key consideration, especially for equipment operating in climates where ambient temperatures may drop significantly during maintenance shutdowns.
From a fabrication perspective, working with SA387 Grade 11 Class 1 requires specialized expertise. The welding of Cr-Mo steels is more complex than that of standard carbon steel due to the risk of hardening in the heat-affected zone (HAZ). To mitigate this, fabricators must adhere to strict preheat temperatures, typically between 150°C and 250°C, and perform Post-Weld Heat Treatment (PWHT) to restore the material's ductility and reduce residual stresses. The PWHT process usually involves heating the welded assembly to approximately 620°C to 700°C for a duration proportional to the thickness of the plate. Furthermore, non-destructive testing (NDT) such as ultrasonic and radiographic examination is standard practice to ensure the integrity of the welds. As we move through 2026, advancements in automated welding technologies and real-time thermal monitoring have further improved the reliability of structures built from SA387 Grade 11 Class 1, reinforcing its status as a foundational material for high-temperature engineering.
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). It's used in petrochemical, refinery, and power generation industries for critical components like heat exchangers, boilers, and vessels, providing superior thermal stability and structural integrity.
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)
Is 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.
What 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.
What 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.
Specifications for ASME SA387 Grade 11 Alloy Steel Plates
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
| SA387 Grade 11 | 1.25% | 0.50% |
Alloy Steel ASTM A387 GR 11 CL. 1 / 2 Plates Chemical Composition :
| C | Mn | P | S | Si | Cr | Mo |
| 0.04 - 0.17 | 0.35 - 0.73 | 0.035 | 0.035 | 0.44 - 0.86 | 0.94 - 1.56 | 0.40 - 0.7 |
Tensile Requirements for ASME SA387 Grade 11 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 11 |
| SA387 Grade 11 | Tensile strength, ksi [MPa] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 43 [310] | |
| Elongation in 8 in. [200mm], min % | 18 | |
| Elongation in 2 in. [50mm], min, % | 22 | |
| Reduction of area, min % | ––– |
1What 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.
2What 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.
3What 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.
4What 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.
5What 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.
6What 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.
7What 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.
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