SA 387 Gr. 22 Cl. 1 is a Chromium-Molybdenum alloy steel plate specified by ASME SA-387 and ASTM A387, designed for high-temperature welded pressure vessels and boilers, offering moderate strength with 2.25% Chromium and 1% Molybdenum, requiring heat treatment like normalizing and tempering. It offers lower tensile strength than Class 2 (60-85 ksi vs. 75-100 ksi) but provides good strength and corrosion resistance at elevated temperatures, making it crucial for the oil, gas, and petrochemical industries.
Tensile Requirements for ASME SA387 Grade 22 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 22 |
| SA387 Grade 22 | Tensile strength, ksi [MPA] | 75 to 100 [515 to 690] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 45 [310] | |
| Elongation in 8 in. [200mm], min % | ... | |
| Elongation in 2 in. [50mm], min, % | 18 | |
| Reduction of area, min % | 45 (measured on round specimen) 40 (measured on flat specimen) |
Chemical Requirements for ASME SA387 Grade 22 Alloy Steel Plates
| Element | Chemical Composition (%) | |
| SA387 Grade 22 | ||
| Carbon: | Heat Analysis: | 0.05 - 0.15 |
| Product Analysis: | 0.04 - 0.15 | |
| Manganese: | Heat Analysis: | 0.30 - 0.60 |
| Product Analysis: | 0.25 - 0.66 | |
| Phosphorus: | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Sulphur (max): | Heat Analysis: | 0.035 |
| Product Analysis: | 0.035 | |
| Silicon: | Heat Analysis: | 0.50 max |
| Product Analysis: | 0.50 max | |
| Chromium: | Heat Analysis: | 2.00 - 2.50 |
| Product Analysis: | 1.88 - 2.62 | |
| Molybdenum: | Heat Analysis: | 0.90 - 1.10 |
| Product Analysis: | 0.85 - 1.15 |
Key Applications
Pressure Vessels:
SA 387 Gr.22 Cl 1 is widely used in the fabrication of pressure vessels for storing and processing various substances under high temperatures and pressures. Its excellent creep strength and resistance to temper embrittlement make it suitable for both general-purpose and severe-service vessels in refineries, chemical plants, and power generation facilities. The material's ability to maintain structural integrity over long periods at elevated temperatures ensures safe and reliable operation even under cyclic loading conditions.
Boilers & Heat Exchangers:
This grade is extensively employed in boilers, superheaters, and heat exchangers where high-heat transfer rates and prolonged exposure to high temperatures are common. Its chromium-molybdenum composition provides good oxidation resistance and stable mechanical properties at elevated temperatures, allowing for efficient heat transfer while minimizing the risk of material degradation. SA 387 Gr.22 Cl 1 is particularly well-suited for applications involving high-pressure steam and hot process fluids.
Piping & Tubing:
In high-temperature piping systems, SA 387 Gr.22 Cl 1 is used for transporting hot fluids, gases, and steam in refineries, petrochemical plants, and power generation facilities. The material's combination of strength, toughness, and resistance to thermal fatigue makes it ideal for service conditions where temperatures and pressures fluctuate. It is often specified for critical piping components that require reliable performance under extreme operating conditions.
Oil & Gas Industry:
Within the oil and gas sector, SA 387 Gr.22 Cl 1 is a preferred material for refineries, petrochemical plants, and offshore platforms. It is used in reactors, separators, and other pressure-containing equipment that handles hydrocarbons and process fluids at high temperatures. Its ability to withstand hydrogen attack and high-temperature corrosion makes it well-suited for harsh environments encountered in this industry.
Power Plants:
SA 387 Gr.22 Cl 1 is commonly specified for power generation applications, including boilers, pressure vessels, and heat recovery systems. The material provides the necessary high-temperature strength and creep resistance required for components exposed to high-pressure steam and elevated temperatures. Its durability and resistance to thermal stress ensure long service life and reliable performance in both conventional and advanced power plants.
Key Process Flow
Smelting and Composition Control:
Steel is melted using an electric arc furnace (EAF), ladle furnace (LF), and other refining equipment, with strict control over the contents of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), and the key alloying elements chromium (Cr) and molybdenum (Mo).In particular, the carbon content is usually kept relatively low to improve weldability while ensuring the standard 2.25%Cr-1%Mo alloy composition is maintained.
Forming and Rolling:
The steel billet is heated to the appropriate rolling temperature and then rolled into plates of the required thickness using rolling mills.
Heat Treatment (after hot working):
Normalizing: This is a critical step. The plate is heated to the austenitizing temperature and then air-cooled to homogenize the microstructure, relieve internal stresses, and achieve a fine-grained pearlite + ferrite structure.
Tempering: Tempering is performed after normalizing (or after quenching, if applied), further adjusting hardness and toughness to meet the required mechanical properties.
Inspection and Testing:
Non-destructive testing (NDT) such as ultrasonic testing (UT) and magnetic particle testing (MT) is carried out to ensure there are no internal or surface defects.Mechanical property tests including tensile, impact, and hardness tests, as well as chemical composition analysis, are performed to ensure compliance with the ASME SA 387 Gr.22 Cl 1 standard.
Main Characteristics (Influenced by Process):
2.25%Cr-1%Mo alloy: Provides high-temperature strength and oxidation resistance.
Low carbon content: Enhances weldability.
Normalizing + tempering: Optimizes the microstructure, ensuring good high-temperature mechanical properties and hydrogen resistance (with control of HAZ embrittlement).
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What are the main alloying elements?
The key alloying elements are chromium and molybdenum. Chromium improves oxidation resistance and high-temperature strength, while molybdenum enhances creep resistance and provides stability under long-term thermal loading. These elements work together to ensure the steel can withstand elevated temperatures without significant degradation. Other elements such as carbon, manganese, and silicon are also carefully controlled to maintain weldability and mechanical properties.
What heat treatment is used?
SA 387 Gr.22 Cl 1 is typically heat treated by normalization followed by tempering. Normalization involves heating the steel to a temperature around 890–940°C, holding it to ensure uniformity, and then cooling in air. This process refines the grain structure and improves toughness. Tempering is done at a minimum of 675°C to reduce residual stresses, enhance ductility, and stabilize the microstructure. The exact temperatures may vary based on plate thickness and manufacturer practice.
What does "Class 1" mean?
"Class 1" indicates that the steel plate must undergo a higher level of ultrasonic testing (UT) compared to Class 2. This stricter inspection ensures that the material has fewer internal defects such as laminations, inclusions, or voids. The goal is to provide a more reliable material for critical pressure vessel applications where structural integrity is essential. Plates that do not meet Class 1 standards may be reclassified as Class 2 if they meet the lower inspection requirements.
How is it welded?
SA 387 Gr.22 Cl 1 can be welded using common processes such as SMAW (stick), GMAW (MIG), FCAW, and SAW. The choice of filler metal is important and usually involves matching Cr-Mo compositions, such as E8018-B2 or ER80S-B2. Proper preheating and post-weld heat treatment (PWHT) are essential to prevent cold cracking and ensure good mechanical properties in the heat-affected zone (HAZ).
Why is preheating needed for welding?
Preheating is necessary to reduce the cooling rate of the weld and HAZ, which helps prevent the formation of hard, brittle microstructures that can lead to cracking. It also helps remove moisture from the joint area, reducing hydrogen pickup. Typical preheat temperatures range from 150–250°C, depending on plate thickness and welding process. Thicker plates generally require higher preheat temperatures.
What NDT is performed on these plates?
SA 387 Gr.22 Cl 1 plates undergo rigorous non-destructive testing. The primary requirement is ultrasonic testing (UT) to ensure internal soundness, as specified for Class 1. Additional inspections may include visual inspection (VI) for surface quality, magnetic particle testing (MT) for surface cracks in ferromagnetic materials, and liquid penetrant testing (PT) for detecting surface discontinuities. Some applications may also require radiographic testing (RT) depending on design and customer specifications.
What is the difference between SA 387 Gr.22 Class 1 and Class 2?
The main difference is the level of ultrasonic inspection. Class 1 requires stricter UT to ensure fewer internal defects such as laminations or inclusions. Class 2 has more lenient inspection criteria. Class 1 is typically chosen for critical pressure vessel components where high reliability is essential, while Class 2 may be used in less critical areas.
How does SA 387 Gr.22 Cl 1 compare to carbon steel plates?
Unlike standard carbon steels, SA 387 Gr.22 Cl 1 contains chromium and molybdenum, which significantly improve its high-temperature strength, creep resistance, and resistance to temper embrittlement. Carbon steels soften and lose strength at elevated temperatures, making them unsuitable for many pressure vessel and boiler applications where Gr.22 excels.
What is the difference between SA 387 Gr.22 Cl 1 and SA 516 Gr.70?
SA 516 Gr.70 is a carbon steel designed for low-to-moderate temperature pressure vessel service, while SA 387 Gr.22 Cl 1 is a Cr-Mo alloy steel for high-temperature applications. SA 516 Gr.70 offers good toughness at lower temperatures but lacks the creep strength and oxidation resistance of Gr.22. Gr.22 is used in refineries and power plants, while SA 516 Gr.70 is common in storage tanks and low-temperature vessels.
How does SA 387 Gr.22 Cl 1 compare to SA 387 Gr.22 Cl 2?
Both grades have the same chemical composition, but Class 1 requires more stringent ultrasonic testing for internal soundness. Class 2 allows slightly more internal discontinuities. Class 1 is preferred for critical applications where failure could have severe consequences, while Class 2 is used when lower inspection levels are acceptable.