A387 Grade 11 Class 1 steel plate is a chromium-molybdenum alloy steel plate (containing 1.25% chromium and 0.5% molybdenum) specifically designed for high-temperature environments in welded boilers and pressure vessels. This steel plate is primarily used in the oil and gas industry, exhibiting excellent corrosion resistance and oxidation resistance, and is particularly suitable for acidic gas environments.
Chemical Composition of A387 Grade 11 Class 1
The performance of A387 Grade 11 Class 1 is primarily derived from its controlled chromium and molybdenum content. The table below summarizes the typical and required chemical composition:
| Element | Typical Value |
|---|---|
| Carbon (C) | 0.10 – 0.14 |
| Manganese (Mn) | 0.50 – 0.60 |
| Phosphorus (P) | ≤ 0.015 |
| Sulfur (S) | ≤ 0.008 |
| Silicon (Si) | 0.55 – 0.70 |
| Chromium (Cr) | 1.15 – 1.35 |
| Molybdenum (Mo) | 0.48 – 0.55 |
The chromium content provides oxidation and corrosion resistance, while molybdenum enhances high-temperature creep strength and resistance to temper embrittlement.
Mechanical Properties of A387 Grade 11 Class 1
The mechanical property requirements for A387 Grade 11 Class 1 are outlined below:
| Property | Typical Achieved Value |
|---|---|
| Tensile Strength (MPa) | 450 – 550 |
| Yield Strength (min, MPa) | 240 – 310 |
| Elongation in 200 mm (min, %) | 22 – 28 |
| Elongation in 50 mm (min, %) | 25 – 32 |
| Hardness (HB) | 130 – 180 |
Class 1 offers a lower yield strength than Class 2 (which requires ≥310 MPa), but this translates into improved toughness, better ductility, and reduced cracking risk during welding and forming operations.
Key Advantages of A387 Grade 11 Class 1
Superior High-Temperature Performance: Designed specifically for the high-temperature environments of power plants and refineries.
High Corrosion and Oxidation Resistance: The chromium-molybdenum alloy composition provides excellent corrosion protection, especially suitable for acidic gas environments.
Excellent Weldability and Machinability: Grade 1 has lower tensile strength than Grade 2, resulting in better ductility and easier, safer welding and forming operations.
Optimized Toughness: This material maintains excellent mechanical properties and structural integrity even at high temperatures.
Wide Range of Applications: Due to its reliable durability, it is widely used in oil and gas refineries, chemical processing, and power generation.
Application of A387 Grade 11 Class 1 For Oil, Gas & Petrochemical Industry
This is the most common sector for A387 Grade 11 Class 1.It is used to manufacture equipment that must handle pressurized fluids at high temperatures:
Reactors & Separators: Used in hydrocracking and hydrotreating units where hydrogen resistance is critical.
Heat Exchangers: Used for transferring heat between high-temperature process fluids.
Storage Tanks & Vessel Shells: Specifically for storing volatile chemicals or gases at temperatures up to 540°C (1000°F).
Sour Service: The chromium content provides essential resistance to oxidation and corrosion in "sour" (high sulfur) environments.
Application of A387 Grade 11 Class 1 For Power Generation
The A387 Grade 11 Class 1 material is a staple in power plants for steam-handling equipment:
Boilers & Steam Drums: Where constant high pressure and thermal stress are present.
High-Temperature Piping: For transporting superheated steam.
Steam Turbine Components: Used in vessel casings or flanges that require stable creep strength (resistance to slow deformation under heat).
In a word,A387 Grade 11 Class 1 offers a reliable, cost-effective solution for pressure vessel applications requiring elevated temperature service up to 540°C. Its balanced combination of chromium and molybdenum provides adequate creep strength and oxidation resistance, while the normalized and tempered condition ensures consistent mechanical properties and good weldability.
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| Standard: ASTM A387 Grade : A387 Gr 11 Class 1 |
| Thickness : 8mm-150mm Width : 1000mm-4000mm Length : 1000mm-20000mm |
| MOQ: 1 PC Product type : Steel plate Delivery time : Promptly ( Stock) or 10-40 days (Production) Payment Terms: L/C, T/T, etc Stock : Available MTC: Available |
| Delivery condition: Q+T or +N |
| MTC: Original |
What preheating temperature is required before welding A387 Grade 11 Class 1?
A minimum preheating temperature of 150–200°C (300–400°F) is required before welding A387 Grade 11 Class 1, with the higher end of this range recommended for thicker plates, restrained joints, or when ambient temperatures are low. The purpose of preheating is to slow the cooling rate of the weld and heat-affected zone, thereby preventing the formation of hard, crack-sensitive martensitic microstructures. Preheating should be applied uniformly across a sufficient area around the joint and maintained during the entire welding process, with interpass temperatures kept below 300°C to avoid excessive heat input and potential property degradation.
Does A387 Grade 11 Class 1 have good oxidation resistance?
A387 Grade 11 Class 1 provides moderate oxidation resistance up to approximately 540–570°C (1000–1050°F) due to its 1.25% chromium content, which forms a thin, protective chromium oxide layer on the steel surface at elevated temperatures. Above this temperature range, oxidation rates increase significantly, leading to scaling and material loss that may compromise wall thickness over long service periods. For applications requiring superior oxidation resistance at higher temperatures or in more aggressive combustion gas environments, higher chromium grades such as A387 Grade 22 (2.25% Cr) or Grade 91 (9% Cr) offer substantially better protection against scaling.
Can this material be repaired by welding if a defect is found during fabrication?
Yes, defects found during fabrication of A387 Grade 11 Class 1 can be repaired by welding, provided that a qualified welding procedure specification (WPS) is followed that includes proper preheating, low-hydrogen practices, and post-weld heat treatment. The defect area must first be completely removed by grinding or machining, confirmed by non-destructive examination (usually magnetic particle or dye penetrant testing), and then repaired using matching or approved welding consumables. After repair welding, the entire component must undergo post-weld heat treatment as required by the construction code, followed by re-inspection to ensure the repair is sound and free of new defects.
What is the typical hardness range for A387 Grade 11 Class 1?
A387 Grade 11 Class 1 in the normalized and tempered condition typically exhibits a Brinell hardness range of approximately 130–180 HB, though slightly higher or lower values may occur depending on plate thickness and specific mill processing. This relatively moderate hardness level reflects the material's balanced strength and toughness, while also ensuring good machinability and drillability. The low hardness also contributes to the material's resistance to hydrogen-induced cracking during welding, as higher hardness levels above 225 HB would indicate increased susceptibility to cracking and potential non-conformance to the standard's mechanical property requirements.