What is A387 Grade 12 Class 2 equivalent material?
ASTM A387 Grade 12 Class 2 is a normalized and tempered chromium-molybdenum (1.25Cr-0.5Mo) alloy steel plate designed for high-temperature service in welded pressure vessels and boilers, offering higher strength than Class 1 through its specific heat treatment.
Direct Equivalent: The universal pressure vessel standard designation is SA-387 Grade 12 Class 2 in the ASME Boiler and Pressure Vessel Code (BPVC). Its Unified Numbering System (UNS) identifier is K11762.
Below is a table of the most commonly referenced international and commercial equivalents. Important Note: These are similar or closely related grades; they are not always chemically identical and have different mechanical property requirements. Full equivalency for a specific application must be verified by an engineer.
| Standard / Region | Equivalent Designation | Notes |
|---|---|---|
| ASME (USA) | SA-387 Gr.12 Cl.2 | The direct equivalent in the BPVC, Section II, Part A. This is the most important designation for pressure vessel construction in North America. |
| UNS (USA) | K11762 | The standardized material number. |
| EN / DIN (Europe) | 13CrMo4-5 (1.7335) | A very common European equivalent, widely used for the same applications. The composition and properties are very close. |
| JIS (Japan) | SCMV 420 | A Japanese pressure vessel steel grade. The specifications are closely aligned. |
| GB (China) | 15CrMoR | The primary Chinese equivalent pressure vessel plate steel. "R" stands for "容" (container/vessel). |
| Common Name / Alloy Group | 1¼Cr-½Mo or 1.25Cr-0.5Mo | This is the industry shorthand name based on its nominal chromium and molybdenum content. |
Critical Distinctions for Equivalency:
Class 2 vs. Class 1: When seeking equivalents, you must specify Class 2. Class 1 is annealed and has lower strength. Most international equivalents (like 13CrMo4-5) are aligned with the normalized and tempered condition of Class 2.
Condition is Key: The true equivalent material must be supplied in the normalized and tempered (N&T) condition to match the mechanical properties of A387 Gr.12 Cl.2.
Application Standard: For building a coded pressure vessel (e.g., to ASME BPVC), you must use material that carries the appropriate ASME SA-387 certification and marking, regardless of the foreign designation.
In summary: For global engineering and procurement, the most direct and important equivalents are SA-387 Gr.12 Cl.2 (ASME), 13CrMo4-5 (EN), and 15CrMoR (GB).
1. What is the typical post-weld heat treatment (PWHT) temperature and hold time for A387 Gr.12 Cl.2?
For A387 Grade 12 Class 2, the typical recommended Post-Weld Heat Treatment (PWHT or stress relief) temperature range is 1100°F to 1250°F (595°C to 675°C). The holding time is usually a minimum of 1 hour per inch (25 mm) of thickness, with a common minimum of 1 hour total. This process is critical to relieve welding stresses, temper the heat-affected zone (HAZ), and restore corrosion resistance, ensuring the integrity of the fabricated pressure vessel component.
2. Why is preheating mandatory before welding A387 Gr.12 Cl.2 steel?
Preheating, typically in the range of 300°F to 450°F (150°C to 230°C), is mandatory for welding A387 Grade 12 Class 2 to prevent hydrogen-induced cracking (HIC), also known as cold cracking. This alloy's hardenability can lead to a brittle microstructure in the weld zone upon rapid cooling. Preheating slows the cooling rate, allowing hydrogen to diffuse out and reducing the risk of forming crack-susceptible martensite, thereby ensuring a sound, defect-free weld.
3. What is the maximum continuous service temperature for A387 Gr.12 Cl.2 plates?
The maximum recommended continuous service temperature for ASTM A387 Grade 12 Class 2 plates is generally up to 1000°F (540°C). At this elevated temperature range, the chromium content provides improved resistance to oxidation (scaling) and corrosion, while the molybdenum enhances strength and reduces creep. For service above this temperature, grades with higher chromium content (like Grade 11 or 22) are typically considered.
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