Specifications for ASTM A387 Grade 12 Alloy Steel Plates
ASTM A387/A387M: Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum
This specification covers chromium-molybdenum alloy steel plates intended primarily for fusion-welded boilers and pressure vessels designed for elevated temperature service.
Grade 12 is one of the standardized grades under this specification. Below are the key technical specifications for ASTM A387 Grade 12 Class 1 and Class 2 plates.
1. CHEMICAL COMPOSITION (Heat Analysis)
| Element | Grade 12, Class 1 (%) | Grade 12, Class 2 (%) |
|---|---|---|
| Carbon (C) | 0.10 max | 0.10 - 0.20 |
| Manganese (Mn) | 0.30 - 0.80 | 0.30 - 0.80 |
| Phosphorus (P) | 0.025 max | 0.025 max |
| Sulfur (S) | 0.025 max | 0.025 max |
| Silicon (Si) | 0.15 - 0.50 | 0.15 - 0.50 |
| Chromium (Cr) | 0.80 - 1.25 | 0.80 - 1.25 |
| Molybdenum (Mo) | 0.44 - 0.65 | 0.44 - 0.65 |
Note: Class 1 is for lower strength, suitable for annealing; Class 2 has higher carbon for higher strength, typically used in normalized and tempered condition.
2. MECHANICAL PROPERTIES
Properties are determined from a test specimen normalized and tempered (Class 2) or as-annealed (Class 1).
Grade 12, Class 1:
Tensile Strength: 380 - 550 MPa (55 - 80 ksi)
Yield Strength (min): 205 MPa (30 ksi)
Elongation in 50 mm (2 in) (min): 22%
Grade 12, Class 2:
Tensile Strength: 485 - 620 MPa (70 - 90 ksi)
Yield Strength (min): 275 MPa (40 ksi)
Elongation in 50 mm (2 in) (min): 20%
3. HEAT TREATMENT
Class 1: Plates are normally supplied in the annealed condition (full anneal or isothermal anneal).
Class 2: Plates are normally supplied in the normalized and tempered condition.
Normalizing Temperature: ~900°C (1650°F)
Tempering Temperature: ~650°C (1200°F) minimum.
Post-weld heat treatment (PWHT) is strongly recommended for fabrication to relieve stresses and restore the heat-affected zone (HAZ) properties.
4. HARDNESS REQUIREMENTS
Class 1 (Annealed): Typically, maximum Brinell hardness of 163 HBW.
Class 2 (Normalized & Tempered): Brinell hardness is generally in the range of 140-207 HBW.
5. IMPACT TESTING
Impact testing (Charpy V-notch) is not a mandatory requirement of the base specification A387 but is often specified in purchase orders for pressure vessel applications (e.g., following ASME BPVC Section II).
When specified, the test temperature and minimum absorbed energy values (e.g., 20 J avg at -30°C) must be agreed upon between purchaser and supplier.
6. METALLURGY & WELDABILITY
Type: Low-alloy, chromium-molybdenum (Cr-Mo) steel.
Primary Alloying Effects:
Chromium: Improves oxidation and corrosion resistance at high temperatures.
Molybdenum: Increases strength at elevated temperatures and reduces susceptibility to temper embrittlement.
Weldability: Good, but requires strict control. Preheating (150-250°C / 300-480°F) and interpass temperature control are essential to prevent hydrogen-induced cracking (HIC). Must be welded with compatible low-alloy electrodes (e.g., E8018-B2).
7. COMMON APPLICATIONS
Pressure vessels operating at elevated temperatures (up to ~525°C / 975°F).
Reactors, heat exchangers, and distillation columns in petrochemical and refining industries.
Steam boilers and superheater sections in power generation.
Hydrocracking and hydrodesulfurization units.
8. EQUIVALENT GRADES
UNS: K11762
ASME: SA-387 Gr.12
EN / DIN: 13CrMo4-5 (similar, not exact)
JIS: SCMV 420
9. ORDERING INFORMATION
When ordering ASTM A387 Grade 12 plates, the following should be specified:
ASTM Designation and Grade (A387 Grade 12).
Class (1 or 2).
Dimensions (thickness, width, length).
Heat treatment condition (if other than standard).
Test requirements (e.g., additional flattening test, ultrasonic examination per ASTM A578).
Any supplemental requirements from the specification's S1-S18.
Important Note: This is a summary for informational purposes. For complete, authoritative details, including tolerances, test methods, and mandatory requirements, always consult the latest official ASTM A387/A387M standard.
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.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
