Key Characteristics:
Standard: ASME SA662/SA662M.
Material: Carbon-manganese-silicon steel.
Application: Primarily for low-temperature, welded pressure vessels.
Heat Treatment: Typically normalized.
Key Properties: Good low-temperature notch toughness.
Typical Industries: Petroleum, chemical, power station, and boiler industries.
Chemical Composition (Typical):
Carbon (C): Maximum 0.20%
Manganese (Mn): 1.00-1.60%
Silicon (Si): 0.15-0.50%
Phosphorus (P): Maximum 0.035%
Sulfur (S): Maximum 0.035%
Mechanical Properties (Typical):
Tensile Strength: 485-620 MPa
Yield Strength: Minimum 295 MPa
Elongation: Minimum 18%
1. What heat treatment and manufacturing controls ensure Grade C's cryogenic performance?
Answer:
Normalized condition (mandatory for all thicknesses)
Fine austenitic grain size (ASTM No. 6 or finer)
Controlled rolling below recrystallization temperature
Optional tempering for thick plates (>50mm) to relieve stresses
100% ultrasonic testing (UT) for critical applications
2. When is SA662 Grade C required instead of SA516 or SA537 steels?
Answer:
Grade C is specified when:
Design temps ≤ -60°C (exceeds SA516 Gr 70's capability)
Fracture-critical applications (LNG tanks, ammonia storage)
Thick sections needing through-thickness toughness
Where ASME UCS-66 Curve B exemptions don't apply
Comparison:
SA516 Gr 70: Only good to -29°C (-20°F) without impact testing
SA537 Class 2: Similar strength but less reliable below -45°C
3. What welding procedures are critical for Grade C plates?
Answer:
Best Practices:
Preheat: 150-200°C (300-400°F) for all thicknesses
Electrodes: AWS E7018-G or E8018-C3 (Guaranteed -70°C toughness)
Heat Input: ≤40 kJ/cm to avoid HAZ embrittlement
PWHT: Mandatory for thicknesses >32mm (1.25")
Weld Testing: Requalification at -70°C Charpy V-notch
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