ASTM SA517 Grade Q Pressure Vessel Steel Plate Chemical Composition & Mechanical Properties

Note: ASTM A517 Grade Q is one of the most alloyed grades in the A517 series, containing Ni, Cr, Mo, and V for excellent hardenability and toughness. It is commonly used for offshore platform rack steel and heavy-duty pressure vessels.

Carbon Equivalent (CE)

Typical value: ~0.73% (for heavy section A517 Gr.Q)

Note: High carbon equivalent indicates significant hardenability; strict welding procedures, preheat, and low hydrogen practice are mandatory [citation:1].

• SA517 must be supplied in quenched + tempered condition
• Austenitizing temperature: not less than 900°C (1650°F)
• Quench in water or oil
• Tempering temperature: not less than 620°C (1150°F) [citation:16]
• Tempering temperature must be carefully controlled to achieve required strength and toughness balance

• A517 Gr.Q has high carbon equivalent (CE~0.73%) and requires strict welding procedures [citation:1]
• Preheat is mandatory to prevent cold cracking
• Control heat input to avoid HAZ softening
• E11018-M electrodes are commonly used for matching strength [citation:14]
• For offshore rack steel, post-weld heating at 250-300°C for 4h may be specified

Maximum thickness for Grade Q: 6 in. [150 mm] [citation:5][citation:6]

Grade Q, along with Grade E, has the highest thickness capability among A517 grades. Domestic manufacturers have produced A517GrQ up to 177.8mm thickness for offshore applications [citation:19].

• Grade Q: Ni-Cr-Mo-V, highest alloy content, maximum thickness capability (150mm)
• Grade E/Q: Both have 150mm max thickness capability [citation:6]
• Grade F: Ni-Cr-Mo, good low-temperature toughness, 65mm max
• Grade S: Mn-Mo-Ti-Cb, optimized weldability, 50mm max

Design Considerations

• High strength: Grade Q provides yield strength of 690 MPa for thickness up to 65mm
• Thickness capability: Maximum thickness for Grade Q is 150mm (6 in.) [citation:5]
• Offshore applications: A517GrQ is commonly used for jack-up rig rack steel [citation:19]
• Impact requirements: Transverse Charpy V-notch with lateral expansion ≥0.38mm; -40°C impact for offshore applications

Fabrication Considerations

• Cold forming: May require stress relief after forming depending on strain level
• Hot forming: Forming temperature 900-960°C, re-quenching and tempering required after forming
• Welding: Low hydrogen practice mandatory; preheat 150-200°C; interpass temperature control
• Machining: High strength requires proper tooling and cutting parameters
• Post-weld heating: For offshore rack steel, 250-300°C for 4h may be specified

Common Failure Mode Prevention

• Hydrogen-induced cold cracking: Strict low-hydrogen practice, preheat, control diffusible hydrogen <=5 mL/100g
• HAZ softening: Control heat input during welding to avoid excessive softening
• Lamellar tearing: Consider through-thickness properties for critical joints
• Stress corrosion cracking: Consider environment and use appropriate protective measures