API 650

Key requirements (11)

• Atmospheric tanks — design pressure –0.25 in WC to 2.5 psig (≈17 mbar) max.
• Design temperature: ambient up to 93 °C (200 °F); higher → API 620 Annex M.
• Bottom plate min thickness: 6 mm (1/4") nominal.
• Shell design: 1-foot method (Section 5.6.3) or variable design point (5.6.4).
• Joint efficiency: 0.85 (lap-welded) or 1.0 (butt-welded with full RT).
• Hydrotest: filled with water to design liquid level; 24-hour holding test.
• Wind girders / top angle stiffeners: Section 5.9.6.
• Annex E: seismic; Annex C: external floating roof; Annex H: internal floating roof.
• Annex F: internal pressure up to 18 in WC; Annex M: elevated temperature; Annex S: stainless.
• Default allowable stress: 2/3 yield or 2/5 UTS (whichever lower) at design temp.
• Foundation: Annex B guidance (ringwall, slab, piled).