Oil Casing Grades J55, N80, P110: A Practical Selection Guide

What API 5CT casing grades mean, the J55 to P110 grade table, depth and pressure logic, sour service with L80, and connections BTC vs STC vs LTC.

• What casing grades mean in ksi, the J55–V150 table, and the depth and pressure logic that drives casing design.
• Key figure: OD range: 60–508 mm
• Key figure: 7-inch (177.8 mm) and 10-3/4 inch (273.05 mm) casing
• Key figure: MOQ 25–100 tons; delivery 15–45 days
• What casing grades mean: API 5CT grade names encode the minimum yield strength in ksi. J55 means 55,000 psi minimum yield; P110 means 110,000 psi. Higher yield strength lets the same wall carry deeper, higher-pressure service — the number is the whole design story.
• Grade table: J55 (55 ksi) and K55 (55 ksi) for shallow wells and surface casing; N80 (80 ksi) for mid-depth general service; L80 (80 ksi) for sour service; P110 (110 ksi) for deep, high-pressure wells; V150 (150 ksi) for ultra-deep programs.
• Depth and pressure logic: Deeper wells mean higher burst and collapse demands, so designers step up grade and wall thickness as depth increases. Collapse and burst ratings per API 5C3 govern the selection; the grade table is where the process starts.