Technical guide
API 5CT Casing & Tubing Grades Explained
Grade groups
| Group | Grades | Notes |
|---|---|---|
| 1 | H40, J55, K55, N80-1, N80-Q, R95 | General service, shallow and medium wells |
| 2 | L80-1, L80-9Cr, L80-13Cr, C90, T95, C110 | Restricted yield and hardness; sour and CO2 service |
| 3 | P110 | High strength for deep wells; not for sour service |
| 4 | Q125 | Very high strength for HPHT wells |
Connections
API connections include short round thread (STC), long round thread (LTC) and buttress (BTC) for casing, and non-upset (NUE) and external-upset (EUE) for tubing. For gas wells, HPHT wells and high-torque applications, operators specify premium connections, which have metal-to-metal seals and are qualified to API RP 5C5 / ISO 13679.
Specifying an order
A complete casing order states the OD, weight (lb/ft), grade, connection, range length, PSL, any special drift, and the inspection and third-party requirements. For example: 9-5/8" 47 lb/ft L80-1 BTC R3 PSL-2, special drift, full-length EMI.
Frequently asked questions
Is P110 suitable for sour service?
Generally no. P110 has no maximum hardness limit and is susceptible to sulfide stress cracking. Restricted-yield grades such as C110 or T95 are used instead for high-strength sour service.
What is L80-13Cr used for?
L80-13Cr is a martensitic stainless tubing grade used in CO2-corrosive wells with little or no H2S. Super 13Cr extends that resistance to higher temperatures and chloride levels.
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