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API (American Petroleum Institute) sets critical standards for casing and tubing to ensure safety and performance in oil and gas wells, which are meticulously followed by every reputable API pipe manufacturer. The primary specifications include:
API Spec 5CT: Defines material, mechanical properties, and testing for seamless/welded casing and tubing.
API Spec 5B: Covers threading, gauging, and inspection requirements.
API RP 5C1: Provides best practices for handling and running casing/tubing.
API TR 5C3: Details technical calculations for burst, collapse, and tensile strength.
These standards ensure uniformity, reliability, and compliance across the industry.
API Spec 5CT defines several casing grades based on strength and application:
Group 1: Standard Grades (H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q-125)
| Grade | Yield Strength (psi) | Common Use |
| H-40 | 40,000 | Low-pressure wells |
| J-55 | 55,000 | Shallow to medium-depth wells |
| K-55 | 55,000 | Similar to J-55 but with tighter controls |
| N-80 | 80,000 | Medium to high-pressure wells |
| L-80 | 80,000 | Corrosive environments (sour service) |
| C-90 | 90,000 | High-pressure, sour service |
| T-95 | 95,000 | High-pressure, sour service |
| P-110 | 110,000 | High-pressure, deep wells |
| Q-125 | 125,000 | Ultra-deep wells, high-pressure/high-temperature (HPHT) |
Tubing is classified under similar grades but with tighter tolerances:
Common Grades: J-55, K-55, N-80, L-80, C-90, T-95, P-110
Special:Grades: BG (Burst-Resistant), SM (Sour Service Modified)
Casing Sizes: Ranges from 4.5" to 20" (commonly 5.5", 7", 9 5/8", 13 3/8")
Tubing Sizes: Typically 1.05" to 4.5" (commonly 2 3/8", 2 7/8", 3 ½")
API Round Thread (STC/LTC): Standard for lower-pressure wells.
API Buttress (BTC): Higher load capacity.
Premium Connections (Non-API): Enhanced sealing (e.g., VAM, Hydril, Tenaris).
This is the first one.
