Pipe Grade Selector

How the Selector Works

Describe your application in plain text — well depth, formation pressure and temperature, H₂S and CO₂ partial pressures, deviation angle, and whether the pipe is for casing, tubing, or a surface line pipe project. The selector interprets this against API 5CT and API 5L grade requirements and NACE MR0175 / ISO 15156 sour service restrictions to return a ranked list of suitable grades with brief reasoning for each. For OCTG, it considers collapse load (from mud weight and external pressure), burst load (from formation pressure and well kill scenarios), and tension (from string weight in deviated wells). For line pipe, it applies the ASME B31.8 design pressure logic against available X-grades.

Grades the Selector Covers

OCTG — API 5CT casing and tubing grades:

• J55 / K55 — 379 MPa minimum yield. Standard shallow casing, surface and intermediate strings, sweet service only.
• N80 Type 1 / N80Q — 552 MPa. Intermediate and production casing, sweet service. N80Q is quenched and tempered with better toughness.
• R95 — 655 MPa. Medium-strength sweet service grade, Q+T only. Alternative to T95 where sour service is not required; no hardness restriction.
• L80 Type 1 — 552 MPa yield, hardness-controlled (≤23 HRC). The standard NACE MR0175-compliant grade for sour service casing; H₂S-resistant.
• L80-3Cr — 552 MPa, 2–3% chromium alloy for mild CO₂ corrosion resistance in sweet wells. Not a sour service grade — added in API 5CT 11th edition (Dec 2023).
• C90 — 621 MPa, sour service grade with controlled hardness (≤25.4 HRC). Higher strength alternative to L80 for elevated load requirements in H₂S environments.
• T95 — 655 MPa. Sour service grade for moderate-to-high H₂S environments; hardness controlled ≤25.4 HRC per API 5CT.
• P110 — 758 MPa. High-strength grade for deep, high-pressure sweet service and HPHT wells where burst and collapse loads govern.
• C110 — 758 MPa yield, sour-service-capable alternative to P110 with tighter hardness and toughness requirements.
• Q125 — 862 MPa. Ultra-high-strength for extreme-depth HPHT wells; sweet service only per NACE MR0175.
• L80 13Cr / Super 13Cr — 552 MPa, 13% chromium alloy steel for CO₂-corrosive and mild H₂S environments; tubing in gas condensate wells.

Line pipe — API 5L grades: Grade B (245 MPa) through X80 (555 MPa), both PSL1 and PSL2. For sour gas service, the selector applies API 5L Annex H (PSL2) requirements per NACE MR0175 Section 3.

Worked Example

Input: "4,000 m vertical gas well, bottom-hole temperature 90°C, max wellhead pressure 350 bar, H₂S partial pressure 0.05 bar (sour), CO₂ present, 9-5/8" production casing."

At 0.05 bar (5 kPa) H₂S partial pressure, the well is well above the NACE MR0175 sour service threshold of 0.0003 MPa (0.003 bar), so it is classified as sour. The selector flags sour service and filters to hardness-controlled grades — L80, T95, or C110. With 350 bar wellhead pressure on 9-5/8" casing, internal yield pressure (Barlow) for L80 47 lb/ft (11.99 mm) = 474 bar — sufficient margin. The selector would recommend L80 as primary with T95 as a higher-safety alternative, and note that CO₂ presence alone does not trigger grade restriction but should be reviewed for tubing material selection.

When to Use the Selector vs Detailed Engineering

The selector is appropriate for early-stage grade shortlisting, RFQ specification preparation, and checking whether an existing grade selection is consistent with well or pipeline conditions. It is not a substitute for full casing design per API TR 5C3 and ISO 10400, or pipeline design per ASME B31.8 or DNV-ST-F101. Final grade and weight selection requires a biaxial load analysis for casing strings, a qualified casing design engineer review, and material certification to the applicable standard. For procurement, contact ZC Steel Pipe with confirmed OD, weight, grade, length, and PSL requirements.