Xenith Steel

P110 yields 758 MPa per API 5CT Table C.3 but max 32 HRC per Table E.2 — that fails the NACE MR0175/ISO 15156 SSC threshold (≤250 HV10 per Section 5.2). L80-1 is Q&T with temper ≥621°C, max 23 HRC per Table E.2, passes NACE TM0177 Method A at 80% SMYS (28 ksi threshold).

For 4,200m, collapse load ~2,000 psi: 7" 26 lb/ft L80 collapse = 3,570 psi per API 5C3 Section 2 (D/t=22.3, plastic regime), design factor 1.79 > minimum 1.125. L80-1 is the call, or upgrade to C95 (26 HRC max) if collapse margin drops below 25%.

26 lb/ft: WT 0.362", D/t=22.3, plastic regime per API 5C3 Section 2, collapse = 4,610 psi. 29 lb/ft: WT 0.408", D/t=19.7, collapse = 5,590 psi. Difference: −980 psi (−17.5%).

Cost side: 3 lb/ft × 4,200m × 3.28 = 41,328 lb = 20.7 tons, at ~$1,200/ton that's ~$24,800 saved. If the well's collapse design factor ≥1.125 is satisfied with 4,610 psi (max allowed CMAP ~4,098 psi), 26 lb/ft is adequate. If not, you need 29 lb/ft — that $24,800 is your insurance against a $200k+ casing failure.

BTC 7" 26 lb/ft N80 spec make-up torque: ~3,450 ft-lb per API RP 5C5 Table A.3. Stall at 70% (2,415 ft-lb) means thread galling — metal-to-metal friction exceeded available torque.

Three usual suspects:

(1) Coupling compound lacks 60–75% Zn dust per API Bul 5A2 — dry dope halves the make-up efficiency.

(2) Thread damage from handling — check taper with API plug gauge, tolerance is +0.003/‑0.000 in/in per API 5CT Section 6.2.

(3) Cross-threading from misaligned stabbing.

Fix: clean threads, fresh Bul 5A2 compound, torque-turn monitoring per API RP 5C5. If it still stalls below 90% of spec torque, that coupling is scrap — rethread or replace.

(1) Hydrostatic test pressure per Table E.4 — 7" 26 lb/ft N80 must hold 0.6 × internal yield = 4,716 psi minimum for ≥5 seconds. MTC shows the actual hold pressure and duration.

(2) Hardness per Table E.2 — N80-Q max 25 HRC, with all three readings per coupling end reported. If they cluster at 22–24 HRC, that heat treatment was controlled.

(3) Wall thickness per Table C.2 — 7" 26 lb/ft nominal WT 0.362", tolerance −5% (0.344") to +10% (0.398"). MTC must show min/max per joint. If min WT is 0.350", you're compliant. Anything below 0.344" is a reject per Table E.4 — and if the MTC doesn't report it, they skipped the measurement.

API 5CT Section 7.6 demands ±14°C uniformity across the full furnace length. P110 is austenitized at ≥900°C then water-quenched at minimum 30°C/s per mm of wall. For 7" 26 lb/ft (WT 0.362" = 9.2mm), the critical cooling rate is ~3.3°C/s — that's handled by a 6-zone accelerated spray quench with independent flow control.

Tempering at 650–700°C is held ≥1 hour per 25mm of cross-section per API 5CT §7.6. Verification: HRC at both ends and mid-body must all fall ≤32 HRC. You'll often see ends at 26–28 HRC and body at 30–32 HRC — that's normal end-quench effect and still within Table E.2. If any reading exceeds 32 HRC, the temper cycle was insufficient.

API 5CT Section 14 says any casing stored >6 months must be reinspected before running. The protocol:

(1) Drift test — API mandrel 6" long for ≤8.625" OD must pass full length.

(2) Threads — visual + gauge check, accept if no cuts, tears, or corrosion pitting deeper than 0.1mm.

(3) OD surface pits ≤0.1mm per Table E.4 are acceptable; anything deeper than 0.2mm is a reject or downgrade.

Real risk: coastal salt spray carries 10–50 mg/m³ NaCl. The varnish coating drops from 15–25μm to roughly 10–12μm after 8 months of exposure, giving a pitting rate of 0.05–0.15 mm/year. If no VCI paper was used, expect some pitting.

Practical plan: 100% drift, 50% thread inspect, spot UT on the worst-looking joints. Cost runs ~$10/joint — cheap compared to a $50k+ fishing job if one parts in the hole.