Oil & Gas
Nickel Alloys for Sour Service, HPHT and Subsea Duty
Industry Overview
Where a well turns sour, standard stainless grades stop being an option. Hydrogen sulfide, CO₂ and chlorides together cause sulfide stress cracking and chloride pitting faster than any single-agent test predicts, and NACE MR0175/ISO 15156 puts hard limits on what may be used. TOKO ALLOY supplies Inconel 625, Alloy 718 and Hastelloy C-276 seamless pipe, tube and bar for wellhead, christmas-tree, flowline and subsea umbilical service — with NACE MR0175 compliance, heat-number traceability and EN 10204 3.1/3.2 documentation on every order.
Key Challenges
Sour Service — H₂S + CO₂ + Cl⁻ Together
Hydrogen sulfide causes sulfide stress cracking and hydrogen-induced cracking, and NACE MR0175/ISO 15156 sets hardness ceilings that ordinary austenitic stainless cannot reliably meet at the strength levels a wellhead needs. Inconel 625 (Ni ≥ 58%, PREN > 45) is the reference alloy for this combination; Alloy 718 is used where the strength requirement dominates.
HPHT Wells Above 15,000 psi
Deep and ultra-deep wells need high yield strength without a corrosion penalty. Alloy 718 in the aged condition reaches 1034–1241 MPa yield — several times what 316L offers — and keeps useful strength to about 700°C, which is why it is the default for high-pressure wellhead and tree components.
Chloride Stress Corrosion Cracking Offshore
Seawater exposure and high-chloride produced fluids crack standard austenitic stainless steels in the heat-affected zone even when the parent metal is unaffected. Nickel alloys with molybdenum above roughly 8% — Inconel 625, Hastelloy C-276, Hastelloy C-22 — are effectively immune at the chloride levels seen in production chemistry.
Subsea Umbilicals and Control Lines
Subsea control systems need continuous tube in lengths measured in kilometres, installed once and unreachable afterwards. Inconel 625 and Alloy 825 are the standard umbilical and chemical-injection materials; the requirement is 100% eddy-current and hydrostatic testing with zero defect tolerance, not a sample-based inspection.
TOKO ALLOY Solutions
Inconel 625 Seamless Pipe and Tube (N06625)
ASTM B444 seamless pipe and ASTM B704/B705 welded tube for flowlines, christmas trees, manifolds and umbilical service. PREN > 45, niobium-strengthened for fatigue and thermal-fatigue resistance, usable to 980°C. Supplied to NACE MR0175 with PMI and full heat-number traceability.
Alloy 718 Bar for Wellhead and Tree Hardware (N07718)
ASTM B637 / API 6A bar in the aged condition at 1034–1241 MPa yield for valve bodies, hangers, tubing hangers and high-pressure fasteners. Age-hardenable via niobium, so the strength is developed by heat treatment rather than by cold work.
Hastelloy C-276 for Acidising and Mixed-Acid Streams (N10276)
ASTM B622/B619 seamless and welded pipe, B626 tube. Where acidising fluids, wet chlorine or mixed mineral acids enter the process, C-276 is the alloy that tolerates both oxidising and reducing conditions at once — the case Inconel 625 cannot cover.
Incoloy 825 for Sour Well Piping and Seawater Cooling (N08825)
ASTM B423 pipe and B704/B705 tube. Copper-bearing, so it handles sulfuric-acid-bearing produced fluids that defeat plain Ni-Cr-Mo grades, and it is NACE MR0175 compliant for sour service. A more economical choice than 625 where temperature stays below about 540°C.
Recommended Materials Oil & Gas
View detailed chemical composition, mechanical properties, and corrosion resistance data for each recommended grade:
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