Ni-Cr-Mo-W Alloy for Broad Corrosion Resistance in Chemical Process Environments

What is Hastelloy C-276?

Hastelloy C-276 (UNS N10276) was developed in the 1960s as an improvement over alloy C, which suffered severe weld heat-affected-zone (HAZ) corrosion. The key innovation: ultra-low carbon (0.01% max) and silicon (0.08% max) to suppress carbide precipitation during welding. This eliminated post-weld solution annealing for most applications — a breakthrough that made C-276 the most widely specified nickel alloy for chemical process equipment. Today it remains the default choice for reactors, heat exchangers, piping, and valves handling mixed acid streams where both oxidizing and reducing conditions may occur.

The balanced Cr (14.5–16.5%), Mo (15–17%), and W (3–4.5%) chemistry provides broad-spectrum resistance: Cr for oxidizing acids via the Cr₂O₃ passive film, Mo+W for reducing acids and pitting resistance. Tungsten contributes to pitting resistance at approximately 50% of Mo's effectiveness per the PREN formula. C-276 is immune to chloride stress-corrosion cracking — the failure mode that limits austenitic stainless steels in chloride-bearing service. It maintains ductility from cryogenic temperatures (−196°C) to elevated temperatures, with useful mechanical properties to approximately 1100°C.

Chemical Composition

Per ASTM B575. Weight percent. The ultra-low C and Si are C-276's defining breakthrough; Mo, Cr, and W are the corrosion-resistance drivers.

⭐ Elements that define C-276's corrosion performance

Mechanical Properties

C-276 is a solid-solution strengthened alloy — no precipitation hardening. Properties are stable after solution annealing and do not degrade with moderate temperature exposure.

Physical Properties

Heat Treatment

C-276 is a solid-solution alloy — no age-hardening step. The only required heat treatment is solution annealing to restore the fully dissolved microstructure after forming or welding:

Corrosion Resistance

C-276's defining advantage is breadth — it resists both oxidizing and reducing environments reasonably well, making it the safe default for chemical process equipment where the corrosive environment may shift between conditions.

General Corrosion

Excellent across sulfuric, hydrochloric, phosphoric, nitric, acetic, and formic acids; wet chlorine; hypochlorite; seawater; and brine. This breadth is C-276's defining advantage — no other single alloy covers so many corrosive environments with acceptable resistance. In concentrated sulfuric acid up to ~60% at elevated temperatures, C-276 outperforms 316L by orders of magnitude.

Pitting & Crevice Corrosion

PREN ≈ 66–74 (calculated as %Cr + 3.3×%Mo + 1.65×%W). Critical pitting temperature in ASTM G48 (6% FeCl₃): 85–95°C — far above 316L (~15°C) and comparable to 6% Mo super-austenitic grades. The W contribution at 50% Mo effectiveness adds ~5–7 PREN points versus a Mo-only alloy at the same Cr level. For even higher pitting resistance, C-22 (PREN ~80) or C-2000 (PREN ~85) are alternatives.

Stress-Corrosion Cracking

Immune to chloride SCC at all temperatures. This is the primary reason to specify C-276 over austenitic stainless steels — 316L cracks in chloride environments above ~60°C, while C-276 does not crack even at boiling concentrations. For sour service in oil and gas, C-276 qualifies under NACE MR0175 / ISO 15156.

Intergranular Corrosion

Passes ASTM G28 Method A and B in the solution-annealed condition. As-welded: passes for most common environments. The ultra-low C (0.01% max) suppresses carbide precipitation, but µ-phase can still form in the weld HAZ during multi-pass welding with prolonged interpass times. For guaranteed as-welded IGC resistance, C-22 or C-2000 are preferred.

Oxidizing vs. Reducing Environments

Good in both but not best-in-class either way. C-276's advantage: handles both reasonably well — the safe default. In purely oxidizing environments (e.g., high-concentration nitric acid), C-22 or C-2000 outperform C-276 due to higher Cr. In purely reducing environments (e.g., concentrated HCl), B-3 outperforms C-276 due to higher Mo and no Cr dilution effect. C-276 wins when the environment is mixed, variable, or uncertain.

Hastelloy C-276 vs Related Grades

C-276 is the proven all-rounder. Here's how it compares with the grades our customers most commonly evaluate for the same applications:

→ For a side-by-side technical deep-dive: Hastelloy C-276 vs C-22 — Full Comparison Guide

Typical Applications by Industry

Applicable Standards & Specifications

Available Product Forms from HT PIPE

We carry C-276 in solution-annealed condition. EN 10204 3.1 certification on every shipment; 3.2 available on request. ASTM G28 IGC testing per heat available on specification.

HT PIPE Project Experience

HT PIPE delivered 15 tons of C-276 seamless pipe (ASTM B622, ¾″–8″ NB, Sch 10S–Sch 80S) to a Southeast Asian chemical complex in 2023 for a new mixed-acid handling system. Order required ASTM G28 Method A IGC testing per heat with max 0.5 mm/year. All 24 heats tested below 0.3 mm/year. EN 10204 3.1 certification with full traceability. Delivered in 12 weeks.

For FGD scrubber projects, we regularly supply C-276 plate (ASTM B575, 6–25 mm) with ASTM G28 Method B testing and ASME SB-575 compliance for pressure vessel fabrication. Contact our sales engineers for a reference case matched to your application.

Frequently Asked Questions