ASME SB423 Incoloy 825 Pipe

ASME SB423 Incoloy 825 pipe (UNS N08825, W.Nr. 2.4858) sits in a useful spot in the nickel alloy family: it carries enough chromium, molybdenum, and copper to handle sulfuric and phosphoric acid service that destroys 316L, but it costs substantially less than Inconel 625 or Hastelloy C276. The titanium stabilization that is built into its chemistry makes it weldable without the sensitization problems that plague non-stabilized grades.

Product Forms

Bar & Rod

Plate & Sheet

Coil & Strip

Pipe & Tube

Fitting: Flange, Tee, Elbow, Reducer etc.

Forging: Ring, Shaft, Circle, Block etc.

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Chemical Composition (ASTM B423)

The titanium is the element that makes 825 different from a standard Ni-Cr-Fe alloy like 800H. Without titanium, welding 800H can cause chromium carbide precipitation at grain boundaries in the HAZ, creating a narrow zone susceptible to intergranular attack. 825's Ti (0.6–1.2%) preferentially forms TiC, leaving the chromium in solution and the HAZ corrosion-resistant as-welded. This is why 825 is specified for welded pipe spools in acid service where 800H would need solution annealing after welding.

The copper (1.5–3.0%) is the other distinguishing element. Copper gives 825 its edge in sulfuric and phosphoric acid - it is the same reason 904L carries copper. Without copper, the alloy would be a general-purpose Ni-Cr-Fe grade; with it, 825 handles dilute-to-intermediate sulfuric acid at temperatures that pit 316L.

Mechanical Properties (ASTM B423 Annealed)

Most process piping is supplied in the cold-worked annealed condition, which delivers the higher mechanical properties. For pressure design, always confirm which condition your MTR references - the yield strength difference between the two conditions is significant (241 vs 172 MPa) and changes wall thickness calculations.

Physical Properties

Corrosion Resistance: Where 825 Works - and Where It Does Not

The practical rule: 825 is the cost-effective choice for sulfuric and phosphoric acid service, chloride-bearing reducing environments, and mixed oxidizing-reducing conditions at moderate temperatures. It is not the right choice for wet chlorine, hot caustic, or warm seawater - and a supplier that tells you so before taking the order is the one to keep.

Sizes, Forms and Standards

Most inquiries we handle are for ASTM B423 seamless pipe in NPS 1/2" to 6", Sch 40S and 80S, cold-worked annealed. For heat exchangers in sulfuric or phosphoric acid service, ASTM B163 tube is the common call-out. Filler metal for 825 welding is ERNiFeCr-2 (AWS A5.14) or Inconel 625 filler for higher-corrosion welds.

Incoloy 825 vs 800H vs 625 vs 316L: When to Choose Each

Buyers often ask "why 825 and not 625 or 800H?" The answer depends on the service chemistry and temperature.

The key decision points:

825 vs 800H: Both are Ni-Cr-Fe, but 825 has Mo + Cu for acid resistance and Ti for as-welded HAZ protection. 800H is for high-temperature structural service (carburizing, oxidizing) where acid resistance is not the concern. If your line carries acid, choose 825. If your line runs at 800 °C in a furnace, choose 800H.

825 vs 625: 625 has 8–10% Mo and 3.15–4.15% Nb - far higher pitting resistance and strength. For seawater or aggressive mixed-acid service at temperature, 625 wins. For moderate sulfuric/phosphoric acid service at ambient-to-moderate temperature, 825 does the same job at a lower price. The upgrade to 625 is justified when chlorides and temperature push 825 past its limits.

825 vs 316L: 316L fails in sulfuric acid above 40 °C at intermediate concentrations and pits in chlorides above 40 °C. 825 handles both. The upgrade from 316L to 825 is the standard move when acid service rules out stainless.

Typical Applications

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