What ASTM B407 Covers
ASTM B407 specifies seamless nickel-iron-chromium alloy pipe and tube in the UNS N08810 composition, a grade widely supplied under the alloy 800H designation. The specification is used where a component must survive hot gas streams, flue products and process atmospheres that would oxidise or carburise carbon steel and many stainless grades within a short campaign. Because the product is seamless, the tube wall carries no weld seam and no weld heat-affected zone, which matters for pressure retention and for the uniformity of high-temperature creep behaviour.
The defining difference between this grade and the standard lower-carbon variant of the same alloy family is deliberate carbon control together with a coarse grain size produced by high-temperature annealing. That combination is what raises the creep and stress-rupture strength above 600°C (1100°F).
Chemical Composition of UNS N08810
| Element (%) | Ni | Cr | Fe | C | Mn | Si | S | Cu | Al | Ti |
|---|---|---|---|---|---|---|---|---|---|---|
| UNS N08810 | 30.0-35.0 | 19.0-23.0 | 39.5 min | 0.05-0.10 | 1.50 max | 1.00 max | 0.015 max | 0.75 max | 0.15-0.60 | 0.15-0.60 |
Nickel at 30-35% stabilises the austenitic matrix and provides resistance to reducing atmospheres, while 19-23% chromium forms the protective oxide scale that limits scaling in air and combustion products. Iron remains the balance at 39.5% minimum. Carbon is held in the 0.05-0.10% range, and aluminium plus titanium are controlled individually so that the alloy develops the creep resistance expected of this grade without losing toughness.
Minimum Mechanical Properties
| Material | Condition | Tensile strength, min | Yield strength, min | Elongation, min |
|---|---|---|---|---|
| UNS N08810 | Hot-finished annealed | 65 ksi (450 MPa) | 25 ksi (170 MPa) | 30% |
| UNS N08810 | Cold-worked annealed | 65 ksi (450 MPa) | 25 ksi (170 MPa) | 30% |
Both the hot-finished and cold-worked annealed routes must meet the same property floor, so the selection between them is usually driven by diameter, wall tolerance and surface requirements rather than by strength.
Heat Treatment and Grain Size Control
Tube in this grade is annealed at 1121-1177°C (2050-2150°F) and cooled, normally in air. The purpose is twofold: to soften the material after forming, and to grow the grains to an average size of ASTM No. 5 or coarser as required by the specification. A coarse grain structure reduces the amount of grain-boundary sliding that limits creep life, so grain size is treated as a tested property rather than a manufacturing by-product.
Annealing temperature: 1121-1177°C (2050-2150°F).
Average grain size: ASTM No. 5 or coarser, verified on finished tube.
Carbon: 0.05-0.10% to keep the required creep strength.
Higher-strength variant: a tighter carbon, aluminium and titanium balance (titanium plus aluminium controlled in the 0.85-1.20% range) raises creep strength further for the most demanding furnace duties.
Oxidation, Carburisation and Creep Performance
The chromium-rich surface oxide resists scaling and spalling in air, flue gas and many oxidising process streams, while the nickel-rich matrix tolerates carburising and sulfidising conditions that embrittle lower-nickel alloys. The practical consequences for design are:
Good creep-rupture strength above 600°C (1100°F), which allows thinner walls in furnace and reformer service.
Metallurgical stability in long-term exposure, with usable ductility reported to about 700°C (1290°F).
The lower-carbon, fine-grain variant of the same family is intended for service below 600°C (1100°F), where creep is not the governing design case.
Resistance to oxidation is maintained in cyclic thermal operation typical of heat exchangers and radiant coils.
Available Sizes and Typical Applications
Standard supply covers outside diameters from 1/2 in. to 12 in., wall thickness from 0.8 mm to 12.7 mm, and lengths up to about 26 m, with cutting, bevelling and tapping available to suit specific fabrication requirements. Larger diameters and heavier walls can be quoted where the mill capacity and the design case allow.
Typical uses include heat exchanger tubing, furnace and radiant coil tube, reformer outlet and pigtail tube, high-temperature process piping, and components exposed to carburising or sulfidising furnace atmospheres in chemical, petrochemical and heat-treatment plants.
Frequently Asked Questions
Q: What does UNS N08810 correspond to in commercial naming?
It is the UNS designation for the alloy commonly sold as alloy 800H. Always quote both the UNS number and ASTM B407 on the purchase order to remove any ambiguity.
Q: Why is grain size specified for this tube?
Coarse grains, ASTM No. 5 or coarser, reduce grain-boundary sliding and therefore improve creep and stress-rupture life at temperatures above 600°C.
Q: How does the 800HT variant differ?
It applies tighter control of carbon, aluminium and titanium, with titanium plus aluminium held in the 0.85-1.20% band, which lifts creep strength further at the top of the temperature range.
Q: Up to what temperature can the tube be used?
Creep-rupture performance is good above 600°C (1100°F) and ductility is retained to roughly 700°C (1290°F) in long-term service, with oxidation resistance provided by the chromium oxide scale.
Q: Is a welded tube acceptable?
Seamless tube is normally required where internal pressure, creep life and inspection access are critical; welded equivalents may be used where the governing code permits and the seam can be fully examined.
Q: What tests are performed on finished tube?
Tension testing, grain size determination and dimensional checks are carried out, together with hydrostatic or non-destructive examination where the order specifies it.
