Scope and Code Position
ASTM B407 covers seamless nickel-iron-chromium alloy pipe and tube in UNS N08810, and the corresponding ASME SB407 edition governs the same product when it is used as pressure-retaining material in vessel and piping construction. This grade is widely known commercially as alloy 800H. It is chosen for pressure vessels and high-temperature piping where the design case combines internal pressure with metal temperatures high enough that creep, oxidation or carburisation, rather than room-temperature tensile strength, controls the wall thickness.
Because the pipe is seamless, the pressure boundary is uniform along the length and there is no longitudinal weld to be examined or to act as a creep-weakness path in service.
Chemical Composition Requirements
| Element | Content (%) |
|---|---|
| Iron, Fe | 39.5 min (balance) |
| Nickel, Ni | 30.0-35.0 |
| Chromium, Cr | 19.0-23.0 |
| Carbon, C | 0.05-0.10 |
| Manganese, Mn | 1.50 max |
| Silicon, Si | 1.00 max |
| Sulphur, S | 0.015 max |
| Copper, Cu | 0.75 max |
| Aluminium, Al | 0.15-0.60 |
| Titanium, Ti | 0.15-0.60 |
Nickel provides the austenitic matrix and resistance to reducing atmospheres; chromium forms the protective oxide that limits scaling; carbon, aluminium and titanium are balanced to generate the carbide and fine dispersed phases that carry creep strength at temperature.
Physical and Mechanical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.94 g/cm³ | 0.287 lb/in³ |
| Tensile strength, annealed, typical | 600 MPa | 87 ksi |
| Yield strength, annealed, typical | 275 MPa | 39.9 ksi |
| Elongation, annealed, typical | 45% | 45% |
| Tensile strength, minimum required | 450 MPa | 65 ksi |
| Yield strength, minimum required | 170 MPa | 25 ksi |
| Elongation, minimum required | 30% | 30% |
The typical annealed figures are the values generally reached in production and give a useful margin above the mandatory minima. For pressure vessel design, the allowable stress is taken from the applicable ASME code tables at the design metal temperature rather than from the room-temperature minima listed here.
Heat Treatment and Hot Working
Pipe is annealed at 1121-1177°C (2050-2150°F) and then cooled, normally in air, to soften the material after forming and to establish the coarse grain structure that the specification requires. Grain size on finished product is verified by the planar method and must average ASTM No. 5 or coarser. Hot working is carried out in the range 593-982°C (1100-1800°F); operations below the lower limit risk cracking, and operations above the upper limit coarsen the structure beyond what the specification intends.
Annealing: 1121-1177°C (2050-2150°F), followed by cooling in air.
Grain size: ASTM No. 5 or coarser, average, determined on finished pipe.
Hot working window: 593-982°C (1100-1800°F).
Cold finishing permitted and normally followed by annealing to restore properties.
Testing and Quality Requirements
Tension testing: tensile strength, yield strength and elongation must meet the specification minima.
Grain size testing: determined by the planar method on the finished product.
Hydrostatic test: applied to demonstrate pressure integrity of every length.
Non-destructive examination: eddy current or equivalent testing where specified, to confirm freedom from surface and wall defects.
Dimensional and visual inspection: outside diameter, wall thickness, length, straightness and finish.
Documentation supplied with the order links each length to its heat number and to the test results, which is what allows the fabrication contractor and the end user's inspector to close out the material traceability package for a pressure vessel.
Formats, Sizes and Applications
Pipe is supplied hot finished or cold finished, seamless or welded, with seamless preferred for pressure-retaining nozzles, internals and high-temperature transfer lines. Common outside diameters run 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 carried out to the fabricator's requirements. Larger diameters and heavier walls can be produced where capacity allows.
Typical applications include pressure vessel shells and nozzle pipe, reactor internals, heat exchanger and furnace tubing, reformer and cracker piping, and other components in chemical, petrochemical and power plants where hot corrosive gas is handled. In each case the design driver is the same: retain strength and a protective oxide scale over a long campaign, without the brittle secondary phases that limit simpler alloys.
Frequently Asked Questions
Q: Which specification applies to pressure vessel use?
ASTM B407 for the material itself and ASME SB407 when the pipe is used as pressure-retaining construction. Both editions describe the same UNS N08810 composition and property minima.
Q: What is the mandatory minimum tensile strength?
450 MPa (65 ksi), with minimum yield strength of 170 MPa (25 ksi) and minimum elongation of 30%. Typical annealed production reaches about 600 MPa tensile.
Q: Why must the pipe be annealed at such a high temperature?
The 1121-1177°C treatment both softens the material after forming and grows the grains to ASTM No. 5 or coarser, which is what delivers creep and rupture strength in service.
Q: What is the hot working range?
593-982°C (1100-1800°F). Working outside that window either risks cracking or produces a structure coarser than intended.
Q: Can cold-finished pipe be supplied?
Yes. Cold finishing is used to obtain tighter dimensions and a better surface, and it is followed by annealing so the finished pipe still meets the specification properties and grain size.
Q: How is the grain size verified?
By the planar method on a sample of the finished pipe, with the result required to average ASTM No. 5 or coarser for this grade.
