What is the difference between 800, 800H and 800HT?

Carbon and grain size. 800H imposes a higher carbon range and a controlled grain size for creep strength; 800HT tightens further and adds a requirement on aluminium and titanium. All three carry different UNS numbers, and substitution is not permitted.

Why is its PREN flagged as not relevant?

Because the alloy is chosen for its behaviour in dry, hot atmospheres. PREN describes pitting in aqueous chlorinated media, which is not its service.

Is it suitable for a steam generator?

That is one of its classic uses. If the design is governed by creep, check that the specification actually calls for an 800H or an 800HT.

GRADE PROFILE

Alloy 800 — N08800

Alloy 800 is a nickel-iron-chromium alloy at 30–35% nickel and 39.5% iron minimum. It is chosen for oxidation, carburisation and nitriding at temperature, never for aqueous corrosion. And "800" covers three distinct grades: 800, 800H and 800HT.

Nickel alloy
PREN 19–23 †
Cost index 200

When to choose it

On heat exchangers and steam generators, furnace components and radiant tubes, in petrochemicals on reforming and cracking units, and on any equipment subject to cyclic oxidation. The nickel-iron-chromium balance gives it good resistance to carburising and nitriding atmospheres at a lower cost than very high nickel alloys.

When not to choose it

Where creep governs the design. Ordinary 800 has neither the carbon content nor the controlled grain size for that: those are the point of 800H and 800HT. Ordering "800" where service requires an 800H is a classic specification error, and it only shows up in service.

In aqueous chlorinated media: without molybdenum, pitting resistance is low.

And by confusing ASTM B407 and B408 when writing the specification — one covers seamless tube, the other bar and shapes.

Composition

Chemical composition (% by mass)
Element	%
Ni	30–35
Cr	19–23
Fe	≥ 39.5
C	≤ 0.1

Mechanical properties

Mechanical properties
Standard	Form	Rm (MPa)	Rp0.2 (MPa)	A (%)	Hardness
ASTM B407	tube sans soudure, état recuit	≥ 520	≥ 205	≥ 30	—

Designations and standards

Equivalent normative designations
Reference	Designation
EN (numeric)	1.4876
EN (symbolic)	—
ASTM / AISI	Alloy 800
UNS	N08800
JIS	—
AFNOR	—

Tube product standards :

ASTM B407
ASTM B163
ASTM B514
ASTM B515
ASME SB407
ASME SB163

Availability

Available in welded and seamless tube to ASTM B407, B163, B514 and B515. Structured dimensional data for this grade is not yet documented in our reference set: send us your sizes. EN 10204 3.1 material certificates supplied with the goods.

Related grades

310S (1.4845) — the heat-resistant austenitic, cheaper, where carburisation is not the issue.
Alloy 600 (N06600) — more nickel, for caustic media and high-purity water.
347H (S34709) — the stabilised stainless route where steam creep governs.

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Frequently asked questions

What is the difference between 800, 800H and 800HT?: Carbon and grain size. 800H imposes a higher carbon range and a controlled grain size for creep strength; 800HT tightens further and adds a requirement on aluminium and titanium. All three carry different UNS numbers, and substitution is not permitted.
Why is its PREN flagged as not relevant?: Because the alloy is chosen for its behaviour in dry, hot atmospheres. PREN describes pitting in aqueous chlorinated media, which is not its service.
Is it suitable for a steam generator?: That is one of its classic uses. If the design is governed by creep, check that the specification actually calls for an 800H or an 800HT.