Creep-critical high-temperature service

Incoloy 800H & 800HT Machining for Creep-Critical High-Temperature Service

UNS N08810 / N08811 components with strict attention to material identity, heat-treatment condition, dimensional stability and final interface control.

800H: UNS N08810
800HT: UNS N08811
High-Temperature Creep/Rupture Duty
MTR + Heat/Lot + Inspection
Heavy Incoloy 800H and 800HT creep-duty rings, flanges and furnace header hardware
Exact definitions

Why 800H and 800HT Must Be Controlled as Exact Material Definitions

INCOLOY® 800H and 800HT are refinements of alloy 800 developed for elevated-temperature creep and stress-rupture performance. 800H uses a controlled carbon range and coarse grain-size requirement. 800HT further restricts chemistry — including carbon and combined aluminum plus titanium — and requires a high-temperature solution heat treatment under the Special Metals material definition.

This is not paperwork trivia. In creep-critical equipment, the intended long-time performance depends on the specified grade and condition. AlloyAccu therefore treats the MTR, UNS designation, material form, heat treatment and purchase specification as inputs to the manufacturing route, not as documents to collect after machining.
Side-by-side

800H vs 800HT

Incoloy 800H

UNSN08810
Carbon conceptControlled higher-carbon range within the 800 family
Grain-size conceptCoarse grain size specified for creep performance
Al + TiBroader permitted range
Traitement thermiqueHigh-temperature solution anneal appropriate to specification
UtiliserHigh-temperature creep/rupture duty

Incoloy 800HT

UNSN08811
Carbon conceptRestricted carbon range within the 800H concept
Grain-size conceptCoarse grain size plus restricted chemistry
Al + TiMore restricted combined Al + Ti range under the material definition
Traitement thermiqueMinimum high-temperature solution treatment is a defining part of the 800HT material concept
UtiliserHigh-temperature service where the 800HT definition/properties are required
Manufacturing sequence

Machining Strategy for High-Temperature 800H/HT Components

Although the design reason for 800H/HT is high-temperature service, the machining challenge occurs at room temperature: nickel-rich austenitic material, work hardening, cutting heat, large sections and often distortion-sensitive furnace or pressure-component geometry. Our route balances productivity with preservation of final dimensions.

Confirm whether the supplied stock is already in the required solution-treated condition before planning machining and any subsequent thermal cycle.
Use rigid roughing with stable chip load and coolant access to prevent local hardening and edge breakdown.
For large rings, flanges and thin shells, distribute stock removal to minimize stress imbalance.
Reserve controlled finish stock on bores, sealing faces and assembly datums until after major distortion-producing operations.
Plan dimensional inspection around features likely to move during machining, forming or welding.
Keep heat/lot identity through all internal and external processes so the final documentation package maps to the shipped parts.
Creep-duty hardware

Typical 800H / 800HT Components

Projects include petrochemical furnace hardware, pigtails and headers, high-temperature piping components, furnace fixtures, heat-treatment equipment, radiant/heater components, anneaux, prend en charge, flanges, burner hardware and custom thermal-processing parts. Where fabrication is involved, we can plan weld sequence and final machining together to control interface geometry.

Incoloy 800H and 800HT pigtail, header fitting, flange and heater support
Standards

Applicable Product Specifications

Common product specifications for 800H/800HT include ASTM B408 for rod/bar, ASTM B564 for forgings, ASTM B409/B906 and in some cases A240/A480 for plate/sheet/strip, ASTM B407/B829 for seamless pipe/tube, ASTM B514/B515 for welded products and ASTM B366 for fittings. ASME code cases and design rules may also apply depending on the equipment. The customer drawing/PO should state the exact governing requirement; AlloyAccu will manufacture to that requirement rather than infer it from the alloy name.

Alternative

When to Use 800 Instead

If the application needs high-temperature oxidation/carburization resistance but does not rely on the enhanced long-time creep/rupture properties associated with H/HT grades, standard 800 may be appropriate and may simplify material sourcing. That decision belongs to the design/code authority. From a manufacturing standpoint, AlloyAccu can quote either route and highlight cost or availability differences without changing the specified material on our own.

Evidence

Traceability and Quality

MTR and heat/lot traceability are especially important on 800H/HT projects. We can add CMM inspection, dimensional reports, surface roughness verification and records for heat treatment, welding or NDT as required. For batch production, critical interfaces can be tracked statistically or by agreed sampling/100% inspection depending on risk.

MTR
Chaleur / lot
MMT
Rugosité / CND

Send the Exact 800H/800HT Requirement

Upload the drawing and model and include UNS grade, ASTM/ASME specification, material condition, service or code notes, quantity and documentation requirements.

Request an 800H / 800HT Quote
FAQ

Material and route questions

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

Both are high-temperature derivatives of alloy 800. 800H controls carbon and grain size for creep properties; 800HT uses a more restricted chemistry and heat-treatment definition to support high-temperature creep/rupture performance.

Can I substitute 800 for 800H or 800HT?

Not without design/code approval. The grades have different material requirements and long-time high-temperature property bases.

Can AlloyAccu verify the exact grade?

Oui. We maintain MTR and heat/lot traceability and can include PMI/OES where appropriate, while also verifying the required product specification and condition from purchasing documents.

Do you machine 800H/800HT before or after heat treatment?

The route depends on supplied condition, required final condition, geometry and specification. We define the sequence during DFM so final dimensions and metallurgical requirements are both protected.

Do you support ASME-related projects?

We can manufacture to drawing and specified material/product requirements and provide traceability/documentation. The customer/design authority is responsible for defining the applicable code and acceptance criteria.

Send the exact grade, code/specification and drawing. AlloyAccu will verify the manufacturing basis before quoting.

Fonctionnalité · Heat-treatment concept