Inconel 718 inspection and measurement methods

Inconel 718 is a nickel chromium super alloy that holds strength at high temperature. It is used for turbine, downhole and high temperature parts where creep and oxidation set the limit. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.

It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, semiconductor is used as the example: cleanliness and surface condition that matter more than the nominal size.

How it is measured

Dimensional inspection with a certificate review. The equipment is calibrated, the uncertainty is recorded, and the part is at room temperature before the first point is taken.

What the report contains

• Every feature called up on the drawing, with a measured value rather than a tick.
• The datum order used, so the report can be reproduced.
• The certificate reference for the material and the calibration dates for the equipment.

Common sources of dispute

Most disagreements are about method, not about the part: a warm part, a burr left on, or a datum taken in a different order. Keep the tool engaged at a constant chip load and never dwell

Applications

Inconel 718 is used for turbine, downhole and high temperature parts where creep and oxidation set the limit, and in practice it appears most often in turbine components, downhole tools, exhaust hardware, high temperature fasteners.

How it fits into a machining route

The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: tool consumption and cutting time. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.

Standards, documentation and what is issued

The documentation requirement is EN 10204 3.1 with a full melt trace. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.

Dimensional inspection with a certificate review is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.

Frequently asked questions

What tolerance should be specified for Inconel 718?

±0.02 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

Inconel 718 is the usual choice, supplied against EN 10204 3.1 with a full melt trace.

How is the result verified?

Dimensional inspection with a certificate review, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

Planning a lead time as if it were steel.

How long does it take and what does it cost?

A realistic cycle is very slow cutting, a small number of parts per tool, and the cost driver is tool consumption and cutting time.

Related capability

If you are specifying Inconel 718 on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.

Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.

Related entries

These entries sit next to Inconel 718 in the encyclopedia: C3604 Brass, Duplex 2205 Stainless Steel, Splined Shafts. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.