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Titanium Flanges: How the Forming Route Changes the Part
The word flange describes a shape, not a process. Two flanges made to the same dimensional drawing can arrive with entirely different grain flow, inspection history and fatigue behaviour depending on the route the supplier chose — and the route is usually left to the supplier, which is why the same part quoted twice can differ by a factor of two.
The word flange describes a shape, not a process. Send the drawing and the duty, and we will state the forming route we are quoting and the property basis behind it. Request a flange quote
Four routes to the same drawing
- Cut from plate. The fastest and cheapest route. A blank is cut by waterjet, plasma or saw, then turned and drilled. It suits large diameters, moderate pressures and one-off or small batches. Its weakness is directionality: plate has a through-thickness direction, and a flange cut from plate has that direction running across the bore.
- Rolled and welded from bar or plate. A ring is formed and seam welded, then machined. Economical for large diameters where a solid blank would be wasteful, but it introduces a weld into a pressure boundary and the weld needs its own qualification and inspection.
- Ring rolled. A pierced blank is expanded between rollers. Grain flow follows the circumference, wall thickness is uniform, and the route scales well from medium to large diameters without the waste of machining from solid.
- Forged. Closed-die or open-die forging gives a continuous grain flow that turns through the hub and into the flange — the configuration the part's stress pattern actually wants. It is the most expensive route per piece and the one that usually appears on a drawing with a fatigue or pressure-cycling requirement.
- Machined from solid bar. Normal for small and medium sizes. No joints, no grain-flow question beyond the bar's own, and the price scales with the volume of metal turned into swarf — which for titanium is the dominant cost.
What the route changes
Mechanically, the difference is grain flow and the direction of the material's weakest axis relative to the load.
| Property | Cut from plate | Forged or ring rolled |
|---|---|---|
| Grain flow | Planar, with a distinct through-thickness direction | Continuous, following the part contour through hub into flange |
| Through-thickness ductility | Lowest of the routes — the direction the load at the hub acts in | Material in the direction that matters is the worked direction |
| Residual stress | Inherited from the plate, released unevenly when the blank is cut | More uniform after the forging sequence and its conditioning |
| Inspection burden | Ultrasonic inspection of the parent plate, then of the finished part | Ultrasonic inspection of the forging billet and the finished part |
| Cost profile | Low tooling, high material utilisation waste | Tooling and process cost amortised over the batch |
Residual stress is the item that surprises people. A flange hogged out of a stress-relieved plate is not stress free when it is finished — the balance changes as material is removed, and the sealing face can move after final machining. On a large, thin, high-aspect flange that movement is measurable, and it shows up as a leak path rather than as a dimensional failure.
Matching the flange type to the duty
- Slip-on and lap joint. The pipe passes through the flange. Cheapest to make and fit, weakest at the hub, and unsuitable where the joint sees significant bending or thermal cycling. Common in low-pressure titanium chemical service where the corrosion duty rather than the mechanical duty drives the material choice.
- Weld neck. The bore matches the pipe and the hub tapers into the wall, so the flange reinforces the transition rather than sitting on top of it. The default for pressure and cyclic service, and the type that benefits most from being forged rather than cut from plate.
- Blind. A solid disc closing the line. Simple to make from plate at any size, and the place where through-thickness properties matter least.
- Custom and non-standard. Faced, drilled and thicknessed to the drawing. Where a drawing is non-standard, the dimensional controls — bolt circle, facing flatness, bore concentricity — have to be stated explicitly, because there is no standard table to fall back on.
Machining titanium flanges
The machining notes for titanium apply in full here, and two of them bite harder on a flange than on a shaft:
- Heat stays in the cut. Titanium conducts heat poorly, so tool edge temperature is high and tool life is the constraint. Deep facing cuts and interrupted cuts on a drilled bolt circle both punish the edge.
- Galling on the sealing face. Titanium has a strong tendency to seize against itself and against tooling. The gasket face must be cut with sharp, dedicated tooling and finished without smearing, because a smeared surface carries cold-welded debris that no amount of flatness measurement will detect.
- Flatness is the specification, not surface finish. A gasket face that measures beautifully on Ra and badly on flatness will leak. The facing operation has to be planned around the flatness tolerance and measured after the last cut, not before.
What to put on the enquiry
Six items let us choose a route rather than guess at one: the type and the dimension table it follows, the size and pressure rating, the grade, the governing standard and the inspection requirement, the quantity, and whether anything about the service is cyclic or thermal. The quantity alone often decides the route: one flange of a given size is usually cheapest machined from bar; fifty are usually cheapest ring rolled.
Where the drawing does not state a route, we state the one we are quoting and the property basis behind it, so the choice is visible before the order rather than after the delivery. Send the drawing with the enquiry, or see the material forms on the titanium material page.
FAQ
Common questions
Is a forged titanium flange better than one cut from plate?
It depends on the duty, not on principle. Forging gives a continuous grain flow that runs through the hub into the flange, which is the direction the hub load acts in, and it gives a more uniform structure than plate cut across the through-thickness direction. For a low-pressure, non-cyclic application — which is most corrosion-driven titanium piping — a flange cut from plate is perfectly adequate and materially cheaper. For pressure cycling, bending at the hub or thermal cycling, the forged route is worth the cost.
Why does a titanium flange cost so much more than a stainless one?
Three reasons compound. Titanium stock costs several times stainless per kilogram. Machining titanium is slower because the material conducts heat poorly, work-hardens and galls, so tool life is short and cycle times long. And more of the blank ends up as swarf, which for titanium has little recovery value compared with stainless. The route choice — how close the starting form is to the finished shape — is therefore the dominant cost lever available.
Can titanium flanges be welded to stainless steel pipe?
Not by direct fusion welding; the interface forms brittle intermetallics and the joint cracks. The usual solutions are a flanged joint with a gasket that separates the metals, a titanium-clad transition component, or a mechanical coupling. If the drawing calls for a direct titanium-to-stainless weld, that is worth raising at enquiry stage rather than at fabrication.
What should be on the drawing for a non-standard flange?
The dimensional controls that a standard table would otherwise define: bolt circle diameter and hole size, facing flatness and surface finish, bore concentricity with the bolt circle, hub radius and thickness, and the inspection basis. Non-standard flanges fail at the sealing face far more often than at the bolt holes, and flatness is the control that gets omitted.
Ask about Titanium flanges
Send the drawing with the grade and the governing specification. We will confirm the material form, the process route, the inspection plan and a date in writing with the quotation.