When purchasing a titanium flange, buyers often focus on the material grade, nominal size, and pressure class. The sealing face deserves the same level of attention. A serrated or "waterline" finish is a functional surface specification that affects gasket contact, assembly, and leakage control.
For the technical scenario discussed in this article, the target surface roughness is commonly stated as Ra 3.2–6.3 μm, with 125–250 RMS often used as a corresponding industrial reference range. The final acceptance value must be confirmed against the approved drawing, applicable standard, gasket, pressure class, and project requirements.
What the Serrated Finish Does
A controlled serrated finish creates a regular surface texture on the flange sealing face. When the bolts apply preload, the gasket conforms to this texture and helps close potential leakage paths at the connection.
The machining pattern may appear as concentric circular lines or a controlled spiral. Its appearance alone does not prove compliance. Buyers should confirm the required roughness value, machining pattern, flatness, and inspection method in the purchasing specification.
Under an ASME B16.5-based flange specification, the facing and surface-finish requirements should be reviewed together with the flange pressure class and gasket arrangement. A suitable surface finish for one connection may not automatically be suitable for another.
Why Titanium Flange Roughness Needs Process Control
Titanium can present machining challenges, including material adhesion, heat accumulation, tool wear, and burr formation. These factors may create an uneven or damaged sealing surface if the machining parameters are not stable.
A supplier's process may include application-appropriate carbide tooling, controlled cooling, and an adjusted finishing strategy. Feed rate, cutting depth, tool geometry, and tool condition can all influence the resulting serrated pattern and roughness value.
The important procurement point is simple: the sealing face should not be accepted by visual inspection alone.
How Ra Roughness Should Be Verified
A stylus-type surface roughness tester can provide a quantitative reading of the machined sealing face. When requesting a titanium flange quotation, buyers should clarify:
- Target Ra value and permitted tolerance
- Whether an RMS reference is also required
- Measurement location and number of readings
- Measurement direction in relation to the serration pattern
- Required flatness and parallelism
- Inspection report format
Applicable drawing, standard, and acceptance criteria
For the technical range described in this article, Ra 3.2–6.3 μm may be used as a working reference. It should not replace the project's own approved specification.
Pressure Class and CNC Finishing Strategy
Flange designs from 150 LB to 2500 LB may have different dimensional, thickness, sealing, and assembly requirements. The finishing strategy should therefore be selected according to the actual flange design rather than applying one fixed CNC program to every pressure class.
A stable machining process should support consistent control of the sealing face, concentricity, perpendicularity, bolt-hole relationship, and overall flange geometry. These points are particularly important when a titanium flange is used in a high-pressure or difficult-to-maintain piping system.
What to Include in a Titanium Flange Inquiry
To obtain a clear quotation and inspection response, provide:
- Titanium grade and applicable material specification
- Flange type, size, pressure class, and quantity
- Drawing number and revision
- Sealing-face type and gasket information
- Required Ra value or surface-finish symbol
- Serration pattern or machining-direction requirement
- Flatness, parallelism, and concentricity requirements
- Inspection method and roughness-report requirements
- MTC, PMI, and other documentation requirements
- Service medium, pressure, temperature, and destination
If the drawing only states "serrated finish" without a roughness value or inspection method, ask the supplier to clarify the interpretation before production. This can reduce the risk of a surface that looks acceptable but does not match the actual assembly requirement.
