A flange is designed to connect piping and equipment, but the reliability of that connection depends heavily on the sealing face. The serrated finish specified for many flange sealing surfaces—often referred to as the “waterline” finish in industrial applications—is not merely a visual machining pattern. Its depth, pitch, and surface roughness directly influence gasket contact and sealing performance.
For titanium flanges, Lihua Titanium focuses on controlling the sealing face within the customer’s specified roughness range, commonly Ra 3.2–6.3 μm for the applications described in this technical context.
The Serrated Sealing Face: The Final Barrier in a Pressure ConnectionUnder the ASME B16.5 framework, flange facing requirements are linked to the way the gasket interacts with the metal surface. When the flange is tightened, the gasket must conform to the controlled surface texture to create stable contact and reduce potential leakage paths.
A properly machined serrated face may appear as precise concentric circles or a controlled spiral trajectory. These fine machining marks are functional: they help create a consistent interface between the flange and gasket when the connection is assembled according to the project requirements.
For high-pressure piping, the sealing face must therefore be treated as a critical engineering surface rather than an ordinary finishing step.
Roughness Control: Turning Ra into a Measurable RequirementTitanium alloys can be challenging to machine. Material adhesion, tool wear, heat generation, and burr formation may affect the final surface if the cutting process is not properly controlled.
To address these factors, Lihua Titanium uses application-appropriate carbide tooling and a controlled cooling system during CNC machining. Feed rate, cutting conditions, tool condition, and machining stability all contribute to the final sealing-face finish.
The target is not determined by visual appearance. A stylus-type surface roughness tester is used to obtain quantitative readings and compare the machined face with the customer’s specified requirement. For the applications covered by this article, the working target is commonly controlled within Ra 3.2–6.3 μm, corresponding to the frequently referenced 125–250 RMS range in industrial surface-finish terminology.
The exact acceptance range should always follow the approved drawing, applicable standard, gasket type, pressure class, and project specification.
The precision of a titanium flange is not reflected only in the final number on an inspection report. It also depends on the toolpath logic used during machining.
For different pressure classes, from 150 LB to 2500 LB, the machining team may need to adjust feed rate, cutting depth, tool geometry, and finishing strategy according to the flange design and customer requirements. The objective is to maintain a stable serrated pattern while controlling the sealing face, concentricity, and perpendicularity.
This is especially important for titanium, where an unstable cutting condition can cause material adhesion, surface tearing, or inconsistent machining marks. A repeatable process helps transform practical machining experience into measurable and traceable quality control.
A well-finished titanium flange sealing face should not be judged by appearance alone. Its performance depends on the relationship between:
For this reason, sealing-face machining should be reviewed together with the complete flange drawing and application data.
With 20 years of experience in titanium materials and titanium flange manufacturing, Lihua Titanium focuses on the details that determine the reliability of industrial connections.
From CNC toolpath planning and cooling control to quantitative roughness measurement, every step is intended to make the sealing face more consistent, more verifiable, and better matched to the customer’s application.
Lihua Titanium — controlling the details behind a reliable titanium flange connection.
