FLANGE FACE FINISH
The American Society of Mechanical Engineers (ASME) has set the standards for flanges face finish, to align the production of flanges and gaskets and ensure that flanged connections made with standard products are safe and durable. The ASME B16.5 norm set standards for few types of flange face finishes, the most important are:
As the name suggests, the stock finish is the most widely used face finish for steel flanges because it is suitable for most service conditions. Once flanges are bolted, gaskets get embedded into the face of the flange and create a very tight seal. The stock finish is used for flange facings that are in direct content with gaskets. The gasket contact surface is manufactured using a phonographic spiral groove featuring a 1.6mm radius round-nose tool with a depth of 0.15mm and a feed-rate of 0.8mm per revolution (that create a finish with a roughness between Ra 3.2 and 12.5 micrometers, i.e. 125 - 500 microinch).
Spiral serrated finish is a phonographic spiral groove type that differs from the stock finish mentioned above as the groove is crafted by a 90 degrees tool (instead of a round nosed one) that creates a "V" geometry with a 45 degree serration angle. A serrated finish, concentric or spiral, is required with 30 to 55 grooves per inch and a consequent roughness between 125 and 500 micro inches.
The concentric serrated finish has concentric grooves vs. spiral. A 90° degree tool is used to craft the grroves, and the serrations are spaced evenly across the face. Concentric serrated finishes use the same tool as the spiral serrated finish. To have concentric grooves, the tool has a feed rate of 0.039mm per revolution and a depth of 0.079mm.
Flanges with a smooth finish do not show visible tool markings at naked eye. The smooth finish is used for gaskets with metal facings such as jacketed, flat steel and corrugated metal. As per the stock finish, this is achieved by having the contact surface machined with a continuous spiral groove generated by a 0.8mm radius round-nosed tool at a feed rate of 0.3mm per revolution with a depth of 0.05mm. This will result in a roughness between Ra 3.2 and 6.3 micrometers (125 - 250 microinch).