ASME B16.5 and B16.47

ASME B16.5

B16.5 covers pipe flanges and flanged fittings in nominal pipe sizes 1/2 inch through 24 inch. Pressure classes are 150, 300, 400, 600, 900, 1500, and 2500. The class designator is not a working pressure - actual P-T ratings depend on material grade and operating temperature, tabulated in the standard as pressure-temperature ratings.

For weld neck construction specifically, B16.5 defines the hub length, hub diameter at small end, hub diameter at face end, bore, and weld bevel geometry. The hub taper is standardized to create the smooth stress transition that distinguishes weld neck from slip-on construction. Standard facings include raised face (RF, the default), flat face (FF), ring-type joint (RTJ), tongue and groove (T&G), and large male and female (LMF).

ASME B16.47

B16.47 covers large diameter pipe flanges from 26 inch through 60 inch nominal. The standard splits into two series. Series A (formerly MSS SP-44) is the heavier pattern with larger bolt circle and bolt count, designed for cyclic and severe service. Series B (formerly API 605) is the lighter pattern, dimensionally compatible with API 605 legacy installations. Series A and Series B are not interchangeable. The project drawing or specification names which series the flange must match.

The two series carry different pressure class ranges. Series A (MSS SP-44 derivative) covers Class 150 and up, through Class 900. Series B (API 605 derivative) covers Class 75 and up and is generally not used above Class 600. Weld neck construction in B16.47 sizes follows the same hub-taper geometry as B16.5 but the hub is longer in proportion to handle the larger pipe wall thickness.

Pressure-Temperature Ratings

P-T ratings drop as temperature rises. A Class 300 A105 weld neck holds 740 psi at 100 degrees F and 365 psi at 850 degrees F. The same dimensional flange in F22 chrome-moly holds rating to higher temperatures because the material yield strength holds. The same flange in F316L stainless has a lower room-temperature rating but holds rating to higher temperatures than carbon. Selecting the material requires reading the P-T table for the design temperature, not just picking the class.

Material Grades

A105 forged carbon is the default. A350 LF2 covers low-temperature service to minus 50 degrees F with charpy impact testing. A694 F-grades cover pipeline pressure service. Chrome-moly F11, F22, F91, F92 cover elevated temperature. Stainless F304L, F316L, F321, and F347 cover corrosion and high-temperature service; for sustained service above 800 degrees F, the H-grade variants (F321H / S32109 and F347H / S34709) are specified for code-credit creep strength. Specialty alloys including Hastelloy, Inconel, Monel, and duplex 2205 cover specific corrosion environments. See Materials for the full grade table.