Stud Bolt Length (ASME B16.5)

What this is: stud bolt sizing for raised-face (RF) flange pairs per ASME B16.5. The two flange thicknesses, gasket, two nuts (and washers if used), and thread projection beyond each nut sum to give the minimum stud length, which is then rounded up to a stocked length. Source data:

• Flange thickness, stud diameter and bolt count: ASME B16.5 (Class 150 to 2500)
• Heavy hex nut thickness: ASME B18.2.2
• Standard stud length increments: ASME B16.5 Table II-1 / typical mill stock

Thread projection rationale: ASME PCC-1 (Appendix N) requires at least 1.5 thread pitches above each nut, which equals roughly 3 mm for most stud sizes. 6 mm is preferred when tensioners or impact tools may be used, or when the assembly may be re-torqued later in the asset's life. Brownfield tip: when replacing studs on an aged flange pair, do not just match the old length. Measure the actual flange thickness — older flanges to legacy specs (B16.5-1968, MSS SP-44, or proprietary patterns) can be 5–15% thinner than current B16.5. Equally, gasket thickness has changed: spiral-wound gaskets switched from 1/8″ (3.2 mm) to 0.175″ (4.5 mm) in the 1980s. Order long, cut to fit, then verify the nut runs to flush before final torque-down. RTJ flanges: the ring takes the place of the gasket but the depth into both flange grooves must be added. Use the dedicated B16.20 dimension table for the specific ring number; a quick approximation is 6–25 mm depending on NPS (e.g., R-26 = 8.4 mm; R-37 = 11.1 mm; R-49 = 17.5 mm).