Flanged joints are pressure-boundary assemblies. A lookup table can help you screen bolt count, bolt diameter, bolt circle, face type, and pressure class, but it cannot approve the joint. Real flange work depends on current standards, flange markings, material group, gasket style, bolting, lubricant, tightening method, tool calibration, service temperature, project specification, and qualified review.
ASME B16.5, ASME PCC-1, ASME B16.20, and ASME B16.21 are source pointers for this topic. Their current text, tables, notes, tolerances, and procedures must be checked from the official standard or adopted project source before pressure-boundary decisions.
Start With the Source Boundary
ASME B16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, bolting, gasket, and joint context for NPS 1/2 through NPS 24 flanges and flanged fittings. A local web reference should never be treated as the current table. Verify edition, class, material group, facing, gasket, bolting, and project code basis before using any value.
Bolt Pattern Screening
Bolt count, bolt diameter, and bolt circle are mating checks, not an assembly signoff. Confirm the actual flange markings, manufacturer drawing, tolerance, face type, material, gasket, and fitting type. If the joint involves Class 2500, B16.47 large-bore flanges, API 6A, AWWA, DIN/EN, lined flanges, special flanges, or damaged field parts, use the applicable source set instead of a B16.5-style local row.
Gasket and Face Selection
Raised face, flat face, and ring-type joint labels only describe the sealing geometry. Gasket material, dimensions, markings, seating stress, surface finish, and service suitability come from ASME B16.20/B16.21, gasket manufacturer data, project specification, and qualified review. RTJ ring numbers are especially easy to overtrust; use cached ring rows only as prompts to check the current gasket source.
Assembly Procedure
Torque is only an indirect control variable for bolt load. Final bolt stress and gasket load depend on lubricant, thread condition, nut condition, washer use, flange rotation, gasket behavior, relaxation, retorque policy, tool calibration, and the tightening method. Use ASME PCC-1, manufacturer instructions, site procedures, and trained/qualified personnel for real assembly work.
Common Source Gaps
Before bolting a pressure-boundary joint, reconcile the current standard edition, adopted piping code, material group, pressure-temperature rating, gasket and bolting selection, corrosion and cyclic service, hydrotest limits, pipe strain, alignment, inspection status, hot-work or confined-space controls, and jurisdictional requirements. A lookup result is a checklist starter, not a signoff.
Flange Bolt Pattern & P-T Reference
ASME B16.5 flange reference: bolt count, diameter, bolt circle, and torque by pipe size and pressure class, plus pressure-temperature ratings (carbon steel Group 1.1) that derate with service temperature, RF / FF / RTJ face types, and RTJ ring numbers. Class is not PSI: see the working pressure at your actual temperature.