Calculate the pump pressure for hydraulic bolt tensioning and lay out the passes for 100% or 50% tool coverage. You will need the tensioner pressure area from your tool supplier. Values are for reference; confirm against the current edition of the governing standard. Send us your bolting list for a quote or call (281) 581-0176.
Related: Hydraulic Bolt Tensioning Guide · Powered Torque Tools · All technical docs
Formula
Required pressure = target bolt stress × bolt area ÷ tensioner pressure area. Use the same bolt area (root or tensile stress area) that the target stress is based on (PCC-1 Q-4.5).
Pass steps
- 100% coverage: Pass 1a at 70% of assembly load, then Pass 1b at the target times 1/NLLF (usually 105–150%). Cycle pressure until nut movement is less than 1/16 of a flat.
- 50% coverage: first set at 70%, then pressure A on the first set (usually 110–200%, multiplier (1 + BLLF)/NLLF), then pressure B on the second set (105–150%). Recheck the first set at pressure B and repeat until the nuts stop moving.
- Measure flange gaps after the early passes and verify a couple of bolts per pass by elongation (Q-4.4).
When to tension
- Tensioning is generally used only on bolts larger than 1 in.; below 1-1/8 in. it is problematic (Q-4.5).
- Studs need at least 1D of thread past the nut on the tool side. Use the Stud Bolt Length Calculator with the tensioner end option.
- Short bolts (length under 5 diameters) give less accurate results (Q-4.3).
References: ASME PCC-1-2026, Guidelines for Pressure Boundary Bolted Flange Joint Assembly. Summaries are paraphrased; clause numbers refer to ASME PCC-1-2026 unless noted. Patriot Bolt manufactures bolting and does not perform bolting, training or joint assembly services.