Process Safety, ASME Section VIII UG-127 & Rupture Disks
Rupture Disk Manufacturing Range, Hot Burst & Kc Formula
Calculate Rupture Disk Upper Stamped 72°F Burst Rating (psig), Elevated-Temperature Maximum Burst Pressure (psig), ASME UG-127 Combination Derated PRV Capacity (lb/hr), and MAWP Margin (psi).
Add upper manufacturing range BEFORE applying temperature weakening—and apply ASME UG-127 Kc = 0.90!
When engineers install a non-fragmenting corrosion-isolation Rupture Disk (RD) upstream of a spring-loaded Pressure Relief Valve (PRV) on corrosive reactor service, ASME Boiler and Pressure Vessel Code Section VIII Division 1 (UG-127) enforces two critical rules: first, unless the exact disk-plus-valve pair holds an ASME flow-tested combination certificate (K_c ≈ 0.97), the valve’s standalone certified relieving capacity MUST be derated by Default Combination Factor K_c = 0.90! Second, if ordered with a positive Manufacturing Design Range (e.g., +5% / -0% at 72°F), Max Stamped 72°F Rating is P_req * (1 + Mfg_Upper_Pct), and Elevated-Temperature Maximum Burst Pressure is P_stamped_max * Temp_Factor <= Vessel MAWP!
Verify on a 155 psig MAWP Lined Chemical Reactor—Requested_72F_Burst = 150.0 psig (B2), Upper_Mfg_Range_Pct = 0.05 (+5.0%, B3 -> Max Stamped 72°F Rating = 157.50 psig in E2), Elevated_Temp_Strength_Factor = 0.96 (B4 -> Max Operating Burst = 157.50 * 0.96 = 151.20 psig in E3), Vessel_MAWP = 155.0 psig (B5 -> +3.80 psi safe headroom below MAWP in E5), and Standalone_PRV_Capacity = 12,000 lb/hr at Default K_c = 0.90 (B6): ASME Derated Combination Capacity equals 12,000 * 0.90 = 10,800.00 lb/hr (E4)!
| ASME UG-127 Rupture Disk + PRV KPI (150 psig Req, +5% Mfg, 0.96 Temp, 155 MAWP) | Formula | Verified Output |
|---|---|---|
| Max Stamped 72°F Burst (psig) | Requested_psig * (1 + Upper_Mfg_Pct) | 157.50 psig (150.00 Zero-Range) |
| Max Operating-Temp Burst (psig) | Max_Stamped_72F * Temp_Strength_Factor | 151.20 psig (144.00 Zero-Range) |
| Derated PRV Capacity (lb/hr) | Standalone_PRV_lb_hr * Combination_Kc | 10,800.00 lb/hr (11,640 @ 0.97) |
| Headroom Below Vessel MAWP (psi) | Vessel_MAWP_psig - Max_Hot_Burst_psig | 3.80 psi (11.00 psi Zero-Range) |
ASME UG-127 Hot Burst & Combination Capacity Formula
Validate Requested_Burst >= 15, Upper_Mfg_Pct in [0, 0.15], Temp_Factor in (0.60, 1.05], MAWP >= Hot_Burst, and Standalone_Capacity > 0!
=LET(rq_p, B2, mf_u, B3, tm_f, B4, mw_p, B5, cp_s, B6, IF(OR(rq_p < 15, mf_u < 0, mf_u > 0.15, tm_f <= 0.6, tm_f > 1.05, mw_p <= 0, cp_s <= 0), "Invalid Rupture Disk Input", LET(ht_b, rq_p * (1 + mf_u) * tm_f, IF(ht_b > mw_p, "OVER MAWP: Reject Disk", ROUND(ht_b, 2)))))Zero-Manufacturing-Range Reverse-Buckling Disk & Cold Startup Over-MAWP Checks
Switch to a modern 0% manufacturing-range reverse-buckling disk (B3 = 0.00): Max Hot Burst E3 drops to 144.00 psig, widening MAWP headroom E5 to 11.00 psi! Conversely, test cold startup at 72°F (B4 = 1.00) with +5% range (B3 = 0.05): Hot Burst 157.50 psig exceeds 155.0 psig MAWP, triggering "OVER MAWP: Reject Disk"!
=IF(ISTEXT(E3), E3, ROUND(B5 - E3, 2))Try the example
Use the original values or change them to test your understanding.