Category
Pressure Vessels & Reactors
Subcategory
Column / Tower
Applicable standards
4
Issuing bodies
2
Description
Tall pressure vessel with internals (trays / packing) for separation.
Applicable Standards (4)
API — 2 standards
API 582
Welding Guidelines for the Chemical, Oil, and Gas Industries
Supplementary welding requirements (PWHT, hardness, impact, NDE) beyond ASME IX.
Key requirements (7)
- Supplementary welding requirements for chemical/oil/gas industries — beyond ASME IX.
- Mandatory PWHT thresholds tighter than ASME VIII.
- Hardness limits: 200 HB (CS), 235 HB (1.25Cr-0.5Mo / 2.25Cr-1Mo) for sour service typical.
- Charpy impact requirements at MDMT for all weldments where production weld is impact-tested.
- PMI (positive material identification) required on alloy components.
- Hydrogen-induced cracking (HIC) prevention: low-hydrogen consumables, preheat, controlled diffusible H ≤ 8 mL/100g.
- Heat input control for impact-toughness-controlled materials.
API 660
Shell-and-Tube Heat Exchangers
Design, materials, fabrication, inspection and testing of shell-and-tube heat exchangers. Identical to ISO 16812.
Key requirements (8)
- Shell-and-tube heat exchangers for petroleum, petrochemical, natural gas.
- Companion to TEMA — provides additional engineering / procurement requirements.
- Min tube wall: 2.1 mm (0.083") CS, 1.65 mm (0.065") SS — 25 mm OD typical.
- Tube-to-tubesheet joint: strength-welded + light-rolled OR full-strength expanded; expansion ≥ 2× tube wall.
- Shellside velocity: 0.6–1.5 m/s liquid; tubeside 1–3 m/s typical.
- Hydrotest per ASME VIII Div 1 (1.3 × MAWP).
- Vibration analysis (TEMA / HEDH): natural frequency, fluid-elastic instability, vortex shedding.
- Differential thermal expansion handled by floating head, U-tube, or expansion bellows.
ASME — 2 standards
ASME BPVC Sec VIII Div 1
Rules for Construction of Pressure Vessels
Mandatory rules for design, fabrication, inspection, testing and certification of pressure vessels operating above 15 psig (~1 barg).
Key requirements (12)
- Applies to vessels with internal pressure > 15 psig (1.03 barg) up to ~3000 psi (Div 1 sweet spot).
- Joint efficiency E: 1.0 (full radiography), 0.85 (spot RT), 0.70 (no RT) for Type 1 butt joints.
- Shell thickness: t = P·R/(S·E – 0.6·P) for circumferential stress (UG-27).
- Head thickness: t = P·D/(2·S·E – 0.2·P) for 2:1 ellipsoidal heads (UG-32).
- Hydrostatic test pressure: 1.3 × MAWP × (S_test/S_design) — UG-99.
- Pneumatic test (when hydro impractical): 1.1 × MAWP — UG-100.
- Corrosion allowance is added to calculated thickness (not included in S formula).
- MDMT and impact testing per UCS-66 / Figure UCS-66; below the curve, Charpy V-notch impacts are required.
- PWHT thresholds per UCS-56 — generally required above 19 mm thickness for P-No. 1 carbon steels.
- Nozzle reinforcement: area replacement method (UG-37) within reinforcement zone.
- Maximum allowable stress S: from ASME II Part D, Table 1A/1B/3 — temperature dependent.
- Flanges per ASME VIII-1 Appendix 2 (or B16.5 for standard sizes).
Note: Most widely used pressure vessel code worldwide.
ASME BPVC Sec VIII Div 2
Alternative Rules for Construction of Pressure Vessels
More rigorous design-by-analysis rules; permits higher allowable stresses and thinner walls.
Key requirements (8)
- Alternative rules — Design by Analysis or Design by Rules (Part 5 vs Part 4).
- Higher allowable stress factor (typically 2/3 of yield, vs 3.5:1 ratio in Div 1) — thinner walls possible.
- Mandatory user's design specification (UDS) certified by registered engineer.
- Mandatory full radiography of butt welds (with limited exceptions).
- Hydrostatic test: 1.25 × MAWP × stress ratio.
- Fatigue analysis required when cyclic conditions are significant (Part 5 screening).
- Class 1 vs Class 2 design — Class 2 allows higher stresses with stricter NDE/inspection.
- Used for high pressure (>3000 psi typical), large vessels, cyclic service, lethal service.