Header Box Stress CalculationsBased On ASMEVIII Stayed Vessels of Rectangular Cross Section

Material Strengths as per ASME II Part D Materials Always Check Notes & Use Worst Case

INPUT

PRIMARY DATAMAWP Estimate 1.3*Design pressure to begin withDesign Temperature From data sheetAllowable Stress From ASME II Part D Materials (Lowest / worse case value)Corrosion Allowance (0mm for St.St / Duplex etc., 3mm M.S)No. Stays / Partitions See fig 1Full Span End Plate Full Span is usual, split if partition plates run through end plate

HEADER BOX DETAILSTop/Bottom Plates Min 12mm (M.S), Min 10mm (St.St / Duplex etc.) API 661 6th Ed 7.1.6.1.6Tube Sheet Min 19mm (M.S), Min 16mm (St.St / Duplex etc.) - API 661 6th Ed 7.1.6.1.6 (Must be 25mm to have double groove which is preferred over single groove)Plug Sheet Min 19mm (M.S) Min 16mm (St.St / Duplex etc.) API 661 6th Ed 7.1.6.1.6Partition Min 12mm (M.S), Min 6mm (St.St / Duplex etc.) API 661 6th Ed 7.1.6.1.6End Plate - Min 12mm (M.S), Min 10mm (St.St / Duplex etc.) API 661 6th Ed 7.1.6.1.6

Note: Start with thinnest materials & work up until acceptable

Internal Box Height No. of rows * Vertical pitch (Vertical pitch = sin (60)*Horizontal pitch)Internal Box Depth Keep as close to 100mm as possibleMaximum Span See Fig 1PLUG DETAILSPlug Type Nearly always standardPlug Dia 1/8 bigger than tube Equiv. Plug Dia Same as plug if standard plugTube Hole Dia Special close fit (19.25mm , 25.65mm 1, 32.03mm 1 , 38.46mm 1 , 51.26mm 2) API 661 6th Ed 9.3.1.3Tube Pitch From Data Sheet

NOZZLE DETAILSBox Type Use stress calc sheet info to fill inNozzle Type Use stress calc sheet info to fill inNozzle OD From data sheet (If squashed nozzle, treat as normal nozzle)Wall Thickness Standard Schd (80, 120, 160) Start with smallest WTWall Tolerance Always 12.5% unless a forging 0% (Long weld neck)Nozzle Length Rough EstimateAllowable Pipe Stress From ASME II Part D - Materials (Lowest / worse case valueWeld Cap Size of weld round nozzle (Usually 6mm or 10mm)

MISCELANEOUS DATAWeld Factor Main Seams Usually spot or full radiography (0.85 for Spot, 1 for Full)C Factor for End Plates Always 0.2Ligament / Weld Factor Ties Always 0.7 (Cannot radiograph internal plates)

RESULTS

Check that maximum value of stresses is less than 100% of allowable & check all outcomes

Required to Resist Pressure

Change top / bottom plate thickness until 100% of max allowable stress and put this thickness into required to resist pressure Change top / bottom plate thickness to previous value

MAWP Maximum allowable working pressure

Increase MAWP until something breaks (end plates unacceptable or stress 100%)

When calculating maximum allowable working pressure ensure that all flanges are capable of withstanding this pressure if not then the maximum allowable working pressure is determined by flange maximum allowable working pressure.

Minimum Test Pressure Cover Sheet Minimum test pressure if not stated by customer spec will be in accordance with UG99(1.3 * MAWP * (Samb/Sdesign)) ASME VIII UG-99

Where:MAWP is Maximum allowable working pressureSamb is Maximum allowable stress at ambient temperature - ASME II Part D - MaterialsSdesign is Maximum allowable stress at design temperature - ASME II Part D - Materials