Pressure Vessel and Piping Codes
What this domain tests
This domain checks code literacy: ASME BPVC Section VIII Div 1/Div 2 for vessels, Section I for boilers, ASME B31.1 and B31.3 for piping, and NBIC for repairs. You need design pressure, MAWP, corrosion allowance, joint efficiency and hydrotest logic.
Core rules and concepts
- MAWP is the maximum allowable working pressure at the design temperature for the current thickness. It is not the same as design pressure or relief set pressure.
- Section VIII Div 1 uses inside dimensions; B31.3 piping thickness uses outside diameter and the Y coefficient.
- Corrosion allowance is added to calculated thickness. Mill tolerance and structural minimum must also be checked for piping.
- Hydrotest proves tightness and strength: typically 1.3 x MAWP for vessels and 1.5 x design pressure for B31.3 piping, subject to code limits.
- Repairs follow NBIC and the original code of construction; altering a vessel may require re-rating and new calculations.
Worked example
NPS 6 pipe, OD = 168.3 mm, design pressure P = 2.0 MPa, allowable stress S = 138 MPa, E = 1.0, Y = 0.4, CA = 3 mm. B31.3: t = PD/[2(SE + PY)] = (2.0 x 168.3)/[2(138 + 2.0 x 0.4)] = 336.6/277.6 = 1.21 mm. Add CA: 1.21 + 3 = 4.21 mm. Select the next nominal schedule and check mill tolerance.
Traps that cost marks
Using inside diameter in the B31.3 formula; setting Y = 0.4 outside its temperature range; forgetting mill tolerance; treating MAWP as design pressure; using the wrong hydrotest multiplier.