Pressure Vessels

ASME Section VIII (Divisions 1 and 2) is the US code, widely accepted internationally, applied under an accredited quality system. In the EU the legal framework is PED 2014/68/EU, with EN 13445 as the harmonized design standard and AD 2000 as an accepted alternative ruleset, and CE marking follows conformity assessment routed by fluid group and hazard category. The codes differ in allowable stress basis, design margin, permitted calculation route (design by rule against design by analysis) and inspection requirements. The applicable code follows the destination country and the project specification.

MAWP is the maximum gauge pressure permitted at the top of the vessel in its operating position at the designated coincident temperature, and it is limited by the weakest pressure part: shell, heads, nozzles, flanges or bolting. It is calculated from geometry, thickness less corrosion allowance, and the allowable stress of the selected material at design temperature. Operating pressure, static head, relief device set pressure and corrosion allowance are all considered when setting design pressure. The value is established by calculation for the specific vessel rather than taken from a generic figure.

Pressure parts are normally documented with EN 10204 3.1 inspection certificates, with 3.2 certification where the specification or the notified body requires third-party endorsement. Certificates cover chemical composition and mechanical properties, including impact testing at the specified low temperature where the service calls for it. Documentation requirements are agreed at specification stage and reflected in the material traceability records for the vessel.

Yes. The medium drives material selection (austenitic stainless steels for cryogenic and corrosive duty, carbon steels with suitable notch toughness for many hydrocarbon duties), corrosion allowance, internal finish, gasket and seal compatibility, and any cladding or lining. It also sets the design temperature range, impact test requirements and cleanliness, including cleaning for oxygen service. The configuration is reviewed against the process data sheet for the application.

Nozzle size, rating, orientation, projection and reinforcement are set by the process and piping requirements, covering inlet, outlet, drain, vent, relief, instrument and access connections. Flanged connections to ASME B16.5 and B16.47 or EN 1092-1, threaded outlets, studded outlets and pad-type reinforcement are all common arrangements. Each opening requires reinforcement calculation per the applicable code, plus minimum spacing from main seams and from adjacent nozzles. The final nozzle schedule comes from the general arrangement drawing agreed for the project.

Typical methods are radiographic (RT) or ultrasonic (UT) examination of butt welds, magnetic particle (MT) or liquid penetrant (PT) examination of fillet welds, nozzle attachment welds and edge preparations, and visual examination throughout. The extent of examination (spot, partial or full) follows the joint efficiency assumed in the design calculation and the code category of the vessel. Hydrostatic testing at the code-defined multiple of design pressure completes verification, with pneumatic testing used only where hydrostatic testing is impractical. The applied methods and coverage are set out in the inspection and test plan.

Post-weld heat treatment is applied where the code requires it based on material group, thickness and service conditions, or where the specification calls for it to reduce residual stress and improve toughness. Cryogenic austenitic stainless steel vessels are generally not subjected to PWHT, since solution-annealed condition and sensitization risk govern instead, while thicker carbon and low-alloy steel vessels frequently are. Heating and cooling rates, soak temperature and hold time follow the applicable code and the qualified welding procedure. Whether PWHT applies is determined during design review of the specific vessel.