A pressure vessel in a food plant has to satisfy two sets of requirements at the same time. One set is structural: the shell, head and nozzle must be thick enough for the design pressure and must not fail. The other set is hygienic: the interior must drain, clean and be safe for product contact. ASME Section VIII Division 1 is the code that governs the first set, and it is worth understanding what it actually fixes, because a vessel can be built to the code and still be unsuited to food production.
What Division 1 fixes
The code sets the allowable stress for each material at the design temperature, the required wall thickness against internal and external pressure, the joint efficiency that follows from the weld type and the extent of radiography, and the rules for openings and reinforcement. It also fixes the tests: a hydrostatic or pneumatic proof test, and the marking that identifies the vessel and its design conditions. The practical consequence is that thickness cannot be decided by comparison with an existing vessel. It is calculated from design pressure, diameter, material allowable and joint efficiency, and it changes if any of those inputs changes.
Where the food requirement adds constraints
Food and beverage vessels are normally 304 or 316L stainless steel with a controlled internal finish, and the internal geometry must be free of dead legs so that cleaning solution reaches every surface. Side outlets and dip pipes create pockets below the drain point, which is why flush bottom discharge, radiused internal corners and a fully drainable shell are specified. Nozzles for CIP, instrumentation and venting are also code items, so they have to be positioned and reinforced to satisfy the code and the cleaning requirement together.
Verification a buyer should ask for
Ask for the design calculation, the material certificates traceable to heat number, the weld procedure and welder qualification records, the non destructive examination report where radiography or dye penetrant is specified, and the test certificate. Where the project falls under European rules, the equivalent route is a design and declaration of conformity under Directive 2014/68/EU (PED). If a stamped vessel is offered, confirm in writing that the certificate scope actually covers the product, the size and the material, because a certificate that covers a different range is not evidence for your vessel.
What to specify
Design pressure and temperature, volume, material and internal finish, jacket or coil duty, nozzle schedule, cleaning and inspection access, and the certification the destination market requires.
