Check the rules, check the building codes.  What is commonly stated for minimum design and construction standards?   ASME plating.  Here is a paragraph from one US state, which is similar to most states rules.    Reimers makes every model comply with ASME and UL standards.          About Reimers Electra Steam  

All boilers, pressure vessels, water heaters, and storage tanks, unless otherwise exempt, shall be registered on an annual basis. All new boilers, pressure vessels, water heaters, and storage tanks unless otherwise exempt, to be operated in this jurisdiction, shall be designed, constructed, inspected, stamped and installed in accordance with the ASME Code and the latest addenda including code cases in effect, and these rules and regulations. Boilers and pressure vessels for which an ASME Manufacturers' Data Report is required shall bear the manufacturer's "NB" number as registered with the National Board. A copy of the Manufacturers' Data Report, signed by the manufacturer's representative and the National Board commissioned inspector shall be filed with the Chief Inspector through the National Board. 

https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select 

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