All Hanson Pressure Vessels EXCEPT lined potable hot water storage tanks are built and tested in accordance with the A.S.M.E. Boiler and Pressure Vessel Code Section IV Division I for unfired pressure vessels and bear a "U" or "M" stamp, National Board number and serial number, as required. (The "M" stamp is on most vessels under 35 gallons). A copy of the A.S.M.E. date sheet U1-A, signed by an A.S.M.E. authorized inspector, will be sent with the invoice if requested at time of order.