ISO 9809-4:2021

This document specifies the minimum requirements for the materials, design, construction and workmanship, manufacturing processes, examinations and testing at time of manufacture for refillable, seamless, stainless steel gas cylinders with water capacities up to and including 150 l.
It is applicable to cylinders for compressed, liquefied and dissolved gases with a maximum actual tensile strength, Rma, of less than 1 100 MPa.
NOTE         If so desired, cylinders of water capacity between 150 l and 450 l can be manufactured to be in full conformance to this document.