This part of ISO 18172 specifies minimum requirements concerning material, design, construction and workmanship, manufacturing processes and testing of refillable transportable welded stainless steel gas cylinders, of water capacities from 0,5 l up to and including 500 l, for compressed, liquefied and dissolved gases. This part of ISO 18172 is applicable only to cylinders manufactured from stainless steels with test pressures up to 6 MPa (60 bar). If required, transportable large cylinders of water capacity above 150 l and up to 500 l may be manufactured and certified to this part of ISO 18172, providing that handling facilities are provided (see 6.5.5). For acetylene service, additional requirements for the cylinder and the basic requirements for the porous mass are given in ISO 3807-1 and ISO 3807-2.