Applies to fusion-weldede steel air receivers of less than 9 inch internal diameter and working pressure not exceeding 250 lb per square inch, but does not apply to: (a) Air or vacuum vessels used on railways or aircraft; (b) Containers used for the independent conveyance of compressed air or other gases; (c) Pressure paint containers; (d) Receivers which have a working pressure exceeding 250 lb per square inch.
