MSS - Manufacturers Standardization Society of the Valve and Fittings Industry.
Scope
"This specification covers factory-made@ seamless and electric fusion-welded carbon and low-alloy steel@ butt-welding fittings for use in high pressure gas and oil transmission and distribution systems@ including pipelines@ compressor stations@ metering and regulating stations@ and mains. This Standard Practice governs dimensions@ tolerances@ ratings@ testing@ materials@ chemical and tensile properties@ heat treatment@ notch toughness properties@ manufacture and marking for high-test@ butt-welding fittings NPS 60 and smaller. Dimensional requirements for NPS 14 and smaller are provided by reference to ASME B16.9. The term ""welding fittings"" applies to butt-welding fittings such as elbows@ segments of elbows@ return bends@ caps@ tees@ single-or multiple-outlet extruded headers@ reducers@ and factory-welded extensions and transition sections.(Footnote 1) Fittings may be made to special dimensions@ sizes@ shapes@ and tolerances@ or of wrought materials other than those covered by this Standard Practice by agreement between the manufacturer and the purchaser. When such fittings meet all other stipulations of this Standard Practice they shall be considered as being in partial compliance therewith@ providing they are appropriately marked. Fittings manufactured in partial compliance@ as provided in Section 1.4@ shall be identified with ""Part"" following the respective grade designation. Footnote 1 - Lengths of extensions and transitions as agreed upon by purchaser and manufacturer."