This specification covers welded pipe line strainers for use in applications above 150 psig and 150 F as well as in marine environment conditions. Strainers covered in this specification are classified into simplex, duplex (or multiplex), and automatic (self-cleaning) based on general construction. However, other bases for further classifying strainers are available: pressure ratings and types of port connection, port alignments relative to unit center lines, cover closures, valve types (in duplex), types of baskets or elements, materials of construction, and other design features. Strainers shall be manufactured by casting or forging or fabricated from plates, tubes, or pipes, with inlet and outlet connections requiring welding joined by butt welding. On the other hand, strainers made of carbon or low alloy steel shall be post-weld heat treated. The strainers shall undergo either hydrostatic or air test, while the welds shall be examined visually or radiographically. All tests shall conform to the requirements specified.