In addition, since codes do impose some limitations on joint applications, joint selection must meet the applicable code requirements. In the paragraphs that follow, the above-mentioned considerations will be briefly discussed for a number of common pipe joint configurations
Butt-welding fittings and pipe system accessories are available down to NPS ¹⁄₂ (DN 15). However, economic penalties associated with pipe end preparation and fit-up, and special weld procedure qualifications normally preclude the use of butt-welded construction in sizes NPS 2 (DN 50) and under, except for those special cases where interior surface smoothness and the elimination of internal crevices are of paramount importance. Smooth external surfaces give butt-welded construction high aesthetic appeal.
Brazed and Soldered Joints
Soldered joints are normally limited to near-ambient temperature systems and domestic water supply. Brazed joints can be used at moderately elevated temperatures. Most brazed and soldered installations are constructed using light-wall tubing; consequently the mechanical strength of these systems is low.
Threaded or Screwed Joints
Vibration can result in fatigue failures of screwed pipe joints due to the high stress intensification effects caused by the sharp notches at the base of the threads. Screwed fittings are normally made of cast gray or malleable iron, cast brass or bronze, or forged alloy and carbon steel. Screwed construction is commonly used with galvanized pipe and fittings for domestic water and drainage applications. While certain types of screwed fittings are available in up to NPS 12 (DN300), economic considerations normally limit industrial applications to NPS 3 (DN 80). Screwed piping systems are useful where disassembly and reassembly are necessary to accommodate maintenance needs or process changes. Threaded or screwed joints must be used within the limitations imposed by the rules and requirements of the applicable code.
Compression joints are frequently used for temporary piping systems or systems that must be dismantled frequently for maintenance. When equipped with the proper gaskets and seals, they may be used for piping systems containing air, other gases, water, and oil; in both aboveground and underground service. Small-diameter compression fittings with all-metal sleeves may be used at elevated temperatures and pressures, when permitted by the rules and requirements of the applicable code. They are common in instrument and control tubing installations and other applications where high seal integrity and easy assembly and disassembly are desirable attributes.