LITTLE P.ENG. FOR ENGINEERS TRAINING / Engineering Consultant

Most threaded joints in ASME B31.3 piping systems are made with taper threads in accordance with ASME B 1.20.1. Figure 5.1 shows a taper thread. These threaded joints are generally acceptable for Normal Fluid Service and Category D Fluid Service. Paragraph 314.1(a) states that threaded joints should be avoided in any service where crevice corrosion, severe erosion, or cyclic load may occur. Cyclic loading is not defined and this limitation is rather unclear, because all syste

Welded and brazed joints are the most commonly used methods for joining piping components because these joints are stronger and more leak-tight than threaded and flanged joints. Furthermore, they do not add weight to the piping system as flanges do, and they do not require an increase in pipe wall thickness to compensate for threading, as threaded joints do. Pipe-Weld Joint Preparation and Design Butt Welds. The most common type of joint employed in the fabrication of welded

Threaded joints are normally used in low-pressure small-bore, nonflammable service, although threaded iron pipe is commonly used in domestic gas piping and threaded joints up to NPS 12 (DN 300) have been used in low-pressure liquid service. For quality joints, it is essential to have smooth, clean threads. Because cut-thread surfaces are somewhat imperfect, thread sealants (pipe dope) and lubricants are often used to ensure a leak-tight joint. Lubricants such as linseed oil o