THE AFFECTS OF ASSEMBLY TORQUE AND POLYETHYLENE PIPE INSERTION DEPTH ON SERVICE HEAD ADAPTER PERFORMANCE

摘要

Polyethylene (PE) pipe has been used as a proven means of conveying and distributing fuel gases since thern1960s.1 In the United States and Canada, PE pipe accounts for over 90% of the natural gas distribution system andrnhas become the de facto industry standard. Although PE pipe is so prevalent, industry codes and regulations do notrnallow plastic pipe to be installed within a structure as a suitable means to convey fuel gas. Therefore, a coupling orrnfitting is used to transition from the exterior PE pipe to the metallic pipe associated with distribution within arnstructure.rnThere are various manufacturers that make fittings with a standard National Pipe Thread (NPT) connection torntransition the PE gas line into a metallic pipe. This type of fitting is commonly referred to as a service head adapterrn(SHA). There are numerous styles and variations of SHAs, but all share a common design factor in that theyrnemploy mechanical compression to form a gas-tight, leak free connection.rnFuel gas leaks resulting in explosions and fires have occurred due to leaks at the SHA/PE tubing connection. Oftenrnthese leaks do not manifest themselves during the initial pressure tests performed following installation, but insteadrnoccur months or years later. Several factors may contribute to these failures, which include: improper installation,rnmanufacturing and design defects, geotechnical issues, and environmental conditions.rnA study was conducted using common ASTM D2513 Category 1i SHAs, both old and new, from variousrnmanufacturers. Tests were performed to specifically explore failure modes associated with the assembly of SHAs.rnTwo variables, assembly torque and insertion depth of the PE pipe, were varied during testing to assess theirrnindividual affects on SHA connection strength. Each SHA assembly, following an initial leak test, was subjected tornan axial tensile test while under pressure. Testing was performed until a failure of the assembly was detected.rnYielding of the PE tubing, pullout of the PE tubing, and/or loss of integrity (i.e. leaking) all constituted a failurernthereby completing a test.