Best Practices for the Design and Installation of Bolted Joints

The cost effective design and construction of liquid pipeline facilities traditionally necessitates the use of bolted joints as opposed to welds. Some of these bolted joints are frequently disassembled and reassembled as part of regular maintenance, while others are assembled at the time of construction and expected to retain a seal for the lifetime of the pipeline. Consequently, the design and installation practices employed for bolted connections are relied upon to produce the same operational life and integrity as welded pipe. In an effort to ensure that the bolted joints used on our pipeline system are as reliable as our welded joints, we investigated industry best practices for flange assembly and the root causes of joint failure. We have completed extensive research of technical literature, including the torquing procedures used in various industries, and performed field-testing on our own system. Generally we have found that: • Flange assembly failures and concerns about this issue are common in the oil and gas industry; • Practices for tightening flanges are inconsistent; and • To accomplish and retain an effective gasket seal, and thus minimize life cycle leaks, one has to consider many factors, including the amount of torque applied to nuts, the stud and nut friction, the type of gasket used, the size of the studs/nuts/flanges, the type of equipment used for tightening, the calibration of the torquing equipment, flange face alignment, and torquing sequence. Using the results of our investigation, we implemented several measures to enhance both the quality and the long-term integrity of our bolted flange connections. This paper describes the results of our investigations, as well as the practices implemented for flange assemblies required for maintenance and new construction activities.