The nonlinear behavior of threaded piping connections: Application using a modified Ramberg-Osgood model

Damage to nonstructural components such as piping systems and mechanical and electrical equipment can result in major economic loss, injuries, and loss of life in critical facilities like offshore structures, nuclear power plants, and hospitals. Failures in piping systems especially due to water leakage can lead to shut-down of a facility, and connections in the pipelines are particularly important since failures often occur at these locations. This paper presents a technique for modeling threaded connections as rotational springs, either linear or nonlinear. Laboratory tests were conducted on 1 and 2-in. diameter specimens of black iron Schedule 40 pipe in a cantilever configuration where the support is a threaded piping flange. The specimens were loaded monotonically into the inelastic region. The piping system was modeled as a straight pipe using Euler-Bernoulli beam theory with a support modeled as the proposed rotational spring. The correlation between test results and analytical predictions was quite good. A modified Ramberg-Osgood equation (1943) was used to model the nonlinear moment-rotational behavior of the support spring, and the criterion specified by ASME Boiler & Pressure Vessel Code (ASME, 2007) was used to determine the rotational limit for the threaded piping connection.