Seismic Assessment of Threaded Connections in the Power Industry

Lifelines refer to a set of structures, facilities, and equipment that perform the task of storing, supplying, transmitting, and distributing vital needs including water, electricity, gas, or collection, storage, treatment or recycling of wastewater and waste, or communication including landline and telephone. The earthquake phenomenon is one of the natural disasters that causes many deaths, financial and environmental damages every year. Earthquake and industrial systems retrofit against earthquake due to repeated changes and evolution of regulations in recent decades is inevitable. The first step in reinforcing structures is to determine their vulnerability to earthquakes. The purpose of seismic vulnerability analysis is to examine the equipment, communication, safety and performance of a complex at the time of the earthquake. Using this approach (checking the performance of pipelines in past earthquakes), with the appropriate speed and cost, one can determine the areas with the highest level of risk, and for the next steps, which include preparation of retrofit plans and finally retrofit implementation, prioritized. One of the ways to assess the vulnerability is to use lessons learned from past earthquakes and the behavior of equipment against seismic forces. This approach is a rational and defensible approach because the actual conditions of the complex are considered and the seismic behavior of similar equipment in past earthquakes is investigated and the results are evaluated by combining information and engineering judgment, showing a common and widely used theme in the industry. According to recent earthquakes, the most common damage occurred in industrial centers and pipelines in joints, which is one of the weakest types of thread joints, with the most damage occurring in past earthquakes. Seismic evaluation of thread connections is one of the most important issues in oil and gas lines, transmission lines, grid lines and in the power plant industry as damage to these lines will cause crisis during and after the earthquake.
The transfer of petroleum and gas products to industrial centers is carried out by pipelines, which are one of the cheapest, fastest and most reliable means of pipeline being a key member of lifelines. Seismic evaluation of thread connections is one of the most important issues in oil and gas lines and in the power plant industry as damage to these lines will cause crisis during and after the earthquake. In this study, one of the most common thread connections is used for modeling. After modeling and loading, the connection was evaluated in both daily and buried conditions. A flexible piece called an accordion is also used at the junction to reinforce the connection. In addition to the accordion length, the support conditions and the accordion material are considered in the modeling. According to the results, the most stress and damage to the connection occurs on the pin as well as in the last thread involved with the pin with the box. It was also found that stress at the joint is independent of the underlying conditions and is directly related to the material of the joints, and the use of accordion was found to be an appropriate approach to reinforce such joints.