Thermomechanical Evaluation of the Performance and Integrity of a HDPE Stub-End Bolted Flange Connection

Abstract

In this study, the integrity of a manhole structure made of a 78 in. high density polyethylene (HDPE) stub-end, steel ring, and blind flange, sealed with a compressed nonasbestos fiber (CNAF) gasket is investigated by means of a parametric finite element analysis (FEA). A coupled thermomechanical nonlinear FEA model is built, comprising of a heat transfer and a structural model, which allows modeling the complex thermal and mechanical loads and their interactions present during the operation of the manhole. The temperature-dependent elastic–plastic HDPE material constitutive behavior and the temperature-dependent nonlinear response of the CNAF gasket are accounted for in the model. Factors influencing the performance and integrity of the manhole such as stud-bolt pretorque level (Tb), internal pressure (Pi), and outer temperature (To) are considered. Based on the results, the integrity and performance of the structure are assessed in view of a leakage through the gasket criterion and a yielding of the HDPE stub-end criterion. The FEA results reveal that both Tb, Pi, and To significantly influence the performance (i.e., leakage) of the gasket and the integrity (i.e., yielding) of the HDPE stub-end. At 40 °C, it is possible to find a safe operational window for a range of Tb and Pi values, where no leakage through the gasket or yielding of the stub-end occurs. However, as the temperature is increased this safe operational window decreases considerably, and at 80 °C safe operation cannot be guaranteed where leakage, yielding, or both simultaneously, will lead to loss in performance and integrity of the manhole structure.

Analysis of a HDPE flanged connection with a time and temperature dependent constitutive behavior

“…All TNM parameters are calibrated based on the experimental short and long term results in Figure 4 and Figure 5, except the thermal expansion coefficient (;), the reference temperature for the thermal expansion ( ) and the bulk modulus. The values of and ; are obtained from [1], while the bulk modulus ( is obtained from [26].…”

“…However, leakage is an issue that plastic pipes with large diameters can suffer from, which in some cases can be difficult to alleviate as these pipes are normally buried underground or submerged in water. In general, some of the major causes for leakage in plastic pipe connections include exposure to high temperatures [1], material stress relaxation [2,3,4,5], loss of bolt preload due to elastic interactions [6,7], insufficient bolt preload and inappropriate J o u r n a l P r e -p r o o f gasket selection in the design [8]. In response, many methods are used to prevent and deal with leakage which include retightening of bolts to higher torques and replacing the gasket altogether.…”

“…In response, many methods are used to prevent and deal with leakage which include retightening of bolts to higher torques and replacing the gasket altogether. Although retightening can prevent leakage, excessive retightening can lead to failure of the connection, especially at high operating pressures and temperatures [1]. Over the years, bolted flanges and their performance and tightness have been the subject of many studies, experimental and numerical ones.…”

“…Barsoum et al [1] conducted a finite element analysis (FEA) to study the performance and integrity of a HDPE stub-end bolted blind flange connection with a CNAF gasket. A temperature dependent elastic-plastic model was used for the HDPE material, whereas a non-linear through thickness compression behavior was used for their compressed non-asbestos fiber gasket.…”

Electro-Mechanical Design and Creep Analysis of Proposed Enclosure for Flexible Gas Insulated Line Regarding Subsurface Metropolitan Applications of High-Voltage Transmission Lines

“…Reference [42] compared the flexibility of FGIL with conventional GIL regarding HDD based underground cable laying in metropolitan vicinities. Moreover, references [43][44][45][46][47][48][49][50][51][52] suggest that aging behavior of thermoplastics due to time, temperature and mechanical loadings, needs careful consideration in order to avoid their excessive structural deformation, rapid strength degradation and early enclosure puncture. Considering the concern of enclosure's strength degradation regarding synergistic impact of aging and mechanical loadings, in this research, a flexible-thermoplastic-enclosure with significantly high structural strength, as well as flexibility, is proposed for FGIL.…”