Finite Element Analysis of a Gasketed Flange Joint Under Combined Internal Pressure and Thermal Transient Loading

Performance of a bolted flange joint is characterized mainly by its ‘strength’ and ‘sealing capability’. A number of analytical and experimental studies have been conducted to study these characteristics only under internal pressure loading. In the available published work, thermal behavior of the pipe flange joints is discussed under steady state loading with and without internal pressure and under transient loading condition without internal pressure. The present design codes also do not address the effects of steady state and thermal transient loading on the structural integrity and sealing ability. It is realized that due to the ignorance of any applied transient thermal loading, the optimized performance of the bolted flange joint can not be achieved. In this paper, in order to investigate gasketed joint’s performance i.e. joint strength and sealing capability under combined internal pressure and transient thermal loading, an extensive nonlinear finite element analysis is carried out and its behavior is discussed.

Self-Loosening Mechanism of Nuts Due to Lateral Motion of Fastened Plate

As self-loosening of nuts is really a problem for bolted joints in practical use, countermeasures for the loosening is highly required. In this situation non-loosening fasteners are one of the resolutions for any fastened machinery as an essential mechanical element. Self-loosening of threaded bolt/nut systems has been researched in number of works and most researches were based on experiment and a few were based on the finite element analysis in these years. Using this new approach, various types of nuts can also be examined. Among these nuts eccentric nuts and slit nuts are especially expected to be the solution, as these nuts are reported to endure NAS vibration tests and were not loosened. In the authors’ previous paper, an eccentric nut and a normal nut were analyzed and compared in the aspect of loosening property. In this paper degree of loosening of various nuts was investigated by experiment and the FEA.

Use of Cohesive Elements in Fatigue Analysis

Cohesive laws describe the resistance to incipient separation of material surfaces. A cohesive finite element is formulated on the basis of a particular cohesive law. Cohesive elements are placed at the boundary between adjacent standard volume finite elements to model fatigue damage that leads to fracture at the separation of the element boundaries per the cohesive law. In this work, a cohesive model for fatigue crack initiation is taken to be the irreversible loading-unloading hysteresis that represents fatigue damage occuring due to cyclic loads leading to the initiation of small cracks. Various cohesive laws are reviewed and one is selected that incorporates a hysteretic cyclic loading that accounts for energetic dissipative mechanisms. A mathematical representation is developed based on an exponential effective load-separation cohesive relationship. A three-dimensional cohesive element is defined using this compliance relationship integrated at four points on the mid-surface of the area element. Implementation into finite element software is discussed and particular attention is applied to numerical convergence issues as the inflection point between loading and unloading in the cohesive law is encountered. A simple example of a displacement-controlled fatigue test is presented in a finite element simulation. Comments are made on applications of the method to prediction of fatigue life for engineering structures such as pressure vessels and piping.

On the Effect of External Bending Loads in Bolted Flange Joints

Most current flange design methods use an equivalent pressure to treat bolted flange connections subjected to external bending loads. This oversimplified approach together with the lack of a proper assessment of the actual affected tightness make these methods inadequate for modern flange design. The substitution of the external applied moment by an equivalent pressure is excessively conservative and not realistic since it assumes that the achieved tightness is that of a gasket unloaded entirely to a minimum stress whereas in reality only a small section of it is, the rest of it is actually at a much higher stress. The successfulness of a valid analytical approach in yielding to an acceptable solution resides in its ability to account for the circumferential distribution of the gasket contact stress and its effect on leakage. This paper presents an analytical model based on the flexibility of the flange to treat flanges subjected to bending loads such as those produced by external moments and misalignments and capable of integrating leakage around the gasket circumference. The bolted joint sealing performance in the presence of such loads is evaluated using the new PVRC gasket constants Gb, a and Gs obtained from ROTT tests. The analytical results including leakage predictions are validated by comparison to those obtained numerically by FEA and experimentally on different size flanges. The over-conservatism of the equivalent pressure is demonstrated.

Distortion of Polymer Matrix Composite Panels Under Transverse Thermal Gradients

This paper discusses the distortion of panels made by fiber reinforced polymer matrix composites under transverse thermal-loading conditions. We formulate thermal distortion from the bending theory of functionally graded materials. General solution for thermal distortion is derived in terms of material variation and temperature profile along the thickness of the panels. Using the general solution, analytical expressions of thermal distortion and associated internal forces for commonly used end supports are obtained. From these solutions, we discuss the failure mechanism induced by thermal distortion and design criteria that can be placed to prevent such failure. The roles of geometry, temperature and temperature gradients, and the competition among them in the process of structural failure are addressed.

Root Cause Analysis of Glovebox Glove Failure

The Nuclear Materials Technology (NMT) Division has the largest inventory of glovebox gloves at Los Alamos National Laboratory (LANL). Consequently, the minimization of unplanned breaches of the glove material, typically resulting in glove failures, is a significant safety concern in the daily operations in NMT Division facilities. To investigate processes and procedures that minimize unplanned breaches in the glovebox, information on glovebox glove failures has been compiled from formal records and analyzed using statistical methods. Based on these research results, the next step of the research is to identify root causes of glove failures and the actions adequate to prevent recurrence. In this paper, root cause analysis was conducted for a cleanup breach case study to demonstrate the computerized root cause analysis process. Based on analysis results, effective recommendations were generated.

An Experimental Investigation of the Factors That Contribute to the Creep-Relaxation of Compressed Non-Asbestos Gaskets

The adequate tightness of flanged joints contributes to maintaining safe working conditions in numerous equipment and industrial installations. The new sealing technologies and materials can require more careful selection, handling and installation than previous asbestos equivalents. Many research studies have been conducted to understand and improve the assembly bolt load of piping joints in order to minimize the likelihood of leakage. The selection of the bolt load must consider many factors, such as: minimum gasket stress to achieve a seal; the maximum stress that will damage the joint components and the amount of gasket stress lost to creep-relaxation under room temperature and service condition. It is well known that the bolt load decrease to some degree after the initial assembly due to creep-relaxation characteristics of the gasket. ASME PCC-1 recommends restoring the gasket load, after a minimum 4 hours, due to short-term creep-relation. This paper intends to investigate factors which may influence the creep-relaxation characteristic of the compressed non-asbestos gasket. In order to reproduce real field condition, ASME B16.5 class 300lbs flanges were used in this experimental investigation.

Evaluation of the Elliptical Flange Configurations for 24-Inch and 30-Inch Heater/Cooler Units

KOCH Heat Transfer Company contracted Stress Engineering Services, Inc. to perform a design/parameter study of a return bonnet used in hairpin heat exchangers that employs an elliptical flange design. The return bonnet is an important component of the heat exchanger as it can be removed to permit inspection of the heat exchanger tubes. The return bonnet is bolted to the hairpin leg flange. To maintain sealing integrity a gasket is placed between the return bonnet flange and the hairpin leg flange. The sealing efficiency of two return bonnet sizes (24-inch and 30-inch) was investigated in this study using finite element analysis. The sealing efficiency is an indication of how the contact pressure changes circumferentially around the gasket and is calculated by dividing the local contact pressure by the maximum contact pressure calculated in the gasket for each respective design. The study assessed the effects of geometric changes to the mating flanges. Using an iterative design process using finite element analysis, the elliptical flanges were optimized to maximize sealing efficiency. Upon completion of the study, the manufacturer successfully employed the modifications as evidenced with multiple successful hydrotests.

Influence of Axially Distributed Force on the Vibration of Euler-Bernoulli Beam Structures Solved by DQEM Using EDQ

The influence of axially distributed force on the vibration of Euler-Bernoulli beam structures is analyzed by differential quadrature element method (DQEM) using extended differential quadrature (EDQ). The DQEM uses the differential quadrature to discretize the governing differential eigenvalue equation defined on each element, the transition conditions defined on the inter-element boundary of two adjacent elements and the boundary conditions of the beam. Numerical results solved by the developed numerical algorithm are presented. The convergence of the developed DQEM analysis model is efficient.

Short Term Relaxation of Stuffing Box Packings

The long term tightness performance of stuffing box packings, used in valves, is conditioned by the capacity of its material to maintain a contact pressure to a predetermined minimal threshold value. Due to creep, this contact pressure decrease with time depending on the creep properties and the stiffness of the housing. Assessing relaxation is a key parameter in determining the tightness performance of the stuffing box packing over time. Using Ansys software, an axisymmetric 2D finite element model is developed to assess the contact pressures between the packing material and the stem and the housing and its variation with time. The assessment of the packing relaxation is a major obstacle to the good leakage performance of the Stuffing Box Packing.