A Collaborative Approach to Achieving a Gas-Tight Seal Using Expanded Polytetrafluorethylene (ePTFE) Gaskets in a Fiberglass-Reinforced Plastic (FRP) Lap-Joint Flanges

The work presented here is a collaborative approach to achieving a reliable gas tight seal in fiberglass reinforced plastic (FRP) flanged joints using expanded polytetrafluoroethylene (ePTFE) gaskets. There are many advantages to incorporating FRP flanged piping systems in today’s chemical process industry plant build. As regulations on reliability and fugitive emissions become stricter, it is more important than ever to eliminate possible damage and leak paths at the flanged connections in these systems. This paper details a case study on a collaboration between a chemical plant operator (end user), an ePTFE gasket manufacturer, and a FRP piping original equipment manufacturer. Over a twenty-four month period a FRP flanged system was designed and validated using a custom FRP stub and ring, also known as a lap joint, flange with an ePTFE gasket. The result was the development of a FRP bolted flange system that successfully achieved a reliable gas tight seal for aggressive chemicals. Beginning with a theoretical model and ending with experimental lab analyses, the conclusive results are included herein.

Derivation of Input Distributions for Probabilistic Evaluation Using In-Reactor Measurements

Candu Energy Inc. (former commercial operation of AECL) has developed probabilistic tools to support nuclear plant operators with a risk-based fuel channel management strategy. One such tool is used to evaluate the probability of pressure tube rupture resulting from pressure tube to calandria tube contact and hydride blisters. This tool assumes that PT rupture occurs when delayed hydride cracking (DHC) initiates in a blister. The objectives of the probabilistic assessments are to: • Determine the overall risk of PT rupture in the reactor core for comparison with the acceptance criteria. • Determine the risk of PT rupture for specific fuel channels to assist in the development of an inspection/maintenance strategy. • Evaluate the risk reduction that would result from different fuel channels inspection/maintenance scenarios. • Optimize inspection/maintenance programs. The distributions of the most critical input distributions can be derived by benchmarking against in-reactor measurements. Two benchmark methods were developed to take advantage of the recent advancements in the accuracy of the inspection tool that measures the gap profile between the PT and the CT.

Large Vessel Nozzle Penetration Geometric Optimisation Study in 3D Incorporating Design of Experiments Techniques

This paper describes the results of an optimisation study into the effects of changing geometrical variables local to the nozzle entry on a large pressure vessel. The purpose of the study was to quantify the effects of altering the geometry, and thereby provide trade-offs between key responses such as primary strength and shakedown performance. A 3D Finite Element model was built of a 90 degree sector of the pressure vessel which was sufficiently detailed to allow the thermal and structural effects of the vessel remote from the nozzle to be included. Specifically, this included the thermal and structural influence of the closure head and bolting assembly. The model was then parameterised for 5 independent variables, including the extent of the nozzle reinforcement, crotch corner fillet radius and nozzle thickness. The parameterised model was then subjected to a number of thermal and structural transient analyses during Level A operation, as well as a representative strength loadcase. A full factorial design study was undertaken, comprising of separate 243 analysis runs covering the 5 independent variables at 3 levels. A number of output metrics were monitored, and the effects on the output metrics resulting from changes to the inputs were quantified. Due to the full factorial nature of the experimental design, interactions between variables could also be investigated. The response for each output metric was then fitted to a response surface, which allows a polynomial (meta-model) of each metric to be calculated. These responses were input to a simple Excel chart which allows the designers to perform rapid what-if design scenarios, and see the resulting effects of their changes on the responses. This allows the trade-offs between responses, for example shakedown and strength trade-off for shell thickness, to be easily seen and quantified.

Serrated Metal Graphite Faced Gaskets for Ring Joint Flanges

Metal Ring Joint gaskets are used in piping and equipment that operate at high pressure and/or temperature. Flange faces for these gaskets are precisely machined and small imperfections on the sealing surface make them unusable, requiring replacement or expensive field machining. During plant shut-downs time constraints may not allow for flange replacement or surface repairs. As a temporary fix gasket manufacturers offer other gasket styles like graphite faced serrated metal or spiral wound. This paper studies the use of graphite faced serrated metal gaskets in ring joint flanges. In addition to laboratory tests, also the results of a successful application of a Double-Rail gasket in a shut-down of a Petrochemical plant are shown.

Properties of Bimetallic Core-Shell Nanoclusters

Gold (Au) and copper (Cu) materials and their combination exhibit the most of the main wanted properties in nanostructures. Nobel metals such as Au and Cu have important magnetic, electronic, optical, catalytic and thermal properties. Compared to monometallic clusters, bimetallic nanoclusters have more degrees of freedom and distinct properties due to the presence of two different metals. It is also well known that the shape, surface topography, segregation, mixing, ordering, energetic stability, and electronic structures of bimetallic nanoclusters may depend significantly on their composition. This affords greater opportunity to control their properties by modifying composition as well as size. In this work, we investigated magnetic and electronic properties for AuCu bimetallic core-shell structures and showed that the CuAu coreshell can have a half-metal property through chemical composition modification. Half-metallic ferromagnets attract increasing research interest as potential materials for spintronic device applications.

Visco-Elastic FEM Stress Analysis of Bolted Flange Connections With PTFE-Blended Gaskets Under Elevated Temperature

Bolted flange connections with gaskets have been used under high temperature and long-term conditions. Sometimes leakage accidents occur from the gasket interfaces due to the creep and relaxation phenomena. In the present paper, the changes of the gasket stress in bolted flange connections under high temperature conditions for a long-term are analyzed using FEM calculations taking into account the gasket temperature dependency. The gaskets used are PTFE-blended (V#GF300). It’s shown that the effect of the temperature on the stress-strain relationship of the gasket is substantial. The changes in the gasket stress of the connections for 12 months are analyzed using the FEM. The effects of nominal diameter of flanges, retightening and the fluid temperature (20 to 300 °C) on the change of gasket stress in the connections under elevated temperature are examined using the FEM calculations. It is found that the reduction in the gasket stress is over 40%. In addition, experiments to measure the axial bolt force were carried out. The calculated results are in a fairly good agreement with the experimental results. The results reveal that the long-term behavior of the bolted flange connections can be estimated in our study. Discussion is made on the effects of the bolt preload and retightening on the reduction of the gasket stress and the sealing performance.

Extreme Value Distribution Theory and its Application in Durability Analysis

Risk based treatment of degradation and failure in engineering components is an important topic in recent years with an emphasis on obtaining more detailed information for extreme events. Fatigue damage and life degradation caused by variable amplitude cyclic loading is dominated by such extreme events, and can be properly treated with the extreme value theory, which could help understand the damage nature of the fatigue damage process as well as to provide more efficient and robust approaches for engineering applications. In this paper, advanced extreme value theory is reviewed first. Methods such as peak counting, block maxima, and peaks over thresholds are investigated and compared in this paper with an emphasis on the relationship between the extreme value theory and the existing methods for fatigue life assessment. A few simple examples of uniaxial and multi-axial fatigue life assessment process are provided and the results are discussed. It is found that, if properly used, the extreme value theories can improve the efficiency of fatigue life assessment. Finally, a hybrid time- and frequency-based multi-axial fatigue life assessment procedure is proposed for wide band loadings.

FEM Stress Analysis and the Sealing Performance Evaluation in Bolted Flange Connections With Ring Joint Gasket Subjected to Internal Pressure: Effect of Scatter in Bolt Preloads

Bolted flange connections with ring joint gaskets have been used to seal the inner fluid under higher internal pressure and higher temperature conditions where soft gaskets such as compressed sheet gaskets cannot be applied. Bolted flange connections are frequently tightened using torque wrench, and it is known that the values of bolt preloads are scattered. The effect of the scatter on the sealing performance for bolted flange connections with compressed sheet gasket or semi-metal gasket has been examined. However, no research on the characteristics for the bolted flange connections with ring joint gasket has been found. It is necessary to know the effect of the scattered bolt preloads on the sealing performance and mechanical behavior of the connection with ring joint gasket. In addition, it is important to know an optimum method for determining the bolt preloads taking account of the scatter in bolt preloads. In this paper, leakage tests for bolted flange connections with octagonal ring joint gaskets were conducted for cases where the bolt preloads are uniform and scattered. The sealing performance of these connections with ring joint gaskets was measured and evaluated. In addition, the leak rate was estimated using the contact gasket stress distributions of the connections when the bolt preloads were uniform and scattered using 3-D FEM. Finally, the measured leak rate for the connection using helium gas was compared with the estimated results. The estimated results are in fairly good agreement with the measured values. It is found that the sealing performance of the connections tightened with the uniform bolt methods is better than that with scattered bolt preloads.

Practical Evaluation of PTFE Thermal Behavior Using the Hot Blowout Thermal Cycling Test

Differential thermal expansion between polytetrafluoroethylene (PTFE) gasket materials and metallic flange/bolt systems, combined with thermally influenced creep relaxation characteristics of all PTFEs, creates limitations in the ability of some PTFE gasket materials to provide long term, reliable sealing performance in process or thermal cycling applications. ASTM F-36 gasket recovery data is sometimes used to assess a gasket’s thermal cycling capabilities; however, it is a poor means of establishing suitability for cycling performance as it is a short duration, ambient temperature test that measures recovery, or springback, of the gasket after the compressive load has been completely released. In order to provide a direct qualification of thermal cycling performance and capabilities, the Hot Blowout Thermal Cycling (HOBTC) test was developed under the guidance of the PVRC (Pressure Vessel Research Council)Bolted Flange Connection Committee as part of the 1995 PTFE Gasket Protocol. The HOBTC test results provide a practically applicable temperature limit under which the tested material, typically a PTFE, can operate safely. In addition, test data reported graphically provide additional insight about the long term behavior of the PTFE material. This paper reviews the current status of the HOBTC test, in the process of being made into an ASTM standard, and practical application of test results to achieve reliable gasket performance.

Comparison of 2D and 3D Welding Simulations of a Simple Plate

Computer analysis of the welding process can now be reasonably carried out in 3D for many simple geometries. This allows direct comparison with more conventional 2D approximations for common heavier-walled joints. Multipass plate butt weld examples are presented, using a range of analysis techniques based on commercial finite element software and the results compared to one another. This project has application to a larger effort to understand the relationship between far-field displacement control boundary conditions and weld residual stress fields. Heat source, high temperature material property, constitutive and element birth and death modeling are also addressed.