Pipe Flange Connections Research Articles

Material tests of composite rings with recyclates for pipe flange connections

This study aims to determine the material properties of the structural components of the composite ring material for pipe flange connections.

Strength and tightness evaluation method for pipe flange connections considering thermal effects

The pipe flange connection is widely applied in chemical, power plants, petrochemical, offshore oil and gas industries, and its strength and tightness are significant for the safe operation. However, there are still no practical and applicable strength and tightness evaluation methods for pipe flange connections working in dramatically varying temperatures. This paper proposed an approach to evaluate the pipeline's strength and sealing performance considering thermal effects in actual operating conditions by combining the experimental measurement and thermostructural analysis. The critical thermodynamic parameters are identified through measured temperature data in operating conditions, and then these parameters are used in the thermostructural analysis to obtain the actual temperature and stress fields. Then, the strength and tightness in complex temperature cases can be evaluated accurately. The pipe flange connection of a liquefied natural gas (LNG) fueling station is analyzed to verify the presented method's effectiveness. This method applies to evaluating the pipeline's strength and tightness and can predict the pipeline's performances under extreme temperatures using the tested data within the measurement range and the corresponding thermostructural analysis. Furthermore, the work in this paper also provides a reference for the design and analysis of pipe flange connections working in complex temperature conditions.

Bending and tensile stressing state features of ductile iron pipe flange connections revealed from tested strain data

The existing theories and methods based on structural ultimate working states with empirical judgment could not estimate the load-bearing capacity of ductile iron pipe flange (DIPF) connections accurately. This paper tries to address the issue applying the novel structural stressing state theory and methods, leading to the revelation of the essential bending and tensile working features of DIPF connections. Firstly, the experimental strain data are transformed into the generalized strain energy density (GSED) values to build the stressing state modes and the characteristic parameters. Then, the Mann-Kendall criterion is adopted to detect the mutation points in the evolution curves of characteristic parameters. Correspondingly, it is verified that the evolutions of stressing state modes also present the mutation features. The mutation features are the embodiment of the natural law from quantitative change to qualitative change of a system, which defines the starting points of DIPF connections’ failure processes. Furthermore, the Mann-Kendall criterion distinguishes the elastoplastic branch (EPB) points in the stressing state evolutions of DIPF connections. Both failure starting points and EPB points provide the new foundation to accurately determine the working capacities of DIPF connections and to improve their design.

Bending working law of corroded ductile iron pipe flange connections revealed by structural stressing state theory

Applying structural stressing state theory, this study finds out the bending working law of corroded ductile iron pipe flange (CDIPF) connections from their tested strain data. Firstly, the strain data are transformed into the generalized strain energy density values to build the stressing state mode and the characteristic parameter. Then, the Mann-Kendall criterion is used to detect the mutation points in the evolution curves of the stressing state characteristic parameters with the load increase according to the natural law from quantitative change to qualitative change of a system. Meanwhile, it is verified that the evolutions of the stressing state modes also present the corresponding mutation features. The mutation points define the starting points of the bending CDIPF connections' failure processes. Furthermore, the Mann-Kendall criterion distinguishes the elastoplastic branch (EPB) points in the normal working processes of CDIPF connections. Both the failure starting point and the EPB point lay the new foundation to analyze the working performances of the CDIPF connections and to improve their design.

Bolt loading effects on the structural integrity assessment of defects in industrial components

Applied loads in bolted geometries of safety critical components can vary with time and operating conditions. Structural integrity and remaining life assessments of such components in aging industrial plants must consider the resultant changes in damage accumulation rates and acceptable defect sizes. Two case studies are presented that demonstrate the effect of bolt pre-load on creep and fatigue lives as well as on the acceptability assessments of defects. In the first case the sensitivity of creep damage accumulation and crack propagation rates to bolt pre-load in high temperature flanged connections are considered. Predicted results were found to compare well with actual damage quantified on a high pressure turbine loop pipe flange connection. It was shown that decreased pre-loads, in this case, leads to an increase the allowable safe defect size during assembly at room temperature. In contrast to this the second case study of corrosion fatigue cracking in a boiler water circulating pump illustrates that an increase in bolt pre-load leads to an increase in fatigue initiation life, a decrease in fatigue crack propagation rate and an increase in the acceptable defect size. Strain gauge measurements of bolt and casing strain, which correlated well with finite element calculations, indicated the necessity for close control of bolt pre-load during assembly to ensure specified levels are attained. In both cases metallurgical analysis and structural integrity assessments of cracked and excavated geometries were conducted which enabled limited continued operation of the components after which repairs and/or replacements will be implemented.

Monitoring of mechanical changes in a pipe assembly with complex geometry using multi-mode acoustic signals

Guided wave ultrasonic testing has been widely used for nondestructive and long-range evaluation of diverse mechanical structures, such as pipes and plates. In general, a large number of guided wave modes exist even in the simplest geometries, and they exhibit highly dispersive characteristics. Thus, sophisticated excitation methods and elaborate modal analyses need to be implemented to excite, acquire, and process well-defined pure modes as part of such a measurement method. If the interrogated structure has complex geometry, for example, with cross-sectional variations or multiple joints, the utilization of pure modes becomes significantly more difficult. To overcome this difficulty, this paper proposes the use of multi-mode, multi-frequency guided waves for long-range inspection of structures with arbitrarily complex geometries. Using broadband chirp signals and multi-mode time–frequency analysis in a prototypical complex pipe assembly that includes multiple pipe diameters, elbows, and flange connections, we experimentally show sensitive detection of mechanical changes (both material addition and loss). In addition, we demonstrate that the complexity of the structure can be modeled in the digital domain with sufficient detail to allow accurate numerical simulation of the acoustic response using this method.

Load condition analysis of pipe flange connection with gasket flat gasket and loose clamping rings

Purpose: This paper describes the study of the connection with loose fixing composite rings of pipe flanges. The elastic properties of the joint components - gasket, pressure flanges, rings and fixing bolts were determined experimentally. Design/methodology/approach: The criterion of joint tightness was formulated. The constructed model was used to determine the analytical dependence of the joint leakage pressure on the assembly torque of bolts tightening. The correctness of the model was confirmed by the agreement of the analytical results with the experimental results. Findings: Quantitative characteristics were determined for the selected type of joint. Practical implications: The formulated conclusions indicate the possibility of using the model to support the design process and to select the structural parameters of the joint meeting the operational requirements and safety criteria. Originality/value: Produced with recycled materials using.

Analysis on the Leakage of the Flange Connection of the Water-Containing Hydrofluoric Acid Pipeline

Leakages of bolted pipe flange connections of water-containing hydrofluoric acid pipelines were frequently reported by the extraction section in the fluorine chemical industry. Water-containing hydrofluoric acid can cause severe injuries to human beings due to its strong causticity. The water-containing hydrofluoric acid pipe was a short lined pipe, so a lot of flange connections and supports were adopted in the pipeline. In this paper, the finite element models of the pipeline were established to analyze the internal force of the pipeline under conditions including internal pressure, temperature, self-weight, and so on. Based on this, the equivalent design pressure of the flange connections was determined. The results of the stress analyses of the pipeline showed that leakages were mainly caused by a large bending moment, due to the unreasonable layout of the piping supports under self-weight. When the pipeline was supported on the beam of the pipe gallery, which is not necessarily beneficial to reduce the bending moment of the pipeline, and the flange connection was close to the supporting beam at the same time, leakages frequently occurred in this flange connection. To support the pipeline reasonably, the flange connection should be placed at zero bending moment positions. Therefore, the positions with zero bending moments of the pipeline with equal and unequal spacing supports were obtained under gravity load, to provide a basis for the rational support of lining piping.

Design of replaceable nozzles for connecting pipelines in electron beam welding

The article is devoted to the use of electron beam welding for connecting pipelines in the oil and gas industry. The analysis of the proposed approach and equipment for creating permanent pipe-flange connections is carried out. The advantages and disadvantages of the proposed approach are considered. During the work, the welded seam was calculated. A set of interchangeable attachments for the turntable has also been developed. Thus, the purpose of this work is to improve the quality of welded joints of oil and gas equipment through the use of electron-beam welding technology and design of replaceable nozzles for a turntable for an electron-beam welding unit.

Leakage characteristic of pipe flange connection including dispersed axial bolt force

Leakage characteristic of pipe flange connection including dispersed axial bolt force

Evaluation of Sealing Performance of Pipe Flange Connections for Low Temperature Fluids by Numerical Analysis

Evaluation of Sealing Performance of Pipe Flange Connections for Low Temperature Fluids by Numerical Analysis

Component Testing and Numerical Calculation of a Bolted High Temperature Power Plant Pipe Flange Under Complex, Near-Service Loads

Abstract To ensure a reliable power supply with a minimum environmental impact in the future, further increases in efficiency and flexibility of fossil-fired power plants are major challenges to address in recent R&D activities. In order to counterbalance substantial fluctuations in the electricity grid due to the rising share of renewable resources, frequent start-ups and shut-downs of turbomachinery will be claimed by the market. Hence, along with the development of advanced materials for elevated steam parameters, contemplations with respect to altered boundary conditions of established materials, e.g., for bolted pipe flange connections, are required. In this paper, a selection of results from a recently finished research work on stress relaxation will be presented. Together with European power plant component manufacturers, a newly developed test rig comprising a scaled intermediate pressure (IP) steam turbine pipe flange now allows investigations under near-service conditions. Before, throughout, and after performance of the experiments, an extensive measurement setup enables the examination of effects that cannot be studied in standardized relaxation tests. Within this work, a loss in bolt pretension of up to almost 50% over a comparatively short period of experimental time was observed. By means of numerical calculations, creep deformation in the transition areas between pipe and flange plate sections was identified to be a major originator of these pretension drops. Particularly, good correlations between experiments and finite element method (FEM) simulations could be achieved through the implementation of enhancements concerning the fitting strategy of the Graham–Walles-type creep model which was used.

A Study of New Tightening Procedure for Bolted Pipe Flange Connections with Metallic Gaskets

A Study of New Tightening Procedure for Bolted Pipe Flange Connections with Metallic Gaskets

IMPACT OF CREEP ON FLANGE CLAMPING FORCE

The study presents a numerical analysis of the impact of creep in thermoplastic stub ends on the flange clamping force of a thermoplastic pipe flange connection. The analysis uses available creep modulus values that depend on the stress level, temperature and time. A method that takes the creep modulus into account is proposed and applied to four different detailed variants with the aid of the finite element method. The calculations were performed for selected times at a constant temperature and with static load. The obtained results show that the influence of creep in thermoplastic stub ends causes a substantial reduction in flange clamping force in less than one year.

Analysis of the metal-to-metal contact flange joint subject to external bending moment

Metal-to-metal contact flange joints are widely used in nuclear and petrochemical industry for severe conditions, because of the relative stability of the sealing gasket stress under complex service condition. In the present work, finite element models were used for analyzing the stress distribution of metal-to-metal contact pipe flange connection under different internal pressures, temperatures, and external bending moments to evaluate the sealing and strength performance. A metal-to-metal contact pipe flange connection device was also experimented. It was found that the results of the axial bolt force and flange hub stress obtained from the experiments were in fairly good agreement with the finite element simulations. The leakage test of metal-to-metal contact type gasket was conducted to highlight its leakage characteristics under different temperatures. The methods to determine the maximum allowable bending moment of a metal-to-metal contact flange joint according the strength criterion and the sealing criterion were analyzed. The results showed that the maximum allowance bending moment was determined by the strength criterion rather than by the sealing criterion with different thermal loadings when the initial bolt-up stress was high enough to achieve metal-to-metal contact contact.

A Simple Method of the Load Factor Using a Circular Plate Theory for Bolted Pipe Flange Connections with Gaskets under Internal Pressure

A Simple Method of the Load Factor Using a Circular Plate Theory for Bolted Pipe Flange Connections with Gaskets under Internal Pressure

Behaviors of Axial Bolt Forces in Larger Diameter Pipe Flange Connection with RJG under Bolt Tightening

Behaviors of Axial Bolt Forces in Larger Diameter Pipe Flange Connection with RJG under Bolt Tightening

Evaluation of Thermal Stress and Sealing Performance of Pipe Flange Connections for Low Temperature Fluids

Evaluation of Thermal Stress and Sealing Performance of Pipe Flange Connections for Low Temperature Fluids

Axial Load Capacity of Cold Formed Pipe Flange Connection

In this paper, a cold forming process is used where the connection between a pipe and a flange is created by means of radially expanding tool segments inside the pipe. The method is investigated with two purposes, to set up a robust procedure for the process that allows for connections to be made on site, and to set up finite element (FE) simulations that can capture the forces and deformations when pulling the pipe axially out of the flange. Experimental data and FE simulations are used to describe and understand the forces and deformations during the connection process. The rapid increase in radial stiffness experienced when the pipe comes in full circumferential contact with the flange is identified as the best end-of-process indicator. Also, experimental data and FE simulations are used to predict the axial load capacity of a pipe flange connection, and the FE model is utilized in designing the appropriate ridge height of the tool segments.

Evaluation of Mechanical Characteristics of Bolted Pipe Flange Connections with PTFE Blended Gaskets Subjected to External Bending Moments

Evaluation of Mechanical Characteristics of Bolted Pipe Flange Connections with PTFE Blended Gaskets Subjected to External Bending Moments