Application of Bolted Flange Joint Assembly Guidelines HPIS Z103 TR to ePTFE Sheet Gasket

Bolt tightening guidelines HPIS Z 103 TR for flange joint assemblies have been developed to provide a simple and effective procedure to tighten flange joint bolts. This assembly procedure is applicable to compressed fiber sheet gaskets and spiral wound gaskets, but is not applicable to expanded PTFE (ePTFE) sheet gaskets for the reason that the ePTFE material has lower modulus of elasticity and higher creep/relaxation rate. In this study, expansion of the application scope of HPIS Z103 TR to ePTFE sheet gaskets is investigated. Tightening tests are conducted using flange joint specimens of JPI 4 inch and 6 inch, and all bolt forces and flange gaps are measured at each tightening step to check for uneven tightening. Uniformity of the bolt forces and flange gaps are comparable to those obtained by other types of gaskets or by tightening procedure ASME PCC-1. The influences of gasket relaxation and elastic interaction on the bolt forces are also demonstrated. As a result, flange joint assembly guidelines HPIS Z 103 TR can be considered applicable to the high-density ePTFE sheet gasket, although a post-tightening step of 1 or 2 passes is necessary to compensate for the bolt force reduction induced by gasket relaxation.

Practical Application of Fastener Preload Guidance Research

Bolted flanged connections (BFC) in North America and throughout the world are designed, fabricated and constructed according to several design codes and component standards including the ASME Boiler and Pressure Vessel Code and ASME B31 Piping Codes. Despite the considerable engineering controls in place to ensure proper equipment design, bolted flange connections are all too often the source of leaks, fugitive emissions and process shutdowns in the process industries. A significant contributing cause of flange leaks is the limited understanding, of and improper selection and application of optimum assembly preloads on flange fasteners. Currently there are several “rule of thumb” approaches for identifying assembly bolt preload; each of these has limitations and short-comings that practitioners of these approaches need to be aware of. A new approach providing guidance to the selection of assembly preload bolt stresses is detailed.

Effect of Coating Thickness on the Friction Coefficients and Torque-Tension Relationship in Threaded Fasteners

This paper experimentally investigates the effect of coating thickness on the thread, bearing friction coefficients and torque-tension relationship in threaded fasteners. The torque-tension relationship is highly sensitive frictional changes. Two different coating thicknesses are investigated using two bolt sizes; realtime test data is collected for two ranges of bolt tension. The experimental set up collects real-time data on the tightening torque, bolt tension, and the corresponding reaction torque. Test data is used for calculating the thread and bearing friction coefficients, as well as the overall torque-tension relationship for two different coating thicknesses. The study would provide an insight into the variation of the torque-tension relationship which is a key factor that significantly affect the reliability and safety of bolted assemblies in many mechanical and structural applications.

Concept for the Guarantee of the Integrity of Bolted Flanged Connections in a German Nuclear Power Plant

In nuclear facilities in Germany a systematic treatment of all sealing connections which are opened during the annual shutdowns is performed since several years. Special attention is paid to a design which meets specifications of the bolted flange connections (BFC’s). Apart from the use of suitable and certified materials this includes also the calculation of the required torques in accordance to the present rules. For the calculation procedure the nuclear code KTA 3211.2 (draft 2003) is applied which allows a tightness proof of the BFC, besides a stress analysis. For this calculation, experimentally achieved gasket characteristics according to DIN 28090-1 are required, which are either supplied by the gasket manufacturers or determined in the amtec test laboratory. The geometry and material data of each BFC are stored in a special data base. In addition, the data of the operating state as well as the design and test loading cases are included in the data base, so that all inputs for a later calculation are available. The results of the calculation which must be checked and approved by an expert third-party are stored in the flange data base, too (assembly state settings of each flange connection). On this base individual flange data sheets can be provided to the flange fitter teams that include all necessary information for assembly of each BFC (bolts, nuts, gasket, geometry and material specifications, lubricant, etc.).

Thermo-Mechanical Behavior of a Stainless Steel Threaded Fitting With a Pre-Compressed Gasket

This paper investigates the clamp load loss in threaded fittings with a collapsible metal gasket for elevated temperature application. Firstly, the joint is tested at room temperature to find the correlation between the joint clamp load, the tightening torque, and the angle of turn. Secondly, a mathematical model for clamp load loss of the bolted joints under temperature cycling is proposed for predicting the clamp load variation. Although the bolt and the joint would normally undergo linear elastic deformation at room temperature, they are more likely to exhibit nonlinear behavior at high temperature due to the reduced material strength. The plastic or creep deformation of the bolt, gasket, and joint would cause permanent clamp load loss that may lead to joint leakage, part separation, or plastic thread deformation that would significantly increase the cost of fitting replacement and/or maintenance. A non-linear finite element model is used with temperature dependent material properties. The FEA model is used to investigate the clamp load loss of the threaded fittings due to plastic and creep behavior. Some measures for enhancing the threaded fitting reliability at elevated temperature are proposed.

Characterization of Sealing Behavior of Gaskets for the Leak Rate Based Design of Gasketed Bolted Flanged Connections

This paper discusses the sealing behavior of gaskets according to the gasket testing procedure HPIS Z104 established in Japan. The testing procedure consists of eleven gasket stress levels while the internal pressure is constant. It takes about 3 hours to complete one test, which is acceptable for gasket manufacturers. The test method is going to be effective as the Japanese Industrial Standard (JIS) soon. Several sheet gaskets and spiral wound gaskets were tested based on the test method HPIS Z104 and test results are compared and discussed in this paper. Based on the test results, experimental formulas are proposed to approximate the sealing behavior of gaskets. It is shown that the sealing behavior of gaskets can be well characterized using the proposed testing procedure and the experimental formulas. The formulas have the possibility of application to the design of gasketed bolted flanged connections. It is also shown that the sealing performance of spiral wound gaskets with graphite and PTFE fillers is as good as that of sheet gaskets under an equal gasket load.

Integral Mean of Yield Criterion in Design and Fitness for Service Assessment

Mura’s variational formulation for determining limit loads, originally developed as an alternative to classical methods, is extended further by allowing the pseudo-elastic distributions of stresses to lie outside the yield surface provided they satisfy the “integral mean of yield” criterion. Consequently, improved lower-bound and upper-bound values for limit loads are obtained. The mα estimation limit load method, reference volume method and the fitness for service assessment procedure (including corrosion damage and thermal hot spot damage), are all applications and extensions of the “integral mean of yield” criterion.

Effective Stress Ratio of Triangular Pattern Perforated Plates

Tubesheet structures utilized in heat exchangers have complex perforated portions. For realistic design analysis, axisymmetric models with equivalent solid materials of perforated plate are conventionally adopted to simplify perforated area (figure1). Sec.III Appendix A-8000 (ASME 2004) provides elastic equivalent solid materials for flat tubesheets. Plastic properties were studied by Porowski et al. (1974), Gorden et al. (2002) and so on. Elevated temperature design of tubesheets requires plastic and creep properties in addition. The purpose of this study is to develop a general determination method of non-linear equivalent material properties for perforated plates and to confirm their applicability to both flat and spherical tubesheets. Main loadings of tubesheets in fast reactor heat exchanges are inner pressure and thermal stress at transient operations. Under above conditions, average stress of perforated area becomes approximately equi-biaxial. Therefore, average inelastic behaviors of various perforated plates subjected to equi-biaxial field were investigated by inelastic finite element method. Though above investigations, Authors clarified that perforated plates have their own effective stress ratio (ESR). ESR is a function of geometry and is independent from their materials. ESR can determine non-linear equivalent material properties of perforated plates for any kind of constitutive equations of base metals. For simplified inelastic analysis of perforated plates, the brief equations were proposed to determine equivalent plastic and creep material properties for perforated plates. It is considered that physical meaning of ESR is an effective stress ratio between perforated plates and equivalent solid plates. ESR is a function of geometry and is independent from constitutive equations. ESR can determine non-linear equivalent material properties for perforated plates from any kind of constitutive equations of base materials. Assumptions in ESR are von Mises’s equivalent stress-strain relationship and equi-biaxial loadings. Applicability of ESR was investigated through finite element analyses of various flat and spherical tubesheets.

Loosening Resistance Evaluation of Double-Nut Tightening Method, Spring Washers, and Conical Spring Washers: Finite Element Study

The mechanisms of loosening resistance components are investigated within the framework of the three-dimensional finite element method (FEM). Here, the results of the double-nut tightening method (DN), spring washers (SW), and conical spring washers (CSW) are shown. This paper focuses on the comparison among the components above based on the results that have been published separately. For details on each analysis, readers are referred to [10–12]. We have found that DN shows significant loosening resistance if the locking is properly realized in the tightening process. However, if the locking is not performed properly, its ability to resist loosening completely disappears. SW shows negative loosening resistance because the sticking area on the contact surfaces is limited to two corner edges of the SW and the rotational force around these edges thus drastically leads to loosening. In regard to CSW, in the case of high axial force, it shows no apparent effect on preventing loosening. On the other hand, in the case of low axial force, it shows two opposite effects. The negative effect is an increase in the loosening rotation angle, while the positive one is the prevention of a decrease in axial force. When complete bearing-surface slip occurs, a CSW can prevent loosening because the positive effect becomes larger than the negative one. However, when only small bearing-surface slip occurs, a CSW cannot prevent loosening because the negative effect cancels the positive one.

Design Parameters Effect on Load Distribution Around the Hole in Mechanically Fastened Pinned Connections

The pinned connection is a principal joining element in many structures. In this article, we present two-dimensional stress analyses for isotropic plate with a pinned circular hole. A study of the pin and the plate material dissimilarity was done by Iyer [6] but still different aspects of the problem are remained to be mentioned. In this work different issues of mechanical engineering interests such as stress distribution in contact area and the magnitude and location of maximum contact pressure and tangential stress are computed with the aid of commercial software ABAQUS 6.6-1 finite element code [7]. In order to have a good evaluation of the stress distribution around the hole, design factors such as plate width to hole diameter ratio (w/d), edge distance to hole diameter ratio (e/d), clearance at the connection area and the contact friction coefficient (μ) were systematically varied during analyses from 2 to 5, 3 to 6, 5% to 25% and 0 to 0.5 respectively. A Coulomb-type friction model is used to simulate the frictional contact at the pin-plate interface. The results obtained in this paper are compared to those available from the paper published by Iyer [6]. Based on the results, it is observed that higher friction at contact interface makes the joints more safe by reducing the peak contact pressure; the same is concluded by reducing the plate width.